Mechanical alternative. Thermal engine on a new thermodynamic principle by reducing the type "Complane"
Effect of temperature on the engine internal combustion
A larger amount of thermal energy is removed from the engine to the cooling system and is carried out with the exhaust gases. The heat dissipation of heat into the cooling system is necessary in order to prevent the burning of the piston rings, the burning of the valve saddles, the bulk and the piston jam, cracking the cylinder heads, the occurrence of detonation, etc. To remove heat to the atmosphere, part of the efficient engine power is spent on the fan and water drive. pump. For air cooling The power consumed on the fan drive is higher due to the need to overcome the large aerodynamic resistance created by the fins of heads and cylinders.
To reduce losses, it is important to find out how much heat you need to get into the engine cooling system and which way it is possible to reduce this amount. Ricardo paid a lot of attention to this issue at the initial stage of engine development. On the experimental single-cylinder engine with separate cooling systems for the cylinder head and for the cylinder, experiments were performed on measuring the amount of heat assigned to these systems. The amount of heat is also measured by cooling over the individual phases of the working cycle.
The combustion time is very small, but during this period, the gas pressure increases significantly, and the temperature reaches 2300-2500 ° C. When combustion in the cylinder, the processes of movement of gases contribute to the heat transfer in the walls of the cylinder are intensively. The heat saved in this phase of the working cycle can be converted to a useful work during the subsequent expansion stroke. When combustion, about 6% of the thermal energy contained in the fuel is lost due to heat transfer walls of the combustion chamber and cylinder.
During the expansion of the walls of the cylinder, about 7% of the thermal energy of the fuel is transmitted. When expanding, the piston moves from NTC in NMT and gradually frees the increasing surface of the cylinder walls. However, only about 20% of heat saved even with prolonged expansion during the time, can be converted to useful work.
About half of the warmth, assigned to the cooling system, falls on the release tact. The spent gases come out of the cylinder at high speed and have a high temperature. Some of their warmth are discharged into the cooling system through the exhaust valve and the exhaust channel of the cylinder head. Directly behind the valve, the flow of gases changes the direction by almost 90 °, while the vortices occur, which intensifies the heat transfer in the walls of the outlet.
The spent gases need to be removed from the cylinder head with the shortest way, since the heat transferred to it noticeably loads the cooling system and for its removal to ambient air It requires the use of a part of the efficient power of the engine. In the period of gas output, about 15% of the heat contained in the fuel is given to the cooling system. The thermal balance of the gasoline engine is given in Table. eight.
Table 8. The thermal balance of the gasoline engine
| Share in the balance% | ||
| 32 | ||
| in phase of combustion | 6 | |
| When expanding | 7 | |
| During release | 15 | |
| General | 28 | 28 |
| 40 | ||
| TOTAL | 100 | |
Diesel engine has the conditions for removal of warmth other. Due to a higher compression, the temperature of gases at the outlet of the cylinder is much lower. For this reason, the amount of heat, allocated during the release of the release, is less and amounts to about 25% of the total heat given to the cooling system.
The pressure and temperature of gases during combustion in the diesel is higher than that of the gasoline engine. Together with high speeds of rotation of gases in the cylinder, these factors contribute to an increase in the amount of heat transmitted by the walls of the combustion chamber. In the process of combustion, this value is about 9%, and with the course of expansion - 6%. During the course of the release into the cooling system, 9% of the energy contained in the fuel is given. The heat balance of the diesel engine is given in Table. nine.
Table 9. Thermal Balance of Diesel
| Components of thermal balance | Share in the balance% | |
| Heat transformed into useful work | 45 | |
| The heat is set into the cooling system: | ||
| in phase of combustion | 8 | |
| When expanding | 6 | |
| During release | 9 | |
| General | 23 | 23 |
| Heat arising from piston friction | 2 | |
| Heat, allotted with spent gases and radiation | 30 | |
| TOTAL | 100 | |
The heat arising from the friction of the piston about the cylinder wall at the gasoline engine is about 1.5%, and the diesel engine is about 2% of its total. This heat is also assigned to the cooling system. It should be noted that the examples presented are the results of measurements made on research single-cylinder engines, and do not characterize car engines, and serve only to demonstrate differences in thermal balances of the gasoline engine and diesel.
Heat, assigned to the cooling system
About 33% of the thermal energy is given to the cooling system, which is contained in the fuel used. Already at the dawn, the development of internal combustion engines began searching for the transformation paths at least parts of the heat, assigned to the cooling system, in the efficient engine power. At that time, a steam engine with a heat insulated cylinder was widely used, and therefore, naturally, they sought to apply this method of thermal insulation and for an internal combustion engine. Experiments in this direction were carried out large specialists, such as, for example, R. Diesel. However, significant problems were revealed during the experiments.
In the inner combustion used in the internal combustion engines, the gas pressure on the piston and the inertia strength of the translation-moving masses press the piston to the cylinder wall, which at high piston velocity requires providing good lubrication of this next pair. The temperature of the oil at the same time should not exceed the permissible boundaries, which limits the temperature of the cylinder wall. For modern engine oils, the temperature of the cylinder wall should not be higher than 220 ° C, while the gas temperature in the cylinder during combustion and the expansion progress is much higher, and the cylinder must be cooled for this reason.
Another problem is associated with maintaining the normal temperature of the exhaust valve. Steel strength at high temperature drops. When using special steels, its maximum allowable temperature can be brought to 900 ° C as the exhaust valve material.
The temperature of gases in the cylinder during combustion reaches 2500-2800 ° C. If the heat transmitted by the walls of the combustion chamber and the cylinder was not discharged, their temperature would exceed the valid values \u200b\u200bfor the materials from which these parties were made. Much depends on the gas speed near the wall. In the combustion chamber, it is almost impossible to determine this speed, as it changes throughout the work cycle. Similarly, it is difficult to determine the temperature difference between the cylinder wall and air. When inlet and at the beginning of compression, the air is colder than the walls of the cylinder and the combustion chamber, and therefore heat is transmitted from the air wall. Starting from a certain position of the piston with compression tact, the air temperature becomes higher than the temperatures of the walls, and the heat flux changes the direction, i.e. the heat is transmitted from the air the cylinder walls. The calculation of heat transfer under such conditions is a task of great complexity.
The sharp changes in the temperature of the gases in the combustion chamber affect the temperature of the walls, which on the walls of the walls and a depth of less than 1.5-2 mm varies during one cycle, and deeper - it is set at some medium value. When calculating heat transfer, it is this average temperature to be taken for the outer surface of the cylinder wall, with which the heat is transferred to the coolant.
The surface of the combustion chamber includes not only forcibly cooled parts, but also the bottom of the piston, the valve plates. The heat transfer in the walls of the combustion chamber is inhibited by a layer of nagar, and in the walls of the cylinder - the oil film. The valve heads must be flat, so that under the influence of hot gases there was a minimal area. When the inlet valve is opened, it is cooled by the flow of an incoming charge, while the exhaust valve in the process of operation is strongly heated by the exhaust gases. The rod of this valve is protected from the effects of hot gases with a long guide, reaching almost its plate.
As already noted, the maximum temperature of the exhaust valve is limited to the temperature strength of the material from which it is manufactured. The heat from the valve is discharged mainly through its saddle to the cooled cylinder head and partly through the guide, which also needs to be cooled. In graduation valves working in severe temperature conditions, the rod is made by the hollow and partially filled with sodium. When the valve is heated, sodium is in a liquid state, and since it does not fill the entire cavity of the rod, then when the valve moves, it is intensively moved in it, thereby reducing the heat from the valve plate to its guide and then in the coolant.
The plate of the outlet valve has the smallest temperature difference with gases in the combustion chamber and therefore, during combustion, it is transmitted a relatively small amount of heat. However, when the exhaust valve is opened by the heat transfer from the flow of exhaust gases to the valve plate, it is very high, which determines its temperature.
Adiabaty engines
The adiabate engine is not cooled with the cylinder and its head, so there are no losses of heat due to cooling. Compression and expansion in the cylinder occur without heat exchange with the walls, i.e., adiabatically, similar to the carno cycle. The practical implementation of such an engine is associated with the following difficulties.
In order for thermal streams between the gases and walls of the cylinder, it is necessary equality at each moment of time the temperature of the gases temperature. Such a rapid change in the temperature of the walls during the cycle is almost impossible. It would be possible to implement close to the adiabatic cycle, if we provide the temperature of the walls during the cycle in the range of 700-1200 ° C. The material of the walls should maintain performance under conditions of such a temperature, and, in addition, the heat insulation of the walls is necessary to eliminate the heat from them.
It is possible to ensure such an average temperature of the cylinder walls only in its upper part, which is not in contact with the head of the piston and its rings and, therefore, does not require lubrication. At the same time, however, it is impossible to ensure that hot gases are not washed with a lubricated part of the cylinder walls when the piston moves to the NMT. At the same time, it is possible to assume the creation of a cylinder and a piston that do not need lubrication.
Further difficulties are associated with valves. The intake valve is partially cooled by air intake when inlet. This cooling occurs due to an increase in air temperature and, ultimately, leads to the loss of part of the efficient power and motor efficiency. Heat transfer to the valve during combustion can be significantly reduced by thermal insulation of the valve plate.
In the exhaust valve, the temperature conditions of work is much harder. Hot gases emerging from the cylinder have at the place of transition to the valve plate in the rod high speed and heat the valve strongly. Therefore, to obtain the effect of adiabacy, thermal insulation is required not only the valve plate, but also its rod, the heat removal from which is carried out with the cooling of its seat and the guide. In addition, the entire outlet channel in the cylinder head should be thermally insulated so that the heat of the exhaust gases emerging from the cylinder is transmitted through its walls.
As already mentioned, a relatively cold air is heated first from the compression of the cylinder first from the hot walls of the cylinder. Next, in the compression process, the air temperature rises, the direction of the heat flux changes to the opposite, and the heat from the heated gases is transmitted by the cylinder walls. At the end of the adiabatic compression is achieved greater in comparison with compression in by the usual engine The value of the gas temperature, but it consumes more energy.
Less energy is spent when air is cooled when compression, since a smaller amount of operation is needed to compress less than the cooling of air. Thus, the cooling of the cylinder in compression improves the mechanical efficiency of the engine. During the course of expansion, on the contrary, it is advisable to heat the cylinder or to bring warmth to the charge at the beginning of this tact. The two of these conditions are mutually exclusive and cannot be implemented simultaneously.
Air cooling in compression can be carried out in indoor combustion engines with supervision, feeding the air after its compression in the compressor into the intermediate cooling radiator.
The heat of heat to the air from the cylinder walls at the beginning of the expansion is possible to a limited degree. Temperature walls of the combustion chamber of the adiabat engine
very high, which causes air heating entering the cylinder. The filling coefficient, and, therefore, the power of such an engine will be lower than that of the engine with forced cooling. This disadvantage is eliminated by turbocharging that uses the energy of exhaust gases; Part of this energy can be transmitted directly to crankshaft Engine through a power turbine (turbocompound engine).
The hot walls of the combustion chamber of the adiabate engine ensure ignition on them fuel, which predetermines the use of a diesel working process in such an engine.
With perfect heat insulation of the combustion chamber and cylinder, the temperature of the walls would increase to reach at a depth of about 1.5 mm from the surface of the average cycle temperature, i.e. It would be 800-1200 ° C. Such temperature conditions determine high requirements for the materials of the cylinder and parts forming the combustion chamber that should be heat-powered and have thermal insulation properties.
The engine cylinder, as already noted, should be lubricated. Conventional oils are used to a temperature of 220 ° C, with an exceedment of which there is a danger of burning and loss of elasticity of piston rings. If the head of the cylinder is made of aluminum alloy, then the strength of such a head is rapidly reduced by a temperature of 250-300 ° C. The permissible heating temperature of the exhaust valve is 900-1000 ° C. These values \u200b\u200bof the maximum permissible temperatures must be guided by creating an adiabatic engine.
The greatest success in the development of adiabate engines was achieved by Kammins (USA). The diagram of the adiabate engine developed by this company is depicted in fig. 75, where the heat insulated cylinder is shown, the piston and the exhaust channel of the cylinder head. The temperature of the exhaust gases in the heat insulated exhaust pipe is 816 ° C. The turbine attached to the exhaust pipe is connected with a crankshaft through a two-stage gearbox, equipped with a spinner of the vibrations.
An experimental sample of the adiabat engine was created on the basis of a six-cylinder diesel engine of the NH type. A schematic transverse section of this engine is shown in Fig. 76, and its parameters are shown below:
The number of cylinders ............................................... 6
Cylinder diameter, mm ...................................... 139.7
Piston move, mm .............................................. ... 152,4.
Rotation frequency, min-1 .................................. 1900
Maximum pressure in the cylinder, MPa ..... 13
Type of lubricant ...............................
Average efficient pressure, MPa ............... 1.3
Mass affect air / fuel ............... 27: 1
Incoming air temperature, ° C ................ 60
Expected results
Power, kW ............................................. 373
Rotation frequency, min-1 ............................. 1900
Emissions nox + chx ..................................... 6.7
Specific fuel consumption, g / (kWh) .......... 170
Service life, h ............................................ 250
In engine design, glass-ceramic materials with high heat resistance are widely used. However, to date, ensure high quality and long service life of parts from these materials failed.
Much attention was paid to creating a composite piston shown in Fig. 77. Ceramic head piston 1 connected to its base 2 special bolt 3 with washer 4 . The maximum temperature in the middle of the head reaches 930 ° C. From the base of the head is thermally insulated with a package of thin steel pads 6 with a strong uneven and rough surface. Each layer of the package due to the small surface of the contact has large thermal resistance. The thermal expansion of the bolt is compensated by car springs 5.
Distill heat into the air and its regulation
The heat removal of the cooling system causes not only the loss of thermal energy, which could be implemented to work, but also direct losses of part of the efficient engine power, due to the fan drive and water pump. The heat dissipation from the cooled surface S into the air medium depends on the temperature difference between this surface and air t., as well as on the coating coefficient of the cooling surface in the air. This coefficient does not change any significantly independently of whether the coolant coolant is formed by the fluid cooling radiator plates or the edges of the air cooling engine parts. First of all, consider engines with liquid cooling systems.
The amount of cooling air is the smaller, the more heat is discharged into a unit of its volume, that is, the more coolant will be heated. ENGE requires a uniform distribution of air throughout the cooling surface and the maximum temperature difference between it and air. In the radiator of the liquid cooling system, conditions are created under which the cooled surface has an almost uniform temperature field, and the temperature of the cooling air, as it moves through the radiator, gradually increases, reaching the maximum value at the output from it. The temperature difference between air and the cooled surface gradually decreases. At first glance, it seems that a deep radiator is preferable, since it is more heated in it, but this question should be considered from the energy position.
