How many parts does the fuel supply system of diesel engine consist of? What is the route of transmission? What are their respective roles?
The fuel supply system consists of diesel tank, diesel coarse (fine) filter, fuel transfer pump, fuel injection pump, fuel injector, governor, oil pipe and combustion chamber, as shown in Figure 3-58. According to the working requirements of the diesel engine, clean fuel with good atomization quality is injected into the cylinder at a fixed time, a fixed quantity and a constant pressure, and it is fully mixed and burned with the air through the action of the combustion chamber.
Fig. 3-58 Fuel supply system of four-cylinder diesel engine
1. Fuel injector 2. Fuel injection pump return pipe 3. Hand pump exhaust bolt 4. Fuel delivery pump 5. Fuel delivery pump inlet pipe 6. Fuel injection pump inlet pipe 7. Fuel injection pump governor assembly 8. Diesel filter 9. Filter inlet pipe 10. Vent bolt 11. High pressure oil pipe 12. Fuel injector return pipe
The diesel oil in the fuel tank is filtered from the fuel tank along the oil pipe through the diesel filter, and then enters the fuel injection pump through the fuel transfer pump (there is no fuel transfer pump for single-cylinder engines, while the fuel transfer pump for multi-cylinder engines is generally installed on the side of the fuel injection pump and driven by the eccentric wheel on the camshaft of the fuel injection pump). Under the action of the fuel injection pump, the low-pressure diesel oil is changed into high-pressure diesel oil, and the fuel is sprayed into the cylinder as a mist through the high-pressure fuel pipe and injector according to the required time and fuel quantity.
The oil supply system is divided into low pressure oil circuit and high pressure oil circuit. The low-pressure oil circuit generally includes the diesel tank, fuel transfer pump, diesel filter and the oil pipe connecting them. Its function is to ensure the normal flow of diesel in the oil circuit and deliver sufficient and clean fuel to the fuel injection pump at a certain pressure. High-pressure oil circuit generally includes fuel injection pump, high-pressure oil pipe and fuel injector. According to the different working conditions of the diesel engine, fuel with good atomization quality can be injected into the cylinder at a fixed time, a fixed quantity, a fixed pressure and quickly.
(1) Diesel engine filter
Before the fuel enters the fuel injection pump, filter it thoroughly to remove mechanical impurities and moisture. Generally, diesel engines are equipped with coarse and fine filters.
(2) Fuel transfer pump
Its function is to overcome the resistance of diesel oil passing through the filter and make it produce a certain oil delivery pressure, so as to ensure continuous delivery of sufficient diesel oil to the fuel injection pump.
(3) Fuel injection pump
The high-pressure diesel fuel produced by the fuel injection pump is fed to each cylinder through the fuel injector regularly, quantitatively and evenly according to the working order and load of the diesel engine.
(4) Fuel injector
The function of the fuel injector is to atomize the high-pressure diesel oil delivered by the fuel injection pump and inject it into the combustion chamber according to certain requirements to form a good combustible mixture. The general requirements for the fuel injector are that the fuel atomization is uniform, the injection is sharp and crisp, and there is no oil drop. The pressure, shape and direction of the fuel spray should meet the specified technical requirements.
(5) Governor
Within the specified speed range, the circulating oil supply is automatically adjusted according to the change of external load to maintain the stable operation of the diesel engine.
