D. Sosnin

We are starting to publish articles on modern fuel injection systems for gasoline internal combustion engines of passenger cars.

1. Preliminary remarks

Fuel supply for gasoline engines on modern passenger cars implemented using injection systems. Based on their operating principle, these systems are usually divided into five main groups (Fig. 1): K, Mono, L, M, D.

2. Advantages of injection systems

The air-fuel mixture (FA mixture) is supplied from the carburetor to the cylinders of the internal combustion engine (ICE) through the long pipes of the intake manifold. The length of these pipes to different engine cylinders is not the same, and in the manifold itself there is uneven heating of the walls, even on a fully warmed-up engine (Fig. 2).

This leads to the fact that from the homogeneous TV mixture created in the carburetor, different cylinders ICE produces unequal fuel-air charges. As a result, the engine does not deliver the calculated power, torque uniformity, fuel consumption and quantity are lost. harmful substances V exhaust gases increase.

It is very difficult to combat this phenomenon in carburetor engines. It should also be noted that a modern carburetor operates on the principle of atomization, in which gasoline is atomized in a stream of air sucked into the cylinders. In this case, quite large drops of fuel are formed (Fig. 3, a),

This does not ensure high-quality mixing of gasoline and air. Poor mixing and large droplets make it easier for gasoline to settle on the walls of the intake manifold and on the walls of the cylinders during the absorption of the TV mixture. But when forced atomization of gasoline under pressure through a calibrated nozzle nozzle, fuel particles can be significantly smaller in size compared to atomization of gasoline during atomization (Fig. 3, b). Gasoline is sprayed especially effectively in a narrow beam under high pressure (Fig. 3, c).

It has been established that when gasoline is sprayed onto particles with a diameter of less than 15...20 microns, its mixing with atmospheric oxygen does not occur as a suspension of particles, but at the molecular level. This makes the TV mixture more resistant to changes in temperature and pressure in the cylinder and long pipes of the intake manifold, which contributes to its more complete combustion.

This is how the idea was born to replace the spray jets of a mechanical inertia carburetor with a central inertia-free injection nozzle (CFI), which opens for a given time according to an electric pulse control signal from the electronic automation unit. At the same time, in addition to high-quality atomization and effective mixing of gasoline with air, it is easy to obtain higher accuracy of their dosing in the TV mixture at all possible modes engine operation.

Thus, due to the use of a fuel supply system with gasoline injection, the engines of modern passenger cars do not have the above-mentioned disadvantages inherent in carburetor engines, i.e. they are more economical, have a higher specific power, maintain constant torque over a wide range of rotation speeds, and the emission of harmful substances into the atmosphere with exhaust gases is minimal.

3. Gasoline injection system "Mono-Jetronic"

The first system of central single-point pulse fuel injection for gasoline engines of passenger cars was developed by BOSCH in 1975. This system was called "Mono-Jetronic" (Monojet - single jet) and was installed on a Volkswagen car.

In Fig. Figure 4 shows the central injection unit of the Mono-Jetronic system. The figure shows that the central injection nozzle (CI) is installed on a standard intake manifold instead of a conventional carburetor.

But unlike a carburetor, in which automatic mixture formation is implemented by mechanical control, a mono injection system uses purely electronic control.

In Fig. 5 shows a simplified functional diagram Mono-Jetronic systems.

The electronic control unit (ECU) operates from input sensors 1-7, which record the current state and operating mode of the engine. Based on the combination of signals from these sensors and using information from the three-dimensional injection characteristics in the computer, the beginning and duration of the open state of the central injector 15 are calculated.

Based on the calculated data, an electric pulse control signal S for the digital filter is generated in the ECU. This signal acts on winding 8 of the injector magnetic solenoid, stop valve 11 which opens, and through the spray nozzle 12 gasoline is forcedly sprayed into the fuel supply line 19 under a pressure of 1.1 bar intake manifold through open throttle valve 14.

Given the dimensions of the throttle valve diaphragm and the calibrated cross-section of the spray nozzle, the mass amount of air passed into the cylinders is determined by the degree of opening of the throttle valve, and the mass amount of gasoline injected into the air flow is determined by the duration of the open state of the nozzle and the retaining (working) pressure in the fuel supply line 19.

