Efficiency Of Steam Engine

Efficiency Of Steam Engine


Efficiency of steam engine is defined as the ratio of work done to the energy supplied to an engine.In this page, we will discuss different efficiency of steam engine and efficiency calculation of steam engine.


Mechanical Efficiency Of Steam Engine:-


Mechanical efficiency of steam engine is the ratio of break power(B.P.) to the indicated power(I.P.).It is expressed as:


mechanical efficiency of steam engine


Mechanical efficiency of steam engine is always less than unity due to some power loss to overcome the engine friction and indicated power is always greater than unity.So frictional power(F.P.) is the difference between indicated power (I.P.) and break power (B.P.).


fractional power of steam engine


Overall Efficiency Of Steam Engine:-


Overall efficiency of steam engine is the ratio of the work obtained at the crank shaft in a given time to the energy supplied by fuel during the same time.


Let, mf = Mass of fuel burnt in kg per hour, and


C = Calorific value of fuel in kJ/kg of fuel.


So, Energy supplied by fuel/min,



and work obtained at the crank shaft/min



Then, overall efficiency,


overall efficiency of steam engine

Indicated Thermal Efficiency Of Steam Engine:-


Indicated thermal effciency of steam engine is the ratio of heat equivalent of indicated power to the energy in the steam supplied per minute.


Let, ms = Mass of steam used in kg/min,


h1 = Enthalpy or total heat of steam supplied at admission pressure p1 in kJ/kg (from steam tables)


hfb = Enthalpy or sensible heat of feed water at back pressure pb in kJ/kg (from steam stable)


Energy in steam supplied/min,



Heat equivalent to I.P.



So, Indicated thermal-efficiency is


Indicated thermal efficiency of steam engine


When only thermal efficiency is mentioned in steam engine without talking about 'break' or 'indicated',then it is mentioned indicated thermal efficiency.


Brake Thermal Efficiency Of Steam Engine:-


Brake thermal efficiency is the ratio of the heat equivalent of brake power to the energy in the steam supplied per minute.


Mathematically brake thermal efficiency is,


Brake thermal efficiency of steam engine


Relative Efficiency Of Steam Engine:-


Relative efficiency is the ratio of thermal efficiency to the Rankine efficiency.It is also known as efficiency ratio.


Mathemetically Relative efficiency of steam engine is,


Relative efficiency of steam engine







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