GOVERNING OF IC ENGINES

Governing is an action to control the fuel supply so that the engine runs at practically constant speed. When load on an engine increases the speed drops and when load decreases the speed increases. Thus to control the fluctuation in engine speed, fuel requirement increases during increasing load and fuel requirement decreases during decreasing load. Governors play an important role to control the supply of fuel according to load requirement. Following are the methods of governing of an IC engine

  Qualitative Governing

In this method, the amount of fuel entering the cylinder is varied by altering the stroke of the oil pump or by passing a part of fuel which would have otherwise been injected into the engine cylinder back to the oil tank or by delaying the closing of the suction valve in the fuel pump with the help of centrifugal governor. The supply of air remains constant but the supply of fuel is varied to control the quality of charge (air–fuel mixture). This method is widely used in oil engines besides being always used on two stroke cycle engines in which the air–fuel mixture has to be admitted to the engine cylinder to drive out the burnt charge of the previous cycle.

 Quantitative Governing

In this system, quality of charge remains constant but quantity of air–fuel mixture supplied to the engine is varied by means of centrifugal governors. Centrifugal governor regulates the throttle valve; whenever the engine starts running at higher speed due to decreasing load, the quantity of charge is reduced till the engine speed reaches to its normal speed. Similarly, whenever the engine runs at lower speed due to increasing load, the quantity of charge is increased to increase the speed to normal speed.

Hit and Miss Governing

This method is used for smaller gas engines. In this system, whenever the engine starts running at higher speed, some explosions are missed or omitted. This is done with the help of governor in which the inlet valve of fuel is closed and the explosions are omitted till the engine speed reaches its normal value. The disadvantage of this method is that there is uneven turning moment due to missing of explosions and requires heavy flywheel to overcome the uneven turning moment.