Measurement Of Friction Horse Power

Introduction:

The difference between indicated power and the brake power output of an engine is the friction power. Almost invariably, the difference between a good engine and a bad engine is due to difference between their frictional losses.

Methods of determining friction horsepower:

The friction force power of an engine is determined by the following methods :

(a) Willan’s line method.

(b) Morse test.

(d) Difference between ip and bp.

Willan's Line Method or Fuel Rate Extrapolation

In this method, gross fuel consumption vs. bp at a constant speed is plotted and the graph is extrapolated back to zero fuel consumption as illustrated in Figure.
The point where this graph cuts the bp axis in an indication of the friction power of the engine at that speed. This negative work represents the combined loss due to mechanical friction, pumping and blowby. The test is applicable only to compression ignition engines.
The main drawback of this method is the long distance to be extrapolated from data measured between 5 and 40% load towards the zero line of fuel input.
The directional margin of error is rather wide because of the graph which may not be a straight line many times.

Morse Test

The Morse test is applicable only to multicylinder engines.

In this test, the engine is first run at the required speed and the output is measured.
Then, one cylinder is cut out by short circuiting the spark plug or by disconnecting the injector as the case may be.
Under this condition all other cylinders ‘motor’ this cut-out cylinder. The output is measured by keeping the speed constant at its original value.
The difference in the outputs is a measure of the indicated horse power of the cut-out cylinder.
Thus, for each cylinder the ip is obtained and is added together to find the total ip of the engine.

Since, the engine is running at the same speed it is quite reasonable to assume that fhp remains constant.

By subtracting bpn from this, fp of the engine can be obtained.

Motoring Test

In the motoring test, the engine is first run up to the desired speed by its own power and allowed to remain at the given speed and load conditions for some time so that oil, water, and engine component temperatures reach stable conditions.
The power of the engine during this period is absorbed by a swinging field type electric dynamometer, which is most suitable for this test.
The fuel supply is then cut-off and by suitable electric-switching devices the dynamometer is converted to run as a motor to drive for ‘motor’ the engine at the same speed at which it was previously running