TERMINOLOGY USED IN STEAM ENGINE

A line diagram of steam engine mechanism is shown in Fig. 5.2.

Cylinder Bore, D: It is the inside diameter of the cylinder

Piston stroke, L: It is the distance travelled by the piston from the cover end of the cylinder to the crank end of cylinder. L = 2r.

Single Acting: Steam is supplied on one side of piston only

Double acting: Steam is supplied on both sides of piston.

Dead centres: The position of piston within the cylinder, when the crank and connecting rod are in the same straight line.

Crank radius, r: It is the distance between the centre of crankshaft and centre of crank pin

Figure 5.2 Line diagram of a steam engine

Swept volume, V_S: It is the volume swept by the piston in one stroke

Mechanical Clearance, L_C: The mechanical clearance is the distance between the cylinder cover and inner dead centre position of the piston. It is specified as percentage of stroke length.

Volumetric Clearance, V_C: It is the volume between the cylinder cover and the piston at the inner dead centre position of piston.

Engine speed, N: It is measured in terms of revolutions of crankshaft per minute.

Piston speed: It is linear speed of the piston.

Compression Ratio, α: It is the fraction of stroke volume completed at the start of compression.

Expansion Ratio, r: It is the ratio of swept volume to col nine at cut-off of steam.

Cut off Ratio,: It is the ratio of volume at cut-off steam to the swept volume 

Mean Effective Pressure, P_m: It defined as that hypothetical constant pressure which will produce same work for the same piston displacement with the variable conditions of temperature pressure and volume.

Where card area = area of indicator diagram, card length = length of stroke in indicator diagram.

Eccentric Throw: It is the distance between the centre of eccentric and centre of crankshaft.

Valve Travel: It is the maximum distance travelled by the valve along one direction. It is equal to twice the eccentric throw.

Back pressure, p_b: The pressure of exhaust steam acting on the other side of the piston is known as back pressure.