EFFICIENCIES OF I.C ENGINES

The Efficiency of the engine is defined as the ratio of the work done by the engine to the energy supplied to an engine. The various efficiencies of an I.C Engines are given below,

a) Mechanical Efficiency ( N mech ) :

It is the ratio of the brake power to the Indicator power .

N mech = Brake Power / Indicated Power = BP / IP

b) Indicated Thermal Efficiency ( N it ) :

It is the ratio of indicated power to the heat supplied to an engine.

N it = Indicated Power / Heat Supplied

Heat Supplied per sec = ( mf * CV / 3600 ) in Kw

where mf = Mass of fuel consumed per hour

CV = Calorific Value of fuel kJ / kg .

Nit = IP / ( mf * CV / 3600 )

c) Brake Thermal Efficiency ( N bt ) :

It is the ratio of Brake power to the heat supplied to an engine.

Nbt = Brake Power / Heat Supplied

Nbt = BP / ( m f * CV / 3600 )

d) Relative Efficiency ( N r ) :

It is also known as efficiency ratio. It is the ratio of the indicated thermal efficiency to the air standard efficiency.

Nr = Indicated Thermal Efficiency / Air Standard Efficiency.

e) Volumetric Efficiency ( N v ) :

It is the ratio of actual volume of the charge admitted during the suction stroke to the swept volume of the piston.

Nv =Volume of Charge during suction stroke /Swept Volume of the piston.

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Mechinopedia For Mechanical Engineers

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