mpfi system

MPFi and Fi

MPFi and Fi

In olden days carburetors were used in petrol engines to mix the fuel and air required for combustion inside the cylinder. The percentage of fuel and air in combination is indicated in terms of air-fuel ratio. For varying conditions of engine operation the air-fuel ratio has to be varied. Carburetors were unable to maintain the correct amount of air-fuel ratio at various conditions. If the amount of air in the air-fuel ratio increases then it is called as lean mixture, if the fuel amount in the mixture goes up then it is said to be rich mixture.

A vehicle may need lean mixture during less or no load conditions, whereas during the time of high engine load (ex: moving up in a hill) engine will need rich mixture to produce high power output. Carburetors were failed to meet these conditions most of the time. Also carburetors failed to satisfy the pollution norms set by the Euro norms. To solve this problem "Fuel injectors" were introduced. The 1990 Subaru (make) Justy (model) was the last car to be sold in US with a carburetor. Fuel injector is nothing but an electrically controlled, solenoid actuated valve mechanism. Fuel from the fuel tank will enter the fuel supply lines of the fuel injector. The fuel injector has a high tension spring fitted at the bottom of the injector. This spring will be actuated by the electronically controllable solenoid. So whenever the engine is in need of fuel signals will be sent to ECU (Electronic Control Unit).

This ECU will read out the required amount of fuel and it will pass the information as electrical pulses to the fuel injector. As the fuel injectors have a high tension spring it will eject the fuel in to the combustion chamber with enormous amount of pressure. This will make the fuel to atomize completely, which is the required criterion for complete combustion. Since fuel injectors were electronically controlled depending upon the engine operating conditions they sent the required amount of fuel at the required time period. Since these injectors sent only the required amount of fuel there is not any wastage and it met the pollution norms set by the Euro norms. If these injectors are used in only one cylinder engine then they are called as fuel injectors whereas if they (injectors) are used in all the cylinders in a multi-cylinder engine then they are called as MPFi (Multi Port Fuel injection). Most of the European and North American countries have set the usage of fuel injectors as mandatory. In MPFi every fuel injector will not function at the same time because each piston will be having their power stroke at different time interval. For this purpose crank position analyzer will be set in the crank or in the cam shaft, this will send the position of the crank to the ECU, so that ECU may direct the fuel injector to send the correct amount of fuel at the correct time. In India this technique has been used in some bikes in order to provide fuel economy, you can find this technique being used in TVS-Apache.