Diesel engines are commonly used in various applications, including locomotives in the railways. The method of governing employed in a diesel engine refers to the control mechanism used to regulate the speed and power output of the engine. There are several methods of governing, but for diesel engines, the method employed is quality governing.

Quality Governing:
Quality governing is a method of engine control that primarily focuses on controlling the fuel-air mixture entering the engine cylinders. In a diesel engine, the air and fuel are mixed inside the combustion chamber during the compression stroke. The fuel injection system injects the fuel into the combustion chamber in precise quantities and at specific timings.

In quality governing, the speed and power output of the engine are regulated by controlling the quantity of fuel injected into the combustion chamber. By adjusting the fuel injection timing and duration, the amount of fuel entering the cylinders can be varied, which directly affects the power output of the engine.

Other Governing Methods:
a) Quantity Governing: Quantity governing, also known as throttling governing, involves controlling the engine speed and power output by regulating the quantity of air entering the engine. This method is commonly used in gasoline engines, where the air-fuel mixture is controlled by a throttle valve.

b) Hit and Miss Governing: Hit and miss governing is a method used in older engines, where the fuel supply to the engine is intermittently cut off to regulate the speed and power output. This method relies on a mechanical mechanism that opens and closes the fuel supply based on the engine's speed.

Conclusion:
In conclusion, for diesel engines, the method of governing employed is quality governing. This method focuses on controlling the fuel-air mixture by adjusting the quantity of fuel injected into the combustion chamber. By regulating the fuel injection timing and duration, the engine's speed and power output can be effectively controlled. Other governing methods like quantity governing and hit and miss governing are commonly used in gasoline engines or older engines, respectively.