Overview

Diesel engine - a piston engine with spontaneous ignition by compression. The principal difference from its gasoline is the preparation of the fuel-air mixture within the cylinder itself.

In a diesel engine, fuel and air are supplied separately. First, the air sucked into the cylinder, then it is compressed, and only then at the end of the compression stroke fuel is injected.

Self-ignition of fuel is accompanied by a sharp, abrupt increase in pressure in the cylinder - this explains the typically noisy "hard" work of the diesel engine. In low-speed diesel engines with a large cylinder capacity, which are used in trucks, this deficiency is manifested to a lesser extent, and put up with it. The diesel engines of cars trying to get rid of it using the vortex chamber or pre-chamber - a small bay of the combustion chamber into which fuel is injected. There is ignited, partially mixed with air, and then distributed over the entire volume of the cylinder. This process reduces the rigidity of the engine, but it slightly reduces the thermal efficiency and fuel economy. For a smoother ignition of the fuel used by the two-stage fuel injection and sophisticated electronic control circuit.

A characteristic feature is the presence of diesel engine exhaust gases in solids - carbon black. For complete combustion of diesel fuel require a significant, even excessive, compared to a gasoline engine, the amount of air.

The compression ratio of the diesel engine is twice higher than that of gasoline. High, not less than 14 (up to 25), the compression ratio is necessary to increase the temperature of air in the cylinder to a value sufficient for ignition of fuel. Generally, in diesel engines the compression ratio of 21-22 and is limited only by the strength characteristics of the engine.

Devices for supplying the fuel in diesel engines is much more complicated than gasoline. Their complexity is determined primarily by the fact that it is necessary to inject very small, just a few milligrams, a quantity of fuel in the high pressure environment. For injection and fuel atomization nozzles are used. High compression requires the use of high pressure fuel pumps - pressure in the injector nozzle should reach several hundred bars. All this complicates and increases the cost significantly and the fuel supply system, respectively, the diesel engine itself.

Fuel from the fuel tank is supplied to the injectors high pressure fuel pump.

To reduce the amount of harmful substances contained in exhaust gases in cars with diesel engines installed oxidation catalyst. For this purpose it is also used a method of mixing (recirculating) the exhaust gas to the fresh air entering the engine, thereby reducing the oxygen content in the air to be fed into the cylinders. By reducing the amount of oxygen decreases the combustion temperature of the combustible mixture and consequently reducing the amount of nitrogen oxides produced.

There are three ways of diesel fuel injection into the cylinders of the engine: through pre-chamber (antechamber), swirl chamber and direct injection.

When injected through a pre-chamber diesel fuel is sprayed on it and instantly ignited. Due to the small amount of oxygen in the settling chamber is burned only a part of the fuel and the rest is expelled from the prechamber into the engine cylinder, where it is burned completely.

When the fuel injection through the vortex chamber combustion process takes place in the same manner as with the fuel injection via the prechamber. The difference lies in the shape and size of a channel connecting the vortex chamber with the combustion chamber. The channel is located at an angle to the axis of the cylinder and the shape of the chamber is chosen so that when compressed air is swirled. By injecting fuel into the swirl chamber and is much better mixed with air, and the combustion process proceeds more smoothly.

With the direct injection of fuel is supplied directly to the combustion chamber. The fuel pump supplies fuel at a pressure of about 900 bar and the fuel injection is carried out in two stages.

Using dual fuel injectors enables to make fuel injection in two stages: first injected and ignited by a small portion, is then fed to the main part. As a result, the combustion process takes place more smoothly. The amount of fuel injected is regulated by the electronic engine control system based on information from the sensors.

The stream of air entering the engine, in the intake channels spirals to improve mixing. Furthermore, with the engine cold start is facilitated, and the engine preheating was necessary to carry out only at temperatures below -10 ?� C.

Before entering the high pressure fuel pump fuel passes through a fuel filter, in which it also separates from the water, which is required periodically drained.

Drive a fuel pump is a toothed belt. Its internal moving parts are lubricated by diesel fuel.

The power supply system of the car consists of a multi-fuel tank, piping, fuel filter, fuel pump, fuel pump and injectors.

The fuel tank is arranged underneath the rear of the vehicle. The ventilation system of the fuel tank closed. When venting fuel vapor from the tank caught by the filter with activated carbon - absorber.

Location of ignition systems and fuel injection four-cylinder engine is shown in Fig. 5.1, the six-cylinder - to Fig. 5.2.