I.C Engines : Types, Working of Governing System | Advantage and Disadvantages


I.C engine


Purpose Of Governing of I.C. Engine: 


When the load on the engine increases, then its speed decreases. When the load on the engine decreases its speed increases. There are certain loads connected with l.C engines where constant speed running of these loads arc necessary. For example, generally a pump and compressor. Hence, I. C. engine used as a prime mover for these types of loads must run at a constant speed. A governor is fitted on the engine for that purpose.

The function of the governer is stated as under:


"A governor is used to control the fluctuation of the speed of the engine within prescribed limits with a variation of the load from no load to maximum load on the engine over a period of time.

The process of keeping speed constant is known as Governing. 

Methods of Governing : 

The various methods are used for governing of I. C. Engines such as :
  1. Qualitative Governing 
  2. Quantitative Governing 
  3. Hit and miss Governing 

1. Qualitative Governing : 

In this method of governing, the supply of air is kept constant while the supply of fuel is varied according to the load on the engine. In short, the air-fuel ratio is changed from cycle to cycle. 

In the case of gas engines, it can be achieved easily by changing the area of flow. 
This can be changed by lifting the gas valve with the help of the link mechanism operated by the centrifugal governor. Or it can be controlled by operating a throttle valve in the gas passages with the help of a governor. 

In the case of C. I. engines, spring-loaded mechanical governor or hydraulic governor controls the amount of fuel varied. The system may vary the quantity of fuel injected to the cylinder either by varying the stroke of the fuel pump or it may pass part of the fuel back to the fuel tank or it may delay the closing action of the fuel pump. 

2. Quantitative Governing : 

In this type of governing, air and fuel ratio is kept constant. On every load, this ratio is remaining constant. But for different loads, the quantity of air-fuel supplied is changed. On a higher load, less quantity of the mixture is supplied. Hence the speed is remaining constant. The pressure in the cylinder also changes because of this. 

In Petrol engine and in a large gas engine, this type of governing is used. In a Petrol engine, quantity is being controlled by the throttle valve. This throttle valve is operated by the accelerator. The accelerator is doing quantity governing. Due to constant air-fuel ratio, this type of governing is also very effective on lower load. In the case of petrol and gas engine (except automobiles) the throttle valve opening and closing are controlled with the help of centrifugal governor. 

3. Hit and Miss Governing : 

In this method, when the engine speed exceeds the prescribed limit due to the decrease in load on the engine, the fuel supply is cut-off to the engine in one or more number of cycles.

Hit and Miss Governing
Hit and Miss Governing 

Because of this, the engines miss the explosion during such cycles. It will be an idle cycle until the engine achieves its mean equilibrium speed. In the case of gas engines, the gas supply is cut off. In the case of Diesel engines, the fuel supply by the fuel injector or is cut off by putting off the plunger of fuel pump out of action. The method used for the gas engine only is described here. 

This system shown in the figure is used for gas engines. At normal speed, the gas valve is lifted from its seat in every stroke. The gas is then supplied to the engine. The lift of the valve is obtained with the help of cam and lever (EGF) as shown in fig. The end of E is lifted once in two revolutions of the crank-shaft. When the speed of the engine increases beyond the certain limit of mean speed, due to a decrease in load on the engines, the balls of the centrifugal governor will fly out due to increased centrifugal force. Hence sleeve A lifts in an upward direction. This operates the bell crank lever ABC. Due to that, link CD and hence D moves to the right. 

It prevents the lifting of the gas valve from its valve seat. Hence the gas supply to the engine is cut off when the speed of the engine drops, the valve is again operated due to the movement the link CD and point D to the left. This is due to the sleeve movement in the downward direction. 

Advantages and disadvantages of Hit and Miss-governing : 


Advantages :
  1. The method gives better fuel economy at low loads on the engine. 

Disadvantages : 

  1. The engine needs a bigger size of the flywheel since the fluctuation of energy increases during the period of a commission of the power stroke. 
  2. The engine is subjected to large variations in speed during the cycle. 
  3. This method also lowers slightly the engine efficiency by increasing the proportion of ideal Stroke to working stroke. 

I.C Engines : Types, Working of Governing System | Advantage and Disadvantages I.C Engines : Types, Working of Governing System | Advantage and Disadvantages Reviewed by Harish on April 28, 2020 Rating: 5

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