Engine with electronic fuel injection. Direct fuel injection system in gasoline engines: operating principle. Types of injection systems

Engines with fuel injection systems, or injection engines, have almost been forced out of the market carburetor engines. Today, there are several types of injection systems, differing in design and operating principle. About how they are structured and work Various types and types of fuel injection systems, read this article.

Design, principle of operation and types of fuel injection systems

Today, most new passenger cars are equipped with fuel injection engines, which have better performance and are more reliable than traditional carburetor engines. We have already written about injection engines (article “Injection engine”), so here we will consider only the types and varieties of fuel injection systems.

There are two fundamentally different types fuel injection systems:

Central injection (or single injection);
- Distributed injection (or multipoint injection).

These systems differ in the number of nozzles and their operating modes, but their operating principle is the same. In an injection engine, instead of a carburetor, one or more fuel injectors are installed, which spray gasoline into intake manifold or directly into the cylinders (air to form fuel-air mixture supplied to the manifold using a throttle assembly). This solution makes it possible to achieve uniformity and High Quality combustible mixture, and most importantly - simple installation of the engine operating mode depending on the load and other conditions.

The system is controlled by a special electronic unit (microcontroller), which collects information from several sensors and instantly changes the engine operating mode. In early systems this function was performed by mechanical devices, but today the engine is completely under electronic control.

Fuel injection systems differ in the number, installation location and operating mode of the injectors.

1 - engine cylinders;
2 - inlet pipeline;
3 - throttle valve;
4 - fuel supply;
5 - electrical wire, through which a control signal is sent to the injector;
6 - air flow;
7 - electromagnetic injector;
8 - fuel torch;
9 - flammable mixture

This solution was historically the first and simplest, so at one time it became quite widespread. In principle, the system is very simple: it uses one nozzle, which constantly sprays gasoline into one intake manifold for all cylinders. Air is also supplied to the manifold, so a fuel-air mixture is formed here, which enters the cylinders through the intake valves.

The advantages of single injection are obvious: this system is very simple, to change the operating mode of the engine you need to control only one nozzle, and the engine itself undergoes minor changes, because the nozzle is placed in place of the carburetor.

However, mono-injection also has disadvantages, first of all - this system cannot meet the ever-increasing requirements for environmental safety. In addition, the failure of one injector actually puts the engine out of action. Therefore, today engines with central injection are practically not produced.

Distributed injection

1 - engine cylinders;
2 - fuel torch;
3 - electrical wire;
4 - fuel supply;
5 - inlet pipeline;
6 - throttle valve;
7 - air flow;
8 - fuel rail;
9 - electromagnetic injector

In systems with distributed injection injectors are used according to the number of cylinders, that is, each cylinder has its own injector located in the intake manifold. All injectors are connected by a fuel rail through which fuel is supplied to them.

There are several types of distributed injection systems, which differ in the operating mode of the injectors:

Simultaneous injection;
- Pair-parallel injection;
- Phased spray.

Simultaneous injection. Everything is simple here - the injectors, although located in the intake manifold of “their” cylinder, open at the same time. We can say that this is an improved version of single injection, since several nozzles work here, but the electronic unit controls them as one. However, simultaneous injection makes it possible to individually adjust fuel injection for each cylinder. In general, simultaneous injection systems are simple and reliable in operation, but are inferior in performance to more modern systems.

Pair-parallel injection. This is an improved version of simultaneous injection; it differs in that the injectors open in turn in pairs. Typically, the operation of the injectors is configured in such a way that one of them opens before the intake stroke of its cylinder, and the second - before the exhaust stroke. Today, this type of injection system is practically not used, but modern engines provided emergency work engine in this mode. Typically, this solution is used when phase sensors (camshaft position sensors) fail, making phased injection impossible.

Phased injection. This is the most modern and providing best characteristics type of injection system. With phased injection, the number of injectors is equal to the number of cylinders, and they all open and close depending on the stroke. Typically, the injector opens immediately before the intake stroke - this is how best mode engine performance and efficiency.

Also distributed injection includes systems with direct injection, however, the latter has cardinal design differences, so it can be distinguished as a separate type.

Direct injection systems are the most complex and expensive, but only they can provide the best performance and efficiency. Direct injection also makes it possible to quickly change the engine operating mode, regulate the fuel supply to each cylinder as precisely as possible, etc.

In direct injection systems, the injectors are mounted directly in the head, spraying fuel directly into the cylinder, avoiding the middleman of the intake manifold and intake valve(s).

This solution is quite difficult technically, since in the cylinder head, where the valves and spark plug are already located, it is also necessary to place an injector. Therefore, direct injection can only be used in sufficiently powerful and therefore large-sized engines. In addition, such a system cannot be installed on serial engine- it has to be modernized, which is associated with high costs. Therefore, direct injection is used today only on expensive cars.

