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Cars with diesel engines
This type of engine has received its name from the German engineer Rudolf Diesel, built in 1897 the first engine with spontaneous ignition of fuel. Structurally similar diesel engine gasoline engine: the same cylinders, pistons, camshaft, valves. But there are some differences, of which the most important, if not fundamental, is that the ignition of the fuel in a diesel engine is produced is not a spark from the spark plug, but due to high temperature, which reaches the air by compressing it in the cylinder piston.
The second important point - the way to the fuel supply. The gasoline engine working fluid is a mixture of gasoline and air. The mixture is prepared in advance (in the carburettor), or directly at the time of supply to the cylinders (injection systems) - importantly, the fuel is supplied together with the air and ignited and combusted relatively homogeneous air-fuel mixture.
In a diesel engine fuel and air takes place separately. Initially, air is sucked into the cylinder, then it is compressed, and only then the fuel is injected, so to speak of a homogeneous air-fuel mixture is not necessary. Injection is performed at the end of the compression stroke, fuel and air are not virtually mixed with each other combustion takes place on the front of the compressed air injected into the fuel stream.
Self-ignition of fuel is accompanied by a sharp, abrupt increase in pressure in the cylinder - this explains the typically noisy and 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 burning the mixture was spread on the main cylinder volume. This method slightly reduces the rigidity of the engine, but it 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 of diesel engines is the presence of particulate matter in the exhaust gas. Due to the heterogeneity of the combustion process on the surface of the individual fuel particles are always there is some lack of oxygen, whereby instead of a partial oxidation to form a thermal decomposition of solids - carbon black. For a good diesel fuel combustion takes considerable even excess air.
Also, the degree of compression in the diesel engine 2 times higher than that of a gasoline engine. High, not less than 14 (up to 25), the compression ratio is necessary in order that the temperature in the cylinder has risen 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. These portions should be very precisely metered - exactly the amount of fuel supplied is controlled by the diesel engine. This requires fast and precise injectors. High compression requires the use of appropriate fuel pump - the 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 taken high pressure fuel pump, and then under high pressure is supplied to the fuel injectors.
To reduce the amount of harmful substances contained in exhaust gases in cars with diesel engines installed oxidation catalyst. Also used admixing exhaust system to the fresh air entering the engine, thereby decreasing the percentage of oxygen in the air to be burnt in the engine cylinders. As a result, it decreases the combustion temperature of the fuel mixture, thereby reducing the amount of nitrogen oxides formed.
There are three ways of diesel fuel injection into the cylinders of the engine: through pre-chamber through the swirl chamber and direct injection.
When injected through a pre-chamber diesel fuel sprayed by the settling chamber and instantly ignited. In connection with a minor amount of oxygen in the prechamber is burned only a part of the fuel and the remaining fuel displaced from the premix chamber into the cylinder, where it is combusted completely.
When the fuel injection through the vortex chamber of combustion produced 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. By injecting fuel into the swirl chamber is much better mixing of fuel with air, and the combustion process is carried out more smoothly.
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