Fuel is sucked from the fuel tank directly by the high-pressure fuel pump of the distribution type. In the high-pressure fuel pump (HPFP), the high pressure necessary for the diesel process is created, and the fuel is distributed to individual cylinders in accordance with their operating order.
In order to significantly reduce the content of harmful substances in the exhaust gases, diesel engines with a working volume of 1.9 liters are equipped with a special oxidation catalyst. At the same time, to further reduce nitrogen oxides (MOx) in the exhaust gases, exhaust gas recirculation is used. In this case, the exhaust gases are mixed with fresh air entering the cylinder (fresh charge), due to which the oxygen content in the air participating in the combustion process decreases. This leads to a decrease in the ignition delay period and combustion temperature, which is accompanied by a decrease in the formation of MOx. However, the amount of recirculated gases must be precisely dosed so as not to cause an increase in soot emissions. For this purpose, the amount of air consumed by the engine is determined by an air flow meter, and the recirculation of exhaust gases is regulated accordingly by the electronic control unit.
Injection in a diesel engine is carried out in two different ways: swirl chamber injection (swirl chamber injection) and injection directly into the combustion chamber (direct injection).
Vortex chamber injection
Engine 1Y(47 kW/64 hp), engine PA/SB (59 kW/80 hp) and AAZ engine (55 kW/75 hp)/
The regulator in the high-pressure fuel pump regulates the amount of injected fuel in accordance with the position of the gas pedal. Through the injectors, diesel fuel is injected into the swirl chambers of the cylinders in question at the right time (injection pressure 140-160 bar). Due to the shape of the swirl chamber, the air entering the cylinder receives a certain swirl motion during compression, which creates optimal conditions for mixing the injected fuel and air. The hot mixture immediately ignites spontaneously. The amount of oxygen in the swirl chamber is sufficient to burn only part of the injected fuel. The remaining, unburned part is ejected under the action of the high pressure formed during combustion into the main combustion chamber located above the piston. Here the fuel burns completely. The advantage of swirl chamber injection compared to direct injection is "soft" combustion and, as a result, less noisy engine operation and smokeless exhaust. The disadvantage is the deterioration of the starting qualities of a cold engine due to the increased surface area of the combustion chamber, as well as higher fuel consumption.
In a cold engine, the temperature required for self-ignition of the fuel is not reached by compression alone. In this case, the engine must be heated. For this purpose, a glow plug is installed in the swirl chamber, which heats the air in the volume of the swirl chamber. The glow plug operating time control unit supplies them with current both during and after starting.
Until 9/94
Starting a cold engine is made easier by the starting accelerator, which is activated by a button on the instrument panel. When the starting accelerator is pulled out, the piston of the injection advance system in the high-pressure fuel pump is moved in the injection advance direction by approximately 2.5°. As a result, the fuel is injected into the hot air earlier, and the cold engine starts faster. As soon as the engine has warmed up to operating temperature, the starting accelerator button must be pushed back in.
Since the diesel engine has self-ignition of fuel and cannot be stopped by turning off the ignition, it is equipped with an electromagnetic valve. When the ignition is turned off, the voltage supply to the valve is cut off, and the valve closes the fuel channel. This ensures that when the steering wheel shaft lock is fixed, the fuel supply is blocked. When the ignition is turned on to start the engine with the starter, voltage is supplied to the electromagnetic valve, and it opens the fuel channel.
Since 10/94
Cold start is regulated by the control unit of the diesel engine pre-heating system and the injection start valve.
The fuel shut-off valve is controlled by a control unit designed for this purpose. The control unit is screwed to the high-pressure fuel pump directly above the fuel shut-off valve. It also serves to stop the engine based on a signal from the anti-theft system control unit. The fuel shut-off valve control unit can also be installed additionally (workshop work).
Direct injection
Engine 1Z(68 kW/90 hp)and AFN engine (81 kW/110 hp)/
Fuel under high pressure is injected by the high-pressure fuel pump directly into the combustion chamber, namely, into the volume of the chamber in the piston. The high-pressure fuel pump creates a pressure of 900 bar to inject fuel in two stages. Initially, a small amount of fuel is pre-injected through the multi-hole nozzle, which improves the conditions for ignition of its main part. The result is "soft" and quiet combustion, similar to combustion in a swirl-chamber engine. The amount of injected fuel is regulated by the electronic engine control unit. The advantages of direct injection are low fuel consumption and increased engine power. Signals from various sensors are used as control variables. These sensors are:
- Crankshaft speed sensor, boost pressure sensor, charge air temperature sensor, coolant temperature sensor, fuel temperature sensor.
- Pedal position sensor. Thanks to it, the position of the gas pedal is transmitted to the control unit. The connection of the gas rod with the fuel injection pump is no longer needed.
- Injector needle lift sensor. It is used to determine the start of injection and to control the injection advance depending on the load and shaft speed.
- Fuel injection pump rack stroke potentiometer. Its signals serve as feedback to the control unit and indicate the exact position of the rack, which corresponds to the actual injected amount of fuel.
In order to achieve good combustion, the intake duct is designed so that the air on its way to the combustion chamber acquires a rotational motion. Due to the better starting properties of direct injection engines, preheating is required for them mainly at temperatures below -10°C.
All engines
Before the fuel reaches the injection pump, it flows through the fuel filter. This is where the dirt and water are trapped. Therefore, it is extremely important to empty the filter of water or replace it in accordance with the service manual.
The high-pressure fuel pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The high-pressure fuel pump is driven by a crankshaft using a toothed belt.
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