Direct injection systems are demanding on fuel quality and require more frequent maintenance, but they provide significant fuel savings and provide more reliable and quality work engine. Now there is a downward trend in the price of cars with such engines, so in the future they can seriously compete with cars with injection engines of other systems.

Today, injection systems are actively used on gasoline and diesel internal combustion engines. It is worth noting that for each engine variation such a system will be significantly different. More on this later in the article.

Injection system, purpose, what is the difference between the injection system of a gasoline engine and the injection system of a diesel engine

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

In gasoline engines, the injection process supports the formation of air fuel mixture, after which it is ignited using a spark. IN diesel engines fuel supply is carried out under high pressure- one part of the combustible mixture is combined with compressed air and almost instantly ignites spontaneously.

Gasoline injection system, design of fuel injection systems for gasoline engines

Fuel injection system - component vehicle fuel system. The main working element of any injection system is the nozzle. Depending on the method of formation of the air-fuel mixture, there are direct injection, distributed injection and central injection systems. Distributed and central injection systems are pre-injection systems, that is, injection into them is carried out in the intake manifold, not reaching the combustion chamber.

Injection systems gasoline engines can have electronic or mechanical control. Electronic injection control is considered the most advanced, which provides significant fuel savings and a reduction in harmful emissions into the atmosphere.

Fuel injection into the system is carried out pulsed (discretely) or continuously. From an economic point of view, pulsed fuel injection, used by all modern systems, is considered promising.

In an engine, the injection system is usually connected to the ignition system and creates a combined ignition and injection system (for example, Fenix, Motronic systems). The motor control system ensures coordinated operation of the systems.

Gasoline engine injection systems, types of fuel injection systems, advantages and disadvantages of each type of gasoline engine injection system

The following fuel supply systems are used on gasoline engines: direct injection, combined injection, distributed injection (multipoint), central injection (single injection).

Central injection. The fuel supply in this system is carried out through a fuel injector located in the intake manifold. And since there is only one nozzle, this system is also called mono-injection.

Today, central injection systems have lost their relevance, which is why they are not provided in new car models, but they can still be found in some older vehicles.

The advantages of single injection are reliability and ease of use. The disadvantages of this system include high consumption fuel and low level of environmental friendliness of the engine. Distributed injection. The multipoint injection system provides a separate fuel supply to each cylinder, which is equipped with an individual fuel injector. FA, in this case, occurs only in the intake manifold.

Today, most gasoline engines are equipped with a distributed fuel supply system. Advantages similar system — optimal consumption fuel, high environmental friendliness, optimal requirements for the quality of consumed fuel.

Direct injection. One of the most progressive and advanced injection systems. The operating principle of this system is based on the direct (direct) supply of fuel to the combustion chamber.

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

The disadvantages of this injection system are its rather complex design and high requirements for fuel quality.

Combined injection. This type of system combines two systems - distributed and direct injection. As a rule, it is used to reduce emissions of toxic components and exhaust gases, with which you can achieve high performance environmental friendliness of the motor.

Diesel engine injection systems, types of systems, advantages and disadvantages of each type of diesel fuel injection system

Modern diesel engines use the following injection systems - system Common Rail, pump-injector system, system with a distribution or in-line high-pressure fuel pump (HPF).

The most popular and progressive are pump injectors and Common Rail. The injection pump is the central component of any diesel engine fuel system.
The fuel mixture in diesel engines can be supplied to the preliminary chamber or directly to the combustion chamber.

Currently, preference is given to a direct injection system, characterized by increased level noise or less smooth operation motor in comparison with feeding into the preliminary chamber, however, this ensures a more important indicator - efficiency.

Pump-injector system. This system is used for supplying and injecting a combustible mixture under high pressure using pump injectors. Key Feature of this system - two functions are combined in one device - injection and pressure creation.

A design disadvantage of this system is that the pump is equipped permanent drive from the engine camshaft (not switchable), which can lead to rapid wear systems. As a result, manufacturers are increasingly choosing common rail systems.

Battery injection (Common Rail). More advanced fuel mixture supply design for many diesel engines. In such a system, fuel is supplied from the ramp to fuel injectors, which is also called a high-pressure accumulator, as a result of which the system has another name - accumulator injection.

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

conclusions

To control injection systems on diesel engines, electronic and mechanical devices. Mechanical systems make it possible to control operating pressure, timing and volume of fuel injection. Electronic systems provide more efficient control of diesel engines in general.

In the late 60s and early 70s of the twentieth century, the problem of pollution arose environment industrial waste, a significant part of which was car exhaust gases. Until this time, no one was interested in the composition of the combustion products of internal combustion engines. In order to maximum use air during the combustion process and achieving the maximum possible engine power, the composition of the mixture was adjusted so that there was an excess of gasoline in it.

