# The mechanical efficiency of a single-cylinder four-stroke engine is 60%. The frictional power is estimated to be 30 kW. What is the indicated power?

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The mechanical efficiency of a single-cylinder four-stroke engine is 60%. The frictional power is estimated to be 30 kW. What is the indicated power?
1. 120 kW
2. 75 kW
3. 150 kW
4. 130 kW
5.

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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