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REPAIR MAINTENANCE OPERATION OF MOTOR VEHICLES
Audi A6 (1997 release)

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Audi A6
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A6
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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.

A WARNING
Do not spill diesel on the cooling hoses. Hoses for which long influenced diesel fuel must be replaced.
The power supply system of the diesel engine is particularly sensitive to pollution, so when working on the system, observe maximum cleanliness. Before disconnecting the fuel thoroughly clean them from dirt. When removing the elements of the system, close the open spaces cloth lint.
Do not use compressed air to clean the elements of the system installed on the engine.
When testing the operation of nozzles never put your hands or any part of the body under the stream of fuel coming out of the nozzle! Fuel exits the nozzle at high pressure and may cause injury.
To protect your eyes from getting into the fuel they use glasses. If you get fuel on your skin, wash the area with plenty of water.
Install only clean parts and components of the power system.
Spare parts unwrap just before installation.


Location of the fuel injection system in the engine compartment of cars with four-cylinder engines
Fig. 5.1. Location of the fuel injection system in the engine compartment of cars with four-cylinder engines: 1 - a pressure sensor in the intake manifold temperature sensor G71 and intake manifold G72; 2 - 3-pin electrical connector of the engine speed sensor G28; 3 - 2-pin electrical connector needle lift sensor G80; 4 - valve EGR N18; 5 - coolant temperature sensor G62; 6 - 8-pin electrical connector fuel temperature sensor G81, the controller number N146 and the modulator piston motion sensor G149; 7 - 3-pin electrical connector injection valve N108 and shut-off the fuel valve N109; 8 - the engine speed sensor G28; 9 - control unit with direct injection J248 height sensor F96, relay J322 direct injection and glow plug fuse; 10 - the fuel pump to the injection valve N108, switch the fuel valve N109, a temperature sensor, the controller number N146 and the modulator piston motion sensor G149; 11 - injector with needle lift sensor G80; 12 - solenoid valve overpressure N75; 13 - mechanical valve EGR; 14 - Air mass meter G70


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

Location of the fuel injection system in the engine compartment of vehicles with six-cylinder engines
Fig. 5.2. Location of the fuel injection system in the engine compartment of vehicles with six-cylinder engines: 1 injector with needle lift sensor G80 (third cylinder); 2 - the valve of system of repeated burning of the fulfilled gases N18; 3 - solenoid valve overpressure N75; 4 - 2-pin electrical connector needle lift sensor G80; 5 - 3-pin electrical connector of the engine speed sensor G28; 6 - oil temperature gauge G8; 7 - control unit with direct injection J248 height sensor F96, relay J322 direct injection and glow plug fuse; 8 - switching valve intake manifold flap N239 (not installed on all vehicles); 9 - Engine speed sensor G28; 10 - a pressure sensor in the intake manifold G71; 11 - vacuum chamber with the intake manifold flap (not installed on all vehicles); 12 - The fuel pump with a control unit, an electromagnetic valve control quantity, speed sensor of the fuel pump, and the starting nozzle of the fuel temperature sensor; 13 - coolant temperature sensor G62; 14 - Air mass meter G70 with temperature sensor to the engine air G42






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