The surface coefficient of surface A is a complex dependence on a number of factors, but the speed of air flow near the cooling surface is the greatest effect on its magnitude. The relationship between them can be represented by the relation ~ 0.6-0.7.
With an increase in air velocity by 10%, heat dissipation increases only by 7%. The speed of the air flow is proportional to its flow through the radiator. If the radiator design does not change, then to increase the amount of heat output, 7% should increase the fan speed by 10%, since the amount of air flowed directly depends on it. The air pressure at a permanent area of \u200b\u200bthe fan cross section depends on the second degree of its rotational speed, and the power of the fan drive is proportional to its third degree. Thus, with an increase in the fan speed by 10%, the drive power increases by 33%, which has negative consequences that are manifested in the deterioration of the mechanical efficiency of the engine.
The dependence of the cooler air from the amount of heat assured, as well as the increase in air pressure and the fan drive power is shown in Fig. 78. From the standpoint of reducing energy costs, this nomogram is very useful. If the windshield surface of the radiator is increased by 7%, then the area of \u200b\u200bthe flow section and the coolant surface of the radiator increase proportionally, and, consequently, the amount of cooling air is sufficient to increase the same 7% to take 7% more heat, i.e. as in The example described above. At the same time, the power of the fan rises only by 22.5% instead of 33%. If the air flow through the fan V. z Enlarge by 20% (point and arrows 1 in fig. 78), then the quantity and heat of q, proportional V. Z.0,3 , it will increase by 11.5%. Changing the air flow rate by increasing the frequency of rotation of the fan to the same 20% leads to an increase in the pressure of the air flow by 44%, and the power of the fan drive is 72.8%. To increase the heat sink by 20% in the same way, an increase in air flow by 35.5% (point and dotted arrows should be increased 2 in fig. 78), which entails an increase in air pressure by 84%, and the power of the fan drive is almost 2.5 times (by 149%). Therefore, it is more profitable to increase the windshield surface of the radiator than with the same radiator and fan to increase the frequency of rotation of the latter.
If the radiator is divided by its depth to two equal parts, then in the front temperature difference t.1 will be more than in the rear t.2 , And, therefore, the front of the radiator will be cooled with air stronger. Two radiator obtained by separating one into two parts, in depth will have smaller resistance to the coolant flow. Therefore, too deep radiator is unprofitable for use.
The radiator must be made of material with good thermal conductivity and its resistance to air and fluid flows should be small. The mass of the radiator and the volume of fluid in it should also be small, as it is important for quick engine warming up and turning on the heating system in the car. For modern passenger cars Low front part of the body requires low height radiators.
To minimize energy costs, it is important to achieve a high fan efficiency, for which a guide air duct is used, having a small gap along the outer diameter of the fan impeller. The impeller of the fan is often made from plastic, which ensures the exact form of the profile of the blades, their smooth surface and low noise. At high speeds, such blades are deformed, thereby reducing air flow, which is very advisable.
High radiator temperature increases its efficiency. Therefore, sealed radiators are used, excessive pressure in which increases the boiling point of the coolant and, therefore, the temperature of the entire radiator matrix, which can be smaller and easier.
For air cooling engine, there are the same patterns as for the liquid cooling engine. The difference is that the edges of the air cooling engine are higher than the radiator matrix, therefore, a smaller amount of cooling air is required to remove the same amount of heat during air-cooled. This advantage is of great importance during the operation of cars in a hot climate. In tab. 10 shows the modes of operation of liquid and air cooling engines when the ambient temperature changes from 0 to 50 ° C. For the liquid cooling engine, the cooling degree decreases by 45.5%, while the engine of air cooling in the same conditions is only 27.8%. For the liquid cooling engine, this means a more cumbersome and more energy-intensive cooling system. For air cooling engine, a small alteration of the fan is sufficient.
Table 10. Engine cooling efficiency with liquid and air cooling systems depending on the external temperature
| Cooling type, ° С | Liquid | Air |
| Cooling surface temperature | 110 | 180 |
| 0 | 0 | |
| Temperature difference | 110 | 180 |
| Cooling air temperature | 50 | 50 |
| Temperature difference | 60 | 130 |
| The deterioration of the mode at a temperature of 50 ° C compared to 0 ° C,% | 45,5 | 27,5 |
Cooling regulation gives greater energy savings. Cooling can be adjusted so that it is satisfactory at maximum engine load and at maximum air temperature. But at a lower ambient temperature and partial engine load, such cooling, naturally, is redundant and to reduce wear and mechanical engine efficiency, it is necessary to adjust the cooling. In liquid cooling engines, this is usually made by throttling fluid flow through the radiator. In this case, the fan power consumed does not change, and from an energy point of view, such regulation does not bring any benefit. For example, for cooling the engine with a power of 50 kW at a temperature of 30 ° C, 2.5 kW is consumed, and at a temperature of 0 ° C and the load of the engine 50% would only need 0.23 kW. Provided that the required amount of cooling air is proportional to the temperature difference between the surface of the radiator and air, with a 50% engine load for its cooling, half of the flow of air, adjustable fan rotation frequency, is also sufficient. Energy savings and, therefore, fuel consumption with such regulation can be quite significant.
Therefore, the cooling regulation is currently paid to special attention. The most convenient adjustment is to change the fan speed, but for its implementation, you must have an adjustable drive.
Turning off the fan drive pursues the same goal as the change in the speed of rotation. To do this, it is convenient to use an electromagnetic coupling, including a thermostat depending on the temperature of the fluid (or cylinder head). If the coupling is turned on with a thermostat, the regulation is carried out not only depending on the ambient temperature, but also from the engine load, which is very effective.
Turning off the fan with viscous coupling produced in several ways. As an example, consider the viscous coupling of the company "Holts" (USA).
With the simplest way, limit the transmitted torque is used. Since with the increasing speed of rotation, the moment required to rotate the fan increases, the slip of the viscous clutch also increases, and with some value of the fan power consumed, its rotational speed is no longer increasing (Fig. 79). The frequency of rotation of the fan with an unregulated clinoramine drive from the engine crankshaft increases in proportion to the engine speed (curve b), whereas in the case of a fan drive through a viscous clutch its frequency is growing only to the value h.v.
\u003d 2500 min - 1 (rotation curve BUTunregulated drive, grows in proportion to the third ).
The power consumed by the fan with the degree of rotation frequency and on the maximum power mode is 8.8 kW. The fan driven through viscosity of the clutter increases, as noted, up to 2500 min-1, and, frequency required on the power of the fan power is 2 kW. Since 1 kW is additionally dissipated in the viscous clutch with a 50% slip in heat, the total energy savings on the fan drive is reduced by fuel consumption. Such a cooling regulation is 5.8 kW, however, it can be considered a satisfactory-separation of the air does not grow directly proportional to the frequency, since the rotation of the engine sprawl engine remains the growth of high-speed pressure, in addition, with an increase in air cooled air.
Another type of viscous coupling of the company "Holts" provides the control of the thermal mode of the engine additionally and on the ambient temperature (Fig. 80). From the previously considered, this clutch differs in that the volume of fluid in it, the transmitting torque depends on the external temperature. Carter coupling is divided by a partition 5 (see Fig. 81) on the camera's chamber 1 and a backup volume chamber 2 interconnected by the valve 3. The valve is controlled by a bimetallic thermostat 4 depending on the air temperature. A snap 6, pressed to the spring disk, serves to reset the fluid from the disk and accelerate the flow of it from the disc camera to the volume 2. Part of the fluid is constantly in the camera of the drive disk and is able to transmit a small torque to the fan. At air temperature of 40 ° C, for example, the maximum fan speed is 1300 min-1, and the power consumption is not more than 0.7 kW. When the engine is heated, the bimetallic thermostat opens the valve, and part of the fluid enters the chamber of the drive disk. As the valve flow rate increases into the disc camera, the amount of fluid increases and with its full opening of the valve level in both half the same. The change in the transmitted torque and the frequency of rotation of the fan is shown by curves A 2 (see Fig. 80).
In this case, the maximum frequency of rotation of the heptilator is 3200 min-1, and the power consumption increases to 3.8 kW. The maximum opening of the valve corresponds to the ambient temperature of 65 ° C. Described engine cooling control can be reduced fuel consumption in passenger cars per 1 l / 100 km.
Powerful engines have even more advanced cooling control systems. Diesels "Tatra" The fan drive is carried out through the hydromefluoron, the oil volume in which is regulated by a thermostat depending on the temperatures of the exhaust gases and the surrounding air. The temperature sensor readings in the exhaust pipeline depend mainly on the engine load and, to a lesser extent, from its rotational speed. The delay of this sensor is very small, so the adjustment of cooling with its help is more completely.
The fan rotation frequency cooling is relatively easily carried out in the internal combustion engine of any type; This reduces the overall noise published by the car.
When the engine is the front of the engine across the car, the fan mechanical drive causes some difficulties and therefore the fan electric drive is used more often. In this case, cooling control is very simplified. The electric drive fan should not have a high power consumption, so they tend to use the cooling effect of the high-speed air pressure when the car moves, since with an increase in the engine load, the speed of the passenger car and, therefore, the high-speed head of the flowing air is growing. The fan electric drive works only for a short time when overcoming the protracted lifts or at high ambient temperature. Cooling air consumption through the fan is controlled by turning the electric motor using a thermostat,
If the radiator is located far from the engine, for example, in the bus with the rear engine, the fan usually has a hydraulic drive. The hydraulic pump drive-driven by the motor is supplied by a piston hydraulic motor with a swinging washer. Such a drive is more complicated and its use is appropriate in high power engines.
ANDUsing heat that worked with the spent gases
The exhaust gases of the engine contain a significant amount of thermal energy. It can be used, for example, for the heating of the car. Air heated by the exhaust gases in the gas-air heat exchanger of the heating system is dangerous due to the possibility of extinguishing or leakage of its tubes. Therefore, for heat transfer, oil or other non-freezing fluid, heated by the spent gases, is used.
It is even more expedient to use the exhaust gases to drive the cooling system fan. With large loads of the engine, the spent gases have the highest temperature, and the engine needs intensive cooling. Therefore, the use of a turbine operating on the exhaust gases to drive the cooling system fan is very advisable and is currently begins to be used. Such a drive can automatically adjust the cooling, although it is quite expensive.
An ejection cooling can be considered more acceptable from the point of view of the cost. The spent gases are sucking from ejector cooling air, which is mixed with them and is assigned to the atmosphere. Such a device is cheap and reliable, as it does not have any moving parts. An example of the ejection cooling system is shown in Fig. 82.
Ejection cooling was successfully applied in the racing cars "Tatra" and in some specialized cars. The disadvantage of the system is a high level of noise, since the exhaust gases must be directly inserted into the ejector, and the location of the noise silencer after it causes difficulties.
The main way to use the exhaust gas energy is their expansion in the turbine, which is most commonly used to drive a centrifugal compressor of the engine superior. It can also be used for other purposes, for example, for the fan drive; In turbocompound engines, it is directly connected to the engine crankshaft.
In engines using hydrogen as fuel, the warmth of the exhaust gases, as well as the reserved cooling system, can be used to heat the hydrides, thus obtaining the hydrogen contained in them. With this method, this warmth is accumulated in hydrides, and with a new refueling of hydride tanks with hydrogen, it can be used for various purposes for heating water, the heating of buildings, etc.
The energy of the exhaust gases is partially used to improve the supervision of the engine using the resulting fluctuations of their pressure in the outlet pipeline. The use of pressure fluctuations is that after opening the valve in the pipeline, a shock wave of pressure occurs, with a sound speed, passing to the open end of the pipeline, reflected from it and returning to the valve in the form of a vacuum wave. During the open state of the wave valve can go through the pipeline several times. At the same time, it is important that a wave of pouring, contributing to the cleaning of the cylinder from the exhaust gas and purging it with fresh air to it to the closing phase of the exhaust valve. Each branching of the pipeline creates obstacles to pressure waves, therefore the most favorable conditions for the use of pressure oscillations are created in the case of individual pipelines from each cylinder, having equal lengths on the area from the cylinder head before combining into the shared pipeline.
The speed of the sound does not depend on the frequency of rotation of the engine, so in the entire range of its favorable and unfavorable cylinders from the point of view of filling and cleaning the conditions of operation. On the engine curves of the NE engine and its average effective PE pressure, this is manifested in the form of "humps", which is clearly visible in fig. 83, where the outer speed characteristics of the engine of the Porsche racing car is depicted. Pressure oscillations are also used in the inlet pipeline: the arrival of the pressure wave to the inlet valve, especially in the phase of its closing, contributes to the purge and cleaning of the combustion chamber.
If several engine cylinders are connected to the total exhaust pipeline, then their number should be no more than three, and the alternation of work is uniform so that the release of exhaust gases from one cylinder does not block and do not affect the release process from the other. In a row four-cylinder engine, two extreme cylinders are usually combined into one common branch, and two medium cylinders to another. In a row six-cylinder engine, these branches are formed according to three front and three rear cylinders. Each of the branches has an independent entrance to the muffler, or at some distance from it, the branches are combined and their shared input into the muffler is organized.
Turbocharged engine
With a turbocharger, the exhaust gas energy is used in a turbine leading a centrifugal compressor for air supply to the engine. The large mass of air entering the engine under pressure from the compressor contributes to an increase in the electrical power of the engine and to reduce its specific fuel consumption. Two-stage air compression and expansion of exhaust gases carried out in the turbocharged engine allow you to get a high indicator engine efficiency.
If a compressor with a mechanical drive from the engine is used for boost, then only the engine power increases due to the supply of larger air. When saving the expansion tact only in the engine cylinders, the spent gases extend from it under high pressure, and if they are not currently used, it causes an increase in the specific fuel consumption.
The degree of superior depends on the purpose of the engine. With higher pressuring pressures, air in the compressor is heavily heated and it must be cooled at the input. Currently, turbochards are used mainly in diesel engines, the increase in the capacity of which by 25-30% does not require large boosting pressure, and the engine cooling does not cause difficulties. This method of increasing the power of the diesel engine is used most often.
