Friday 6 November 2015

Multi Point Fuel Injection (MPFI)

Multi Point Fuel Injection (MPFI) is fuel injection system used for gasoline engines. Each cylinder will be assigned with its own injector just above the inlet valve. It is of 3 types:

  1. Sequential: the fuel injection can be made sequential by adjusting the injection timing with the inlet stroke.

  2. Batched: Fuel is injected in groups to the cylinders without synchronizing with the inlet strokes of any of the cylinders.

  3. Simultaneous: Fuel is injected at the same time to all the cylinders.

The main reason behind introducing MPFI is to reduce the emission. Although the working principle is somewhat similar to carburetors, MPFI uses injectors that atomize the fuel to tiny droplets which make the combustion process easier and hence reduces emission. It also increases the power generated.

With the introduction of fuel injection, carburetors have become almost obsolete. Carburetors are only used in some two wheeler where emission is not a bigger issue. With the introduction of Electronic Control Unit (ECU), the MPFI system is even more efficient.

WORKING:

Air enters the inlet manifold from the atmosphere and the air flow is constantly checked by the air-flow sensor. The air-flow to the cylinders can be varied by using a throttle valve which is connected to the accelerator pedal. The ECU senses the engine crank speed, air flow, accelerator pedal position and based on all the inputs it sends a signal to micro-controller.



 Micro-controller monitors fuel injectors and also controls the quantity of fuel to be injected. As already mentioned, each cylinder will be having its own injector and the fuel quantity can be varied for each cylinder based on the requirements. This helps in increasing the fuel efficiency.

ADVANTAGES OVER CARBURETORS:

  • Cranking of engine can be eliminated during cold start.

  • Better response from the engine.

  • Higher fuel efficiency.

  • Each cylinder can be supplied with precise air-fuel mixture.

  • Lesser engine emission.

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