Low Pressure Electric Fuel Pump

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A mechanical or electrical pump for drawing fuel from a storage tank and forcing it to an engine or furnace. The type of pump chosen for a given fuel depends to a great extent on the volatility of the liquid to be pumped. In a gasoline engine the fuel is highly volatile at ambient temperature. Therefore, the fuel line is completely sealed from the tank to the carburetor or fuel-injection system to prevent escape of fuel and to enable the pump to purge the line of vapor in the event of vapor lock—a condition in which the fuel vaporizes owing to abnormally high ambient temperature. See Carburetor, Fuel injection, Fuel system.

Most carbureted gasoline engines use a spring-loaded diaphragm-type mechanical pump which is normally actuated by a rocker arm or pushrod that rides on an eccentric on the engine camshaft. Electric motor‐driven and solenoid-operated diaphragm pumps and plunger pumps are also available that can be mounted near the main fuel tank to minimize vapor lock in the fuel lines. Many gasoline-engine vehicles have a submersible electric fuel pump, which serves as the main supply pump, located ...
... in the fuel tank. In some fuel-injection systems, the in-tank pump is used as the supply pump for a high-pressure fuel-injection pump. The in-tank pump may be of the gear, plunger, sliding-vane, or impeller type.

Diesel engines normally use a gear, plunger, or vane-type pump to supply fuel to the injection pump. In the diesel engine, where fuel is injected at high pressure through an injection nozzle into the highly compressed air in the combustion chamber, a plunger or piston serves as its own inlet valve and as the compression member of the injection pump. When the required high pressure is reached in the injection nozzle, a spring-biased needle valve opens and fuel sprays into the combustion chamber. In an oil-fired furnace, although nozzle pressures need not be so high as in diesel engines, a piston pump is also used to provide positive shutoff of the fuel line when the pump stops. See Diesel engine

Single Point Fuel Injection (SPI):

SPI is used to inject fuel with the help of injector inside the throttle body, where mixing of air and fuel takes place just like the conventional carburetor and is fed to the respective engine cylinder. SPI is however, not so efficient but requires less modification if it is used in place of a carburetor. SPI has also been known as throttle body injection and central fuel injection by automotive manufacturers. SPI works under pressure of 10-12 psi and as a result it is less costly to be implemented on a conventional engine.

Continuous Injection:

As the name depicts, this system injects the fuel constantly inside the intake manifold irrespective of the engine stroke. The fuel is injected outside the intake valve and the amount of fuel to be supplied is regulated with the help of the intake valve. This system is useful where a very precise quantity of fuel mixture has to be delivered. Fuel pump is the only part that functions continuously in this system. This system rather than automotive finds its application in aircraft.