As a result, there was absolutely no oxygen in the combustion products, but unburned fuel remained, and substances harmful to health were formed mainly during incomplete combustion. In an effort to increase power, designers installed accelerator pumps on carburetors that inject fuel into the intake manifold with each sharp press on the accelerator pedal, i.e. when sudden acceleration of the vehicle is required. In this case, an excessive amount of fuel does not correspond to the amount of air entering the cylinders.

In city traffic conditions, the accelerator pump is activated at almost all intersections with traffic lights, where cars must either stop or quickly move away. Incomplete combustion also occurs when the engine is idling, and especially when the engine is braking. When the throttle is closed, air flows through the channels idle move carburetor at high speed, drawing in too much fuel.

Due to the significant vacuum in intake manifold little air is drawn into the cylinders, the pressure in the combustion chamber remains relatively low at the end of the compression stroke, the combustion process is excessive rich mixture passes slowly and exhaust gases There is a lot of unburned fuel left. The described engine operating modes sharply increase the content of toxic compounds in combustion products.

It became obvious that in order to reduce emissions into the atmosphere harmful to human life, it is necessary to radically change the approach to the design of fuel equipment.

To reduce harmful emissions into the exhaust system, it was proposed to install a catalytic exhaust gas converter. But the catalyst works effectively only when the so-called normal fuel-air mixture is burned in the engine (air/gasoline weight ratio 14.7:1). Any deviation of the mixture composition from the specified one led to a drop in its operating efficiency and accelerated failure. To consistently maintain this ratio working mixture carburetor systems were no longer suitable. The only alternative could be injection systems.

The first systems were purely mechanical with little use of electronic components. But the practice of using these systems has shown that the mixture parameters, the stability of which the developers counted on, change as the vehicle is used. This result is quite natural, taking into account the wear and contamination of system elements and the internal combustion engine itself during its service. The question arose about a system that could correct itself during operation, flexibly shifting the conditions for preparing the working mixture depending on external conditions.

The following solution was found. Injected into the injection system feedback– a sensor for oxygen content in the exhaust gases, the so-called lambda probe, was installed in the exhaust system, directly in front of the catalyst. This system was developed taking into account the presence of such a fundamental element for all subsequent systems as an electronic control unit (ECU). Based on signals from the oxygen sensor, the ECU adjusts the fuel supply to the engine, accurately maintaining the right composition mixtures.

Today, the injection (or, in Russian, injection) engine has almost completely replaced the outdated
carburetor system. The injection engine significantly improves the performance and power performance of the car
(acceleration dynamics, environmental characteristics, fuel consumption).

Fuel injection systems have the following main advantages over carburetor systems:

precise dosing of fuel and, therefore, more economical fuel consumption.
reduced toxicity exhaust gases. Achieved through optimal fuel-air mixture and the use of exhaust gas parameter sensors.
increase in engine power by approximately 7-10%. Occurs due to improved cylinder filling, optimal setting of the ignition timing corresponding to the operating mode of the engine.
improvement dynamic properties car. The injection system immediately responds to any load changes, adjusting the parameters of the fuel-air mixture.
ease of starting regardless of weather conditions.

Design and principle of operation (using the example of an electronic distributed injection system)

Modern injection engines have an individual injector for each cylinder. All injectors are connected to the fuel rail, where the fuel is under pressure, which is created by an electric fuel pump. The amount of fuel injected depends on the duration of the injector opening. The opening moment is regulated by an electronic control unit (controller) based on the data it processes from various sensors.

The mass air flow sensor is used to calculate the cyclic filling of the cylinders. Measured mass flow air, which is then recalculated by the program into cylinder cyclic filling. If a sensor fails, its readings are ignored and calculations are made using emergency tables.

Position sensor throttle valve serves to calculate the load factor on the engine and its change depending on the throttle opening angle, engine speed and cyclic filling.

The coolant temperature sensor is used to determine fuel supply and ignition temperature correction and to control the electric fan. If the sensor fails, its readings are ignored, the temperature is taken from the table depending on the engine operating time.

The crankshaft position sensor serves for overall system synchronization, calculating engine speed and crankshaft position at certain points in time. DPKV – polar sensor. If turned on incorrectly, the engine will not start. If the sensor fails, the system cannot operate. This is the only “vital” sensor in the system that makes it impossible for the vehicle to move. Failures of all other sensors allow you to get to the service center on your own.

The oxygen sensor is designed to determine the oxygen concentration in the exhaust gases. The information that the sensor provides is used by the electronic control unit to adjust the amount of fuel supplied. The oxygen sensor is used only in systems with a catalytic converter under Euro-2 and Euro-3 toxicity standards (in Euro-3 two oxygen sensors are used - before the catalyst and after it).

The knock sensor is used to monitor knock. When the latter is detected, the ECU turns on the detonation damping algorithm, quickly adjusting the ignition timing.

