The main pros and cons of direct injection engines. Fuel injection systems for the engine Types of fuel injection for gasoline engines

14.07.2021

Material from the Encyclopedia of the magazine "Behind the wheel"

Schematic diagram of a Volkswagen FSI engine with direct petrol injection

The first systems for injecting gasoline directly into engine cylinders appeared in the first half of the 20th century. and were used on aircraft engines. Attempts to use direct injection in gasoline engines of cars were discontinued in the 40s of the twentieth century, because such engines were expensive, uneconomical and smoked heavily at high power modes. Injecting gasoline directly into the cylinders is a challenge. Gasoline direct injection injectors operate in more difficult conditions than those installed in the intake manifold. The head of the block, into which such nozzles are to be installed, turns out to be more complicated and expensive. The time allotted for the mixture formation process with direct injection is significantly reduced, which means that for good mixture formation it is necessary to supply gasoline under high pressure.
The specialists of Mitsubishi managed to cope with all these difficulties, which for the first time applied a gasoline direct injection system on automobile engines. The first production car Mitsubishi Galant with a 1.8 GDI (Gasoline Direct Injection) engine appeared in 1996.
The advantages of the direct injection system are mainly in the improvement of fuel economy, as well as some increase in power. The first is due to the ability of a direct injection engine to run very lean mixtures. The increase in power is mainly due to the fact that the organization of the process of supplying fuel to the engine cylinders makes it possible to increase the compression ratio to 12.5 (in conventional gasoline engines, it is rarely possible to set the compression ratio above 10 due to the onset of detonation).

The nozzle of the GDI engine can operate in two modes, providing a powerful (a) or compact (b) torch of sprayed gasoline

In the GDI engine, the fuel pump provides a pressure of 5 MPa. An electromagnetic injector, installed in the cylinder head, injects gasoline directly into the engine cylinder and can operate in two modes. Depending on the supplied electrical signal, it can inject fuel either with a powerful conical torch or with a compact jet.

The piston of a direct petrol injection engine has a special shape (combustion process above the piston)

The piston bottom has a special shape in the form of a spherical recess. This shape allows the incoming air to swirl, directing the injected fuel to the spark plug installed in the center of the combustion chamber. The inlet line is not located at the side, but vertically from above. It does not have sharp bends and therefore the air flows in at a high speed.

In the operation of an engine with a direct injection system, three different modes can be distinguished:
1) the mode of operation on super-lean mixtures;
2) the mode of operation on a stoichiometric mixture;
3) mode of sharp accelerations from low revs;
The first mode is used when the car is moving without sudden acceleration at a speed of about 100–120 km / h. This mode uses a very lean fuel mixture with an excess air ratio of more than 2.7. Under normal conditions, such a mixture cannot be ignited by a spark, so the injector injects fuel in a compact torch at the end of the compression stroke (like in a diesel engine). A spherical recess in the piston directs a jet of fuel to the spark plug electrodes, where the high concentration of gasoline vapors allows the mixture to ignite.
The second mode is used when the car is moving at high speed and during sharp accelerations, when it is necessary to obtain high power. This mode of movement requires a stoichiometric composition of the mixture. A mixture of this composition is highly flammable, but the GDI engine has an increased compression ratio, and in order to prevent detonation, the injector injects fuel with a powerful torch. Finely atomized fuel fills the cylinder and evaporates to cool the cylinder surfaces, reducing the likelihood of knocking.
The third mode is necessary to obtain a large torque when the accelerator pedal is pressed sharply when the engine is running at low revs. This operating mode of the engine differs in that the injector is triggered twice during one cycle. During the intake stroke, an ultra-lean mixture (α = 4.1) is injected into the cylinder to cool it with a powerful torch. At the end of the compression stroke, the injector once again injects fuel, but with a compact torch. In this case, the mixture in the cylinder is enriched and detonation does not occur.
Compared to a conventional engine with distributed petrol injection, a GDI engine is about 10% more economical and emits 20% less carbon dioxide. The increase in engine power reaches 10%. However, as shown by the operation of cars with engines of this type, they are very sensitive to the sulfur content in gasoline. Orbital developed the original direct petrol injection process. In this process, gasoline is injected into the engine cylinders, which is pre-mixed with air using a special nozzle. The Orbital nozzle consists of two nozzles, fuel and air.

Orbital nozzle operation

Air is supplied to the air jets in a compressed form from a special compressor at a pressure of 0.65 MPa. The fuel pressure is 0.8 MPa. First, the fuel jet is triggered, and then, at the right time, the air jet, therefore, a fuel-air mixture in the form of an aerosol is injected into the cylinder with a powerful torch.
An injector located in the cylinder head next to the spark plug injects a jet of fuel and air directly onto the spark plug electrodes for good ignition.

