When starting a very cold engine, it is not possible to reach the autoignition temperature solely due to the compression ratio. In this case, the fresh charge must be preheated. For this purpose, a glow plug is installed in each swirl chamber, which heats the charge.
In addition, the diesel engine has a thermostat that moves the piston of the injection advance clutch in the high-pressure fuel pump in the advance direction. Due to this, the fuel is injected into the hot air earlier, and the cold engine starts faster. When the engine reaches operating temperature, the thermostat automatically returns the clutch piston back.
Fuel is sucked from the fuel tank directly by the high-pressure fuel pump of the distribution type. The high pressure of approximately 130 bar required for the diesel process is created in the high-pressure fuel pump, and the fuel is distributed to individual cylinders in accordance with their operating order. At the same time, the regulator in the high-pressure fuel pump changes the cyclic fuel supply in accordance with the position of the accelerator pedal. Through the injectors, diesel fuel is injected into the swirl chambers of the corresponding cylinders with a given advance angle. Due to the shape of the pre-chamber or swirl chamber, the air entering the cylinder receives a certain swirl motion during the compression process, which creates optimal conditions for mixing the injected fuel and air.
Before the fuel gets to the injection pump, it passes through the fuel filter. The filter retains impurities and water. Therefore, it is extremely important to remove water from the filter in a timely manner and replace the filter element in accordance with the maintenance instructions.
The high-pressure fuel pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The high-pressure fuel pump, like the camshaft, is driven by a chain. Since the diesel engine has a self-ignition of the fuel-air mixture and cannot be stopped by turning off the ignition, it has an electromagnetic valve that closes the fuel supply channel. When the ignition is turned off, the voltage supply to the valve is cut off, and the valve closes the fuel channel. This ensures that the fuel supply is cut off before the steering wheel shaft lock is locked. When the ignition is turned on to start the engine with the starter, voltage is supplied to the electromagnetic valve, and it opens the fuel channel. When the engine starts, the anti-theft system unlocks the electromagnetic valve, which allows the engine to be started. About the anti-theft system see p. 154.
Operating a car in winter
As the ambient temperature drops, the fluidity of diesel fuel decreases due to the crystallization of the paraffin contained in the fuel. Diesel fuel becomes as thick as honey. For this reason, in winter, oil refineries mix additives into diesel fuel that increase its fluidity and allow the engine to start at temperatures down to -20°C. In car models manufactured since 9/93, an electric heater is also installed before the fuel filter, which is automatically switched on by a thermal switch at temperatures below 0°C. In addition, if a malfunction occurs, the thermal switch protects the fuel from possible overheating.
However, these additives are not always sufficient for normal operation, so diesel engines of cars are equipped with electric heating. Thanks to this, even in extreme frost, crystallization of diesel fuel is prevented. The heating is switched on at temperatures below +6°C after starting the engine and switched off at temperatures above +16°C. This guarantees reliable operation of the car at all temperatures.