When the engine is cold, the ignition temperature of the fuel is not reached by compression alone. In this case, the engine must be preheated. For this purpose, each combustion chamber has a glow plug that heats the combustion chamber. The duration of the warm-up depends on the ambient temperature and is regulated by the engine control unit via the preheating relay.
Fuel injection into the cylinders of a diesel engine can be carried out in two ways: injection into a swirl or preliminary chamber and direct injection.
When fuel is injected into a swirl or pre-chamber, it is injected into the pre-combustion chamber of the corresponding cylinder. The hot mixture ignites immediately. However, the volume of oxygen in the pre-chamber is sufficient to burn only part of the injected fuel. The remaining, unburned part is blown into the combustion chamber by the excess pressure that occurs during combustion. There, the fuel burns completely.
With direct injection, fuel is injected directly into the combustion chamber, namely into the combustion groove in the piston, via the high-pressure fuel pump. The high-pressure fuel pump creates a pressure of about 900 bar to inject fuel in two stages via a nozzle with a multi-jet sprayer. At first, a small amount of fuel is injected, which improves the ignition conditions of the main portion of fuel. This leads to a softer and at the same time quieter combustion, similar to what happens in a swirl chamber.
The injected portions are fully regulated by the electronic engine control unit. The advantages of this principle are lower fuel consumption and higher engine power.
The high-pressure fuel pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The pump is driven by the crankshaft via a toothed belt.
Operating principle of the fuel injection pump
The high-pressure fuel pump of a diesel engine creates high pressure, which ensures the supply of fuel to the high-pressure fuel lines and to the injectors, and from them to the combustion chambers.
The air needed to burn the fuel is drawn into the engine through the air filter and forced into the compressor.
Engine control unit (microprocessor) receives and processes information from sensors and, based on this information, calculates the volume of injected fuel, as well as the injection moment, and then gives the corresponding commands to the executive systems and mechanisms. At the same time, the actions are coordinated with the control units of other vehicle systems, for example, the gearbox control unit, air conditioning or anti-theft system.
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