In a very cold engine, the temperature required for self-ignition of the fuel may not be reached only by compressing the air. In this case, the engine must be preheated. To do this, a glow plug is installed in each combustion chamber, which heats this chamber. The preheat duration depends on the ambient temperature and is controlled by the engine management system via the preheat relay.
Injection in a diesel engine is carried out in three different ways: injection into a swirl chamber or prechamber (vortex-chamber or pre-chamber mixing) and injection directly into the combustion chamber (direct mixing).
With vortex-chamber or pre-chamber mixture formation, fuel is injected into the pre-chamber of the corresponding cylinder. The resulting mixture of fuel with air immediately ignites spontaneously. The amount of oxygen present in the prechamber is sufficient to burn only a portion of the injected fuel. The rest, not burnt, 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.
With direct carburetion, the fuel is injected directly into the combustion chamber located in the piston.
Direct carburetion in the 1.9-I-SDI engine
Fuel is sucked from the fuel tank by the high pressure fuel pump (injection pump) distribution type. Under high pressure, the injection pump delivers fuel to the cylinder injectors in accordance with the order of their operation.
At the same time, the high-pressure fuel pump creates a pressure of 900 bar in order to inject fuel through the multi-hole nozzle nozzle in two stages. First, a small amount of fuel is pre-injected, thereby improving the conditions for igniting the main part of it. The result of this is «soft» and low-noise combustion, similar to combustion in a vortex-chamber engine.
The injection pump does not require maintenance. All moving parts of the pump are lubricated with diesel fuel. The injection pump is driven from the crankshaft through a toothed belt.
Direct mixing in the 1.4-/1.9-I-PD-TDI engine
Direct mixture formation is carried out using a pump-injector system. Unlike a conventional injection system, where one injection pump supplies fuel pressure to all injectors, here each cylinder has its own high pressure fuel pump. This pump, control valve and nozzle are combined into one unit, which is called the pump-injector. Diesel fuel is supplied to the unit 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, respectively, four unit injectors is carried out by additional camshaft cams through a rocker with a roller. Due to the high injection pressure of approximately 2000 bar, a very fine atomization of the fuel is achieved. The cyclic fuel supply is regulated by the engine control unit using solenoid control valves located in the unit injectors.
Due to the high compression in the unit injectors, the fuel is very hot, which negatively affects the operation of the fuel level sensor in the tank. To cool the fuel, a fuel cooler is installed in the return line under the bottom of the body.
Before getting to the booster pump and, accordingly, to the pump injectors, the fuel passes through the fuel filter, in which contaminants and water are retained. Therefore, it is very important to remove water from the filter in a timely manner or replace it accordingly, in accordance with the maintenance instructions.
Attention: When working on the fuel supply system, strictly follow the rules safety and cleanliness.
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