In order for gasoline to burn completely and most efficiently, the masses of gasoline and air in the TV mixture must be in a strictly defined ratio, equal to 1/14.7 (for high-octane grades of gasoline). This ratio is called stoichiometric, and it corresponds to the coefficient a of excess air, equal to one. Coefficient a = Md/M0, where M0 is the amount of air mass theoretically required for complete combustion of a given portion of gasoline, and Md is the mass of actually burned air.

Hence it is clear that any fuel injection system must have a meter for the mass of air admitted into the engine cylinders during suction.

In the "Mono-Jetronic" system, the air mass is calculated in the ECU based on the readings of two sensors (see Fig. 4): intake air temperature (IAT) and throttle valve position (ATP). The first is located directly in the air flow path at the top of the central injection nozzle and is a miniature semiconductor thermistor, and the second is a resistive potentiometer, the motor of which is mounted on the rotary axis (PS) of the throttle valve.

Since a specific angular position of the throttle valve corresponds to a strictly defined volumetric amount of air passed through, the throttle potentiometer functions as an air flow meter. In the Mono-Jetronic system it is also an engine load sensor.

But the mass of intake air largely depends on temperature. Cold air is denser and therefore heavier. As the temperature rises, the density of air and its mass decrease. The influence of temperature is taken into account by the DTV sensor.

The DTV intake air temperature sensor, like a semiconductor thermistor with a negative temperature coefficient of resistance, changes the resistivity value from 10 to 2.5 kOhm when the temperature changes from -30 to +20°C. The DTV sensor signal is used only in this temperature range. In this case, the basic duration of gasoline injection is adjusted by the ECU in the range of 20...0%. If the intake air temperature is above +20°C, then the signal from the DTV sensor is blocked in the ECU and the sensor is not used.

Signals from the throttle position (TAP) and intake air temperature (IAT) sensors in cases of their failures are duplicated in the ECU by signals from the engine speed sensors (RPS) and engine coolant temperature (ITC).

Based on the air volume calculated in the ECU, as well as the signal about the engine speed, which comes from the ignition system speed sensor, the required (basic) duration of the open state of the central injection nozzle is determined.

Since the supporting pressure Рт in the fuel supply line (FBM) is constant (for "Mono-Jetronic" Рт = 1...1.1 bar), and the throughput of the nozzle is specified by the total cross-section of the holes of the spray nozzle, the time of the open state of the nozzle uniquely determines the amount injected gasoline. The injection moment (in Fig. 5, the signal from the UHF sensor) is usually set simultaneously with the signal to ignite the TV mixture from the ignition system (through 180° of rotation of the internal combustion engine crankshaft).

Thus, with electronic control of the mixture formation process, ensuring high accuracy of dosage of injected gasoline into a measured amount of air mass is an easily solved problem and, ultimately, dosing accuracy is determined not by electronic automation, but by the manufacturing accuracy and functional reliability of the input sensors and injection nozzle.

In Fig. Figure 6 shows the main part of the Mono-Jetronic system - the central injection nozzle (CI).

The central injection nozzle is a gas valve that is opened by an electrical impulse coming from the electronic control unit. For this purpose, the nozzle contains an electromagnetic solenoid 8 with a movable magnetic core 14. The main problem when creating valves for pulse injection is the need to ensure high speed of operation of the valve shut-off device 9 for both opening and closing. The solution to the problem is achieved by lightening the magnetic core of the solenoid, increasing the current in the pulse control signal, selecting the elasticity of the return spring 13, as well as the shape of the ground surfaces for the spray nozzle 10.

The nozzle nozzle (Fig. 6, a) is made in the form of a bell of capillary tubules, the number of which is usually at least six. The angle at the top of the bell determines the opening of the injection jet, which has the shape of a funnel. With this shape, a stream of gasoline does not hit the throttle valve even when it is opened slightly, but flies through two thin crescents of the opened gap.

