In a very cold engine, the temperature required for self-ignition of the fuel may not be reached by air compression alone. In this case, the engine must be preheated. For this purpose, a glow plug is installed in each combustion chamber, which heats this chamber. The duration of the preheating depends on the ambient air temperature and is regulated by the engine management system via the preheating system relay.
Injection in a diesel engine is carried out in three different ways: swirl chamber injection or pre-chamber injection (swirl chamber or pre-chamber mixture formation) and injection directly into the combustion chamber (direct mixture formation).
In swirl-chamber or pre-chamber mixture formation, fuel is injected into the pre-chamber of the corresponding cylinder. The resulting mixture of fuel and air immediately self-ignites. The amount of oxygen in the pre-chamber is sufficient to burn only part of the injected fuel. The remaining, unburned part is ejected under the action of the high pressure formed during combustion into the main combustion chamber located above the piston. Here the fuel burns completely.
In direct combustion, fuel is injected directly into the combustion chamber located in the piston.
Direct mixture formation in the 1.9-I-SDI engine
Fuel is sucked from the fuel tank by a high-pressure fuel pump (HPFP) of the distribution type. Under high pressure, the HPFP delivers fuel to the cylinder injectors in accordance with their operating order.
The high-pressure fuel pump creates a pressure of 900 bar to inject fuel in two stages through the multi-hole nozzle. First, a small amount of fuel is pre-injected, which improves the conditions for ignition of the main part of it. The result is "soft" and low-noise combustion, similar to combustion in a swirl-chamber engine.
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 is driven by the crankshaft via a toothed belt.
Direct mixture formation in the 1.4-/1.9-I-PD-TDI engine
Direct mixture formation is carried out using a system of pump-injectors. Unlike a conventional injection system, where one high-pressure fuel pump creates fuel pressure for all injectors, here each cylinder has its own high-pressure fuel pump. This pump, control valve and injector are combined into one unit, which is called a pump-injector. Diesel fuel is supplied to the pump-injectors using an electric pump located in the fuel tank, as well as using a mechanical booster pump. The mechanical booster pump, together with the vacuum pump, is mounted on the cylinder head and is driven directly from the camshaft. The drive of three or four pump-injectors is carried out by additional cams of the camshaft via a rocker arm with a roller. Thanks to the high injection pressure of approximately 2000 bar, very fine atomization of the fuel is achieved. The cyclic fuel supply is regulated by the engine control unit using electromagnetic control valves located in the pump-injectors.
Due to high compression in the pump-injectors, the fuel heats up strongly, which negatively affects the operation of the fuel level sensor in the tank. To cool the fuel, a fuel refrigerator is installed in the return line under the bottom of the body.
Before reaching the booster pump and, respectively, the pump-injectors, the fuel passes through a fuel filter, where impurities and water are retained. Therefore, it is very important to promptly remove water from the filter or, respectively, replace it in accordance with the maintenance instructions.
Attention: When working with the fuel supply system, strictly follow the rules safety and cleanliness techniques.
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