Listed here are only some of the basic sensors required for the system to operate. Sensor configurations for various cars depend on the injection system, toxicity standards, etc.

Based on the results of polling the sensors defined in the program, the ECU program carries out control actuators, which include: injectors, fuel pump, ignition module, idle air control, canister valve for the gasoline vapor recovery system, cooling system fan, etc. (all again depends on the specific model)

Of all the above, perhaps not everyone knows what an adsorber is. The adsorber is an element of a closed circuit for recirculating gasoline vapors. Euro-2 standards prohibit contact of the gas tank ventilation with the atmosphere; gasoline vapors must be collected (adsorbed) and, when purged, sent to the cylinders for afterburning. On engine not running gasoline vapors enter the adsorber from the tank and intake manifold, where they are absorbed. When the engine starts, the adsorber, at the command of the ECU, is purged with a flow of air sucked in by the engine, the vapors are carried away by this flow and are burned in the combustion chamber.

Types of fuel injection systems

Depending on the number of injectors and the location of the fuel supply, injection systems are divided into three types: single-point or mono-injection (one injector in the intake manifold for all cylinders), multi-point or distributed (each cylinder has its own injector that supplies fuel to the manifold) and direct ( fuel is supplied by injectors directly to the cylinders, like diesel engines).

Single point injection simpler, it is less stuffed with control electronics, but also less efficient. The control electronics allows you to read information from the sensors and immediately change the injection parameters. It is also important that they are easily adapted to single injection carburetor engines almost without design alterations or technological changes in production. Single-point injection has an advantage over a carburetor in fuel economy, environmental friendliness and relative stability and reliability of parameters. But single-point injection loses in engine throttle response. Another drawback: when using single-point injection, as when using a carburetor, up to 30% of gasoline settles on the walls of the manifold.

Single point injection systems were certainly a step forward compared to carburetor systems nutrition, but no longer meet modern requirements.

Systems are more advanced multipoint injection, in which fuel is supplied to each cylinder individually. Distributed injection is more powerful, more economical and more complex. The use of such injection increases engine power by approximately 7-10 percent. The main advantages of distributed injection:

the possibility of automatic adjustment at different speeds and, accordingly, improved cylinder filling, ultimately at the same maximum power the car accelerates much faster;
gasoline is injected close to the intake valve, which significantly reduces losses due to sedimentation in the intake manifold and allows for more precise adjustment of the fuel supply.

As another and effective remedy in optimizing the combustion of the mixture and increasing the efficiency of a gasoline engine, it implements simple
principles. Namely: it atomizes fuel more thoroughly, mixes it with air better and manages the finished mixture more competently at different engine operating modes. As a result, engines with direct injection consume less fuel than conventional injection engines (especially when quiet ride at low speed); with the same displacement, they provide more intense acceleration of the car; they have cleaner exhaust; they guarantee higher liter power due to a higher compression ratio and the cooling effect of the air as the fuel evaporates in the cylinders. At the same time they need quality gasoline with a low content of sulfur and mechanical impurities to ensure normal operation of fuel equipment.

And the main discrepancy between the GOSTs currently in force in Russia and Ukraine and European standards is the increased content of sulfur, aromatic hydrocarbons and benzene. For example, the Russian-Ukrainian standard allows the presence of 500 mg of sulfur in 1 kg of fuel, while Euro-3 - 150 mg, Euro-4 - only 50 mg, and Euro-5 - only 10 mg. Sulfur and water can activate corrosion processes on the surface of parts, and debris is a source of abrasive wear of calibrated holes in nozzles and plunger pairs of pumps. As a result of wear, the operating pressure of the pump decreases and the quality of gasoline atomization deteriorates. All this is reflected in the characteristics of engines and the uniformity of their operation.

First to use direct injection engine production car Mitsubishi company. Therefore, let’s look at the design and operating principles of direct injection using the example of a GDI (Gasoline Direct Injection) engine. The GDI engine can operate in the combustion mode of an ultra-lean air-fuel mixture: the air-to-fuel mass ratio is up to 30-40:1.

The maximum possible ratio for traditional injection engines with distributed injection is 20-24:1 (it is worth recalling that the optimal, so-called stoichiometric, composition is 14.7:1) - if there is more excess air, the lean mixture simply will not ignite. On a GDI engine, atomized fuel is present in the cylinder as a cloud, concentrated around the spark plug.

Therefore, although the mixture as a whole is lean, at the spark plug it is close to the stoichiometric composition and ignites easily. At the same time, the lean mixture in the rest of the volume has a much lower tendency to detonation than the stoichiometric one. The latter circumstance allows you to increase the compression ratio, and therefore increase both power and torque. Due to the fact that when fuel is injected and evaporated into the cylinder, the air charge is cooled - the filling of the cylinders is somewhat improved, and the likelihood of detonation again decreases.