The central nozzle of the Mono-Jetronic system reliably ensures the minimum duration of the open state of the spray nozzle 11 for 1 ± 0.1 ms. During this time and at an operating pressure of 1 bar, about one milligram of gasoline is injected through a spray nozzle with an area of ​​0.08 mm2. This corresponds to a fuel consumption of 4 l/h at minimum idle speed (600 rpm) of a warm engine. When starting and warming up a cold engine, the injector opens for a longer time (up to 5...7 ms). But on the other hand, the maximum injection duration on a warm engine (injector open time) is limited by the maximum engine crankshaft speed (6500...7000 min-1) in full throttle mode and cannot be more than 4 ms. In this case, the clock frequency of the injector shut-off device at idle is at least 20 Hz, and at full load - no more than 200...230 Hz.

The DPD throttle position sensor (throttle potentiometer), shown in Fig. 1, is manufactured with special care. 7. Its sensitivity to engine rotation must meet the requirement of ±0.5 angular degrees of rotation of the throttle axis 13. The strict angular position of the throttle axis determines the beginning of two engine operating modes: idle mode (3±0.5°) and full load mode (72.5±0.5°).

To ensure high accuracy and reliability, the resistive potentiometer tracks, of which there are four, are connected according to the circuit shown in Fig. 7, b, and the axis of the potentiometer engine (two-contact engine) is seated in a backlash-free Teflon plain bearing.

The potentiometer and the ECU are connected to each other by a four-wire cable through a contact connector. To increase the reliability of connections, the contacts in the connector and in the potentiometer chip are gold-plated. Contacts 1 and 5 are intended for supplying a reference voltage of 5±0.01 V. Contacts 1 and 2 are for removing signal voltage when turning the throttle valve at an angle from 0 to 24° (0...30 - idle mode; 3.. .24° - low engine load mode). Contacts 1 and 4 - to relieve signal voltage when turning the throttle valve at an angle from 18 to 90° (18...72.5° - medium load mode, 72.5...90° - full engine load mode).

The signal voltage from the throttle potentiometer is additionally used:
to enrich the TV mixture when accelerating the car (the speed of change of the signal from the potentiometer is recorded);
to enrich the TV mixture in full load mode (the signal value from the potentiometer is recorded after turning the throttle valve 72.5° upward);
to stop fuel injection in forced idle mode (a potentiometer signal is registered if the throttle valve open angle is less than 3°. At the same time, the engine speed W is monitored: if W>2100 min-1, then the fuel supply is stopped and restored again at W
Interesting feature The "Mono-Jetronic" injection system is the presence in its composition of a subsystem for stabilizing idle speed using an electric servo drive, which acts on the throttle axis (Fig. 8). The electric servo drive is equipped with a reverse DC electric motor 11.

The servo drive is switched on in idle mode and, together with the circuit for disabling the vacuum ignition timing regulator (idling stabilization - Fig. 2), ensures stabilization of the engine speed in this mode.

This idle stabilization subsystem works as follows.

When the throttle valve open angle is less than 3°, signal K (see Fig. 9)

It is a signal for the ECU in idle mode (the VC limit switch is closed by the servo drive rod). Based on this signal, the shut-off pneumatic valve ZPK is activated and the vacuum channel from the after-throttle zone of the intake manifold to the vacuum regulator VR is closed. Vacuum regulator from this moment it does not work and the ignition timing becomes equal to the value of the installation angle (6° before TDC). At the same time, the engine runs stably at idle speed. If at this time the air conditioner or other powerful consumer of engine energy is turned on (for example, headlights high beam indirectly through the generator), then its speed begins to fall. The engine may stall. To prevent this from happening, on command from electronic circuit Idle speed control (ESCH) in the controller turns on the electric servo drive, which slightly opens the throttle valve. The speed increases to the nominal value for the given engine temperature. It is clear that when the load is removed from the engine, its speed is reduced to normal by the same electric servo drive.