An increase in the amount of air entering the air allows you to work on poor mixtures, which reduces the output of CO and CHX. Since the power of diesel engines is regulated by the fuel supply, and the air supply is not throttered, then with partial loads, very poor mixes are used, which helps to reduce the specific fuel consumption. Flammation of the poor mixture in dyes with superior does not cause difficulties, as it occurs at high air temperatures. The purge of the combustion chamber with the air in the diesels is permissible, since, unlike the fuel supply engine, there is no fuel injection engine.
Diesel with a superior degree of compression is usually somewhat reduced in order to limit maximum pressure in the cylinder. Higher pressure and air temperature at the end of the compression tact reduce the ignition delay, and the engine hardness becomes less.
Diesels with turbocharged, certain problems exist, if necessary, quickly increase engine power. When you press the control pedal, the supply of air supply due to the inertia of the turbocharger lags behind increasing the supply of fuel, so at first the engine operates on a rich mixture with increased smoke and only after a certain period of time the composition of the mixture reaches the desired value. The duration of this period depends on the moment of inertia of the turbocharger rotor. Attempting to reduce the inertia of the rotor to a minimum by a decrease in the diameter of the turbine and compressor impeller entails the need to increase the frequency of rotation of the turbocharger to 100,000 minutes. Such turbochargers have small size and mass, an example of one of them is shown in Fig. 84. To get high revs Turbocompressor, use centripetal turbines. The heat transfer from the turbine housing to the compressor body must be minimal, so both housings are well insulated from each other. Depending on the number of cylinders and the scheme for combining their exhaust pipelines, the turbine have one or two inputs for exhaust gases. Diesel with reducing due to the disposal of the exhaust gas energy makes it possible to achieve a very low specific fuel consumption. Recall that the thermal balances of internal combustion engines are shown in Table. 1 and 2.
For passenger cars, a lack of diesel engine is its big mass. Therefore, the new diesel engines for passenger cars are based, mainly on high-speed gasoline engines as the use of high speeds of rotation allows you to reduce the mass of diesel to an acceptable value.
Fuel consumption in diesel, especially when driving in the city, in the modes of partial loads is noticeably less. The further development of these diesel engines is associated with turbocharged, in which the content of harmful carbon-containing components in the exhaust gases is reduced, and its work becomes softer. An increase in NOx due to higher combustion temperatures can be reduced by the recycling of exhaust gases. The cost of a diesel engine is higher than gasoline, however, with a lack of oil, its use is more profitable, as it can be out of oil! Claimed more diesel fuel than high-octane gasoline
The turbocharging of gasoline engines has some features of the operating temperatures of RAWS gasoline engines above, it makes higher demands on the material of the turbine, but is not a factor limiting the use of superimposure. WMU It is necessary to adjust the colollers of the supplied air, which is especially important at high frequencies of the battle, when the compressor supplies a large amount of air. Unlike a diesel engine where power regulation is made by a decrease in the supply of fuel, in the gasoline engine, the similar method is not applicable, since the composition of the mixture would be so poor in these modes that the ignition would not be guaranteed. Therefore, air supply at the modes of the maximum frequency of rotation of the turbocharger must be limited. There are several ways of such a limitation. The most commonly used by the exhaust gases through a special channel past the turbine, thereby reducing the frequency of rotation of the turbocharger and the amount of air supplied. The scheme of this regulation is given in Fig. 85.
The exhaust gases from the engine are entered into the exhaust pipeline 10, and then through the turbine 11 in the silencer of the noise of release 12. At maximum load and high engine speed, the pressure in the inlet canal 7 transmitted through the channel 15 opens the reversal valve 13, through which spent gases on the pipeline 14 enroll directly into the muffler, bypassing the turbine. There is a smaller amount of exhaust gases in the turbine, and air supply to the compressor 4 in the intake canal 6 decreases 6-8 times. (The construction of the exhaust gas cord valve is shown in Fig. 86.)
The considered method of regulating air supply has the disadvantage that the reduction in the power of the engine when the engine control pedal is released instantly and lasts, moreover, longer than the frequency of the turbine rotation drops. When you press the pedal, the required power is achieved with a delay, the frequency of rotation of the turbocharger is slowly increasing even after closing the bypass channel. Such a delay is undesirable with a lively movement, if necessary, quick braking and the subsequent rapid acceleration of the car. Therefore, a different method of regulation is used, namely, use additionally and airflow through the compressor bypass canal. 4.
Air enters the engine through the air filter 1, the composition of the mixture composition 2 firms "Bosch" (Germany) type "K-jetronics", controlling fuel injectors 9 (see ch. 13), then in the inlet pipe 5, and then the compressor 4 putting into intake canals and nozzles 6 -five. With the quick release of the control pedal, the compressor rotates, and to reduce pressure in the channel 6 bypass valve 5 vacuum in the inlet nozzle 8 opens and air pressure from the channel 6 through the same valve 5 is repospected again into the pipeline 3 in front of the compressor. Pressure alignment occurs very quickly, the frequency of rotation of the turbocharger does not fall sharply. Next click on the Pedal of the Bypass Valve 5 quickly closes, and the compressor with a minor delay serves air air under pressure into the engine. This method allows you to achieve the total engine power for the split second after clicking on the control pedal.
A good example of a gasoline engine with superior is the "Porsche 911" engine (Germany). Initially, he was an undelated six-cylinder air cooling engine with a working volume of 2000 cm3, which had a power of 96 kW. In an embodiment with a superposition, its working volume was increased to 3000 cm3, and the power was adjusted to 220 kW in accordance with the requirements for the level of noise and the presence of harmful substances in the exhaust gases. The size of the engine did not increase. When developing the engine "911", a wide experience was used, accumulated when creating a twelve-cylinder riding engine model "917", which already in 1978 developed the power of 810 kW at a rotational speed of 7800 min-1 and pressuring pressure of 140 kPa. Two turbocharger was installed on the engine, its maximum torque was 1100 N · m, and the mass is 285 kg. In the mode of the nominal power of the engine, the air supply of tubes by tubes at a speed of 90,000 min-1 was 0.55 kg / s at an air temperature of 150-160 ° C. At maximum engine power, the temperature of the exhaust gases reached 1000-1100 ° C. The acceleration of the racing car from space up to 100 km / h with this engine lasted 2.3 s. When creating this racing engine, a perfect turbocharging system was developed, which made it possible to achieve good dynamic quality vehicles. The same regulatory scheme was also applied in the "Porsche 911" engine.
With the full opening of the throttle, the maximum pressurization pressure in the engine "Porsche 911" of the reversal valve 13 (See Fig. 85) Limited 80 kPa. This pressure is already achieved at a speed of 3000 min-1, in the engine speed of 3000-5500 min-1, the superior pressure is constantly and the air temperature behind the compressor is 125 ° C. At maximum engine power, the purge value reaches 22% of the exhaust gases. The safety valve installed in the inlet channel is adjusted to the pressure of 110-140 kPa, and when the exhaust valve valve accident, it turns off the fuel supply, thereby limiting the uncontrolled increase in engine power. At maximum engine power, the air supply compressor is 0.24 kg / s. The degree of compression equal to the undead engine E \u003d 8.5, with the introduction of the superior was reduced to 6.5. In addition, output valves with sodium cooling were used, the gas distribution phases were changed and the cooling system was improved. At maximum engine power, the frequency of rotation of the turbocharger is 90,000 min-1, while the power of the turbine reaches 26 kW. Cars intended for exports to the United States must meet the requirements for the content of harmful substances in the exhaust gases, and therefore supplied in the USA cars "Porsche 911" are additionally equipped with two thermal reactors, the system of feeding the secondary air from spent gases for their afterburning, as well as The recycling system of exhaust gases. The power of the Porsche 911 engine decreases to 195 kW.
In some other turbocharging systems, such as system Ars.the Swedish company SAAB, electronics applied to regulate the pressure. The pressure limit is carried out by a valve regulating the flow of exhaust gases through the bypass channel by the turbine. The valve opens in the occurrence of a vacuum in the inlet pipeline, the value of which is regulated by throttle the air flow between the inlet pipeline and the input to the compressor.
Adjusting permission in the bypass valve The throttle has an electric drive controlled by an electronic device by signals of pressure sensors, detonation and rotational speed. The detonation sensor is a sensitive piezoelectric element installed in the cylinder block and detecting the occurrence of detonation stuffs. At the signal of this sensor, the vacuum is limited in the control chamber of the bypass valve.
Such a turbocharging system allows you to provide good dynamic qualities of the vehicle necessary, for example, for quick overtaking in conditions of intensive movement. To do this, you can quickly translate the engine to the mode with maximum pressure pressure, as detonation in a relatively cold, working on a partial load, the engine does not occur instantly. After a few seconds, when the temperatures increase and detonation will begin to appear, the control device will reduce the pressure on the detonation sensor signal.
The advantage of such regulation is that it allows you to use in the engine without any fuel changes with different octane numbers. When using fuel with an octane number 91, the Saab engine with such a regulatory system can work for a long time with a pressurization of up to 70 kPa. At the same time, the degree of compression of this engine, which uses the gasoline injection instrument "Bosch K-jetronics", is E \u003d 8.5. The successes achieved in reducing the fuel consumption of passenger cars due to the use of turbochargedwood, contributed to its use in the construction motorcycle. Here you should call the Japanese company "Honda", which for the first time applied turbocharging in a two-cylinder engine of liquid cooling model "SK.500 "To increase its power and reduce fuel consumption. The use of turbocompressors in engines with a small working volume has a number of difficulties associated with the need to obtain the same pressure pressures, as in high power engines, but at low air flow. The pressurization pressure depends mainly on the circumferential velocity of the wheel of the compressor, and the diameter of this wheel is determined by the required air supply. It is consequently necessary that the turbocharger has a very high speed of rotation at small diameters of the working wheels. The diameter of the compressor wheel in said engine "Honda" with a volume of 500 cm3 is 48.3 mm and at a pressure of 0.13 MPa, the turbocharger rotor rotates with a frequency of 180,000 min-1. The maximum allowable speed of rotation of this turbocharger reaches 240000 min-1.
With increasing pressure of the superior above 0.13 MPa, the valve (Figure 87) of the exhaust gases is opened, controlled by pressure pressure in the chamber, and part of the exhaust gases, bypassing the turbine, is sent to the exhaust pipeline, which limits the further increase in the speed of rotation of the compressor. The opening of the reversal valve occurs at the engine speed of about 6500 min-1 and with further increases to increase the pressure pressure no longer grows.
The amount of injected fuel injector required to obtain the required composition of the mixture is determined by the computing device placed above rear wheel Motorcycle, which also processes information of incoming air and coolant temperature sensors, throttle position sensor, air pressure sensors, engine speed sensor.
The main advantage of the engine with superior is manifested in reducing fuel consumption while increasing engine power. Motorcycle "Honda SK500 "With a hopeless engine consumes 4.8 l / 100 km, and the same motorcycle equipped with an engine with a superior model" CX 500 7x is only 4.28 l / 100 km. Mass Motorcycle "Honda SK500 g "is 248 kg, which is more than 50 kg above the mass of motorcycles of a similar class with an engine capacity 500-550 cm3 (for example, motorcycle" Kawasaki KZ.550 "has a mass of 190 kg). At the same time, however, the dynamic qualities and maximum speed at the Honda CX 500 7 motorcycle are the same as motorcycles with twice as large working volume. The brake system is improved due to the growth of the high-speed qualities of this motorcycle. The engine "Honda CX 500 g" is designed for even higher speeds and its maximum rotation frequency is 9000 min-1.
The decrease in the average fuel consumption is also achieved by the fact that when the motorcycle moves with an average operating speed, the pressure in the inlet pipeline is equal to an atmospheric or even somewhat lower it, that is, the use of the superior is very slightly. Only with the full opening of the throttle and, consequently, the growth of the number and temperature of the exhaust gases increases the frequency of rotation of the turbocharger, the pressure of the superior and increase the power of the engine. Some retardation of the engine power increases with a sharp opening of the throttle, occurs and is associated with the time necessary for overclocking the turbocharger.
General scheme of power installation of a motorcycle "Honda CX 500 T "with turbocharging shown in Fig. 87. Large fluctuations in air pressure in the inlet pipeline of the two-cylinder engine with an uneven order of operation of the cylinders are distributed by the camera and the damping receiver. When starting the motor, the valves prevent the reverse airflow caused by the large overlap of the gas distribution phases. The liquid cooling system eliminates the supply of hot air to the driver's feet having a place with air cooling. By blowing the radiator of the cooling system is carried out by an electric fan. A short exhaust pipeline to the turbine reduces the weight loss of exhaust gases and helps reduce the fuel consumption. Maximum motorcycle speed 177 km / h.
Advanced like "Complane"
A very interesting way to reducing the "Complane", developed by Brown & Bovteri, Switzerland, is to use the pressure of the exhaust gases acting directly to the air flow supplied to the engine. The engine indicators obtained at the same time, as in the case of the use of turbocharger-sera, but the turbine and centrifugal compressor, for the manufacture and balancing of which are required special materials and high-precision equipment are absent.
The scheme of the system of supervision of the "Complane" type is presented in Fig. 88. The main part is a blade rotor rotating in the housing with the speed of rotation, three times the rotor of the engine crankshaft rotor is installed in the case on rolling bearings and is driven by a wedge or gear strap. Compressor type "Command" consumes no more than 2% of the engine power. The "Comprelex" unit is not a compressor in the full sense of the word, since its rotor has only channels parallel to the axis of rotation. In these channels, the air flowing into the engine is compressed by the pressure of the exhaust gases. Rotor's ending gaps guarantee the distribution of exhaust gases and air through the rotor channels. At the outer circuit of the rotor there are radial plates having small gaps with the inner surface of the housing, so that the channels are formed closed on both sides by the end lids.
In the right lid there are windows and to supply exhaust gases from the engine to the unit of the unit and g -to remove the exhaust gases from the housing to the exhaust pipeline and then - in the atmosphere in the left lid there are windows b.for supplying compressed air into the engine and windows d.for the supply of fresh air into the housing from the inlet pipeline e.Moving the channels during rotation of the rotor causes them alternately with the exhaust and intake pipelines of the engine.
When opening the window buta shock wave of pressure occurs, which, at the speed of sound, moves to another end of the exhaust pipeline and simultaneously sends the spent gases into the rotor channel, without mixing them with air. When this pressure wave reaches the other end of the exhaust pipeline, the window b and the air compressed air in the rotor channel will be pushed out of it in the pipeline into the engine. However, even before the exhaust gases in this channel of the rotor approach its left end, the sleep closes the window butand then the window b., And this rotor canal with the exhaust gases being under pressure from both sides will be closed with the end walls of the case.
