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Two Types Of Fuel System For Automobiles

In a vehicle, the fuel system has a simple function of delivering fuel to the carburetor. The peculiar thing is that the engine never requires a steady amount of fuel. Its demand keeps on changing with the dynamics of driving. Sometimes engine accelerates and sometimes it is braked. This requires that fuel system of our car should have proper controlling mechanisms.

The fuel system should be able to manage the fuel delivery at the required pressure to the engine in proportion of engine’s air intake. This delivery involves fuel tank, fuel pump, fuel lines and pressure regulator. The fuel flow is related to pressure control and we want to utilize the fuel system to deliver maximum horse power.

Understanding Pressure In The Fuel System

Whenever the fuel supply exceeds the fuel demanded by the engine, there is a back pressure. Hence, the pressure is directly related to fuel flow. We can easily control the fuel pressure by controlling the fuel flow. Now, we can focus on controlling the fuel flow. Fuel flow can be controlled by either diverting the fuel or stopping it.

The Two Types Of Fuel System

The classification of the fuel system into the two categories Dynamic fuel system and Static fuel system has its origin in the manner we control the fuel flow. The static fuel system stops the fuel flow to the carburetor when the float bowl is full, whereas the dynamic fuel system deliver continuous fuel flow on the injector inlet and diverts the extra fuel through return line back into the tank.

Static Or Dead Head

The strict definition for a dead head fuel system is that the fuel makes one way journey that is from tank to the carburetor. Static fuel system is normally used in conjunction with carburetor. Its peculiar feature is that it delivers fuel as it is demanded. The static fuel system consists of a regulator which responds to the pressure changes in the carburetor inlet. When the car accelerates the fuel demand rises and the pressure falls, then the regulator opens up to rush in more fuel into the bowl of the carburetor. Thus, the fuel pump works in exact tandem with the demands of the engine. The column of the fuel in feed line stops (deadheads) at the regulator itself maintaining a pressure of 4-9 psi between regulator and the carburetor.

The Two Types Of Pressures In The Static Fuel System

1. Line pressure : It is set by flow bypass between the fuel pump and the regulator. The pressure may vary between 12 to 35 psi.

2. Regulator pressure: It is set by the regulator between the regulator and the carburater. Normal value of this pressure is between 4 to 9 psi.

The main issue with the static fuel system is the fluctuating line pressure. The cause for the drop in line pressure is poor bypass valve.

Dynamic Or Return Type

As the name suggests they provide dynamic response to pressure changes. Dynamic fuel system finds its application in electronic fuel injection system because they maintain a high rate of fuel at every instant. Dynamic fuel system responds in lightening fast speed to any change in speed. A dynamic (return type) fuel system differs from a static fuel system in a sense that it has two more additional components : one is bypass pressure regulator and other is return line.

When car slows down, the demand for fuel is less, the extra fuel is passed by the bypass regulator through the return line back to the tank. Thus in dynamic fuel system fuel is constantly circulated maintaining a pressure of about 7 psi.

The benefits of dynamic system are as follows:

1. The unwanted drops in pressure are eliminated.
2. There is a significant increase in pump to horse power ratings.
3. The pump operation is noiseless.
4. The dynamic system delivers more consistent air to fuel ratio across rpm band.
5. Power delivered in dynamic system is more reliable and predictable.

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