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Steam engine works with steam made in the boiler. It converts heat energy of steam into mechanical motion. Then it is converted into electrical energy. It is achieved  with the help of a generator coupled with the steam engine.

   Cycle used

The Rankine cycle is used in the analysis of steam engine. The Rankine cycle is a modified Carnot Cycle and is thus most efficient. Thomas Savery , Thomas Newcomen and James Watt made the best contribution in the invention and improvement of the steam engine.

    Advantages of a steam engine

It made an industrial revolution. Even today steam engine is the most widely used method of electricity generation. It has  high efficiency. The limitations of a steam engine are many.


The efficiency of Carnot Cycle is

η= [ (Th-Tl)/Th] x 100

The efficiency of the Rankine cycle is

η=[(h1—h2)/(h1—hl)] x 100

The efficiency of the modified Rankine cycle is

η =[(p1v1+(u1-u2)p3v2)/(h1—hl)] x 100

  Mean effective pressure

he mean effective pressure is a constant pressure which acts on the piston throughout the stroke will produce the same work as is being produced under actual operating conditions.

Mean effective pressure with zero clearance volume is

pm = (p1/re)(1+lnre -pb)

Mean effective pressure with clearance volume, Vc is given by

pm = [(p1/re)(1+lnre) -pbV2-(p1-p2)Vc]/Vs

  Missing quantity

Missing quantity in a steam engine is contributed by the followings:

  • Leakage
  • Condensation of steam in the condenser

Steps to reduce the missing quantity

  • Use compound compression
  • Provide efficient jacket to the cylinder

   Specific steam consumption

It means steam consumed per hour per indicated power produced.

    Willan’s law of steam consumption

Steam consumption by a steam engine with throttled governor is directly proportional to the indicated power.


  1. m. = a x ip +b

Where b is the intercept on y axis at no lad condition

  1. m. is the stem consumption in kg/h

a and b are constants

ip is the indicated power produced per h