In the further rotation of the rotor, this channel with flutter gases will fit the window g.in the graduation pipe, the wire and the spent gases will come to it from the channel. When moving the channel past windows g.leaving exhaust gases are ejected through windows d.fresh air, which, filling the entire canal, blows and cools the rotor. Passing the windows g.and d,the rotor channel filled with fresh air is again closed on both sides by the ends of the housing and, thus, ready for the next cycle. The described cycle is very simplified in comparison with what is happening in reality and is carried out only in the narrow range of the engine rotation frequency. Here the reason for the fact that known for the past 40 years this way is not applied in cars. Over the past 10 years, the works of Brown & Bovery, the completion of the "Complan" is significantly improved, in particular, an additional chamber in the end cover was introduced, providing reliable air supply in a wide range of engine speed, including at its small values.
Superior "Complane" was tested on all-wheel drive cars Increased loss of the Austrian Firm "Steeher-Daimler-Pooh", on which Diesels "Opel Record 2,3d" and Mercedes-Benz 200D were installed.
The advantage of the "Complart" method in comparison with the turbocharger is the lack of delaying the increase in pressure pressure after pressing the control pedal. The efficiency of the turbocharged system is determined by the energy of exhaust gas depending on their temperature. If, for example, with the total engine power, the exhaust gas temperature is 400 ° C, then in winter it takes several minutes to achieve it. A significant advantage of the Complane method also consists in obtaining a large torque of the engine at low rotational frequencies, which makes it possible to apply a gearbox with a smaller number of steps.
The fast set of engine power while pressing the control pedal is especially desirable for racing cars The Italian Farrari firm is experiencing a way of reducing the "Complan" on its racing cars, since when using a turbocharger for a quick engine response to the position of the control pedal when the racing car of turns, it is necessary to use the previously complex regulatory system.
When testing a system of superior "Complates" on SHES-Ticillion engines of racing cars "Ferrari" class F1.there was a very fast engine response to move the pedal of control
To obtain the maximum pressurization pressure on these engines, an adequation air cooling was used. Through the rotor of the complex "Complane" passes a larger amount of air than the engine is required, since the air portion is used to cool the hardened unit. It is very beneficial for racing engines, which and at the start work almost with full flow Air through an intermediate cooling radiator. Under these conditions, the engine with the unit "Complane" will be at the time of the start to be in the best temperature state to enter full power.
The use of a comprehension unit "Complan" instead of a turbocharger reduces engine noise, as it works at a lower rotational speed. At the initial stage of development, the rotor speed was the reason for the appearance of noise of the same frequency as the turbocharger. This disadvantage was eliminated by an uneven step of channels around the rotor circumference.
When applying the Comprelex system, the recycling of exhaust gases is significantly simplified, used to reduce the content in them. NOX.Usually recycling is carried out by selecting a part of the exhaust gases from the exhaust pipe, their dosing, cooling and supplying the engine in the intake pipeline. In the Command system, this scheme can be significantly easier, since the mixing of exhaust gases with a stream of fresh air and their cooling occurs directly in the rotor channels.
Ways to increase the mechanical efficiency of the internal combustion engine
Mechanical efficiency reflects the ratio between the indicator and efficient engine power. The difference in these values \u200b\u200bis caused by losses associated with the transfer of gas forces from the bottom of the piston to the flywheel and with the drive of the engine auxiliary equipment. All these losses must know exactly when the task is to improve the fuel efficiency of the engine.
The most significant part of the losses is caused by friction in the cylinder, smaller - friction in well-lubricated bearings and the drive required for the engine hardware. The losses associated with the air intake into the engine (pump losses) are very important, since they increase in proportion to the square of the engine rotation frequency.
Power loss required to drive equipment that provides engine operation includes power to the drive of the mechanism of gas distribution, oil, water and fuel pumps, fan of the cooling system. When cooled, the air supply fan is an integral engine element when testing it on the stand, while in the liquid cooling engines during testing the fan and the radiator are often absent, and water from the external cooling circuit is used for cooling. If the power consumption of the fan of the engine of the liquid cooling is not taken into account, then this gives a noticeable overestimation of its economic and power-premissors in comparison with the air cooler engine.
Other equipment drive losses are associated with a generator, pneumocompressor, hydraulic pumps needed for lighting, ensuring instrument, brake system, car steering. When testing the engine on the brake stand, it is necessary to accurately determine what to consider additional equipment and how to load it, as it is necessary for objective comparison characteristics. different engines. In particular, this refers to the cooling system of the oil, which, when moving the car, is cooled by blowing the oil pan with air, absent when testing on the brake stand. When testing on the engine stand without a fan, the conditions of blowing pipelines are not reproduced, which causes an increase in the temperatures in the inlet pipe and leads to a decrease in the magnitude of the filling coefficient and engine power.
The placement of the air filter and the amount of resistance of the exhaust pipeline must comply with the engine in the vehicle in the car. These important features must be taken into account when comparing the characteristics of various engines or one engine intended for use in various conditions, for example, in a passenger or cargo car, a tractor or to drive a stationary generator, compressor, etc.
When the engine load decreases, its mechanical efficiency deteriorates, since the absolute value of most losses does not depend on the load. A visual example is the operation of the engine without a load, that is, at idle when the mechanical efficiency is zero and the entire indicator power of the engine is spent on overcoming its losses. When the engine loads by 50% or less, the specific fuel consumption compared to the full load increases significantly, and therefore use to drive an engine greater than it is required, the power is completely uneconomical.
Mechanical engine efficiency depends on the type of oil used. Application B. winter time Increased viscosity oils leads to an increase in fuel consumption. The engine power at high altitudes above sea level drops due to a decrease in the pressure of the atmosphere, but its losses are practically not changed, as a result of which the specific fuel consumption increases in the same way as it takes place at partial load of the engine.
Friction losses in the cylindrophone group and bearings
The largest losses in the engine are caused by the friction of the piston in the cylinder. The conditions for lubricating the walls of the cylinder are far unsatisfactory. The layer of oil on the wall of the cylinder when the piston position in NMT is under the action of hot exhaust gases. To reduce the oil consumption, the oil-chain ring removes part of it from the cylinder wall when the piston moves to the NMT, however, the lubrication layer between the piston skirt and the cylinder is preserved.
The greatest friction causes the first compression ring. When the piston moves to the VMT, this ring is based on the bottom surface of the piston groove and pressure arising from compression, and then combustion of the working mixture, presses it to the cylinder wall. Since the lubrication regime of the piston ring is least favorable due to the presence of dry friction and high temperature, then friction losses here are the highest. The lubrication mode of the second compression ring is more favorable, but the friction remains significant. Therefore, the number of piston rings also affects the magnitude of the friction loss of the cylindrophone group.
Another unfavorable factor is the pressing of the piston near the NMT to the wall of the cylinder of the pressure of gases and the inertia forces of reciprocating moving masses. At high-speed car engines Inertial forces have a greater amount than gas. Therefore, the largest load connecting connecting rod bearings in the VTC of the output clock when the connecting rod is stretched by inertial forces attached to its upper and lower heads.
The force acting along the connecting rod is folded on the forces directed along the axis of the cylinder and normally to its wall.
Rolling bearings in the engine profitably use with large efforts on them. It is advisable, for example, to place "valve rockers on needle bearings. As roller bearings, roller bearings were also used as the piston finger bearings, especially in the two-stroke high power engines. The piston and the piston finger bearing of the two-stroke motor in most cases are loaded only in one direction, so The required oil film cannot be formed in the sliding bearing. For good lubrication of the sliding bearing in the top head of the rod, along the entire length of its sleeve in this case, transverse lubricating grooves are performed at such a distance from each other so that oil films can form when swinging in this place. .
To obtain small friction losses in the cylinder-portion group, it is necessary to have pistons with yebal weight, a small number of piston rings and a protective layer on a piston skirt, protecting the piston from bully and jamming.
Losses in gas exchange
To fill the cylinder with air, it is necessary to avoid pressure drops between the cylinder and the external environment. The cutting of the cylinder at the intake, operating in the direction opposite to the movement of the piston, and the braking rotation of the crankshaft depends on the phases of the gas distribution, the diameter of the inlet pipeline, as well as from the shape of the inlet channel, necessary, for example, to create air in the cylinder. The engine in this part of the cycle acts as an air pump and part of the engine indicator power is consumed on its drive.
For a good filling of the cylinder, it is necessary that pressure losses proportional to the square of the engine rotation frequency when filling were the smallest. A similar nature of the dependence on the rotational speeds also have friction losses in the cylindropional group, and since this type of losses prevails among others, the total losses also depend on the second degree of engine speed. Therefore, mechanical efficiency with increasing rotational speed drops, and the specific fuel consumption is worse.
At maximum engine power, the mechanical efficiency is usually 0.75, and with a further increase in the speed of rotation, a rapid drop in efficient power occurs. At maximum speed and partial engine loads, efficient efficiency is minimal.
The losses for gas exchange include energy costs associated with purging the crankshaft crankcase. Single-cylinder four-stroke engines have the greatest losses, in which the air is absorbed into the crankcase at each piston and is repeatedly pushed out of it. Large volume of pumpable air is also also two-cylinder engines with V-shaped and peposite positions of cylinders. This type of loss can be reduced by setting the check valve that creates per capita in the crankcase. Carter cuts also reduces oil losses due to leaks. In multi-cylinder engines, which one piston moves down, and the other upward, the volume of gas in the crankcase does not change, but the neighboring sections of the cylinders should have a good one with each other.
Losses on the drive auxiliary engine equipment
The value of the equipment losses is often underestimated, although they have a big impact on the mechanical efficiency of the engine. Well investigated losses on the drive mechanism of gas distribution. The work spent when the valve is opened is partially refundable when the valve spring closes it and thereby moves camshaft. Losses on the drive of gas distribution relatively small and with their decrease, it is possible to obtain only a small cost savings for drives. Sometimes the camshaft is placed on rolling bearings, but it applies only to the engines of racing cars.
More attention should be paid to the oil pump. If the size of the pump and the oil consumption through it is overestimated, most of the oil is reset through a reduction valve at a large pressure, there are significant losses on the oil pump drive. At the same time, it is necessary to have reserves in the lubricant system in order to provide sufficient pressure for lubricating the bearings of sliding, including for worn. In this case, the small supply of oil pump leads to a decrease in pressure at low engine rotation frequencies and during its long-term operation with full load. The reduction valve in these conditions should be closed and the entire oil supply should be used for lubrication. On the drive fuel pump And the ignition distributor is consumed by a small power. Also, a little energy consumes an AC generator. A significant part of efficient power, namely 5-10%, is spent on the fan drive and the cooling system pump required to remove heat from the engine. This was already mentioned. There is some ways to see, several ways to improve the mechanical engine efficiency.
On the drive of the fuel pump and opening the nozzles, you can save a small amount of energy. In a slightly large extent, it is possible in diesel.
Losses on the drive of additional equipment of the car
The car is also equipped with equipment that consumes part of the efficient engine power, and thereby reduces the rest of its part that is on the car drive. In a passenger car, such equipment is used in limited quantities, mostly these are various amplifiers used to facilitate the control of the car, for example, steering, adhesion drive, brake drive. For a climate installation of a car, a certain energy is also required, especially for air conditioning air conditioner. Energy is also needed for various hydraulic drives, for example, moving seats, opening windows, roofs, etc.
In the cargo car, the volume of additional equipment is much more. Usually used the brake system using a separate source of energy, dump truck, self-loading devices, a device for raising spare wheels, etc. special purpose Such mechanisms are applied even wider. In the total fuel consumption, these cases of energy consumption must be taken into account.
The most important of these devices is a compressor to create a constant air pressure in a pneumatic brake system. The compressor works constantly, filling the air resheffer, part of the air from which through a reduction valve without further use enters the atmosphere. For hydraulic system high pressureservicing optional equipmentCharacteristic mainly loss in reduction valves. They usually use a valve, which, after reaching the operating pressure in the hydroaccumulator, turns off the further submission to it working fluid and controls the bypass line between the pump and the tank.
Comparison of mechanical losses in gasoline and diesel engines
Comparative data on mechanical losses measured in the same operating conditions of the gasoline engine with a degree of compression E \u003d 6 and a diesel engine with a compression ratio E \u003d 16 (Table 11, a).
For a gasoline engine, in addition, in Table. 11, used also a comparison of mechanical losses in full and partial loads.
Table 11.A. The average pressure of various types of mechanical losses in gasoline and diesel engines (1600 min - 1), MPa
| Type of loss | engine's type | |
| Petrol \u003d 6. | Diesel \u003d 16. | |
| 0,025 | 0,025 | |
| Water, oil and fuel pump drive | 0,0072 | 0,0108 |
| Gas distribution mechanism drive | 0,0108 | 0,0108 |
| Losses in indigenous and brass bearings | 0,029 | 0,043 |
| 0,057 | 0,09 | |
| Mechanical losses, total | 0,129 | 0,18 |
| Average effective pressure | 0,933 | 0,846 |
| Mechanical efficiency,% | 87,8 | 82,5 |
Table 11.B. The average pressure of various types of mechanical losses in the gasoline engine (1600 min-1, E \u003d 6) at various loads, MPa
| Type of loss | ||
| 100 % | 30 % | |
| Pump losses (gas exchange losses) | 0,025 | 0,043 |
| Gas distribution mechanism drive and auxiliary equipment | 0,0179 |
0,0179 |
| Losses in the crank-connecting mechanism | 0,0287 | 0,0251 |
| Losses in the cylindrophone group | 0,0574 | 0,05 |
| Mechanical losses, total | 0,129 | 0,136 |
| Average effective pressure | 0,933 | 0,280 |
| Mechanical efficiency,% | 87,8 | 67,3 |
Common losses, as can be seen from the table. 11, relatively small, since they were measured at a low rotational speed (1600 min-1). With increasing speed of rotation, the loss increases due to the action of the inertia forces of progressively moving masses, increasing in proportion to the second degree of rotation frequency, as well as the relative speed in the bearing, as the viscous friction is also proportional to the speed square. It is interesting to compare also the indicator diagrams in the cylinders of the two engines under consideration (Fig. 89). The pressure in the diesel cylinder is somewhat higher than that of the gasoline engine, and the duration of its action is greater. Thus, the gases pressed the rings to the cylinder wall with greater force and for a longer time, therefore, the losses for friction in the cylindrophone group of diesel more. Increased dimensions compared to gasoline engine, especially the diameter of the bearing in the diesel engine, also contribute to the increase in mechanical losses.
