Correct Answer - Option 2 : 75 kW
Concept:
Friction Power:
It is the power loss in overcoming the friction between piston and cylinder walls, between the crankshaft and camshaft and their bearings, etc.
It is the difference between Indicated power and Brake power.
F.P = I.P - B.P
∴ B.P = I.P - F.P
Mechanical Efficiency:
It is the ratio of brake power to indicated power.
\({η _m} = \frac{{B.P}}{{I.P}} = \frac{{{η _{bth}}}}{{{η _{ith}}}}\)
Calculation:
Given:
ηm = 60% = 0.6, FP = 30 kW
Mechanical Efficiency:
\({η _m} = \frac{{B.P}}{{I.P}} \)
\({η _m} = \frac{{I.P\;-\;F.P}}{{I.P}} \)
\(0.6 = \frac{{I.P\;-\;30}}{{I.P}} \)
I.P - 0.6I.P = 30
0.4I.P = 30
I.P = 75 kW