Design features of the Audi 2.0 FSI direct petrol injection engine

Reading 5 min.

In this article you will find all the main information about such a part of a road vehicle as a fuel injection system. Start reading now!

In the article presented by us, you can easily find answers to such fairly common questions:

What is the injection system and how does it work?
The main types of injection schemes;
What is fuel injection and what effect does it have on engine performance?

What is the fuel injection system and how does it work?

Modern cars are equipped with various gasoline supply systems. The fuel injection system, or as it is also called injection, provides a gasoline mixture. On modern engines, the injection system has completely replaced the carburetor power circuit. Despite this, among motorists to this day there is no single opinion about which one is better, because each of them has its own advantages and disadvantages. Before dealing with the principle of operation and types of fuel injection systems, you need to understand its elements. So, the fuel injection system consists of the following basic elements:

Throttle valve;
Receiver;
Four nozzles;
Channel.

Now let's look at the principle of operation of the fuel supply system to the engine. The air supply is regulated by the throttle valve and accumulates in the receiver before being divided into four flows. The receiver is needed to correctly calculate the mass flow rate of air, because the measurement of the total mass flow rate or pressure in the receiver is carried out. The receiver must be of sufficient size in order to exclude the possibility of air starvation of the cylinders during high air consumption, as well as to smooth out the pulsation at the start. Four injectors are located in the channel in the immediate vicinity of the intake valves.

The fuel injection system is used on both gasoline and diesel engines. In addition, there are significant differences in the design and operation of the gasoline supply between diesel and gasoline engines. On gasoline engines, a homogeneous air-fuel mixture is formed by means of fuel supply, which is forcibly ignited by sparks. On diesel engines, the fuel mixture is supplied under high pressure, the dose of the fuel mixture is mixed with hot air and ignites almost immediately. The pressure determines the size of the portion of the injected fuel mixture, and therefore the power of the engine. Therefore, the engine power is directly proportional to the pressure. That is, the greater the fuel supply pressure, the greater the engine power. The fuel mixture diagram is an integral part of the vehicle. The main working "body" of absolutely every injection scheme is the nozzle.

Fuel injection system for gasoline engines

Depending on the method of forming the air-fuel mixture, such systems of central injection, direct and distributed type are distinguished. The distributed and central injection system is a pre-injection system. That is, injection into them takes place without reaching the combustion chamber, which is located in the intake manifold.

Central injection (or mono injection) takes place using a single nozzle, which is installed in the intake manifold. At the moment, a system of this type is not produced, but it is still found on passenger cars. This type is quite simple and reliable, but has increased fuel costs and low environmental performance.

Distribution fuel injection is the delivery of the fuel mixture to the intake manifold through a separate fuel injector for each cylinder. An air / fuel mixture is formed in the intake manifold. It is the most common fuel mixture injection scheme for gasoline engines. The first and main advantage of the distributed type is cost-effectiveness. In addition, due to the more complete combustion of fuel in one cycle, cars with this type of injection bring less harm to the environment with harmful emissions. With accurate metering of the fuel mixture, the risk of unforeseen failures in operation at extreme conditions is reduced to almost zero. The disadvantage of this type of injection system is that it is quite complex and totally dependent on the electronics. Due to the large number of components, repair and diagnostics of this type are possible exclusively in the conditions of an automobile service center.

One of the most promising types of fuel delivery is the direct fuel injection system. The mixture is fed directly into the combustion chamber of all cylinders. The feed scheme makes it possible to create an optimal composition of the fuel-air mixture during the operation of all engine operating modes, to increase the compression level, fuel economy, increase power, as well as reduce harmful emissions. The disadvantage of this type of injection is its complex design and high operational requirements. In order to reduce the level of emissions of particulate matter into the atmosphere together with the exhaust gases, combined injection is used, which combines the scheme of direct and distributed gasoline supply on a single internal combustion engine.

Fuel injection into the engine can be electronically or mechanically controlled. The best is electronic control, which provides significant savings in the combustible mixture, as well as the reduction of harmful emissions. The injection of the fuel mixture in the circuit can be pulsed or continuous. Pulse injection of a combustible mixture, which uses all modern types, is considered the most promising and economical. In an engine, this circuit is usually combined with ignition to form a combined fuel and ignition circuit. The coordination of the fuel supply circuits is ensured by the engine control circuit.