Friction in bearings is caused by the shear stresses in the oil film. It linearly depends on the sizes of friction surfaces and in proportion to the square of the shift speed. An essence of oil viscosity has a significant effect on friction and, to a lesser extent, the thickness of the oil film in the bearings. Gas pressure in the cylinder almost does not affect losses in bearings.
The effect of the diameter of the cylinder and the stroke of the piston on the effective efficiency of the internal combustion engine
Previously, it was about reducing to a minimum of heat loss to increase the indicator efficiency of the engine, and it was mainly said to reduce the surface ratio of the combustion chamber to its volume. The volume of the combustion chamber to a certain extent indicates the amount of warmth introduced. The calorific value of the incoming charge in the gasoline engine is determined by the ratio of air and fuel close to the stoichiometric. Clean air is supplied to diesel, and the fuel supply is limited by the degree of combustion incomplete, in which smoke appears in the exhaust gases. Therefore, the connection of the amount of heat inserted with the volume of the combustion chamber is quite obvious
The smallest relationship of the surface to the specified volume has the sphere. Heat into the surrounding space is assigned to the surface, so the mass having the shape of the ball is cooled into the smallest. These obvious relations are taken into account when designing the combustion chamber, it should, however, keep in mind the geometric similarity of the parts of the engines of different sizes. As is known, the volume of the sphere is 4 / 3lr3, and its surface is 4LR2, and thus the volume with increasing diameter increases faster than the surface, and, therefore, the sector of the larger diameter will have a smaller surface ratio to the volume. If the surfaces of the sphere of different diameters have the same temperature differences and the same heat transfer coefficients A, then a large sphere will cool slowly.
Engines are geometrically similar when they have the same design, but differ in size. If the first engine has a cylinder diameter, for example, equal to one, and the second engine he is 2.once larger, then all linear dimensions of the second engine will be 2 times, the surface is 4 times, and the volumes are 8 times more than that of the first engine. The complete geometric similarity to achieve, however, cannot, since dimensions, for example, spark plugs and fuel injectors are the same in engines with different sizes of the diameter of the cylinder.
From the geometric similarity, it can be done that the cylinder larger in size has a more acceptable surface ratio to the volume, therefore its thermal losses when cooling the surface in the same conditions will be less.
When determining power, it is necessary, however, consider some limiting factors. The engine power depends not only on the size, i.e. the volume of engine cylinders, but also on the frequency of its rotation, as well as the average effective pressure. The engine speed is limited to the maximum average piston rate, mass and perfection of the design of the crank-connecting mechanism. The maximum average piston velocities of gasoline engines lie within 10-22 m / s. In the passenger cars, the maximum value of the average piston rate reaches 15 m / s, and the values \u200b\u200bof the value of the average effective pressure at full load are close to 1 MPa.
The operating volume of the engine and its dimensions determine not only geometric factors. For example, the wall thickness is given by technology, and not a load on them. The heat transfer through the walls does not depend on their thickness, but from the thermal conductivity of their material, the heat transfer coefficients of the surface of the walls, the temperature difference, etc. etc. Some conclusions regarding the influence of the geometric sizes of cylinders, however, it is necessary to do.
Advantages and disadvantages of the cylinder with a large working volume
The cylinder of the larger working volume has smaller relative loss of heat in the wall. This is well confirmed by examples of stationary diesel engines with large operating volumes of cylinders, which have very low specific fuel costs. With regard to passenger cars, this position, however, is not always confirmed.
Analysis of the engine power equation shows that the greatest engine power can be achieved with a small amount of the piston stroke.
The average piston rate can be calculated as
where: s-like piston, m; N is the speed of rotation, min-1.
When restricting the average piston speed with p frequency of rotation may be the higher, the smaller the piston move. The power equation of the four-stroke engine has the form
where: VH - engine volume, dm3; n is the speed of rotation, min-1; PE - average pressure, MPa.
Consequently, the engine power is directly proportional to the frequency of its rotation and the working volume. Thus, the opposite requirements are simultaneously presented to the engine - a large working volume of the cylinder and a short move. A compromise solution consists in applying a larger number of cylinders.
The most preferred working volume of one high-speed gasoline engine cylinder is 300-500 cm3. The engine with a small number of such cylinders is poorly balanced, and with large - has significant mechanical losses and has it therefore increased specific fuel consumption. The eight-cylinder engine with a working volume of 3000 cm3 has a smaller specific consumption of fuel than the twelve-cylinder with the same working volume.
To achieve a small fuel consumption, it is advisable to use engines with a small number of cylinders. However, the single-cylinder engine with a large working volume does not find applications in vehicles, since its relative mass is large, and balancing is possible only when using special mechanisms, which leads to an additional increase in its mass, sizes and costs. In addition, a large non-uniformity of the torque of a single-cylinder engine is unacceptable for vehicle transmissions.
The smallest number of cylinders at the modern automotive engine is two. Such engines are successfully used in highly small class cars ("Citroen 2 CV", "Fiat 126"). Stacks of view of the equilibrium, following a number of expedient use, a four-cylinder engine is worth using three-cylinder engines at present, and three-cylinder engines with a small working capacity of cylinders are also started, as they allow you to obtain small fuel costs. In addition, a smaller number of cylinders simplifies and reduces the accessories of the engine, as the number of spark plugs, nozzles, plunger pairs of high pressure fuel pump are reduced. With a transverse location in the car, such an engine has a smaller length and does not limit the rotation of the controlled wheels.
The three-cylinder engine allows the use of the main parts unified with four-cylinder: cylinder sleeve, piston kit, connecting rod set, valve mechanism. The same solution is possible for a five-cylinder engine, which allows, if necessary, an increase in the power row of up from the base four-cylinder engine to avoid transition to a longer six-cylinder.
The advantages of using diesel engines with a large working volume of the cylinder has already been indicated. In addition to reducing the loss of heat during combustion, it makes it possible to obtain a more compact combustion chamber, in which higher temperatures are created with moderate compression degrees by the time of fuel injection. At the cylinder with a large working volume, you can use nozzles with a large number of nozzle holes with less sensitivity to nagara formation.
The ratio of the stroke of the piston to the diameter of the cylinder
Private from dividing the magnitude of the stroke of the piston s by the size of the diameter of the cylinder D.represents a widely used value of the S / D ratio . The point of view on the magnitude of the stroke of the piston during the development of the engine was changed.
At the initial stage of the automotive engine, the so-called tax formula was operating, on the basis of which the climax of the power tax was calculated taking into account the number and diameter D his cylinders. The classification of engines was also carried out in accordance with this formula. Therefore, preference was given to engines with a large amount of piston stroke in order to increase the engine power within the framework of this tax category. The engine power grew, but the increase in the rotational speed was limited to the permissible average piston rate. Since the mechanism of the engine gas distribution during this period was not designed for high restraint, then the speed limit of the speed of the piston did not matter.
As soon as the described tax formula was abolished, and the classification of the engines was carried out in accordance with the working volume of the cylinder, the piston move began to decrease sharply, which made it possible to increase the speed of rotation and, thus, the engine power. In the larger diameter cylinders, the use of large size valves was possible. Therefore, short-terrestrial engines were created with a S / D ratio reaching 0.5. The improvement of the gas distribution mechanism, especially when using four valves in the cylinder, made it possible to bring the nominal frequency of rotation of the engine to 10,000 min-1 or more, as a result of which the specific capacity has increased rapidly
Currently, great attention is paid to the decrease in the inside of fuel conducted for this purpose, the effect of S / D influence has shown that short-spectal engines have an increased specific fuel consumption. This is caused by a large surface of the combustion chamber, as well as a reduction in the mechanical efficiency of the engine due to the relatively large value of the properly moving masses of the part of the connecting rod-piston set and the growth of losses for the drives of the auxiliary equipment with a very short circuit should be lengthened the connecting rod so that the lower part of the piston skirt is not He refined with counterweights of the crankshaft. The weight of the piston, with a decrease in its stroke, has decreased little and when using recesses and cutouts on the piston skirt to reduce emissions of toxic substances in the exhaust gases, it is more expedient to use engines with a compact combustion chamber and with a longer piston stroke so currently from high-rate engines S / D refuse.
The dependence of the average effective pressure from the S / D relationship the best racing engines where the decrease d is clearly visible, with low respects S / D, is shown in Fig. 90 Currently, the S / D ratio is considered to be more profitable or a few more units. Although with a short piston progress, the ratio of the surface of the cylinder to its working volume at the position of the piston in NMT is less than that of long-time engines, the lower zone of the cylinder is not so important for removal of heat, since the gases temperature drops noticeably
The long-point engine has a more advantageous ratio of the cooled surface to the volume of the combustion chamber at the position of the piston in the VMT, which is more important, since during this period cycle the gas temperature determining the loss of heat is highest. Reducing the surface of the heat transfer in this phase of the expansion process reduces thermal - loss and improves the indicator efficiency of the engine.
Other ways to reduce fuel consumption by engine
The engine works with minimal fuel consumption only in a specific area of \u200b\u200bits characteristic.
When operating the car, the power of its engine should always be located on the minimum specific fuel consumption curve. In a passenger car, this condition is feasible if you use the four- and five-speed gearbox, and the less gear, the harder it is to perform this condition. When moving along the horizontal section of the road, the engine does not work in optimal mode even when the fourth transmission is turned on. Therefore, for optimal engine loading, the car must be accessed on top gear until the speed of speed is achieved. Further, it is advisable to translate the gearbox to a neutral position, turn off the engine and go through the inertia to a speed drop, for example, up to 60 km / h, and then turn on the engine and the highest transmission in the box and when the engine is optimal when the engine control pedal again touches the speed to 90 km / h
Such driving a car by the way "acceleration-roll". This way of driving is acceptable for efficiency competitions, since the engine or works in an economical field characteristic, or disabled. However, it is not suitable for real exploitation of the car at intensive motion.
This example shows one of the ways to reduce fuel consumption. Another way to minimize the specific fuel consumption is the engine power limit while maintaining its good mechanical efficiency. The negative effect of partial load on the mechanical efficiency has already been shown in Table. 11a. In particular, from Table. 11.Bo it is clear that with a decrease in the engine load from 100% to 30%, the proportion of mechanical losses in the indicator work increases from 12% to 33%, and the mechanical efficiency drops from 88% to 67%. The value of the power equal to 30% of the maximum can be achieved when only two cylinders of the four-cylinder engine.
Turning off cylinders
If you turn off several cylinders with a partial load of the multi-cylinder engine, then the rest will work with a larger load with the best efficiency. So, when operating an eight-cylinder engine with a partial load, the entire air volume can be directed only by four cylinders, their load will double and efficient engine efficiency will increase. The cooling surface of combustion chambers in four cylinders is less than eight, therefore the amount of heat, the reserved cooling system is reduced, and fuel consumption can decrease by 25%.
To disable cylinders, the valve drive control is usually used. If both valves are closed, then the mixture does not enter the cylinder and the gas constantly located in it is consistently compressed and expands. The work spent at the same time on the compression of the gas is re-released when expanding under conditions of a small removal of heat with the walls of the cylinder. Mechanical and indicator efficiency in this case are improved compared to an eight-cylinder engines operating on all cylinders at the same efficient power.
This method of turning off cylinders is very convenient, since the cylinder turns off automatically when the engine is moving to partial loads and is turned on almost instant when the control pedal is pressed. Consequently, the driver at any time can use the full engine power to complete overtaking or rapid overcoming lifting. When driving in the city, fuel savings manifests itself especially clearly. In the turned off cylinders there are no pumping losses, and they do not supply air to the exhaust pipeline. When driving under the slope, the turned off cylinders have a smaller resistance, the engine braking is reduced, and the car in the inertia passes a greater way, as if there is a free-running coupling.
The shutdown of the cylinder of the topless motor with the lower distribution shaft is conveniently carried out with the help of a valve rocker scholars movable by the electromagnet. When the electromagnet is turned off, the valve remains closed, since the rocker rotates the camshaft cams around the touch point with the end of the valve rod, and the fishe stop can move freely.
In an eight-cylinder engine, two or four cylinders are turned off in such a way that the alternation of working cylinders can be uniform. In a six-cylinder engine, it turns off from one to three cylinders. Now they are also carried out to test the two cylinders of the four-cylinder engine.
Such a disconnection of the valve in the engine with the upper arrangement of the camshaft is difficult, therefore, other ways to disable cylinders are used. For example, half the cylinders of the six-cylinder engine BMW (FRG) are turned off so that in three cylinders, ignitions and injection are disconnected, and the spent gases of three working cylinders are discharged through three disconnected cylinders and can expand further. This process is carried out by valves in the inlet and exhaust pipelines. The advantage of this method is that the covered cylinders are constantly heated by passing exhaust gases.
In the eight-cylinder V-engine "Porsche 928" with a disconnection of cylinders there are two almost completely separated four-cylinder V-shaped sections. Each of them is equipped with an independent intake pipeline, the gas distribution mechanism does not have to disconnect the valve drives. One of the engines is disconnected by closing the throttle and stopping gasoline injection, and the tests have shown that pumping losses will be the smallest with a small opening of the throttle. Throttle valves of both sections are equipped with independent drives. The disconnected section constantly supplies a small amount of air into a common exhaust pipe, which is used for afterburning the exhaust gases in the thermal reactor. This eliminates the use of a special pump for feeding secondary air.
When the eight-cylinder engine is separated into two four-cylinder sections, one of them is adjusted at a large moment at a low speed of rotation and is constantly in operation, and the second - to maximum power and turns on only if necessary to have a power close to maximum. Engine sections can have different phases of gas distribution and different inlet pipes.
Multi-parameter characteristics of the "Porsche 928" engine at operation of eight (solid curves) and four cylinders (bar curves) are shown in Fig. 91. Areas of improving the specific fuel consumption due to the trip of the four engine cylinders are shaded. For example, at a speed of 2000 min-1 and torque of 80 N · m, the specific fuel consumption during the operation of all eight engine cylinders is 400 g / (kWh), while the engine with four turned off cylinders on the same mode it is a little more 350 g / (kWh).
An even more prominent savings can be obtained at low speed vehicles of the car. The difference in fuel consumption with uniform motion along the horizontal section of the highway is given in Fig. 92. The engine with four shut-off cylinders (dotted curve) at a speed of 40 km / h fuel consumption drops by 25%: from 8 to 6 l / 100 km.
