Governor Vs Flywheel

Function of Governor

The function of a governor is to automatically maintain the speed of an engine within specified limits whenever there is a variation of load.
If the load on the engine increases, its speed decreases. So it becomes necessary to increase the fuel supply by opening the throttle valve. On the other hand, when the load on the engine decreases, its speed increases and the fuel supply is to be decreased by closing the throttle valve. The supply of fuel is regulated by means of throttle valve which is operated by the governor through a mechanism.
Thus the governor keeps the speed of the engine within certain limits by regulating the fuel supply as per load requirements.
In petrol engines, governor manipulates the throttle valve and in diesel engines, it manipulates the fuel pump.

Illustration

The governor is an automatic speed control mechanism. Consider a diesel engine (or steam turbine) driving an a.c. generator in a diesel (or steam) power plant. Suppose, there is a need to keep the engine connected to the a.c. generator at a constant speed for a specific grid frequency of 50Hz. But, in practice, demand on the generator may vary from time to time (as the usage varies from day-time to night-time). This situation demands automatic control of fuel (or steam) to the diesel engine (or steam turbine) to keep the generator speed constant. If the grid frequency varies too much from its designed value, a catastrophic failure of equipment connected to the grid will occur. To prevent such occurrence, governor is used to automatically control the fuel (or steam) supply to the engine (or turbine) depending on the load variations.

Due to this reason, the governor is known to be a mechanical feedback control device.

The governor regulates the mean speed of an engine whenever there are load variations, whereas the flywheel reduces the fluctuations of speed caused by the fluctuation of the engine turning moment during each cycle of operation.

Table presents the comparison between the function of governor and that of flywheel.

Table Governor Vs Flywheel

S.No	Governor	Flywheel
1	The function of a governor is to regulate the mean speed of an engine, when there are variations in the load.	The function of a flywheel is to reduce the fluctuations of speed caused by the fluctuation of the engine turning moment during each cycle of operation.
2	It is provided on prime movers such as engines and turbines.	It is provided on engines and fabricating machines viz., rolling mills, punching machines, shear machines, presses, etc.
3	It works intermittently, i.e., only when there is change in the load.	It works continuously from cycle to cycle.
4	It has no influence over cyclic speed fluctuation.	It has no influence on mean speed of the prime mover.
5	Mathematically, a governor controls δN.	Mathematically, a flywheel controls $\frac{\delta \mathrm{N}}{\delta t}$