The ECU of the "Mono-Jetronic" system has a MCP microprocessor (see Fig. 5) with permanent and random access memory (storage unit). The reference three-dimensional injection characteristic (TCI) is “hardwired” into the permanent memory. This characteristic is to some extent similar to the three-dimensional ignition characteristic, but differs in that its output parameter is not the ignition timing, but the time (duration) of the open state of the central injection nozzle. The input coordinates of the TCV characteristic are the engine speed (the signal comes from the ignition system controller) and the volume of intake air (calculated by the microprocessor in the injection ECU). The reference characteristic of the TC contains reference (basic) information about the stoichiometric ratio of gasoline and air in the TC mixture under all possible modes and operating conditions of the engine. This information is selected from the memory of the memory into the microprocessor of the ECU according to the input coordinates of the TC characteristics (according to signals from the sensors DOD, DPD, DTV) and is corrected according to signals from the coolant temperature sensor (LTD) and oxygen sensor(KD).

Separate mention must be made about the oxygen sensor. Its presence in the injection system allows the composition of the TV mixture to be kept constantly in a stoichiometric ratio (a = 1). This is achieved by the fact that the CD sensor operates in a deep adaptive circuit feedback from the exhaust system to the fuel supply system (to the injection system).

It reacts to the difference in oxygen concentration in the atmosphere and in the exhaust gases. In essence, the CD sensor is chemical source current of the first kind (galvanic cell) with a solid electrolyte (special honeycomb metal ceramics) and with high (not lower than 300°C) operating temperature. The EMF of such a sensor depends almost according to a stepwise law on the difference in oxygen concentration on its electrodes (platinum-radium film coating on different sides of the porous ceramic). The greatest steepness (difference) of the EMF step occurs at the value a=1.

The pressure sensor is screwed into the exhaust pipe (for example, into the exhaust manifold) and its sensitive surface (positive electrode) is in the flow exhaust gases. There are slots above the sensor mounting thread through which the outer negative electrode communicates with atmospheric air. On cars with a catalytic gas neutralizer, the oxygen sensor is installed in front of the converter and has an electrical heating coil, since the temperature of the exhaust gases in front of the converter can be below 300°C. In addition, electrical heating of the oxygen sensor speeds up its preparation for operation.

The sensor is connected to the injection computer by signal wires. When a lean mixture (a>1) enters the cylinders, the oxygen concentration in the exhaust gases is slightly higher than the standard one (at a=1). The pressure sensor produces a low voltage (about 0.1 V) and the ECU, based on this signal, adjusts the duration of gasoline injection to increase it. Coefficient a is again approaching unity. When the engine is running on a rich mixture, the oxygen sensor produces a voltage of about 0.9 V and works in the reverse order.

It is interesting to note that the oxygen sensor is involved in the process of mixture formation only in engine operating modes in which the enrichment of the TV mixture is limited to a>0.9. These are modes such as load at low and medium speeds and idling on a warm engine. Otherwise, the pressure sensor is turned off (blocked) in the ECU and the composition of the TV mixture is not adjusted based on the oxygen concentration in the exhaust gases. This occurs, for example, in the modes of starting and warming up a cold engine and in its forced modes (acceleration and full load). In these modes, a significant enrichment of the TV mixture is required and therefore the activation of the oxygen sensor ("pressing" coefficient a to unity) is unacceptable here.

In Fig. 10 shows a functional diagram of the Mono-Jetronic injection system with all its components.

Any injection system in its fuel supply subsystem necessarily contains a closed fuel ring, which starts from the gas tank and ends there. This includes: a fuel tank BB, an electric fuel pump EBN, a fine fuel filter FTOT, a fuel distributor PT (in the Mono-Jetronic system this is the central injection nozzle) and a pressure regulator RD, which operates on the principle of a bleed valve when the specified operating pressure in a closed ring is exceeded (for the Mono-Jetronic system 1...1.1 bar).

Closed fuel ring performs three functions:

Using a pressure regulator, maintains the required constant operating pressure for fuel distributor;

By means of a spring-loaded diaphragm in the pressure regulator, a certain residual pressure (0.5 bar) is maintained after the engine is switched off, thereby preventing the formation of steam and air jams in the fuel lines when the engine cools down;

Provides cooling of the injection system due to constant circulation of gasoline in a closed circuit. In conclusion, it should be noted that the "Mono-Jetronic" system is used only on passenger cars of the average consumer class, for example, such West German cars as "Volkswagen-Passat", "Volkswagen-Polo", "Audi-80".
REPAIR&SERVICE-2"2000

Now one of the main tasks before the design bureaus of automakers is the creation of power plants that consume as much energy as possible. less fuel and emitting reduced amounts of harmful substances into the atmosphere. 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 of the process of injection of components 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 an additional pump, after which gasoline is 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);
• highways high pressure;
• 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. There is a bypass valve that 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 a fine fuel filter, where large impurities are removed.