The main design differences between GDI and conventional injection:

High pressure fuel pump (HFP). Mechanical pump (similar to injection pump diesel engine) develops a pressure of 50 bar (for an injection engine, the electric pump in the tank creates a pressure of about 3-3.5 bar in the line).

High-pressure injectors with swirl atomizers create a fuel spray shape in accordance with the engine operating mode. In the power mode of operation, injection occurs in the intake mode and a conical fuel-air torch is formed. In the ultra-lean mixture operating mode, injection occurs at the end of the compression stroke and a compact air-fuel mixture is formed.
a torch that the concave piston crown directs directly to the spark plug.
Piston. A specially shaped recess is made in the bottom, with the help of which the fuel-air mixture is directed to the spark plug area.
Inlet channels. The GDI engine uses vertical intake channels, which ensure the formation of the so-called. “reverse vortex”, directing the air-fuel mixture to the spark plug and improving the filling of the cylinders with air (in a conventional engine, the vortex in the cylinder is twisted in the opposite direction).

GDI engine operating modes

There are three engine operating modes in total:

Combustion mode over lean mixture(fuel injection on the compression stroke).
Power mode (injection on the intake stroke).
Two-stage mode (injection on the intake and compression strokes) (used on European modifications).

Ultra-lean mixture combustion mode(fuel injection on the compression stroke). This mode is used under light loads: during quiet city driving and when driving outside the city at a constant speed (up to 120 km/h). The fuel is injected in a compact spray at the end of the compression stroke in the direction of the piston, reflected from it, mixed with air and evaporated, heading towards the spark plug area. Although the mixture in the main volume of the combustion chamber is extremely lean, the charge in the spark plug area is rich enough to ignite with a spark and ignite the rest of the mixture. As a result, the engine operates stably even with an overall air to fuel ratio of 40:1 in the cylinder.

Running the engine on a very lean mixture caused new problem– neutralization of exhaust gases. The fact is that in this mode, the majority of them are nitrogen oxides, and therefore a conventional catalytic converter becomes ineffective. To solve this problem, exhaust gas recirculation (EGR-Exhaust Gas Recirculation) was used, which sharply reduces the amount of nitrogen oxides formed and an additional NO catalyst was installed.

The EGR system, by “diluting” the fuel-air mixture with exhaust gases, reduces the combustion temperature in the combustion chamber, thereby “muffling” the active formation of harmful oxides, including NOx. However, it is impossible to ensure complete and stable neutralization of NOx only through EGR, since as the load on the engine increases, the amount of bypassed exhaust gas must be reduced. Therefore, a NO catalyst was introduced into the direct injection engine.

There are two types of catalysts for reducing NOx emissions - Selective Reduction Type and
storage type (NOx Trap Type). Storage-type catalysts are more efficient, but are extremely sensitive to high-sulfur fuels, to which selective ones are less susceptible. In accordance with this, storage catalysts are installed on models for countries with low sulfur content in gasoline, and selective catalysts for the rest.

Power mode(injection on the intake stroke). The so-called “uniform mixture formation mode” is used for intense city driving, high-speed suburban traffic and overtaking. The fuel is injected during the intake stroke with a conical jet, mixing with air and forming a homogeneous mixture, as in normal engine with distributed injection. The composition of the mixture is close to stoichiometric (14.7:1)

Two-stage mode(injection on intake and compression strokes). This mode allows you to increase engine torque when the driver, moving at low speeds, sharply presses the accelerator pedal. When the engine is running at low speeds and is suddenly supplied with a rich mixture, the likelihood of detonation increases. Therefore, injection is carried out in two stages. A small amount of fuel is injected into the cylinder during the intake stroke and cools the air in the cylinder. In this case, the cylinder is filled with an ultra-lean mixture (approximately 60:1), in which detonation processes do not occur. Then, at the end of the measure
compression, a compact jet of fuel is supplied, which brings the air-to-fuel ratio in the cylinder to a “rich” 12:1.

Why is this mode introduced only for cars for European market? Yes, because Japan is not characterized by high speeds movement and constant traffic jams, and Europe has long highways and high speeds (and therefore high engine loads).

Mitsubishi pioneered the use of direct fuel injection. Today, similar technology is used by Mercedes (CGI), BMW (HPI), Volkswagen (FSI, TFSI, TSI) and Toyota (JIS). Main principle the operation of these power systems is similar - the supply of gasoline is not intake tract, but directly into the combustion chamber and the formation of layer-by-layer or homogeneous mixture formation in various modes motor operation. But such fuel systems also have differences, sometimes quite significant. The main ones are the operating pressure in the fuel system, the location of the injectors and their design.

Now one of the main tasks before the design bureaus of automakers is the creation of power plants that consume as little fuel as possible and emit a reduced amount of fuel into the atmosphere. harmful substances. Moreover, all this must be achieved with the condition that the impact on operating parameters (power, torque) will be minimal. That is, it is necessary to make the engine economical, and at the same time powerful and high-torque.

