Self-ignition of fuel is accompanied by a sharp, spasmodic increase in pressure in the cylinder - this usually explains the noisy, «tough» diesel engine operation. For smoother fuel ignition, two-stage injection and a sophisticated electronic control system are used.
A characteristic feature of diesel engines is the presence of solid particles in the exhaust gases - soot. For better combustion of diesel fuel, a significant, even excessive, amount of air is required.
For injection and atomization of fuel, as well as for the distribution of its particles throughout the volume of the combustion chamber, nozzles are used. A high compression ratio requires the use of appropriate fuel pumps - the pressure in the injector nozzle must reach several hundred bar. All this complicates and significantly increases the cost of the fuel supply system and, accordingly, the diesel engine itself.
Fuel is supplied to the injectors by a high pressure fuel pump (injection pump).
To reduce the amount of harmful substances contained in the exhaust gases, an oxidative catalytic converter is installed on vehicles with diesel engines. For this purpose, an exhaust gas recirculation system is also used, when part of them is mixed with fresh air entering the engine, as a result of which the oxygen content that will be burned in the engine cylinders decreases. As a result, the combustion temperature of the combustible mixture decreases and, consequently, the amount of nitrogen oxides formed decreases.
With direct injection, the fuel immediately enters the combustion chamber.
The air flow entering the engine is twisted in a spiral in the intake ducts, as a result of which the combustion process in the engine cylinders is improved.
Before entering the high pressure fuel pump, the fuel passes through a fuel filter where water is separated from the fuel. This water must be drained periodically.
The fuel pump is driven by a toothed belt. Its internal moving parts are lubricated with diesel fuel.
The vehicle power system consists of a fuel tank, fuel lines, a fuel filter, a high pressure fuel pump and injectors.
Attention! Do not allow diesel fuel to enter the cooling system hoses. Hoses that have been exposed to diesel fuel for a long time must be replaced. The fuel system of a diesel engine is particularly sensitive to contamination, therefore, when working on the fuel system, be as clean as possible. Before disconnecting the fuel lines, thoroughly clean them of dirt. When removing system components, cover exposed areas with a lint-free cloth. Do not use compressed air to clean engine-mounted system components. When checking the operation of the injectors, never put your hands or any part of your body under the jet of fuel coming out of the injector. The fuel exits the nozzle at high pressure and can penetrate through the skin. Use goggles to protect your eyes from getting fuel in them. If fuel comes into contact with skin, wash with plenty of water. Install only clean power elements. Remove spare parts from the packaging just before installing them.
Attention! Use goggles to protect your eyes from getting fuel in them. If fuel comes into contact with skin, wash with plenty of water. Install only clean power elements. Remove spare parts from the packaging just before installing them.
Conditions for working with the BOSCH power system
Attention! Additives such as fuel system cleaner must not be added to diesel fuel.
Security measures
All work on the fuel injection system must be carried out in accordance with established requirements and regulations that ensure the prevention of accidents and the protection of the environment.
The work must be carried out by specially trained personnel who are aware of the safety recommendations and the measures to be taken.
Given the very high pressures (1350 bar), that are created in the fuel system, follow these recommendations:
- smoking is prohibited in the immediate vicinity of the high pressure hydraulic circuit during work;
- it is forbidden to work near an open flame or sparking objects;
- it is forbidden to carry out work on the high-pressure hydraulic fuel circuit with the engine running;
- After stopping the engine, use the DIAG 2000 to make sure that the pressure in the fuel distribution line has been reduced to atmospheric pressure before carrying out any work. This process may take several minutes.
With the engine running:
- always stay out of reach of the jet of fuel, which may accidentally escape from the nozzle, as this can cause serious injury;
- keep your hands away from the leak in the high pressure fuel circuit.
The place of work must be clean and away from the work area with other vehicles. Parts removed during repairs should be stored in places protected from dust.
Before starting work on the fuel system, clean the parts and components of the fuel system:
- fuel filter;
- high pressure fuel pump;
- fuel distributor (Common Rail);
Attention! Before carrying out any work on the engine, read the memory of the injection control unit.
- high pressure fuel pipes;
- nozzles.
Plug the high pressure pipes immediately after removal to prevent dirt from entering the high pressure circuit.
The following items must not be disconnected or removed from the high pressure fuel pump:
- switch of the 3rd piston of the high pressure fuel pump;
- a sealing sleeve on the side of the pump drive shaft;
- high pressure fuel outlet.
Do not disconnect the high pressure sensor from the end of the fuel distribution pipe.
Attention! It is forbidden to clean carbon deposits from the nozzle spray tip, as well as clean with diesel fuel or ultrasonic. All work on high-pressure fuel pipes must always be accompanied by their mandatory replacement.
It is forbidden to disconnect or remove the following items from the injector:
- spray;
- solenoid valve winding;
- turn or loosen the hex nuts.
When replacing the fuel system control unit, it is necessary to initialize the engine blocking system.
To perform initialization, the following conditions must be met:
- have an access code to the analog module (recorded on a confidential client card);
- have a new fuel system control unit and diagnostic tool;
- to initialize the engine control unit;
- code the engine control unit.
Attention! Swapping the injection system control units on two vehicles makes it impossible to start the engine.