The plunger pairs of the pump create fuel pressure, which, when different modes engine operation varies from 3 to 11 MPa. 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 at very high 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. Whatever happens detonation combustion, during the transition double injection is used.

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 gaining speed, when the driving mode is measured and without sudden changes, the power plant 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, 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.

Conceptually, internal combustion engines - gasoline and diesel - are almost identical, but there are a number of differences between them distinctive features. One of the main ones is the different occurrence of combustion processes in the cylinders. In a diesel engine, fuel ignites due to exposure to high temperatures and pressure. But for this it is necessary that diesel fuel is supplied directly to the combustion chambers not only at a strictly defined moment, but also under high pressure. And this is provided by diesel engine injection systems.

Constant tightening environmental standards, attempts to obtain greater power output with lower fuel costs ensure the emergence of more and more new design solutions in.

Everyone's working principle existing species diesel injection is identical. The main power elements are the high-pressure fuel pump (HFP) and the injector. The task of the first component is to inject diesel fuel, due to which the pressure in the system increases significantly. The nozzle ensures the supply of fuel (in a compressed state) to the combustion chambers, while atomizing it to ensure better mixture formation.

It is worth noting that fuel pressure directly affects the quality of combustion of the mixture. The higher it is, the better the diesel fuel burns, providing greater power output and less pollutants in the exhaust gases. And for more high performance a variety of pressures were used Constructive decisions, which led to the emergence different types diesel power systems. Moreover, all the changes concerned exclusively the two indicated elements - fuel injection pump and injectors. The remaining components - tank, fuel lines, filter elements, are essentially identical in all available types.

Types of diesel power systems

Diesel power plants can be equipped with an injection system:

• with in-line high pressure pump;
• with distribution type pumps;
• battery type ( Common Rail).

With in-line pump

In-line injection pump with 8 injectors

Initially, this system was completely mechanical, but later electromechanical elements began to be used in its design (applies to regulators for changing the cyclic supply of diesel fuel).

The main feature of this system is the pump. In it, plunger pairs (precision elements that create pressure) each served their own nozzle (their number corresponded to the number of nozzles). Moreover, these pairs were placed in a row, hence the name.

The advantages of a system with an in-line pump include:

• Reliability of the design. The pump had a lubrication system, which provided the unit with a long service life;
• Low sensitivity to fuel purity;
• Comparative simplicity and high maintainability;
• Long pump life;
• The ability to operate the motor if one section or nozzle fails.

But the shortcomings of such a system are more significant, which led to a gradual abandonment of it and preference for more modern ones. The negative aspects of such an injection are:

• Low speed and accuracy of fuel dosage. Mechanical design simply cannot provide this;
• Relatively low generated pressure;
• The task of the fuel injection pump is not only to create fuel pressure, but also to regulate the cyclic supply and injection timing;
• The pressure created directly depends on the crankshaft speed;
• Large dimensions and weight of the pump.

These shortcomings, and primarily the low pressure generated, led to the abandonment of this system, since it simply no longer fit into environmental standards.

With distributed pump

injection pump distributed injection became the next stage in the development of power systems for diesel units.

Initially, such a system was also mechanical and differed from the one described above only in the design of the pump. But over time, a system was added to her device electronic control, which improved the injection adjustment process, which had a positive effect on engine efficiency. For a certain period, such a system fit into environmental standards.

The peculiarity of this type of injection was that the designers abandoned the use of a multi-section pump design. The fuel injection pump began to use only one plunger pair, servicing all available injectors, the number of which varies from 2 to 6. To ensure the supply of fuel to all injectors, the plunger makes not only translational movements, but also rotational ones, which ensure the distribution of diesel fuel.