To achieve the result, almost all components and systems of the power unit are subject to alterations and modifications. This is especially true for the power system, because it is responsible for the flow of fuel into the cylinders. Latest development In this direction, direct injection of fuel into the combustion chambers of a power plant operating on gasoline is considered.

The essence of this system comes down to the separate supply of the components of the combustible mixture - gasoline and air - into the cylinders. That is, the principle of its operation is very similar to the work diesel units, where mixture formation is carried out in combustion chambers. But gasoline unit, on which a direct injection system is installed, there are a number of features in the process of injection of the components of the fuel mixture, its mixing and combustion.

A little history

Direct injection is not a new idea; there are a number of examples in history where such a system was used. The first widespread use of this type of motor power was in aviation in the middle of the last century. They also tried to use it on vehicles, but it did not become widespread. The system of those years can be considered as a kind of prototype, since it was completely mechanical.

The direct injection system received a “second life” in the mid-90s of the 20th century. The Japanese were the first to equip their cars with direct injection units. Designed in Mitsubishi unit received the designation GDI, which is an abbreviation for “Gasoline Direct Injection,” which stands for direct fuel injection. A little later, Toyota created its own engine - the D4.

Direct fuel injection

Over time, engines that use direct injection appeared from other manufacturers:

VAG Concern – TSI, FSI, TFSI;
Mercedes-Benz – CGI;
Ford - EcoBoost;
GM – EcoTech;

Direct injection is not a separate, completely new type, and it belongs to injection systems fuel supply. But unlike its predecessors, its fuel is injected under pressure directly into the cylinders, and not, as before, into the intake manifold, where gasoline was mixed with air before being supplied to the combustion chambers.

Design features and operating principle

Direct injection of gasoline is very similar in principle to diesel. The design of such a power system has additional pump, after which gasoline is already supplied under pressure to the injectors installed in the cylinder head with nozzles located in the combustion chamber. At the required moment, the injector supplies fuel to the cylinder, where air has already been pumped through the intake manifold.

The design of this power system includes:

a tank with a fuel priming pump installed in it;
highways low pressure;
fuel purification filter elements;
a pump that creates increased pressure with an installed regulator (fuel pump);
high pressure lines;
ramp with nozzles;
bypass and safety valves.

Direct injection fuel system diagram

The purpose of some elements, such as a tank with a pump and a filter, are described in other articles. Therefore, we will consider the purpose of a number of components used only in the direct injection system.

One of the main elements in this system is the high pressure pump. It ensures that fuel flows under significant pressure into the fuel rail. Its design different manufacturers differs - single or multi-plunger. The drive is carried out from camshafts.

The system also includes valves that prevent the fuel pressure in the system from exceeding critical values. In general, pressure regulation is carried out in several places - at the outlet of the high-pressure pump by a regulator, which is part of the design of the injection pump. Available bypass valve, which controls the pressure at the pump inlet. The safety valve monitors the pressure in the rail.

It all works like this: the fuel priming pump from the tank supplies gasoline to the injection pump via a low-pressure line, while the gasoline passes through the filter fine cleaning fuel, where large impurities are removed.

The plunger pairs of the pump create fuel pressure, which varies from 3 to 11 MPa under different engine operating modes. Already under pressure, the fuel enters the ramp through high-pressure lines, which is distributed among its injectors.

The operation of the injectors is controlled by an electronic control unit. At the same time, it is based on the readings of many engine sensors; after analyzing the data, it controls the injectors - injection timing, fuel amount and spray method.

If more fuel is supplied to the fuel injection pump than required, the bypass valve is activated, which returns part of the fuel to the tank. Also, part of the fuel is discharged into the tank if the pressure in the ramp is exceeded, but this is done by a safety valve.

Direct injection

Types of mixture formation

Using direct fuel injection, engineers managed to reduce gasoline consumption. And everything is achieved by the possibility of using several types of mixture formation. That is, under certain operating conditions of the power plant, its own type of mixture is supplied. Moreover, the system monitors and controls not only the fuel supply; to ensure one or another type of mixture formation, a certain mode of air supply to the cylinders is also established.

In total, direct injection is capable of providing two main types of mixture in the cylinders:

Layered;
Stoichiometric homogeneous;

This allows you to select a mixture that, under certain engine operation, will provide the greatest efficiency.

Layer-by-layer mixture formation allows the engine to operate on a very lean mixture, in which the mass part of air is more than 40 times greater than the fuel part. That is, a very large amount of air is supplied to the cylinders, and then a small amount of fuel is added to it.

Under normal conditions, such a mixture will not ignite from a spark. In order for ignition to occur, the designers gave the piston bottom a special shape that provides swirl.

