The difference between Indicated Power (IP) and Brake Power (BO) is called frictional power which includes friction losses in the flywheel, governor, oil pump, water pump, and other moving parts. Therefore you can calculate frictional power (FP) by using the formula:

F.P = I.P - B.P

There are different methods of measurement of friction power(F.P) as follows:

1. Measuring I.P and B.P

2.Morse test

3. Willan's line method

4. Motoring test.

## Measurement of friction power by Willan's line method:

Willan's line method |

1. In this article, we are going to know more about the measurement of friction power by Willan's line method. Willan's line method is also known as fuel rate extrapolation method. In this method, we draw a graph where we take brake power (B.P)(kW) on X-axis and fuel flow rate (kg/hr) on Y-axis on a condition that engine is running at a constant speed.

2. As shown in the figure, the graph is anticipated back to zero fuel flow rate of zero fuel where it cuts at point A on negative X-axis.

3. Point A on the negative X-axis shows the friction power at the same speed on the engine. When break power becomes zero, then fuel consumption at the same power represents the fuel consumed to overcome the friction loss of the engine.

4. As per the graph, variation in the fuel flow rate and brake power is linear. It results in the anticipation of the straight part of the main curve as a negative crossing on X-axis at zero fuel flow rate will represent the friction power (F.P).

2. As shown in the figure, the graph is anticipated back to zero fuel flow rate of zero fuel where it cuts at point A on negative X-axis.

3. Point A on the negative X-axis shows the friction power at the same speed on the engine. When break power becomes zero, then fuel consumption at the same power represents the fuel consumed to overcome the friction loss of the engine.

4. As per the graph, variation in the fuel flow rate and brake power is linear. It results in the anticipation of the straight part of the main curve as a negative crossing on X-axis at zero fuel flow rate will represent the friction power (F.P).

## Limitations of Willan's line method of measurement of friction power:

1. Willan's line method is only used in compression ignition (C.I) engine. It is not applicable in S.I engine.

2. Friction power given by this method is approximate.

3. Friction power changes while an increase in engine speed. That's why engine should run at a constant speed throughout the Willan's line test

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