It is a method to determine the frictional power of an engine. In this method, gross fuel consumption v’s brake power at a constant speed is plotted and the graph is extrapolated back to zero fuel consumption as shown in Fig. 11.1. The point where this graph cuts the BP axis is an indication of the frictional power of the engine at that speed. The test is applicable to only compression ignition engines.
Figure 11.1 Willan’s line method
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