Governor In Fuel Supply

In the case of a compression-ignition engine, the governor is there to prevent the engine accelerating without limit and blowing itself apart.

The governor mechanism was used on the stationary reciprocating steam engine as a method of maintaining near-constant speed despite fluctuating load.

IS GOVRNER ONLY USED IN STATIONARY ENGINE AREN"T THEY USED IN MOVING ENGINES

Governors are used in both stationary and mobile engines. A governor can either serve to limit engine speed to a particular value, or to hold a particular speed. Common examples:

Truck engines are often governed to prevent overspeeding, and consequent engine damage.

Modern auto engines often have rev-limiters built into the fuel injection systems,for the same function.

Generators have governors to keep the engine running at a constant speed, so the the frequency of the generated power is constant.

Lawn mowers have simple governors to keep the engine at a safe speed (both for the engine's safety, and to lower velocity of projectiles) and to eliminate a control that would otherwise have to be set by the operator.

Re throttle valve: generally diesels do not have one, so the governor must act on fuel flow. In spark ignition engines, the throttle is used as the governing control -- except in the case of rev-limiters, where fuel flow, ignition or both can be shut off.

cant we limit the fuel supply to the engine by just turning the valves acording to our needs like in case of petrol engine where we control the butterfly valve .why should we use governer to control the speed of the engine according to the load requirements.its just makes tings complex.

Yes, you can do it just by turning the valves, in a way. For instance, in an older petrol car (1960's) there was nothing to control engine speed other than the throttle. With a light load on the engine (such as in first gear on a level road) it was very easy to exceed the engine's redline, possibly destroying the engine, or parts of it from contact of pistons and valves, excessive acceleration stresses, etc. On some engines (generally low to medium performance) valve float (a condition in which the valve train can no longer follow the camshaft profile, due to inertia loads being higher than the force applied by the valve springs) could prevent catastrophic damage to an engine -- in other words, when the valves were floating, the engine's output fell off, protecting itself. But in other engines valve float would result in collisions between the pistons and valves, potentially destroying the engine. So in either case, a careful driver would just keep an eye on the tachometer, or simply listen to tell when an engine was running too fast. The governor on a truck engine of that day just acted like an automated, diligent driver, preventing overspeed even if the driver was not so careful.

But with things like a generator, an operator could not keep up with the changes in load quickly enough, and the engine would speed up and slow down constantly. Imagine a generator feeding just one house. Every time the electric hot water heater cycled on, the generator would slow down from the load. Both voltage and frequency would drop, and motors in the house would slow down, lights would dim, etc. So the governor does just what a diligent operator would do: increase the throttle setting to bring the speed back up. It's just that a governor can do it much faster, and never has to stop to take a bathroom break.

Considering their important function, generators are often remarkably simple. Those in a lawn mower often have only two or three key parts.

In a marine C.I engine where engine load changes frequently due to sea conditions we can't use throttle valve to control the fuel supply. Ships run over long distances at a steady speed where auto manouvering is followed. In this case governor maintains steady R.P.M of engine according to the fluctuating loads. This applys to generators also where frequency(R.P.M) is maintained irrespective of load.