Steam engine in detail and governing of simple steam engine.

Steam Engine :-

A simple steam engine is one in which the expansion of steam is completed in one cylinder, and the compound steam engine is one in which the steam progressively expands in two or more cylinders. Compound engines may have the cylinders arranged in various ways such as tandem thin compound-cylinders placed one behind the other in line; angle compound-cylinders axes placed at right angle to one of another cross compound-cylinders arranged side by side etc. An engine may operate non-condensing, ie. exhausting er to atmosphere, or condensing i e, exhausting to a condenser In a single acting engine, steam is admitted only to one side of the piston, and in double-acting engine, steam is nis admitted alternately to each side of the piston A slide valve is a valve which controls the inlet and ed exhaust of steam by sliding across the ports. A poppet valve C is a disc, fitting a port which is raised or lowered for the d control of inlet and exhaust. A Corliss valve has a cylindrical r surface which oscillates through a small angle to open or close the port. In uniflow engine, piston itself acts as exhaust valve.

Fig:- indicator diagram of a simple steam engine. 

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Losses of available energy in the steam engine are due to following causes (arranged in the approximate order of magnitude of loss).

 (1) Initial or surface condensation

 (2) Incomplete expansion and early release (3) Throttling of steam flowing through partly open valves 

(4) Leakage of steam past piston and closed valves

 (5) Friction of moving parts

 (6) Heat loss by radiation and conduction (7) Compression and early admission. 

                               Initial condensation can be reduced by adopting late cut off and small expansion ratio, superheat, separate valves for admission and exhaust, short valve passages, high compression compounding, and uniflow principle. 

Governing of simple steam Engine 

(a)  Throttle Governing :-

       In this method, steam inlet pressure is varied by a throttle valve, and the cut-off ratio is kept constant. In the throttle governing, the steam consumption is directly proportional to the indicated horse power. Hence graph between consumption of steam and indicated horse power is a straight line known as Willan's line.

(b)  Cut-off Governing :-

    In it the ratio of cut off is varied and the admission pressure is kept constant. It is more efficient and economical.