But fuel economy in the engine can be achieved not only to turn off the cylinders. In new engines "Porsche" models TOR("Thermodynamically optimized" Porsche "engine) has implemented all possible ways to increase the indicator efficiency of the traditional gasoline engine. The compression ratio was increased first from 8.5 to 10, and then, by changing the shape of the bottom of the piston, - to 12.5, while simultaneously increasing the intensity of the rotation of the charge in the cylinder when compression tact. In this way, the "Porsche 924" and "Porsche 928" and Porsche 928 engines have decreased by 6-12%. The electronic ignition system used, setting the optimal ignition advance angle, depending on the speed and engine load, increases the engine efficiency when it works on partial loads under the conditions of mixtures of the poor composition, and also eliminates detonation on the maximum load modes.
Turning off the engine at stopping the car at the intersections also brings fuel economy. When the engine is idling at idle, the rotation frequency is lower than 1000 min-1, and the coolant temperature of more than 40 ° C after 3.5 with ignition is turned off. The engine is again started only after pressing the control pedal. This reduces fuel consumption by 25-35%, and therefore gasoline engines "Porsche" models TORin terms of fuel economy can compete with diesel engines.
Mercedhey-Benz also made attempts to reduce fuel consumption in an eight-cylinder engine by turning off the cylinders. The shutdown was achieved using an electromagnetic device that breaks the rigid bond between the cam and the valve. In the conditions of movement in the city, fuel consumption has decreased by 32%.
Plasma ignition
Reduce fuel consumption and the content of harmful substances in the exhaust gases can be using poor blends, but their spark ignition causes difficulties. The guaranteed ignition by the spark discharge takes place with a mass ratio of air / fuel not more than 17. With poorer compositions there are ignition missions, which leads to an increase in the content of harmful substances in the exhaust gases.
When creating a stratified charge in a cylinder, it is possible to burn a very poor mixture, provided that a mixture of rich composition is formed in the ignition candle. The rich mixture is easily flammorated, and the flame torch, thrown into the volume of the combustion chamber, flammifies there, there is a poor mixture.
IN last years Studies are underway to ignite the poor with plasma and laser methods, in which several foci of combustion is formed in the combustion chamber, since the ignition of the mixture occurs simultaneously in different zones of the chamber. As a result, the problems of detonation disappear, and the compression ratio can be increased even with the use of low-fuel fuel. It is possible to ignite the poor mixtures with the air / fuel ratio reaching 27.
When plasma ignition, the electric arc forms a high concentration of electrical energy in the ionized spark gap of a sufficiently large volume. At the same time, temperatures are developing up to 40,000 ° C, i.e., conditions similar to arc welding are created.
Implement a plasma method of ignition in an internal combustion engine, however, not so simple. Plasma spark plug is shown in Fig. 93. Under the central electrode in the candle insulator, a small chamber was performed. In the event of an electrical discharge of a large length between the central electrode and the gas body, the gas in the chamber is heated to a very high temperature and, expanding, it turns out through the hole in the body of the candle in the combustion chamber. A plasma torch is formed with a length of about 6 mm, thereby arising several foci of flames that contribute to the ignition and combustion of the poor mixture.
Another type of plasma ignition system uses a small high pressure pump, which supplies air to the electrodes at the time of the formation of an arc discharge. The volume of ionized air is formed during the discharge between the electrodes enter the combustion chamber.
These methods are very complex and do not apply in automotive engines. Therefore, another method was developed, in which the ignition candle forms a permanent electrical arc for 30 ° Crankshaft rotation angle. In this case, up to 20 MJ energy is released, which is much larger than with the usual spark discharge. It is known that if a sufficient amount of energy is not formed during the spark ignition, the mixture is not ignited.
Plasma arc in combination with the rotation of the charge in the combustion chamber forms a large surface of ignition, since when the form and the size of the plasma arc change to a large extent. Along with increasing the duration of the ignition period, this also means the presence of energy highly released for it.
Unlike the standard system in the secondary contour of the plasma ignition system, there is a constant voltage of 3000 V. At the time of the discharge in the spark gap of the candle, an ordinary spark arises. At the same time, the resistance on the electrodes of the candle is decreased, and the constant voltage of 3000V forms an arc grilled at the time of discharge. To maintain the arc, there is enough voltage of about 900 V.
The plasma ignition system differs from the standard built-in high-frequency (12 kHz) DC terminator with a voltage of 12 V. The induction coil increases the voltage up to 3000 V, which is further straightened. It should be indicated that the continuous arc discharge on the ignition candle significantly reduces its life.
When plasma ignition, the flame applies to the combustion chamber faster, therefore appropriate change in the ignition advance angle is required. Tests of the plasma ignition system by Ford Pinto (USA) with an engine capacity of 2300 cm3 and automatic transmission gave the results in Table. 12.
Table 12. Test results of the plasma ignition system by car "Ford Pinto"
| Ignition type type | Emissions of toxicism, g | Fuel consumption, l / 100 km | |||
| SN | SO | NOX |
urban test cycle | road testing cycle |
|
| Standard | 0,172 | 3,48 | 1,12 | 15,35 | 11,41 |
| Plasma with optimal adjustment of the ignition advance angle | 0,160 | 3,17 | 1,16 | 14,26 | 10,90 |
| Plasma with optimal adjustment of the angle of the ignition and composition of the mixture | 0,301 | 2,29 | 1,82 | 13,39 | 9,98 |
When plasma ignition, it is possible to carry out high-quality control of the gasoline engine, in which the amount of air supplied remains unchanged, and the engine power control is performed only by adjusting the amount of fuel supplied. When the plasma ignition system is used in the engine without changing the control of the ignition advance and composition of the mixture, the fuel consumption decreased by 0.9%, when adjusting the ignition angle - by 4.5%, and with optimal adjustment of the ignition angle and the mixture composition - by 14% ( See Table 12). Plasma ignition improves engine operation, especially with partial loads, and fuel consumption can be the same as a diesel engine.
Reducing emission of toxic substances with exhaust gases
The growth of motorization brings with them the need for environmental protection measures. The air in cities is increasingly contaminated with substances harmful to human health, especially carbon oxide, unburned hydrocarbons, nitrogen oxides, lead, sulfur compounds, sulfur, and so on. Almost in car engines.
Along with the toxic substances during the operation of cars, their noise has a harmful effect on the population. Recently, in cities, the noise level increased annually by 1 dB, so it is necessary not only to suspend the increasing level of noise, but also to achieve its decline. The constant effects of noise causes nerve diseases, reduces the working capacity of people, especially engaged in mental activities. Motorization brings noise in previously quiet remote places. Reducing the noise created by woodworking and agricultural machines, unfortunately, is still not paying due attention. The chain benzaw creates noise in a significant part of the forest, which causes changes in animal living conditions and often the reason for the disappearance of their individual species.
Most often, however, it causes complaints of the pollution of the atmosphere by the spent gases of cars.
Table 13. Permissible emission of harmful substances with spent gases of passenger cars according to the legislation pcs. California, USA
With a lively movement, the spent gases accumulate at the surface of the soil and in the presence of solar radiation, especially in industrial cities located in poorly ventilated by the basins, the so-called could be formed. The atmosphere is polluted to such an extent that the stay in it harms health. Road service staff standing on some busy intersections, in order to preserve their health apply oxygen masks. Especially harmful is a relatively heavy carbon monoxide, penetrating the lower floors of buildings, garages and no longer once caused to death.
Legislative enterprises limit the content of harmful substances in the exhaust gases of cars, and they are constantly tightened (Table 13).
Prescriptions bring large care cars; They also indirectly affect the efficiency of road transport.
For complete combustion of the fuel, some excess air can be allowed to provide a good mixing with it fuel. The required excess air depends on the degree of mixing fuel with air. In carburetor engines, considerable time is given to this process, since the fuel path from the mixing device to the spark plug is quite large.
A modern carburetor allows for various types of mixtures. The most "rich mixture is needed for the cold start of the engine, since a significant share of fuel condenses on the walls of the intake pipeline and immediately into the cylinder does not fall. Only a small part of the light fuel fractions is evaporated. When driving the engine, a mixture of a rich composition is also required.
When the car moves, the composition of the fuel and air mixture should be poor, which will ensure a good efficiency and a small specific fuel consumption. To achieve maximum engine power, you need to have a rich mixture to fully utilize the entire mass of the air entered the cylinder. To ensure good dynamic performance of the engine with a quick opening of the throttle, it is necessary to additionally subjected to a certain amount of fuel in the intake pipeline, which compensates for the fuel, which is settled and condensed on the walls of the pipeline as a result of an increase in pressure in it.
For good mixing of fuel with air, you should create a high air speed and its rotation. If the cross section of the carburetor diffuser is constantly, then at low engine speeds for good mixture formation, the air velocity in it is small, and at high - the impedance of the diffuser leads to a decrease in the mass of the air entering the air. This disadvantage can be eliminated using a carburetor with a variable diffuser cross section or fuel injection into the inlet pipeline.
There are several types of gasoline injection systems in the inlet pipeline. In the most frequently used systems, the fuel is fed through a separate nozzle for each cylinder, thereby achieving a uniform distribution of fuel between the cylinders, the sedimentation and condensation of fuel on the cold walls of the intake pipeline is eliminated. The amount of fuel injected is easier to bring closer to the optimal desired engine at the moment. The need for diffuser disappears, the energy loss of energy occurs during its passage. As an example of such a fuel supply system, a frequently used bosch k-jet iron injection system can be brought, which already mentioned earlier at 9.5 when considering engines with turbocharging.
The diagram of this system is presented in Fig. 94. Conical nozzle / in which the rocking on the lever moves 2 the valve 5 is designed so that the lifting of the valve is proportional to the mass consumption of air. Window 5 for the passage of fuel open with a spool 6 in the chassis of the regulator when moving the lever under the influence of the incoming air trailer. The necessary changes in the composition of the mixture in accordance with the individual characteristics of the engine are achieved by the form of a conical nozzle. The lever with the valve is balanced by the counterweight, the inertia strength during car oscillations do not affect the valve.
Air flow coming into the engine is adjusted by throttle 4. The damping of the valve oscillations, and with it and the spool arising at low frequencies of the engine rotation due to the pulsations of the air pressure in the intake pipeline, is achieved with bikes in the fuel system. To regulate the amount of fuel supplied, the screw 7 is also served as located in the valve lever.
Between window 5 and nozzle 8 placed camshaft valve 10, springs 13 and saddles 12, lowing on the membrane //, constant injection pressure in "Spray nozzle 0.33 MPa at a pressure of 0.47 MPa valve.
Fuel from tank 16 served by electric fuel pump 15 through pressure regulator 18 and fuel filter 17 to the bottom of the chamber 9 controller housing. Permanent fuel pressure in the regulator is supported by a reduction valve 14. Membrane regulator 18 designed to maintain fuel pressure while not working engine. This prevents the formation of air traffic jams and provides a good launch of a hot engine. The regulator also slows down the growth of fuel pressure while starting the engine and extinguishes its oscillations in the pipeline.
The cold engine start facilitate several devices. Bypass valve 20, a controlled bimetallic spring opens with a cold start a drain highway into the fuel tank, which reduces the fuel pressure on the shovers end. This violates the equilibrium of the lever and the same amount of incoming air will correspond to a larger amount of injected fuel. Another device is an additional air regulator 19, the diaphragm of which also opens the bimetallic spring. Additional air is necessary to overcome the increased resistance of the friction of the cold engine. The third device is a fuel nozzle 21 cold start driven by thermostat 22 in the water shirt, the engine that keeps the nozzle is open until the cooling motor does not reach the specified temperature.
Equipment of electronics of the considered gasoline injection system is limited to a minimum. Electric fuel pump with a stopped engine is turned off and, for example, when an accident, the fuel feed is stopped, which prevents the fire in the car. In the non-working engine, the lever in the lower position presses the switch located under it, which interrupts the current supplied to the starter and heating spiral of the thermostat. The operation of the cold start nozzle depends on the temperature of the engine and its work time.
If more air is in one cylinder from the intake pipeline than in others, the fuel supply is determined by the operating conditions of the cylinder with a large amount of air, that is, with a poor mixture so that reliable ignition is ensured. The remaining cylinders will work with mixtures enriched, which is economically unprofitable and leads to an increase in the content of harmful substances.
In dieselms, the mixing formation is more difficult, since a very short time is given to mix fuel and air. The process of fuel ignition begins with a slight delay after the start of the fuel injection into the combustion chamber. In the process of combustion, the fuel injection is still continuing and in such conditions it is impossible to achieve complete use of air.
In diesels, therefore, there must be an excess of air and even at the smoke (which indicates incomplete combustion of the mixture) in the exhaust gases there is unused oxygen. This is caused by poor stirring of fuel drops with air. In the center of the fuel torch there is a lack of air, which leads to the smoke, although unused air is in the immediate vicinity around the torch. Partially about this was mentioned at 8.7.
The advantage of diesel engines is that the ignition of the mixture is guaranteed and with a large excess of air. Non-use of the entire number of air cylinder during combustion is the cause of a relatively small dyel power per unit of weight and working volume, despite its high degree of compression.
More advanced blending occurs in diesel engines with separated combustion chambers, in which a burning rich mixture from an additional chamber enters the main combustion chamber filled with air, mixed well with it and burns. For this, a smaller amount of over-air is required than with the direct fuel injection, however, the large cooling surface of the walls leads to large heat loss, which causes a drop in the indicator efficiency.
13.1. Formation of carbon monoxide and hydrocarbons CHX
When combining a mixture of stoichiometric composition, harmless carbon dioxide CO2 and water vapor should be formed, and with a lack of air due to the fact that part of the fuel combusts with incompleteness, is additionally toxic carbon monoxide and unburned hydrocarbons SNX.
These well-harmful components of the exhaust gases can be caught and neutralized. To this end, it is necessary for a special compressor to (Fig. 95) to serve fresh air into such a place of the exhaust pipeline, where harmful products of incomplete combustion can be burned. Sometimes for this air is served directly on the hot exhaust valve.
As a rule, the thermal reactor for afterburning CO and SNX is placed immediately behind the engine directly at the exit of the exhaust gases. Exhaust gases M.complete into the center of the reactor, and are discharged from its periphery in the exhaust pipeline V.The outer surface of the reactor has thermal insulation I.
In the most heated central part of the reactor, heat chamber is placed, heated by speaking gases,
where the products of incomplete combustion of fuel are survived. It is released heat that supports the high temperature of the reactor.
Unburned components in the exhaust gases can be oxidized and without combustion using a catalyst. To do this, it is necessary to add the secondary air, which is necessary for oxidation, the chemical reaction to the catalyst should be added to the spent gases. It is also released heat. Catalyst usually serve rare and precious metals, so it is very expensive.
