In a very cold engine, it may happen that 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 each combustion chamber, which heats the air in the volume of the chamber. The preheating time depends on the ambient temperature and is controlled by the DDE control unit via the preheating relay.
Fuel injection in a diesel engine is carried out in three different ways: (pre-chamber mixing) or swirl chamber (vortex chamber mixing), as well as injection directly into the combustion chamber (direct mixing).
In the case of vortex-chamber and pre-chamber mixture formation, an electric booster pump located in the fuel tank supplies fuel to the fuel injection pump of the distribution type. The necessary high pressure is created in the high-pressure fuel pump and diesel fuel is injected in the vortex - or pre-chambers of the corresponding cylinders in accordance with the order of their operation. The resulting mixture immediately ignites spontaneously. The amount of oxygen in the pre-chamber is sufficient to burn only part of the injected fuel. The unburned part of the fuel under pressure, formed as a result of the combustion that has begun, is ejected into the main combustion chamber, where it burns completely. With direct mixture formation, the fuel is sucked in by the booster pump from the tank and fed to the high pressure pump (NVD). In HP, even at a low crankshaft speed, a constant high pressure of approximately 1350 bar is created.
From NVD through a common fuel line (Common Rail) fuel is supplied to the injectors of individual cylinders. The common top-beer line serves as a pressure accumulator and distributes fuel at a constant pressure to the injectors. The necessary cyclic fuel supply is accurately dosed by the engine control unit using the solenoid valves of the injectors. If the engine control unit microcomputer commands the solenoid valve to close, fuel injection stops immediately. In other words: high pressure generation and fuel injection are carried out independently of each other. This has the advantage of optimizing the injection process in terms of cyclic delivery and exhaust gas parameters, regardless of the crankshaft speed.
Fuel is injected through a multi-hole nozzle atomizer in two stages. First, a preliminary injection of a small amount of fuel is carried out, as a result of which the conditions for igniting its main part are improved. The result of this is "soft" and low-noise combustion, similar to combustion in a vortex-chamber engine. In contrast to other camshaft-controlled direct injection systems, the pre-injection parameters of the BMW injection system change depending on the operating conditions.
Before the fuel reaches the high pressure pump / injection pump, it flows through the fuel filter. It retains dirt and water. Therefore, it is extremely important to change the filter regularly in accordance with the instruction manual.
NVD / high pressure fuel pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The drive HP / high pressure fuel pump is carried out from the crankshaft using a chain.