Injection pump with a distributed type pump

TO positive qualities such systems included:

• Small dimensions and pump mass;
• The best indicators for fuel efficiency;
• The use of electronic control has improved the system's performance.

The disadvantages of a system with a distributed type pump include:

• Small life of the plunger pair;
• Components are lubricated with fuel;
• Multifunctionality of the pump (in addition to creating pressure, it is also controlled by the flow and injection timing);
• If the pump failed, the system stopped working;
• Sensitivity to air;
• Dependence of pressure on engine speed.

This type of injection has become widespread in passenger cars and small commercial vehicles.

Pump injectors

The peculiarity of this system is that the nozzle and plunger pair are combined into a single structure. The drive of the section of this fuel unit is carried out from the camshaft.

It is noteworthy that such a system can be either completely mechanical (injection control is carried out by a rack and regulators) or electronic (solenoid valves are used).

Pump nozzle

A variation of this type of injection is the use of individual pumps. That is, each injector has its own section, driven by the camshaft. The section can be located directly in the cylinder head or placed in a separate housing. This design uses conventional hydraulic nozzles (that is, the system is mechanical). Unlike injection with a high-pressure fuel pump, the high-pressure lines are very short, which made it possible to significantly increase the pressure. But this design was not particularly widespread.

The positive qualities of power pump injectors include:

• Significant indicators of the created pressure (the highest among all injection types used);
• Low metal consumption of the structure;
• Accuracy of dosage and implementation of multiple injections (in injectors with solenoid valves);
• Possibility of engine operation if one of the injectors fails;
• Replacing a damaged element is not difficult.

But there are disadvantages to this type of injection, including:

• Unrepairable pump injectors (if they break down, they need to be replaced);
• High sensitivity to fuel quality;
• The pressure generated depends on the engine speed.

Pump injectors are widely used in commercial and truck vehicles, and this technology has also been used by some passenger car manufacturers. Nowadays it is not used very often due to the high cost of maintenance.

Common Rail

So far it is the most advanced in terms of efficiency. It also fully complies with the latest environmental standards. Additional “advantages” include its applicability on any diesel engines, ranging from passenger cars to sea vessels.

Common rail injection system

Its peculiarity lies in the fact that the multifunctionality of the injection pump is not required, and its task is only to pump up pressure, not for each injector separately, but for a common line (fuel rail), and from it diesel fuel is supplied to the injectors.

At the same time, the fuel pipelines between the pump, ramp and injectors have a relatively short length, which made it possible to increase the generated pressure.

The work in this system is controlled by an electronic unit, which significantly increased the dosage accuracy and speed of the system.

Positive qualities of Common Rail:

• High dosage accuracy and use of multi-mode injection;
• Reliability of injection pump;
• There is no dependence of the pressure value on engine speed.

The negative qualities of this system are:

• Sensitivity to fuel quality;
• Complex design of nozzles;
• System failure at the slightest pressure loss due to depressurization;
• The complexity of the design due to the presence of a number of additional elements.

Despite these disadvantages, automakers increasingly prefer Common Rail over other types of injection systems.

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

Volkswagen FSI engine diagram with direct gasoline 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 cars were discontinued in the 40s of the twentieth century, because such engines were expensive, uneconomical and smoked heavily at high power levels. Injecting gasoline directly into the cylinders poses certain difficulties. Injectors for direct injection of gasoline operate in more difficult conditions than those installed in the intake manifold. The block head into which such injectors must be installed turns out to be more complex 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.
All these difficulties were overcome by specialists from Mitsubishi, which was the first to use a direct gasoline injection system in car engines. First production car Mitsubishi Galant with a 1.8 GDI engine (Gasoline Direct Injection - direct gasoline injection) appeared in 1996.
The benefits of the direct injection system are mainly improved fuel economy, but also some increase in power. The first is explained by the ability of an engine with a direct injection system to operate on 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 engines running on gasoline, it is rarely possible to set the compression ratio above 10 due to the onset of detonation).

The GDI engine injector can operate in two modes, providing a powerful (a) or compact (b) spray of atomized gasoline

In a 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 electrical signal supplied, it can inject fuel either with a powerful conical torch or with a compact jet.