Catalysts can be applied in any type of engine, but they have a relatively short service life. If lead is present in the fuel, the catalyst surface is quickly poisoned, and it comes to disrepair. The preparation of high-octane gasoline without lead anti-knock is a rather complicated process, in which many oil is consumed, which is economically impractical in its shortage. It is clear that afterburning fuel in the thermal reactor leads to energy losses, although heat is allocated during combustion, which can be disposed of. It is why it is why it is so organized the process in the engine so that when combustion in it, the fuel has formed a minimum amount of harmful substances. At the same time, it should be noted that to fulfill the promising legislative prescriptions, the use of catalysts will be inevitable.
NOX Nitrogen Oxidesry
Harmful nitrogen oxides are formed at high combustion temperature under the conditions of the stoichiometric composition of the mixture. Reducing the emission of nitrogen compounds is associated with certain difficulties, since the conditions for their reduction coincide with the conditions for the formation of harmful products of incomplete combustion and vice versa. At the same time, the combustion temperature can be reduced by introducing into a mixture of any inert gas or water vapor.
For this purpose, it is advisable to recycle in the intake pipeline cooled exhaust gases. Reduced due to this power requires a mixture to enrich, larger opening of the throttle, which increases the overall emission of harmful CO and CHX with exhaust gases.
Recycling of exhaust gases in conjunction with a decrease in the degree of compression, a change in gas distribution phases and later ignition can reduce the NOX content by 80%.
Nitrogen oxides are eliminated from exhaust gases using also catalytic methods. In this case, the spent gases are first passed through the regeneration catalyst in which the NOX content is reduced and then together with the added air - through the oxidizing catalyst, where CO and SNX are eliminated. The diagram of such a two component system is given in Fig. 96.
To reduce the content of harmful substances in the exhaust gases, so-called-bands are used, which can also be used in conjunction with a two-component catalyst. The peculiarity of the system with the-zonda is that the addition air for oxidation is not supplied to the catalyst, but the-band is constantly monitored by the oxygen content in the exhaust gases and controls the fuel supply so that the composition of the mixture always corresponds to the stoichiometric. In this case, CO, CHX and NOX will be present in the exhaust gases in minimal quantities.
The principle of operation is that there is that in the narrow range near the stoichiometric composition of the mixture \u003d 1, the voltage between the inner and the outer surface of the probe changes dramatically, which serves as a control pulse for a device that controls the fuel supply. Sensitive element 1 the probe is made of zirconium dioxide, and its surface 2 covered with layers of platinum. The voltage characteristic of US between the inner and outer surfaces of the sensing element is shown in Fig. 97.
Other toxic substances
To increase the octane number of fuel, anti-pedonators are usually used, for example, tetraethylswin. So that the lead compounds are not sedated on the walls of the combustion chamber and valves, the so-called endurances are used, in particular, Diberomethyl.
These compounds enter the atmosphere with the exhaust gases and pollute the vegetation along the roads. Finding food to the human body, lead joints harmful effect on his health. The precipitation of the sovereign in the exhaust gas catalysts has already been mentioned. In this regard, an important task is to remove lead lead from gasoline.
The oil penetrating into the combustion chamber does not fully burn, and the content of CO and SNX increases in the exhaust gases. To eliminate this phenomenon, high tightness of piston rings and maintaining a good engine technical condition are necessary.
The combustion of a large amount of oil is especially characteristic of two-stroke engines, which it is added to the fuel. The negative effects of the use of benzo-oil mixtures are partially softened by the dispensing of oil with a special pump in accordance with the engine load. Similar difficulties exist when using the Vankel engine.
Harmful effects on human health are also a pair of gasoline. Therefore, the ventilation of the crankcase must be carried out in such a way that gases and pairs penetrating into the crankcase due to bad tightness did not go into the atmosphere. Leakage of gasoline vapor fuel tank You can prevent adsorption and sucking the vapors into the inlet system. Oil leakage from the engine and gearbox, car pollution due to this oils are also prohibited in order to preserve the purity of the environment.
Reducing the flow of oil from an economic point of view is as important as fuel economy, since oils are much more expensive than fuel. Regular control and maintenance reduces oil consumption due to engine faults. The leaks of the oil in the engine can be observed, for example, due to poor tightness of the cylinder head cover. Due to oil leakage, the engine is polluted, which is the cause of the fire.
It is unsafe oil leakage and due to the low tightness of the crankshaft seal. Oil consumption in this case increases significantly, and the car leaves dirty traces on the road.
The car pollution with oil is very dangerous, and oil spots under the vehicle serve as a reason for the prohibition of its operation.
The oil flowing through the seal of the crankshaft can get into the clutch and cause it to slip. However, more negative consequences cause oil entering the combustion chamber. And although oil consumption is relatively small, but its incomplete combustion increases the emission of harmful components with exhaust gases. The combustion of the oil is manifested in excessive chimples of the car, which is typically for two-stroke, as well as significantly worn four-stroke engines.
IN four-stroke engines oil penetrates into the combustion chamber through piston ringsthat is especially noticeable with the large wear of their and cylinder. The main cause of oil penetration into the combustion chamber consists in the unevenness of the fitting of the compression rings to the cylinder circle. Retraction of oil from the walls of the cylinder is carried out through the slots of the oil surcharge ring and the holes in its groove.
Through the gap between the rod and the guide intake valve, the oil easily penetrates into the inlet pipeline where there is a vacuum. This is particularly often observed when using low viscosity oils. Prevent oil consumption through this node can use rubber gland on the end of the valve guide.
Engine crankcase gases containing many harmful substances are usually discharged by a special pipeline into the inlet system. By entering it into the cylinder, the crankcase gases burn along with the fuel and air mixture.
Lumping oils reduce friction losses, improve mechanical engine efficiency and reduce fuel consumption. However, it is not recommended to use oils with a viscosity of less than prescribed by the norms. This can cause increased oil consumption and large engine wear.
Due to the need to save oil, the collection and use of spent oil are becoming more and more important problems. By regenerating old oils, you can get a significant amount of high-quality liquid lubricants and at the same time prevent environmental pollution, stopping the waste oils to the aqueous streams.
Determination of the permissible amount of harmful substances
The elimination of harmful substances from the exhaust gases is a rather complicated task. In large concentrations, these components are very harmful to health. Of course, it is impossible to immediately change the created position, especially with respect to the operated car park. Therefore, legislative prescriptions for the control of the content of harmful substances in the exhaust gases are designed for produced new cars. These regulations will gradually improve taking into account new achievements of science and technology.
Cleaning the exhaust gases is associated with an increase in fuel consumption by almost 10%, reduced engine power and the increase in the cost of the car. The cost of car maintenance increases. Catalysts are also expensive, since their components consist of rare metals. The service life must be designed for 80,000 km of car run, but now it has not yet been reached. Currently used catalysts are about 40,000 km of run, and at the same time gasoline is used without lead impurities.
The current situation sets doubt on the effectiveness of harsh prescriptions for the content of harmful impurities, as it causes a significant increase in the cost of the car and its operation, and also results in an increase in oil consumption.
The fulfillment of tight requirements put forward on the prospect of the prospect of the exhaust gases during the modern state of gasoline and diesel engines is not yet possible. Therefore, it is advisable to pay attention to the radical change in the power plant of mechanical vehicles.
If the engine overheated ...
Spring always brings problems to car owners. They arise not only of those who held the car in the garage all over the winter, after which a long-acting car presents surprises in the form of failures of systems and aggregates. But also those who go all year round. Some defects, "dreamed" for the time being, make themselves to know as soon as the thermometer is steadily passing into the area of \u200b\u200bpositive temperatures. And one of these dangerous surprises is overheating the engine.
Overheating is in principle possible at any time of the year - both in winter and in summer. But, as practice shows, the greatest number of such cases accounts for the spring. This is simply explained. In winter, all car systems, including the engine cooling system, work in very difficult conditions. Large temperature differences - from "minus" at night to very high workers after a short movement - negatively act on many aggregates and systems.
How to detect overheating?
The answer, it seems, is obvious - to look at the coolant temperature pointer. In fact, everything is much more difficult. When the movement on the road is intense, the driver does not immediately notice that the arrow of the pointer moved away towards the red zone of the scale. However, there are a number of indirect signs, knowing which you can catch the moment of overheating and without looking at the instruments.
So, if overheating occurs because of the small amount of antifreeze in the cooling system, the first to which it will respond to the heater located at a high point of the system, - hot antifreeze will no longer come there. The same will occur when boiling antifreeze, because It begins in the hottest place - in the head of the cylinder block at the walls of the combustion chamber, and the resulting steam stoppers lock the coolant passage to the heater. As a result, hot air supply to the cabin stops.
The fact that the temperature in the system has reached a critical value, and exactly indicates suddenly appeared. Since the temperature of the walls of the combustion chamber during overheating is significantly higher than the norm, this certainly provokes the occurrence of abnormal burning. As a result, the superheated engine while pressing the gas pedal will remind the fault of a characteristic ringing knife.
Unfortunately, these signs often can remain unnoticed: at elevated air temperature, the heater is turned off, and the detonation, with good noise insulation of the cabin, can simply not hear. Then, with further movement of the car with an overheated engine, the power will begin to fall, and a knock will appear, stronger and uniform than during detonation. The thermal expansion of the pistons in the cylinder will lead to an increase in their pressure on the walls and a significant increase in friction forces. If this feature will not be seen by the driver, then with further operation, the engine will receive solid damage, and without serious repair, unfortunately, not to do.
Moreover, overheating occurs
Carefully look at the cooling system scheme. Almost every element in certain circumstances can be a starting point of overheating. And its root causes in most cases are: poor cooling of antifreeze in the radiator; violation of combustion chamber seal; The insufficient amount of coolant, as well as leaks in the system and, as a result, is an excessive pressure in it.
The first group, in addition to the obvious outer contamination of the radiator, dust, poplar foliage, foliage, includes a thermostat, sensor, electric motor or fan power clutch. There is also an internal pollution of the radiator, however, not because of the scale, as it happened many years ago after long-term operation of the engine on the water. The same effect, and sometimes it is much stronger, it gives the use of various sealants for the radiator. And if the latter is really clogged with such a means, then clean his thin tubes is a rather serious problem. Usually, the faults of this group are easily detected, and to get to the parking or a service station, it is enough to replenish the fluid level in the system and turn on the heater.
Violation of the combustion chamber seal is also a fairly common cause of overheating. Fuel combustion products, being under high pressure in the cylinder, penetrate into the cooling shirt and squeeze the cooling fluid from the walls of the combustion chamber. A hot gas "pillow" is formed, an additionally heated wall. A similar picture arises due to the slot of the head, cracks in the head and the cylinder sleeve, deformation of the caustic plane of the head or block, is most often due to the preceding overheating. It is possible to determine that such a leakage occurs, it is possible by the smell of exhaust gases in an expansion tank, leakage antifreeze from the tank when the engine is running, rapidly increase the pressure in the cooling system immediately after starting, as well as according to the characteristic water-oil emulsion in the crankcase. But to establish specifically, with which the leakage is associated, it is usually possible, only after partial disassembly of the engine.
Explicit leaks in the cooling system occurs most often due to cracks in the hoses, weakening the tightening of the clamps, the wear of the pump sealing, the fault of the heater crane, radiator and other reasons. It should be noted that the flow of the radiator often appears after the "corrosion" of the tubes so-called "toosol" of unknown origin, and flow the pump seals - after long-term operation on the water. To establish that the coolant in the system is not enough, visually just as simple as determining the place of leakage.
The slowness of the cooling system in its upper part, including due to the malfunction of the radiator cork valve, leads to a pressure drop in the system to atmospheric. As you know, the less pressure, the lower the boiling point of the fluid. If the operating temperature in the system is close to 100 degrees C, then the fluid can boil. Often, boiling in a leakage system occurs even without the engine operation, and after it is turned off. It is possible to determine that the system is really notometric, one can in the absence of pressure in the upper radiator hose on a heated engine.
What happens when overheating
As noted above, when the engine overheating, the boiling of fluid begins in the cylinder head cooling shirt. The resulting steam plug (or pillow) prevents the direct contact of the coolant with metal walls. Because of this, the efficiency of their cooling decreases sharply, and the temperature increases significantly.
Such a phenomenon is usually local in nature - near the boiling area, the temperature of the wall may be noticeably higher than on the index (and all because the sensor is installed on the outer wall of the head). As a result, defects may appear in the block head, first of all cracks. In gasoline engines - usually between valve beds, and in diesel engines - between the graduation valve seat and the cutter lid. In cast iron heads, there are sometimes cracks across the seaside of the exhaust valve. Cracks also arise in a cooling shirt, for example, by beds of a camshaft or on the holes of the bolts of the block head. Such defects are better to eliminate the head replacement, and not welding, which is not yet possible to perform with high reliability.
When overheating, even if the crack does not occur, the block head often gets significant deformations. Since, along the edges, the head is pressed against the bolt block, and its middle part overheats, the following occurs. Most modern engines head made of aluminum alloy, which, when heated, expands more than steel fastener bolts. With a strong heating, the head expansion leads to a sharp increase in the force of compression of the gasket along the edges, where the bolts are located, while the expansion of the overheated middle part of the head does not restrain the bolts. Because of this, there is, on the one hand, the deformation (failure from the plane) of the middle part of the head, and on the other - additional compression and deformation of the gasket with efforts that are significantly higher than operational.
Obviously, after cooling the engine in separate places, especially at the edges of the cylinders, the gasket will not be pressed properly, which can cause leak. With the further operation of such an engine, the metal edging of the gasket, having lost the heat contact with the planes of the head and the block, overheats, and then roasts. This is especially characteristic of engines with plug-in "wet" sleeves or if there are too narrow jumpers between the cylinders.
To top it off, the deformation of the head leads, as a rule, to curvature the axis of the camshaft beds located in its upper part. And without serious repair, these consequences of overheating can not be eliminated.
No less dangerous overheating and for a cylinder-piston group. Since the boiling of coolant applies gradually from the head to an increasingly part of the cooling shirt, the cooling efficiency of cylinders is sharply reduced. And this means that the heat removal from the piston heated by hot gases is worse (heat from it is allocated mainly through the piston rings into the wall of the cylinder). The temperature of the piston grows, at the same time its thermal expansion occurs. Since the aluminum piston, and the cylinder is usually cast iron, then the difference in thermal expansion of materials leads to a decrease in the working clearance in the cylinder.