We hope that this article helped you find a solution to your problems and you found answers to all questions that relate to this topic. Observe the traffic rules and be vigilant when traveling!

In the case of a fuel injection system, your engine still sucks, but instead of relying only on the amount of fuel being drawn in, the fuel injection system shoots exactly the right amount of fuel into the combustion chamber. Fuel injection systems have already gone through several stages of evolution, electronics were added to them - this was perhaps the biggest step in the development of this system. But the idea of such systems remains the same: an electrically activated valve (injector) sprays a metered amount of fuel into the engine. In fact, the main difference between the carburetor and the injector is precisely in the electronic control of the ECU - it is the on-board computer that supplies exactly the right amount of fuel to the engine combustion chamber.

Let's take a look at how the fuel injection system and the injector in particular work.

This is what the fuel injection system looks like

If the heart of a car is its engine, then its brain is the engine control unit (ECU). It optimizes engine performance using sensors to decide how to control some of the drives in the engine. First of all, the computer is responsible for 4 main tasks:

manages the fuel mixture,
controls idle speed,
is responsible for the ignition timing,
controls the valve timing.

Before we talk about how the ECU performs its tasks, let's talk about the most important thing - let's trace the path of gasoline from the gas tank to the engine - this is the work of the fuel injection system. Initially, after a drop of gasoline leaves the walls of the gas tank, it is sucked into the engine by an electric fuel pump. An electric fuel pump, as a rule, consists of a pump itself, as well as a filter and a transfer device.

The fuel pressure regulator at the end of the vacuum fed fuel rail ensures that the fuel pressure is constant with respect to the suction pressure. For a gasoline engine, fuel pressure is typically in the order of 2-3.5 atmospheres (200-350 kPa, 35-50 PSI (psi)). The fuel injector nozzles are connected to the engine, but their valves remain closed until the ECU allows fuel to be sent to the cylinders.

But what happens when the engine needs fuel? This is where the injector comes into play. Usually, injectors have two contacts: one terminal is connected to the battery through the ignition relay, and the other contact goes to the ECU. The ECU sends pulsating signals to the injector. Due to the magnet, to which such pulsating signals are supplied, the injector valve opens, and a certain amount of fuel is supplied to its nozzle. Since the injector has a very high pressure (as shown above), the open valve directs fuel at a high velocity into the injector nozzle. The duration with which the injector valve is open affects how much fuel is supplied to the cylinder, and this duration, accordingly, depends on the pulse width (i.e., on how long the ECU sends a signal to the injector).

When the valve opens, the fuel injector transfers fuel through the spray tip, which atomizes the liquid fuel into mist directly into the cylinder. Such a system is called direct injection system... But the atomized fuel may not be supplied directly to the cylinders, but first to the intake manifolds.

How the injector works

But how does the ECU determine how much fuel should be supplied to the engine at a given moment? When the driver presses the accelerator pedal, he actually opens the throttle by the amount of pedal pressure, through which air is supplied to the engine. Thus, we can confidently call the gas pedal "air regulator" to the engine. So, the car's computer is guided, among other things, by the throttle opening value, but is not limited to this indicator - it reads information from many sensors, and let's find out about all of them!

Mass air flow sensor

First things first, the mass air flow (MAF) sensor detects how much air enters the throttle body and sends this information to the ECU. The ECU uses this information to decide how much fuel to inject into the cylinders to keep the mixture in perfect proportions.

Throttle position sensor

The computer constantly uses this sensor to check the throttle position and thus know how much air is passing through the air intake in order to regulate the impulse sent to the injectors, ensuring that the correct amount of fuel enters the system.

Oxygen sensor

In addition, the ECU uses an O2 sensor to find out how much oxygen is in the vehicle's exhaust gas. The oxygen content in the exhaust provides an indication of how well the fuel is burning. Using the associated data from two sensors: oxygen and mass air flow, the ECU also monitors the saturation of the fuel-air mixture supplied to the combustion chamber of the engine cylinders.

Crankshaft position sensor

This is perhaps the main sensor of the fuel injection system - it is from him that the ECU learns about the number of engine revolutions at a given time and adjusts the amount of fuel supplied depending on the number of revolutions and, of course, the position of the gas pedal.

These are three main sensors that directly and dynamically affect the amount of fuel supplied to the injector and subsequently to the engine. But there are also a number of sensors:

The voltage sensor in the electrical network of the machine is needed so that the ECU understands how discharged the battery is and whether it is necessary to increase the speed to charge it.
Coolant temperature sensor - The ECU ramps up if the engine is cold and vice versa if the engine is warmed up.

