How a diesel engine works (Opel Omega B)

Engine compartment of a diesel engine with a DDE 2.1 regulator



In a diesel engine, clean air is sucked into the cylinders and is subjected to strong compression. Due to this, the air temperature in the cylinders rises above the ignition temperature of diesel fuel. When the piston is slightly above TDC, diesel fuel is injected into the highly compressed air heated to +600°C. Diesel fuel ignites itself, no spark plugs are required.

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When the engine is very cold, the ignition temperature is not reached by compression alone.

In this case, the engine must be preheated. For this purpose, each swirl chamber contains a glow plug, which heats the air in the combustion chamber. In order for the cold engine to work better, the fuel is injected into the hot air earlier. As soon as the engine has reached operating temperature, the injection point is automatically shifted back. The start of injection is regulated by the DDE control unit (DDE = Digital Diesel Electronic), as well as the injection quantity and boost pressure for the turbocharger.



The fuel is supplied from the fuel tank by the fuel supply pump and the injection pump to the engine. In the injection pump, a high pressure of about 160 bar is created and the fuel is distributed to the individual cylinders according to the firing order. The injected fuel quantity is determined by the DDE control unit, with the corresponding action on the accelerator pedal, whose position is monitored by a potentiometer. Through the injectors, the diesel fuel is supplied at a certain time into the swirl chambers of the corresponding cylinders. During the compression phase, the sucked air acquires a certain swirl motion according to the shape of the swirl chamber and is thus optimally mixed with the injected fuel.

Before the fuel gets to the injection pump, it passes through the fuel filter. There it is cleaned of dirt and water. Therefore, it is important to replace the fuel filter according to the maintenance recommendations.

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 through a chain.

Since the diesel engine is a device with spontaneous combustion of fuel and does not turn off when the voltage in the ignition system is interrupted, it is equipped with an electromagnetic valve. When the ignition is turned off, the voltage on the electromagnetic valve is disconnected, and the valve closes the fuel channel. Thanks to this, the fuel supply is stopped before the steering column lock is locked. When the engine is started by the starter switch, voltage is supplied to the electromagnetic valve, and thus the fuel channel is opened.

The DDE control unit monitors and prevents faults in the injection system. OPEL workshops can provide a fault finding device that is connected to the control unit, interrogates and reads faults.