In a very cold engine, it may happen that the compression does not provide the combustion temperature. In this case, the engine needs to be warmed up. For this purpose, a glow plug is installed in each swirl chamber, which heats up the combustion chamber. To make it easier to start a cold engine, the injection start of the high-pressure fuel pump is set to an earlier injection. As the engine warms up to operating temperature, the injection start point moves to its normal position. In this case, the DDE control unit (DDE - digital diesel engine control system) takes over the control of the injection start, as well as the control of the amount of fuel injected and the discharge pressure of the exhaust turbocharger.
The fuel is supplied from the fuel tank by the fuel pump and the high-pressure fuel distributor pump. The high pressure of about 160 bar required for the injection of diesel fuel is generated in the high-pressure fuel pump and distributed to the individual cylinders in accordance with the ignition sequence. The amount of fuel injected is determined by the DDE control unit in accordance with the position of the gas pedal, according to the signal of the potentiometer associated with it. At the right time, the diesel fuel is injected by the injectors into the pre-chambers of the corresponding cylinders. Due to the shape of the swirl chamber, the air in the compression stroke receives a certain swirl movement, which ensures optimal mixing of the injected fuel.
Before the fuel enters the high-pressure fuel pump, it passes through the fuel filter. However, fuel is supplied only if there is no air in the system. Dirt and water are deposited in the filter. Therefore, it is extremely important to replace the filter in accordance with the maintenance schedule.
The high-pressure fuel pump is maintenance-free. Its drive of the high-pressure fuel pump is carried out via a toothed belt, which also drives the camshaft.
Since the diesel engine has the property of spontaneous combustion of the fuel mixture and therefore cannot be stopped by removing the voltage of the ignition system, it has a magnetic valve for this purpose. When the engine is started, the magnetic valve is supplied with voltage from the ignition switch. When the ignition is turned off, the magnetic valve is de-energized and the valve closes the fuel supply channel, the engine stops. By stopping the fuel supply with a relay, it is guaranteed that when the ignition key is removed, fuel is not supplied. When the engine is started, the magnetic valve is supplied with voltage from the ignition switch and opens the fuel supply channel.
(The original text can be read on the website: BMWman.ru)