The main purpose of the injection system (another name is the injection system) is to ensure the timely supply of fuel to the working cylinders of the internal combustion engine.

Currently, a similar system is actively used on diesel and gasoline internal combustion engines. It is important to understand that the injection system will be very different for each type of engine.

Photo: rsbp (flickr.com/photos/rsbp/)

So in gasoline internal combustion engines, the injection process contributes to the formation of a fuel-air mixture, after which it is forcedly ignited by a spark.

In diesel internal combustion engines, fuel is supplied under high pressure, when one part of the fuel mixture is combined with hot compressed air and spontaneously ignites almost instantly.

The injection system remains a key part of any vehicle's overall fuel system. The central working element of such a system is the fuel injector (injector).

As mentioned earlier, various types of injection systems are used in gasoline engines and diesels, which we will consider briefly in this article, and we will analyze in detail in subsequent publications.

Types of injection systems on gasoline internal combustion engines

Gasoline engines use the following fuel delivery systems - central injection (mono injection), multipoint injection (multipoint), combined injection and direct injection.

Central injection

Fuel is supplied to the central injection system by a fuel injector located in the intake manifold. Since there is only one nozzle, this injection system is also called mono injection.

Systems of this type have lost their relevance today, so they are not provided for in new car models, however, in some old models of some car brands they can be found.

The advantages of mono injection include reliability and ease of use. The disadvantages of such a system are the low level of environmental friendliness of the engine and high fuel consumption.

Distributed injection

The multi-point injection system supplies fuel separately to each cylinder equipped with its own fuel injector. In this case, the fuel assembly is formed only in the intake manifold.

Currently, most gasoline engines are equipped with a distributed fuel delivery system. The advantages of such a system are high environmental friendliness, optimal fuel consumption, moderate requirements for the quality of the fuel consumed.

Direct injection

One of the most advanced and advanced injection systems. The principle of operation of such a system is the direct supply (injection) of fuel into the combustion chamber of the cylinders.

The direct fuel supply system makes it possible to obtain a high-quality composition of fuel assemblies at all stages of ICE operation in order to improve the combustion of the combustible mixture, increase the engine operating power, and reduce the level of exhaust gases.

The disadvantages of this injection system include a complex design and high requirements for fuel quality.

Combined injection

The system of this type combines two systems - direct and distributed injection. It is often used to reduce emissions of toxic elements and exhaust gases, thereby achieving high levels of engine environmental friendliness.

All fuel supply systems used on gasoline internal combustion engines can be equipped with mechanical or electronic control devices, of which the latter is the most advanced, since it provides the best indicators of efficiency and environmental friendliness of the engine.

Fuel supply in such systems can be carried out continuously or discretely (impulse). According to experts, impulse fuel supply is the most appropriate and efficient and is currently used in all modern engines.

Types of injection systems for diesel internal combustion engines

Modern diesel engines use injection systems such as a pump-injector system, a common rail system, a system with an in-line or distribution injection pump (high pressure fuel pump).

The most popular and considered to be the most progressive of them are the systems: Common Rail and unit injectors, which we will talk about in more detail below.

The injection pump is the central element of any diesel engine fuel system.

In diesel engines, the supply of the combustible mixture can be carried out both into the preliminary chamber and directly into the combustion chamber (direct injection).

Today, the preference is given to the direct injection system, which is distinguished by an increased noise level and a less smooth engine operation compared to injection into the pre-chamber, but at the same time a much more important indicator is provided - efficiency.

Injection system unit-injector

A similar system is used to supply and inject a fuel mixture under high pressure by a central device - pump nozzles.

As the name suggests, the key feature of this system is that in a single device (pump nozzle) two functions are combined at once: pressure generation and injection.

The design drawback of this system is that the pump is equipped with a constant-type drive from the engine camshaft (not shut off), which leads to rapid wear of the structure. Because of this, manufacturers are increasingly opting for the Common Rail injection system.

Common Rail injection system (accumulator injection)

This is a more advanced vehicle supply system for most diesel engines. Its name comes from the main structural element - the fuel rail, common to all injectors. Common Rail in translation from English just means - a common ramp.

In such a system, fuel is supplied to the fuel injectors from the rail, which is also called the high-pressure accumulator, which is why the system has a second name - the accumulator injection system.

The Common Rail system provides for three stages of injection - preliminary, main and additional. This makes it possible to reduce engine noise and vibration, make the fuel self-ignition process more efficient, and reduce the amount of harmful emissions into the atmosphere.

To control injection systems on diesel engines, mechanical and electronic devices are provided. Systems on the mechanics allow you to control the working pressure, volume and timing of fuel injection. Electronic systems allow for more efficient control of diesel internal combustion engines in general.

