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Gasolene engines use low pressure mechanical pumps. These are mounted outside the tank. On the other hand, compression ignition (diesel) engines use electric fuel pumps fixed inside the tank. Some diesel engines have two fuel pumps one for low pressure supply in the tank and one for high pressure pump near to the engine.
Types of fuel pumps include mechanical fuel pumps, electrical fuel pump and turbo fuel pump. We'll discuss each of them briefly.
A mechanical fuel pump is a device that delivers fuel to the engine. Mechanical fuel pumps are mostly used in spark ignition (petrol) engines. These are located between the fuel tank and the engine.
How a mechanical fuel pump worksThe mechanical fuel pump is driven by a camshaft. It's connected to crank shaft. As the shaft rotates the camshaft, it passes over the pivot lever and forces it to lift at one end. The lever fulcrum point is very close to the part that actuates the diaphragm, so very little movement of the arm at the camshaft results in significant movement of the diaphragm.
As the diaphragm is pushed up, the fuel is pressurized and moves out of the pump into the fuel line. From there it enters the carburetor. The lever arm allows the diaphragm to return to its original position. The one-way valves in the pump prevent the return of fuel from the carburetor and a path is opened for fuel to be drawn from the fuel tank. Vacuum is created by the diaphragm which causes fuel getting sucked into the chamber from the fuel tank.
Electrical fuel pump
The electric fuel pump is a commonly used one. It's located inside the fuel tank. The electric fuel pump pumps fuel from fuel tank to the fuel injection system at a higher pressure its mechanical counterpart does. Because of this reason electrical pumps are placed replacing mechanical pumps. The electric fuel pump works with the fuel injector in cars.
Working of electrical fuel pump
As the pump is located in the interior of the tank, it is protected from heat as gas and diesel are cold in liquid state.
The electromagnetic switch called solenoid is used to pull the diaphragm. The solenoid consists of iron rod that pulls the diaphragm downwards and fuel is drawn into the ignition chamber. The rod that pulls the diaphragm returns to it position.
When you turn the key on the pump gets an electric signal, which leads creating pressure on fuel in the tank. When the engine is just to start, the pump sends fuel at pressure down the line for ignition.
Turbo fuel pump
Turbo pumps are not very popular because they are used mainly in jet and rocket engines.
They are centrifugal pumps and get their propulsion from a gas turbine.
Working of a turbo pump
In a turbo molecular pump, the gas molecules move in bulk and interact more with each other than with the walls of the container.
Turbo pumps do not work in this case because the momentum imparted the by rotors is insignificant compared to intermolecular interactions. This is known as molecular flow. Now the turbo pump can impart momentum on each molecule individually.
The rotor blades rotates around 90,000 rpm. When they hit the gas molecules in the engine, they impart momentum. The angles of the rotor and stator blades drive the gas molecules towards the exhaust.
The fuel pump is an important part in your car's engine system and therefore it's worth to know about it.
