Power Plant Engineering

240 POWER PLANT ENGINEERING

where Pm = LM.E.P. in kg/cm^2

L = Length of stroke in metres

A = Piston areas in cm^2

N = Speed in R.P.M.

n = Number of cylinders

k = 1 for two stroke engine

= 2 for four stroke engine.

8.8.3 Brake Horse Power (B.H.P.)

Brake horse power is defined as the net power available at the crankshaft. It is found by measur-
ing the output torque with a dynamometer.

B.H.P. =

2NT

4500

Π

where T = Torque in kg.m.

N = Speed in R.P.NT.

8.8.4 Frictional Horse Power (F.H.P.)

The difference of I.H.P. and B.H.P. is called F.H.P. It is utilized in overcoming frictional resist-

ance of rotating and sliding parts of the engine.

F.H.P. = I.H.P. – B.H.P.

8.8.5 INDICATED THERMAL EFFICIENCY (ηηηηηi)

It is defined as the ratio of indicated work to thermal input.

ηi =

(I.H.P. 4500)

(W Cv J)

×

××

where W = Weight of fuel supplied in kg per minute.

CV = Calorific value of fuel oil in kcal/kg.

J = Joules equivalent = 427.

8.8.6 Brake Thermal Efficiency (Overall Efficiency)

It is defined as the ratio of brake output to thermal input.

ηb =

(B.H.P. 4500)

(W C J)

×

××v

8.8.7 MECHANICAL EFFICIENCY (ηηηηηm)

It is defined as the ratio of B.H.P. to L.H.P. Therefore,

ηm =

B.H.P.

L.H.P.