The fuel injection system is used to meter fuel into an internal combustion engine at a specific point in time. Power, efficiency, etc., depends on the characteristics of this system. Injection systems can be of various designs and versions, which characterizes their efficiency and scope.

Brief history of appearance

The fuel injection system began to be actively implemented in the 70s, as a reaction to the increased level of emissions of pollutants into the atmosphere. It was borrowed from the aircraft industry and was an environmentally safer alternative to the carburetor engine. The latter was equipped with a mechanical fuel supply system, in which fuel entered the combustion chamber due to the pressure difference.

The first injection system was almost completely mechanical and was characterized by low efficiency. The reason for this was the insufficient level of technical progress, which could not fully reveal its potential. The situation changed in the late 90s with the development of electronic engine control systems. The electronic control unit began to control the amount of fuel injected into the cylinders and the percentage of the components of the fuel-air mixture.

Types of injection systems for gasoline engines

There are several main types of fuel injection systems, which differ in the way the air-fuel mixture is formed.

Mono injection, or central injection

Scheme of the mono injection system

The central injection scheme provides for the presence of one, which is located in the intake manifold. Such injection systems can only be found on older passenger cars. It consists of the following elements:

Pressure regulator - provides a constant operating pressure of 0.1 MPa and prevents air pockets c.
Injection nozzle - impulses gasoline to the intake manifold of the engine.
- regulates the volume of the supplied air. It can be mechanically or electrically driven.
Control unit - consists of a microprocessor and a memory unit that contains the reference data for the fuel injection characteristics.
Sensors for engine crankshaft position, throttle position, temperature, etc.

Gasoline injection systems with one injector operate according to the following scheme:

The engine is running.
Sensors read and transmit information about the state of the system to the control unit.
The obtained data is compared with the reference characteristic, and, based on this information, the control unit calculates the moment and duration of the injector opening.
A signal is sent to the solenoid coil to open the injector, which leads to the supply of fuel to the intake manifold, where it mixes with air.
A mixture of fuel and air is fed into the cylinders.

Multiple injection (MPI)

The distributed injection system consists of similar elements, but this design provides separate nozzles for each cylinder, which can be opened simultaneously, in pairs or one at a time. Mixing of air and gasoline also occurs in the intake manifold, but, unlike single injection, fuel is supplied only to the intake tracts of the corresponding cylinders.

Scheme of the system with distributed injection

The control is carried out electronically (KE-Jetronic, L-Jetronic). These are universal Bosch fuel injection systems that are widely used.

The principle of operation of distributed injection:

Air is supplied to the engine.
A number of sensors determine the volume of air, its temperature, the speed of rotation of the crankshaft, as well as the parameters of the throttle valve position.
Based on the data received, the electronic control unit determines the optimal fuel volume for the incoming air volume.
A signal is given and the corresponding injectors are opened for the required period of time.

Direct fuel injection (GDI)

The system provides for the supply of gasoline by separate injectors directly to the combustion chambers of each cylinder at high pressure, where air is simultaneously supplied. This injection system provides the most accurate concentration of the air-fuel mixture, regardless of the engine operating mode. At the same time, the mixture burns out almost completely, thereby reducing the volume of harmful emissions into the atmosphere.

Diagram of the direct injection system

Such an injection system is complex in design and is sensitive to fuel quality, which makes it costly to manufacture and operate. Since the injectors operate in more aggressive conditions, for the correct operation of such a system, it is necessary to ensure a high fuel pressure, which must be at least 5 MPa.

Structurally, the direct injection system includes:

High pressure fuel pump.
Fuel pressure control.
Fuel rail.
Safety valve (installed on the fuel rail to protect the system elements from pressure increase above the permissible level).
High pressure sensor.
Injectors.

An electronic injection system of this type from Bosch is named MED-Motronic. The principle of its operation depends on the type of mixture formation:

Layer-by-layer - is implemented at low and medium engine speeds. Air is fed into the combustion chamber at high speed. Fuel is injected towards and, mixing with air along the way, ignites.
Stoichiometric. When you press the gas pedal, the throttle valve is opened and fuel is injected simultaneously with the supply of air, after which the mixture ignites and completely burns out.
Homogeneous. Intensive air movement is provoked in the cylinders, while gasoline is injected at the intake stroke.

The gasoline engine is the most promising direction in the evolution of injection systems. It was first implemented in 1996 on Mitsubishi Galant passenger cars, and today it is installed on their cars by most of the largest automakers.

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