The piston of a gasoline direct 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 you to swirl the incoming air and direct the injected fuel to the spark plug installed in the center of the combustion chamber. Inlet pipe located not on the side, but vertically on top. It does not have sharp bends, and therefore the air comes from high speed.

In the operation of an engine with a direct injection system, three different modes can be distinguished:
1) operating mode on ultra-lean mixtures;
2) operating mode on a stoichiometric mixture;
3) mode of sharp acceleration from low speeds;
The first mode is used when the car moves without sudden acceleration at a speed of about 100–120 km/h. This mode uses a very lean combustible 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 (as in a diesel engine). A spherical recess in the piston directs a stream of fuel to the spark plug electrodes, where a high concentration of gasoline vapor 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 mixture composition. A mixture of this composition is easily ignited, 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, as it evaporates, cools the cylinder surfaces, reducing the likelihood of detonation.
The third mode is necessary to obtain high torque when the gas pedal is sharply pressed when the engine is running at low speeds. This mode of engine operation is different in that during one cycle the injector fires twice. 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 injects fuel again, but with a compact spray. In this case, the mixture in the cylinder is enriched and detonation does not occur.
Compared with conventional engine with a fuel injection system, the GDI engine is approximately 10% more fuel efficient and emits 20% less carbon dioxide. The increase in engine power reaches 10%. However, as the operation of cars with engines of this type has shown, they are very sensitive to the sulfur content in gasoline. The original direct gasoline injection process was developed by Orbital. In this process, gasoline is injected into the engine cylinders, pre-mixed with air using a special nozzle. The Orbital injector consists of two jets, fuel and air.

Operation of the Orbital nozzle

Air is supplied to the air jets in compressed form from a special compressor at a pressure of 0.65 MPa. The fuel pressure is 0.8 MPa. First the fuel nozzle fires, and then right moment and air, so the fuel-air mixture in the form of an aerosol is injected into the cylinder with a powerful torch.
The injector, located in the cylinder head next to the spark plug, injects a stream of fuel and air directly onto the spark plug electrodes, which ensures good ignition.

Design features of the Audi 2.0 FSI engine with direct gasoline injection

Modern cars are equipped with different fuel injection systems. In gasoline engines, a mixture of fuel and air is forced to ignite using a spark.

The fuel injection system is an integral element. The nozzle is the main working element of any injection system.

Gasoline engines are equipped with injection systems, which differ in the way they form a mixture of fuel and air:

• systems with central injection;
• systems with distributed injection;
• direct injection systems.

Central injection, or otherwise called monojetronic, is carried out by one central electromagnetic injector, which injects fuel into the intake manifold. This is somewhat reminiscent of a carburetor. Nowadays, cars with such an injection system are not produced, since a car with such a system also has low environmental properties of the car.

The multipoint injection system has been constantly improved over the years. The system started K-jetronic. The injection was mechanical, which gave it good reliability, but fuel consumption was very high. Fuel was supplied not pulsed, but constantly. This system was replaced by the system KE-jetronic.

She was not fundamentally different from K-jetronic, but an electronic control unit (ECU) appeared, which made it possible to slightly reduce fuel consumption. But this system did not bring the expected results. A system has appeared L-jetronic.

In which the ECU received signals from the sensors and sent an electromagnetic pulse to each injector. The system had good economic and environmental performance, but the designers did not stop there and developed a completely new system Motronic.

The control unit began to control both fuel injection and the ignition system. The fuel began to burn better in the cylinder, the engine power increased, and the consumption and harmful emissions of the car decreased. In all of these systems presented above, injection is carried out by a separate nozzle for each cylinder into the intake manifold, where a mixture of fuel and air is formed, which enters the cylinder.

The most promising system today is the direct injection system.

The essence of this system is that fuel is injected directly into the combustion chamber of each cylinder, and is mixed with air there. The system determines and supplies the optimal mixture composition to the cylinder, which ensures good power at various engine operating modes, good efficiency and high environmental properties of the engine.

But on the other hand, engines with this injection system have a higher price compared to their predecessors due to the complexity of their design. Also this system very demanding on fuel quality.