At the moment when the piston of the cylinder almost reaches top dead center, diesel fuel is injected into the air, compressed and heated to about +600°C. The fuel is self-igniting, so spark plugs are not needed.
With a very cold engine, compression alone will not reach the ignition temperature. In this case, the engine must be preheated. To do this, in the combustion chamber of each cylinder there is a glow plug that heats up the combustion chamber.
The duration of the warm-up depends on the ambient temperature and is regulated by the engine control unit via the warm-up relay.
The fuel is sucked in by the fuel pump directly from the fuel tank and forced to the injection pump at a pressure of approx. 3.5 bar.
In the high pressure fuel pump, even at low engine speeds, a constant pressure of just over 1300 bar is created.
A main fuel distribution line with fuel injectors for each cylinder is connected to the high pressure fuel pump (see illustration 1.0).
1.0 Distribution line of diesel engine with direct fuel injection (CDI)
1 - distribution line
2 - fuel filter
3 - fuel return line
4 - fuel supply line to high pressure fuel pump
5 - fuel shutoff solenoid valve
6 - fuel pump
7 - injection pump (high pressure fuel pump)
8 - injection fuel line (to the distribution line)
9 - nozzle
10 - injection fuel line (to nozzle)
11 - return fuel line)
The main fuel line is a kind of fuel and high pressure accumulator that distributes the incoming fuel between the injectors with constant pressure.
Solenoid fuel injectors inject fuel into their cylinders. However, the amount of injected fuel is determined and set by the engine control unit. If, for example, the control unit closes the injectors, then the fuel injection stops.
In other words, the injection of fuel and its injection are carried out independently of each other.
The advantage is that the amount of fuel injected depends on the current operating load on the engine, which also optimizes the content of harmful substances in the exhaust gas.
However, the amount of injected fuel does not depend on the number of engine revolutions.
Fuel is injected through a multi-jet nozzle in two stages.
Initially, a small, preliminary amount of fuel is injected, which improves the ignition conditions for the main portion of the fuel. This leads to a softer and at the same time quiet combustion of the mixture.
Before getting to the fuel pump and injection pump, the fuel passes through the fuel filter, where contaminants and water are trapped. Therefore, it is extremely important to replace the fuel filter at the time required by the maintenance conditions.
The fuel pump and high pressure fuel pump do not require maintenance. All moving parts of the pump are lubricated with diesel fuel.
Air for the formation of the air-fuel mixture is taken in by the engine or forced by the turbocharger through the air filter.
The turbocharger compresses air and delivers it to the engine through the charge air cooler radiator (intercooler). The intercooler cools the hot charge air. This ensures an improvement in the filling of the cylinders, which in turn leads to an increase in engine torque and power.
Diesel engine operation in winter conditions
As the temperature decreases, the fluidity of diesel fuel decreases, it thickens and waxes.
Diesel fuel can become viscous, and its fluidity can be compared in this state to the viscosity of honey.
As a result of thickening, the fuel filter becomes clogged. For this reason, diesel fuel manufacturers add additives to diesel fuel in winter to maintain the desired fluidity and ensure engine start at temperatures down to -22°C.
To prevent clogging of the fuel filter in the cold season, hot fuel is discharged through the fuel heating valve into the filter (return line) from the injection pump.
Fuel injection in diesel engines is fully controlled by the control unit. This provides the following benefits:
- A) self-diagnosis of the engine, which allows you to quickly detect a malfunction;
- b) accurate dosing of injected fuel. This provides a reduction in the content of harmful substances in the exhaust gas and reduces fuel consumption;
- V) there is no need to adjust the idle speed, as well as the set speed at which the regulator begins to limit the fuel supply.
All parts of the engine management system are designed for a long service life and practically do not require repair.
As part of the maintenance, it is only necessary to change the air filter element and the fuel filter.
Diesel engine preheater
If the engine is cold, the temperature of the air generated during its compression is insufficient for self-ignition of the injected fuel. In this case, the engine needs to be preheated.
For this purpose, a glow plug is installed in the combustion chamber of each cylinder. The glow plug is a housing with a pressed glow plug.
The filament pin has a filament spiral and a current regulation winding.
When voltage is applied, the spiral inside the pin heats up within a few seconds to a temperature above +850°C.
In this case, a current of approximately 30 amperes passes through the pin of each candle.
As the temperature in the chamber increases, the resistance of the control winding increases, reducing the current strength to 15 - 25 Amps. This protects the glow plug from overheating.
As soon as the preheat indicator light on the instrument panel goes out, the engine can be started.
The duration of the engine preheat rarely exceeds 10 seconds and is regulated by the engine control unit, which requests the engine coolant temperature sensor for data on the current engine temperature.
Based on the data obtained, the control unit determines the duration of the heating and the current strength of the glow of the candles.
Attention! Diesel engine with good cold start ability. Therefore, preheating is only necessary at air temperatures below 0°C.