Further fate of such an engine is known - overhaul with a boring block and a replacement of pistons and rings for repair. The list of works on the head of the block is generally unpredictable. Better still motor before you do not bring. Opening periodically hood and checking the level of fluid, you can to some extent to secure yourself. Can. But not 100 percent.
If the engine is still overheated
Obviously, you need to immediately stop on the side of the road or at the sidewalk, turn off the engine and open the hood - so the engine will cool faster. By the way, at this stage, all drivers do this in such situations. But on, they allow serious mistakes from which we want to warn.
In no case cannot be opened by the radiator cork. On traffic jams, there are no worst "Never Open Hot" - never open if the radiator is hot! After all, this is so clear: with a working plug, the cooling system is under pressure. The focus of the boil is located in the engine, and the plug - on the radiator or the expansion tank. Opening a plug, we provoke the release of a significant amount of hot cooling fluid - a pair will push it out, like from the gun. At the same time, the burning of the hands and the face is almost inevitable -standing boiling water hits in the hood and ricochet - in the driver!
Unfortunately, all (or almost all) drivers are so coming from the unfortunately, apparently, believing that there is thereby discharge the situation. In fact, they, splashing the remnants of antifreeze from the system, create additional problems. The fact is that the liquid, boiling "inside" the engine, still lines the temperature of the details, thereby reducing it in the most overheated places.
Overheating of the engine is just the case when, not knowing what to do, it is better not to do anything. For ten minutes to fifteen, at least. During this time, boiling will stop, the pressure in the system will fall. And then you can proceed to action.
Making sure that the upper radiator hose lost its former elasticity (it means there is no pressure in the system), carefully open the radiator cork. Now you can add the bulk liquid.
We do it carefully and slowly, because Cold liquid, falling on the hot walls of the block head shirt, causes their rapid cooling, which can lead to crack formation.
Closing the cork, run the engine. Watching the temperature pointer, check how the upper and lower radiator hoses are heated, whether the fan is turned on after warming up and there is no liquid leaks.
The most, maybe unpleasant - the refusal of the thermostat. At the same time, if the valve is "hung" in the open position, there are no troubles. Just the engine will slowly warm up, since the entire flow of coolant will head for a large contour, through the radiator.
If the thermostat remains closed (the arrow of the pointer, slowly reaching the middle of the scale, quickly rushes to the red zone, and the radiator hoses, especially the lower, remain cold), the movement is impossible even in winter - the engine will immediately overheat again. In this case, you need to dismantle the thermostat or at least its valve.
If the coolant is detected, it is desirable to eliminate or at least reduce to reasonable limits. Usually "flows" radiator due to corrosion of tubes on ribs or in places soldering. Sometimes such tubes can be drowning, having rebuild them and bent the edges of the passage.
In cases where it is not possible to completely eliminate a serious malfunction in the cooling system, you need to at least get to the nearest service station or settlement.
If a fan is faulty, you can continue to move with the heater on the maximum, which takes on a significant part of the heat load. In the cabin will be "slightly" hot - not trouble. As you know, "pairs of bones will not lomit."
Worse, if the thermostat refused. Above, we have already considered one option. But if you can't cope with this device (do not want, you do not have tools, etc.), you can try another way. Start the move - but as soon as the pointer arrow approaches the red zone, turn off the engine and move the roller. When the speed falls, turn on the ignition (it is easy to make sure that after only 10-15 seconds the temperature will already be less), start the engine again and repeat everything first, continuously by the arrow of the temperature pointer.
With certain accuracy and suitable road conditions (no cool lifts), we can drive tens of kilometers in such a way, even when the coolant in the system remains very small. At one time, the author was able to overcome about 30 km in this way, without causing a noticeable harm engine.
In the engine cylinder with some frequency, thermodynamic cycles are carried out, which are accompanied by a continuous change in the thermodynamic parameters of the working fluid - pressure, volume, temperature. The energy of fuel combustion when the volume changes turns into mechanical work. The condition for the transformation of heat into mechanical work is a clock sequence. These clocks in the internal combustion engine include the inlet (filling) of cylinders of a combustible mixture or air, compression, combustion, expansion and release. The changing volume is the volume of the cylinder, which increases (decreases) with the progressive movement of the piston. An increase in volume occurs due to the expansion of products when combustion of a combustible mixture, a decrease - when compressed by a new charge of a combustible mixture or air. Gas pressure for the cylinder walls and the piston with expansion tact turn into mechanical work.
The energy-accumulated energy turns into thermal energy when performing thermodynamic cycles, is transmitted by the walls of the cylinders by heat and light radiation, radiation and the walls of the cylinder - coolant and the mass of the engine through thermal conductivity and into the surrounding space from the surfaces of the free and forced engine
convection. In the engine there are all types of heat transfer, which indicates the complexity of the processes occurring.
The use of heat in the engine is characterized by an efficiency, the smaller the heat of the combustion of the fuel is given to the cooling system and into the mass of the engine, the more work is performed above the efficiency.
The operating cycle of the engine is carried out in two or four tact. The main processes of each working cycle are intake tacts, compression, working stroke and release. Introduction to the workflow of engine tact engines made it possible to reduce the cooling surface as much as possible and optimize the fuel combustion pressure. The combustion products are expanding according to the compression of a combustible mixture. Such a process reduces thermal losses in the cylinder walls and with exhaust gases, increase the pressure of gases to the piston, which significantly increases the power and economic indicators of the engine.
Real thermal processes in the engine differ significantly from theoretical, based thermodynamic laws. The theoretical thermodynamic cycle is closed, the prerequisite for its implementation is the transmission of heat with a cold body. In accordance with the second law of thermodynamics and in the theoretical thermal machine, it is completely impossible to completely turn thermal energy into mechanical. In diesels, the cylinders of which are filled with fresh air charge and have high degrees of compression, the temperature of the combustible mixture at the end of the intake tact is 310 ... 350 K, which is explained by a relatively small amount of residual gases, in gasoline engines The intake temperature at the end of the tact is 340 .. .400 k. The heat balance of the combustible mixture when the intake tact can be represented as
where?) R T is the amount of heat of the working fluid at the beginning of the intake clock; OS.TS - the amount of heat entered into the working fluid when contacting the heated surfaces of the inlet path and cylinder; Qo g - the amount of heat in the residual gases.
From the heat balance equation, you can determine the temperature at the end of the intake tact. We will take a massive value of the number of fresh charge t with s residual gases - t o g With a well-known heat capacity of fresh charge with p, residual gases c "R. and working mixture with R. Equation (2.34) is presented in the form of
where T S. h - the temperature of fresh charge before the inlet; BUT T NW - heated fresh charge when inlet of it in a cylinder; T. - The temperature of the residual gases at the end of the release. Perhaps with sufficient accuracy to assume that c "R. = with R. and with "r - s, with p, where with; - correction coefficient depending on T NW and composition of the mixture. At a \u003d 1.8 and diesel fuel
When solving equation (2.35) regarding T A. Denote by attitude 
The formula for determining the temperature in the cylinder at the intake is
This formula is valid for both four-stroke and two-stroke engines, for turbocharging engines, the temperature at the end of the intake is calculated by formula (2.36), provided that q \u003d 1. The assured condition does not contribute large errors. The parameter values \u200b\u200bat the end of the intake clock defined experimentally on the nominal mode are presented in Table. 2.2.
Table 2.2.
|
Four-stroke DVS |
Two-stroke |
||
|
Indicator |
with spark ignition |
with a straight-flow scheme of gas exchange |
|
|
The coefficient of residual gases |
|||
|
The temperature of the exhaust gases at the end of the release |
|||
|
Heated fresh charge, to |
|||
|
The temperature of the working fluid at the end of the intake T A TO |
|||
When the intake valve intake tact in the diesel engine is opened by 20 ... 30 ° to the arrival of the piston in the NMT and closes after the NMT passage by 40 ... 60 °. The duration of the opening of the ink valve is 240 ... 290 °. The temperature in the cylinder at the end of the previous tact - release is equal T. \u003d 600 ... 900 K. Air charge having a temperature is significantly lower, mixed with residual gases in the cylinder, which reduces the temperature in the cylinder at the end of the intake to T a \u003d. 310 ... 350 K. Delta of temperatures in the cylinder between the output clocks and the inlet is equal ATA r \u003d t a - tInsofar as T A. ATA T \u003d 290 ... 550 °.
The speed of temperature change in the cylinder per unit time is equal to:
For diesel, the speed of temperature change when the intake tact when p. \u003d 2400 min -1 and Φ a \u003d 260 ° is CO d \u003d (2.9 ... 3.9) 10 4 hail / s. Thus, the temperature at the end of the intake tact in the cylinder is determined by the mass and temperature of the residual gases after the release tact and the heating of the fresh charge from the engine parts. Graphs of the function CO RT \u003d / (D E) intake tact for diesel engines and gasoline engines, presented to PA Fig. 2.13 and 2.14 indicate a significantly higher rate of temperature change in the gasoline engine cylinder in comparison with the diesel engine and, therefore, the greater the intensity of the heat flux from the working fluid and its growth with increasing the rotational speed of the crankshaft. The average estimated value of the temperature change rate when the diesel inlet tact within the speed of the crankshaft rotation of 1500 ... 2500 min -1 is equal to \u003d 2.3 10 4 ± 0.18 degrees / s, and in gasoline
the engine is within the frequency of 2,000 ... 6000 min -1 - with me \u003d 4.38 10 4 ± 0.16 deg / s. With the intake tact, the temperature of the working fluid is approximately equal to the operating temperature of the coolant,
Fig. 2.13.
Fig. 2.14.
the heat of the cylinder walls is spent on the heating of the working fluid and does not have a significant effect on the cooling fluid temperature of the cooling system.
For tact of compression There are quite complex heat exchange processes inside the cylinder. At the beginning of the compression tact, the charge temperature of the combustible mixture is less than the temperature of the surfaces of the walls of the cylinder and the charge is heated, continuing to take the heat from the walls of the cylinder. The mechanical work of compression is accompanied by the absorption of heat from the external environment. In a certain (infinitely small), the temperature range of the surface of the cylinder and the charge of the mixture is leveled, as a result of which heat exchange between them is terminated. With further compression, the temperature of the combustible mixture exceeds the temperature of the surfaces of the cylinder walls and the heat flux changes the direction, i.e. The heat enters the cylinder walls. The overall return of heat from the charge of a combustible mixture is insignificant, it is about 1.0 ... 1.5% of the amount of heat entering with the fuel.
The temperature of the working fluid at the end of the intake and its same temperature at the end of compression are related to the compression polytropic equation:
where 8 is a compression ratio; p l - Indicator polytropags.
The temperature at the end of the compression tact of the general rule is calculated by the average constant for the entire process of the polytropic indicator. sh. In a particular case, the polytropic indicator is calculated on the balance of heat during the compression process in the form of
where and S. and and "- Internal energy of 1 km of fresh charge; and A. and and "-internal energy of 1 km of residual gases.
Joint solution of equations (2.37) and (2.39) with a known temperature value T A. Allows you to determine the indicator of polytropags sh. The polytropope indicator affects the intensity of the cooling of the cylinder. At low cooling fluid temperatures, the surface temperature of the cylinder is below, therefore, and p L. will be less.
The values \u200b\u200bof the terminal parameters of the compression tact are shown in Table. 2.3.
Table23
With the intake and exhaust valve compression tact, the piston moves to the VTC. Take time of compression tact in diesel engines at a speed of 1500 ... 2400 min -1 is 1.49 1 SG 2 ... 9.31 kg 3 C, which corresponds to the rotation of the crankshaft at an angle f (. \u003d 134 °, in gasoline engines At a speed of 2400 ... 5600 min -1 and CP g \u003d 116 ° - (3.45 ... 8.06) 1 (g 4 s. The temperature difference in the cylinder between compression and intake clocks At from _ a = T C - T A Diesels are within 390 ... 550 ° C, in gasoline engines - 280 ... 370 ° C.
The rate of temperature change in the cylinder for compression tact is:
and for diesel engines at a speed of 1500 ... 2500 min -1 The rate of temperature change is (3.3 ... 5.5) 10 4 degrees / s, gasoline engines at a rotational speed of 2000 ... 6000 min -1 - ( 3.2 ... 9.5) x x 10 4 hail / s. The heat flux with compression tact is directed from the working fluid in the cylinder to the walls and into the coolant. Graphics function CO \u003d f (N. e) for diesel engines and gasoline engines are presented in Fig. 2.13 and 2.14. It follows that the rate of changes in the temperature of the working fluid in diesel engines compared with gasoline engines at one rotational speed above.
The heat exchange processes with compression tact are caused by the temperature drop between the surface of the cylinder and the charge of a combustible mixture, relatively small surface of the cylinder at the end of the tact, mass of the combustible mixture and limitedly a short period of time at which heat transfer occurs from a combustible mixture to the surface of the cylinder. It is assumed that compression tact does not have a significant impact on temperature mode cooling systems.
Expansion tact It is the only tact of the engine working cycle, in which useful mechanical work is performed. This clock is preceded by the combustion process of a combustible mixture. The result of combustion is to increase the internal energy of the working fluid transformed into the work of the expansion.
The combustion process is a complex of physical and chemical phenomena of fuel oxidation with intensive selection
warm. For liquid hydrocarbon fuels (gasoline, diesel fuel), the combustion process is chemical reactions of carbon and hydrogen compound with air oxygen. The heat of combustion of the charge of a combustible mixture is spent on the heating of the working fluid, performing mechanical work. Part of the heat from the working fluid through the walls of the cylinders and the head heats the block cartridge and other parts of the engine, as well as the coolant. The thermodynamic process of the real workflow, taking into account the loss of heat of the combustion of fuel, taking into account the incompleteness of combustion, heat transfer in the walls of the cylinders and so on is extremely complex. In diesel engines and gasoline engines, the combustion process varies and has its own characteristics. In diesel engines, combustion occurs with different intensity depending on the stroke of the piston: first intensively and then slowed down. In gasoline engines, combustion occurs instantly, it is believed that it is performed at a constant volume.
To account for heat in the component of losses, including heat transfer in the walls of cylinders, the coefficient of use of heat combustion The coefficient of use of heat is determined experimentally for diesel engines \u003d 0.70 ... 0.85 and gasoline engines?, \u003d 0.85 ... 0.90 of the equation of state states at the beginning and end of the expansion:
where is the degree of preliminary expansion.
For diesel engines
then 
For gasoline engines 
then
Values \u200b\u200bof parameters in the combustion process and at the end of the engine expansion clock)
