Fuel supply system of diesel engine consists of the following components

  1. Fuel tank
  2. Fuel lift pump or fuel feed pump
  3. Fuel filter
  4. Fuel injection pump
  5. High pressure pipe
  6. Over flow valve
  7. Fuel injector
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Fuel is drawn from fuel tank by fuel feed pump and forced to injection pump through fuel filter. The injection pump supplies high pressure fuel to injection nozzles through delivery valves and high pressure pipes. Fuel is injected into the combustion chamber through injection nozzles. The fuel that leaks out from the injection nozzles passes out through leakage pipe and returns to the fuel tank through the over flow pipe.
Over flow valve installed at the top of the filter keeps the feed pressure under specified limit. If the feed pressure exceeds the specified limit , the over flow valve opens and then the excess fuel returns to fuel tank through over flow pipe.

Fuel tank
It is a storage tank for diesel. A wire gauge strainer is provided under the cap to prevent foreign particles entering the tank

Fuel lift pump
It transfers fuel from fuel tank to inlet gallery of fuel injection pump

Preliminary filter (sediment bowl assembly)
This filter is mostly fitted on fuel lkift pump. It prevents foreign materials from reaching inside he fuel line. It consists of a glass cap with a gasket.

Fuel filter
Mostly two stage filters are used in diesel engines
1. Primary filter 2. Secondary filter
Primary filter removes coarse materials, water and dust. Secondary filter removes fine dust particles.

Fuel injection pump 
It is a high pressure pump which supplies fuel to the injectors according to the firing order of the engine. It is used to create pressure varying from 120 kg/cm2 to 300 kg/cm2. It supplies the required quantity of fuel to each cylinder at appropriate time.

Air venting of fuel system 
When air has entered the fuel lines or suction chamber of the injection pump, venting should be done properly.. Air is removed by the priming pump through the bleeding holes of the injection pump.

Fuel injector 
It is the component which delivers finely atomized fuel under high pressure to combustion chamber of the engine. Modern tractor engines use fuel injectors which have multiple holes. Main parts of injectors are nozzle body, and needle valve. The needle valve is pressed against a conical seat in the nozzle body by a spring. The injection pressure is adjusted by adjusting a screw. In operation, fuel from injection pump enters the nozzle body through high pressure pipe. When fuel pressure becomes so high that it exceeds the set spring pressure, the needle valve lifts off its seat. The fuel is forced out of the nozzle spray holes into the combustion chamber.

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