Fuel injection System


Automobile engineers have been using carburetors for very long period of time as fuel supplying mechanism in SI engines. They had been quite useful and effective for a considerable duration of time. They were very basic and simple devices working purely on mechanical principles. Even today, you can find carburetors on most of the two wheelers. Way back in 1990s, automobile engineers started using fuel injectors in petrol engines. Before this they were only used in Diesel engines. This change improved the performance and efficiency of SI engines considerably. This led to a significant increase in mileage and performance of the engines. It also opened a way to introduce different sensors and electronic control on engines. So let us understand the working of Fuel injectors in detail.

Also Read : Chassis Of Motorbikes

Electronic fuel injection system 

The electronic fuel injection system has four main components:
1) Fuel injector
2) ECU
3) Fuel Pump
4) Pressure release Valve

1. Fuel Injector and the ECU

Fuel injectors are small electronically or mechanically controlled valves which can open or close with in a fraction of seconds. These valves are used to supply fuel to the engines. The opening and closing time of fuel injectors can be controlled using Engine control module and hence the amount of fuel supply to the engines can be regulated. The cross sectional view of an electronic fuel injector can be seen below
Fuel injection system autoqurious

2. Fuel Pump

Fuel injection system also consists of a fuel supply pump, fitted below fuel tank.  This pump maintains the supply of fuel in fuel circuit at a constant rate. The fuel enters the injector from the top and is collected in cavity around the plunger. The Engine control unit (ECU), also called engine control module is an electronic control circuit which controls the amount of fuel supplied through Fuel Injector. 

3.Pressure Release Valve (PRV) 

The pump keeps on pumping the fuel uniformly in the fuel circuit , irrespective of whether the supply is needed or not. The opening and closing of the injector nozzle depends upon the riding requirements, and is non uniform. The difference in the rates of fuel pumping and spraying through nozzles can lead to abrupt increase in the pressure inside the fuel pipe and the injector. This may damage them or may lead to the leakage of fuel from the joints. To prevent all this, a Pressure Regulating Valve or PRV is provided in the fuel supply circuit. The PRV releases the pressure inside the fuel circuit whenever it exceeds the optimum values. Hence maintaining the fuel supply at constant pressure preventing any damage to fuel pipe or the injector. 

Fuel Injectors

The main components of a fuel injector are: 
1) Plunger
2) Return Spring and
3) Solenoid

The fuel pump keeps on supplying the fuel to the fuel injector. This fuel remains stored in the cavity around the plunger. The tip of the plunger is of needle shape. It sits on the orifice of spray tip, and blocks it completely. Till the plunger sits on the spray tip, fuel remains completely blocked inside the injector.
The solenoid acts as electromagnet. It can be magnetized or de magnetized as per the commands given by the ECU.

Autoqurious solenoid magnet in fuel injectors
Picture Representing The Magnetic Field Of A Solenoid

When the fuel supply is required, the ECU sends current supply to the solenoid and it gets magnetized. The magnetized solenoid now pulls up the plunger and the pressurised fuel in the injector is sprayed out.  The amount of fuel to be injected is controlled by varying the time for which the spray nozzle tip is open. The spray nozzle sprays very fine and minute fuel droplets , which can mix up very easily with the air and create a uniform mixture. This helps in uniform combustion of the fuel leading to improved efficiency and performance of the engine. 

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