Working principle of diesel engine

In a diesel engine, clean air is sucked into the cylinders and compressed there. Due to this, the temperature in the cylinders rises above the auto-ignition temperature of diesel fuel. When the piston reaches top dead center (TDC), diesel fuel is injected into highly compressed and heated to a temperature of approximately 700-900°C. Diesel fuel is self-igniting, so spark plugs are not needed.

Fuel is sucked from the fuel tank directly by the distributor type high pressure fuel pump. In the high pressure fuel pump (injection pump) the high pressure necessary for the diesel process is created, and the fuel is distributed to the individual cylinders in accordance with the order of their operation.

In order to significantly reduce the content of harmful substances in exhaust gases, diesel engines with a working volume of 1.9 liters are equipped with a special oxidizing catalyst. At the same time, to further reduce nitrogen oxides in the exhaust gases (Moss), exhaust gas recirculation is used. At the same time, the exhaust gases are mixed with fresh air entering the cylinder (fresh charge), thereby reducing the oxygen content in the air involved in the combustion process. This leads to a decrease in the ignition delay period and combustion temperature, which is accompanied by a decrease in the formation of MO_X. However, the amount of recirculated gases must be accurately metered so as not to cause an increase in soot emissions. For this purpose, the amount of air consumed by the engine is determined using an air mass meter, and the exhaust gas recirculation is regulated accordingly by the electronic control unit.


Injection in a diesel engine is carried out in two different ways: swirl chamber injection (vortex chamber injection) and injection directly into the combustion chamber (direct injection).

Vortex chamber injection

Engine 1Y (47 kW/64 hp. With.), motor RA/SB (59kw/80hp) and AAZ engine (55 kW/75 hp. With.) /

The regulator in the injection pump regulates the amount of injected fuel in accordance with the position of the gas pedal. Through the nozzles, diesel fuel is injected at the right time into the swirl chambers of the cylinders under consideration (injection pressure 140-160 bar). Due to the shape of the vortex chamber, the air entering the cylinder receives a certain vortex motion during compression, which creates optimal conditions for mixing the injected fuel and air. The hot mixture immediately ignites spontaneously. The amount of oxygen available in the swirl chamber is sufficient to burn only part of the injected fuel. The rest, not burnt, 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 over 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 warm up. To do this, a glow plug is installed in the vortex chamber, which heats the air in the volume of the vortex chamber. The control unit for the duration of the glow plugs provides them with current both during start-up and after it.

Until 9/94

Starting a cold engine is facilitated by the starter, which is activated by a button on the instrument panel. When the accelerator is pulled out, the injection advance piston in the high pressure fuel pump is moved in the injection advance direction by approximately 2.5°. Thanks to this, 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 start accelerator button must be pushed back.

Since the diesel engine self-ignites the fuel and cannot be stopped by turning off the ignition, a solenoid valve is installed on it. When the ignition is turned off, the voltage supply to the valve stops and the valve closes the fuel channel. This ensures that when the steering wheel lock is engaged, the fuel supply is blocked. When the ignition is turned on to start the engine with a starter, voltage is applied to the solenoid valve, and it opens the fuel channel.

From 10/94

Cold start is controlled by the diesel engine preheating control unit and injection start valve.

The fuel cutoff valve is controlled by a dedicated control unit. The control unit is bolted to the injection pump directly above the fuel shutoff valve. It also serves to stop the engine based on a signal from the anti-theft control unit. The control unit for the fuel cut-off valve 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 injection pump directly into the volume of the combustion chamber, namely, into the volume of the chamber in the piston. At the same time, the injection pump creates a pressure of 900 bar to inject fuel in two stages. Through the multi-hole atomizer of the nozzle, a preliminary injection of a small amount of fuel is first carried out, thereby improving the conditions for igniting the main part of it. The result of this is «soft» and quiet combustion, similar to combustion in a swirl-chamber engine. The amount of injected fuel is controlled 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 thrust with the injection pump is no longer needed.
• Nozzle needle lift sensor. It detects the start of injection and controls the load- and shaft speed-dependent injection advance.
• Potentiometer for the travel of the injection pump rail. Its signals serve as feedback to the control unit and indicate the exact position of the rail, which corresponds to the amount of fuel actually injected.

In order to achieve good combustion, the inlet passage is designed in such a way 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 mainly at temperatures below -10°C.

All engines

Before fuel reaches the injection pump, it flows through the fuel filter. It retains dirt and water. Therefore, it is extremely important to empty the filter from water or replace it in accordance with the maintenance manual.

HPF does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The injection pump is driven from the crankshaft using a toothed belt.