Fuel Injection

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INTRODUCTION:

Fuel Injection is the alternative method of supplying the engine with its working charge of fuel. The pressurization of fuel leads to improved automization which is considered to be good for performance.
Although, the modern carburettor is cheep and reliable, it has number of inherent disadvantages that make the supply of correct A: F mixture at all times difficult. The problem is further accentuated when a single carburettor has to supply the mixture to multicylinder engine. In addition to this, the throat restricts the flow of air to the engine. The maximum power can be increased by using a large throat by this affect the economy of fuel. Multiple carburettors assist the distribution problem but it also increases fuel consumption due to low air velocity at low engine speed and capital cost.
For these reasons, many attempts have been made to design a satisfactory Petrol Injection system. In which, each cylinder is supplied with its correct quantity of petrol for each working cycle under all operating conditions.



ELECTRONIC FUEL INJECTION SYSTEM (EFI) FOR PASSENGIER CARS


In the case of carburettor, the entire working is depends on the throttle position and all the system must be tailored so that proper mixture delivery takes place at every throttle position. The fuel delivered to engine by carburettor cannot easily be adjusted to suit certain important operating conditions of the engine such as water temperature, oil temperature, air temperature etc. to level of precision called for with stringent emission control requirements. In the case of fuel injection, this is achieved by Electronic means. It is possible to make the system recognized and respond to every operating condition of the engine and to deliver the required mixture at all operating conditions.


SYSTEM DISCRIPTION:

There are two types of fuel injection systems, namely Single Point Injection (SPI) and Multi Point Fuel Injection (MPFI) systems. Both systems are low pressure injection systems with pump pressure of 3 to 4 bar. In the SPI system, which is also called throttle body injection system, fuel delivery takes place at one point adjacent to the throttle. The Electronic Control Unit (ECU) senses many engine parameters including measurement of air flow and oxygen content in the exhaust so that the fuel is delivered in the right quantity at all operating points.