Components of a Diesel Engine Fuel Supply System and Its Working

Diesel engines are getting more popular among car owners as well as manufacturers. The later are increasingly adding more features to the existing ones. In this article we’ll discuss briefly the components of a diesel fuel supply system.

The components of a diesel fuel supply system include the following.

  • The fuel Tank
  • Fuel Filters
  • Lift Pump
  • Priming Pump
  • Inline Injection Pump
  • Distributor Type Injection Pump
  • Diesel Injectors

The fuel tank
The tank stores fuel necessary to keep the engine operating. Inside the fuel tank contains the fuel transfer pump and the return lines

    • Fuel transfer pump

The pumps the fuel and transferred it to filter and into the injection system.

    • Return linesReturn lines are used to send the unused fuel back to the fuel tank.
      • The baffle plates are mounted in the fuel tank. The baffle plates are designed with holes on them to prevent splashing of fuel. Fuel tanks are manufactured in many shapes, sizes depending on the need of space. They may be in cylindrical or square shape. The tank is made of aluminum alloy, steel, etc.
    • In vehicles like cars, bikes the fuel tank is made of aluminum as it is light weight.

Lift pump
The lift pump gets fuel from the tank and filter, and sends it the secondary fuel filter and into the fuel injection pump. The lift pump is mounted on the injection pump to lift the fuel from the fuel tank.

A few engines are fitted with electrical lift pumps, which are always sealed and cannot be rebuilt,and have to be replaced when they fail. But most of are mechanical pumps that can be easily rebuilt.

Lift pumps are used in the vehicles where the fuel tank is mounted below the engine and the fuel has to be lifted up to the level of combustion chamber. If the lift pump supplies more fuel than required, it is the indication that the diaphragm in the lift pump is not good.

The time taken by a vehicle to accelerate improves with an effective lift pump. The lift pump is also used to build the pressure before the fuel goes into the fuel injection system.

Fuel filters
Diesel engine fuel system is equipped with a single or multiple filters. The fuel filters remove dirt, debris and rust particle from the fuel. The fuel filters play a vital role in a fuel system.

For effective fuel filtering, a series of filters. In the first filter, large materials are removed and in the subsequent filters smaller particles are removed. The filters need to be maintained at regular intervals to improve performance, as the fewer contaminants present in the fuel are, the more efficiently it can be burnt. If fuel filtering is not effective, it can cause clogging of fuel injector.

Inline injection pump
An in-line injection pump is used to raise the pressure of a fuel. In-line injection pumps are used primarily in diesel engines. The basic principle is to lift the injector needle off from its position. The in-line injection pump should pump the fuel accurately at a predetermined number of times under very high pressure to the single nozzles. The use of this type of pump is important in large-capacity engines with a higher fuel necessity. This kind of injection pumps are used in multi-cylinder engines.

Distributor type injection pump
The distributor-type injection pump is used in small to medium-sized diesel engine vehicles. It uses a vane type transfer pump to fill individual pumping elements to raise the fuel to injection pressure. Its operation is similar to an ignition distributor that distributes fuel to the pumping elements.

A rotating part called the rotor, within the pump distributes fuel at a high pressure to the individual injectors at the time of engine firing-order. Distribution type injection pumps are used in diesel multi-cyllinder engines with a maximum of six cylinders.

Diesel injector
Fuel injection is a way of supplying fuel in an I.C engine. It has become the primary fuel delivery system used in engines and has replaced carburetors. Fuel is delivered to the injectors. Each injector is fitted in the cylinder on its head. The injectors are made of good quality material to withstand the high temperature and pressure during the combustion process.

Working of diesel engine
In a diesel engine, the fuel is injected into the combustion chamber during the end of the compression stroke and the start of the power stroke. This is responsible for the combustion in a diesel engine. Mixing of fuel and air occurs inside the cylinder.

Air is sucked by a suction stroke and is compressed at high pressure. The injector injects fine spray of fuel with high velocity causes power stroke which is converted to mechanical work through the transmission system.

Soot is formed during combustion because the fuel burns with insufficient oxygen, and the combustion of the fuel is not completed. As additional fuel is injected, more and more soot is produced. The air/fuel ratio of the diesel engine should always be smaller to prevent high amount of smoke. A diesel engine is more efficient than a petrol engine as it has high compression ratio. The air-fuel ratio of compression ignition engines ranges from 18:1 to 22:1.

Major processes in the combustion mechanism

The physical processes

  • Oil is injected into the combustion chamber
  • Fuel droplets undergo evaporation
  • Vapors are mixed with hot air

The chemical processes

  • Low-temperature oxidation of hydrocarbons
  • Hot flames