With such mixture formation, air directed by the damper enters the combustion chamber high speed. At the end of the compression stroke, the injector injects fuel, which, reaching the bottom of the piston, rises upward to the spark plug due to swirl. As a result, in the electrode zone the mixture is enriched and flammable, while around this mixture there is air with virtually no fuel particles. Therefore, such mixture formation is called layer-by-layer - inside there is a layer with an enriched mixture, on top of which there is another layer, practically without fuel.

This mixture formation ensures minimal gasoline consumption, but the system prepares such a mixture only when uniform motion, without sudden accelerations.

Stoichiometric mixture formation is the production of a fuel mixture in optimal proportions (14.7 parts air to 1 part gasoline), which ensures maximum power output. Such a mixture already ignites easily, so there is no need to create an enriched layer near the spark plug; on the contrary, for efficient combustion it is necessary that the gasoline is evenly distributed in the air.

Therefore, fuel is injected by compression nozzles, and before ignition it has time to move well with air.

This mixture formation is ensured in the cylinders during acceleration, when maximum power output is required, and not efficiency.

The designers also had to resolve the issue of switching the engine from a lean mixture to a rich one during sharp accelerations. To prevent detonation combustion, double injection is used during the transition.

The first injection of fuel is performed on the intake stroke, while the fuel acts as a coolant for the walls of the combustion chamber, which eliminates detonation. The second portion of gasoline is supplied at the end of the compression stroke.

The direct fuel injection system, thanks to the use of several types of mixture formation at once, allows for good fuel savings without much impact on power performance.

During acceleration, the engine runs on a normal mixture, and after picking up speed, when the driving mode is measured and without sudden changes, power point switches to a very lean mixture, thereby saving fuel.

This is the main advantage of such a power system. But it also has an important drawback. The high pressure fuel pump as well as the injectors use highly refined, precision pairs. They are exactly what they are weak point, since these vapors are very sensitive to the quality of gasoline. The presence of foreign impurities, sulfur and water can damage the injection pump and injectors. Additionally, gasoline has very weak lubricating properties. Therefore, the wear of precision pairs is higher than that of the same diesel engine.

In addition, the direct fuel supply system itself is structurally more complex and expensive than the same separate injection system.

New developments

The designers do not stop there. A kind of modification of direct injection was made in VAG concern in the TFSI power unit. His power system was combined with a turbocharger.

An interesting solution was proposed by Orbital. They developed a special nozzle that, in addition to fuel, also injects compressed air into the cylinders, supplied from an additional compressor. Such air-fuel mixture has excellent flammability and burns well. But this is still only a development and whether it will find application on cars is still unknown.

In general, direct injection is now the most the best system nutrition in terms of efficiency and environmental friendliness, although it has its drawbacks.

Slightly different from gasoline counterparts. The main difference can be considered the ignition of the fuel-air mixture, which does not occur from external source(ignition sparks), but from strong compression and heating.

In other words, self-ignition of the fuel occurs in a diesel engine. In this case, the fuel must be supplied under extremely high pressure, since it is necessary to atomize the fuel as efficiently as possible in the cylinders of the diesel engine. In this article we will talk about which diesel engine injection systems are actively used today, and also consider their design and operating principle.

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How does the diesel engine fuel system work?

As mentioned above, in a diesel engine, self-ignition of the working mixture of fuel and air occurs. In this case, at first only air is supplied to the cylinder, then this air is strongly compressed and heated by compression. For combustion to occur, it must be applied near the end of the compression stroke.

Given that air is highly compressed, fuel must also be injected under high pressure and atomized effectively. In different diesel engines, the injection pressure may differ, starting, on average, from 100 atmospheres and ending with an impressive figure of more than 2 thousand atmospheres.

To ensure the most efficient supply of fuel and ensure optimal conditions for self-ignition of the charge followed by complete combustion of the mixture, fuel injection is implemented through a diesel injector.

It turns out that no matter what type of power system is used, two main elements are always present in diesel engines:

device for creating high fuel pressure;

In other words, on many diesel engines, pressure is created by a (high pressure fuel pump), and diesel fuel is supplied to the cylinders through injectors. As for the differences, in different fuel supply systems the pump may have one design or another, and the diesel injectors themselves also differ in their design.

Power systems may also differ in the location of certain components, have different control circuits, etc. Let's look at diesel engine injection systems in more detail.

Diesel engine power systems: overview

If we divide the power supply systems of diesel engines that received greatest distribution, the following solutions can be distinguished:

A power supply system based on an in-line injection pump (in-line injection pump);
A fuel supply system that has a distribution-type injection pump;
Unit injector solutions;
Common Rail fuel injection (high pressure accumulator in a common rail).

These systems also have a large number of subtypes, and in each case one or another type is the main one.

