Page 73 - CITS - WCS - Mechanical

WORKSHOP SCIENCE - CITS

Concept of HP, IHP, BHP & FHP – Related Calculations with Mechanical Efficiency. S.I. Unit of Power and
their Relations.
Simple terms BHP= IHP - FP, where FP is the frictional power loss, Frictional loss is directly proportional to
square of the engine speed. Indicated horse power (IHP) - It is the power generated in the engine cylinder and
received by the piston. It is the power developed in a cylinder without accounting frictional losses. Brake horse
power (BHP) - It is the power delivered by the engine at the end of the crankshaft.
ihp = P × L × A × N 33,000 where P = Mean indicated pressure, in psi L = Length of stroke, in feet A = Effective
area of the piston, in square inches N = Number of power strokes per minute 33,000 = Unit of power (one
horsepower), or foot pounds per minute.

In the International System of Units (SI), the unit of power is the watt (W), which is equal to one joule per second.
Horsepower (hp) is a unit of measurement of power (the rate at which work is done) It was originally defined
as 550 foot-pounds per second (ft-lb/s). A power level of 1 hp is approximately equivalent to746 watt s (W) or
0.746 kilowatts (kW). To convert from horsepower to watts, multiply by 746.mechanical efficiency, measure of
the effectiveness with which a mechanical system performs. It is usually the ratio of the power delivered by a
mechanical system to the power supplied to it, and, because of friction, this efficiency is always less than one.
There are three main ways of describing mechanical efficiency during exercise: gross efficiency, net efficiency
and mechanical efficiency.
If the useful output energy is 200 J and the total input energy is 400 J, then the mechanical efficiency is (200/400)
x 100 = 50%.

The equation that links efficiency and power can be expressed as Efficiency = Output power / Input power. The
rate at which energy is transferred is called power and the amount of energy that is usefully transferred is called
efficiency.

Assignment

1 m= 55 kg 4 m = 75 kg
a) s = 1.82 metres s = 100 metres
W = ______ joules t = 12 secs
b) s = 1.40 metres W = ______ Nm
W= ____ joules
P = ______ Watts
c) s = 0.85 metres
W =Joules

5 V = 1 m /min
3
2 t = 8 secs
H = 2 m
a) P = _____ Watts
b) P = _____ Watts η = 0.75
Power input = __ kW
c) P = _____ Watts

6 P = 12 kw
3 W = 1312.5 Joules s = 4 metres

m = 350 kg t = 20 secs
s = _____ metres m = ______ kg

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CITS : WCS - Mechanical - Exercise 5