PISTON-CYLINDER ARRANGEMENT

The piston-cylinder arrangement is shown in Fig. 9.1. The various definitions are:

Bore (d): is the cylinder or piston diameter.

Stroke (L): is the distance moved by the piston in one direction. It is equal to twice the crank radius.

Figure 9.1 Piston-cylinder arrangement

Top Dead centre (T.D.C.): is the extreme position of the piston near to the head of cylinder. It is also called inner dead centre (I.D.C) position

Bottom Dead centre (B.D.C.): is the extreme position of the piston opposite to the head of
cylinder. It is also called outer dead centre (O.D.C) position

L = T.D.C. − B.D.C.

Clearance Volume (V_c): is the minimum volume of clearance between the cylinder head and the piston at T.D.C. position.

Swept Volume (V_s): is the maximum volume swept by the piston in moving from T.D.C. to B.D.C. position or vice versa. 

Cylinder Volume (V): is the sum of clearance volume and swept volume

V = V_c +V_s

Compression ratio (r): is the ratio of cylinder volume to the clearance volume. Thus

Clearance ratio (c): is the ratio of clearance volume to stroke volume. Thus

Mean effective pressure (p_m): is the average pressure which, if acted on the piston during the entire power or outward stroke, would produce the same work output as the network output for the actual cyclic process. Thus

Work done per cycle, 

Work done per minute = p_m L An

Where 

n = number of strokes per minute.

= N, for two stroke engines.

= N/2, for four stroke engines.

N = rpm

where p_m is in kPa.