So, let's start with the simplest scheme, which assumes the presence of an in-line fuel pump. The in-line injection pump is a long-known and proven solution that has been used on diesel engines for decades. This type of pump is widely used on special equipment, trucks, buses, etc. When compared to other systems, the pump is quite large in size and weight.

In a nutshell, the in-line injection pump is based on. Their number is equal to the number of engine cylinders. The plunger pair is a cylinder that moves in the “glass” (sleeve). When moving upward, the fuel is compressed. Then, when the pressure reaches the required value, a special valve opens.

As a result, pre-compressed fuel enters the injector, after which injection occurs. After the plunger begins to move back down, the fuel inlet channel opens. Through the channel, fuel fills the space above the plunger, then the cycle is repeated. To ensure that diesel fuel gets into the plunger pairs, the system additionally has a separate booster pump.

The plungers themselves work due to the fact that the pump has a cam shaft. This shaft works similar to where the cams "push" the valve. The pump shaft itself is driven from the engine, since the injection pump is connected to the engine using an injection advance clutch. This coupling allows you to correct the operation and adjust the fuel injection pump during engine operation.

The power supply system with a distribution pump is not very different from the circuit with an in-line injection pump. The distribution injection pump is similar in design to the in-line one, but the number of plunger pairs in it is reduced.

In other words, if in an in-line pump pairs are needed for each cylinder, then in a distribution pump 1 or 2 plunger pairs are sufficient. The fact is that one pair in this case is enough to supply fuel to 2, 3 or even 6 cylinders.

This became possible due to the fact that the plunger was able to not only move up (compression) and down (intake), but also rotate around its axis. This rotation made it possible to realize the alternate opening of the outlet holes, through which diesel fuel is supplied to the injectors under high pressure.

Further development of this scheme led to the emergence of a more modern rotary injection pump. This pump uses a rotor in which plungers are installed. These plungers move towards each other, and the rotor rotates. This is how diesel fuel is compressed and distributed among the engine cylinders.

The main advantage of the distribution pump and its varieties is its reduced weight and compactness. At the same time, configure this device more difficult. For this reason, circuits are additionally used electronic control and adjustments.

The pump-injector power supply system is a circuit that initially does not have a separate injection pump. More precisely, the injector and pump section were combined in one housing. It is based on the already familiar plunger pair.

The solution has a number of advantages compared to systems that use fuel injection pumps. First of all, the fuel supply to individual cylinders can be easily adjusted. Also, if one injector fails, the rest will work.

Also, the use of pump injectors allows you to get rid of a separate injection pump drive. The plungers in the pump injector are driven by the timing camshaft, which is installed in. Such features allowed diesel engines with pump injectors to become widespread not only on trucks, but also on large passenger cars(eg diesel SUVs).

The Common Rail system is one of the most modern solutions in the field fuel injection. Also, this power scheme allows you to achieve maximum efficiency at the same time as high. At the same time, the toxicity of exhaust gases is reduced.

The system was developed by the German company Bosch in the 90s. Taking into account the obvious advantages, in a short time the vast majority of diesel internal combustion engines in passenger cars and trucks began to be equipped exclusively with Common Rail.

The general design of the device is based on the so-called high-pressure accumulator. Simply put, the fuel is under constant pressure and then supplied to the injectors. As for the pressure accumulator, this accumulator is actually a fuel line into which fuel is pumped using a separate injection pump.

The Common Rail system is partially reminiscent of gasoline injection engine, which has a fuel rail with injectors. Gasoline is pumped into the ramp (fuel rail) under low pressure by a gasoline pump from the tank. In a diesel engine, the pressure is much higher; the fuel is pumped by an injection pump.

Due to the fact that the pressure in the accumulator is constant, it has become possible to implement fast and “multi-layer” fuel injection through the injectors. Modern systems in Common Rail engines allow injectors to make up to 9 metered injections.

As a result, a diesel engine with such a power system is economical, productive, runs smoothly, quietly and elastically. Also, the use of a pressure accumulator made it possible to make the design of fuel injection pumps on diesel engines simpler.

Let us add that high-precision injection on Common Rail engines is completely electronic, since the operation of the system is monitored by a separate control unit. The system uses a group of sensors that allow the controller to determine exactly how much diesel fuel needs to be supplied to the cylinders and at what moment.

Let's sum it up

As you can see, each of the considered diesel engine power systems has its own advantages and disadvantages. If we talk about the simplest solutions with an in-line injection pump, their main advantage can be considered the possibility of repair and availability of maintenance.

In schemes with pump injectors, you need to remember that these elements are sensitive to the quality of the fuel and its purity. Even the smallest particles can damage the pump injector, causing the expensive element to require replacement.

As for Common Rail systems, the main disadvantage is not only the high initial cost of such solutions, but also the complexity and high cost of subsequent repairs and maintenance. For this reason, the fuel quality and condition fuel filters You need to constantly monitor it and carry out scheduled maintenance in a timely manner.