Engine Performance
Production of power is the primary function of an engine. In order to determine
how well an engine is performing, or to compare the performance of one engine with
that of other engines, it is necessary to measure various results and express them in
standard engineering terms and parameters, which can be used as an indicator of
performance. This chapter deals with various terms like, displacement, compression
ratio, specific fuel consumption, power, efficiencies etc. related to engine specifica-
tions and performance.
4.1.
Some Terms Pertaining to the Engine
Top Dead Centre (TDC) is the farthest point of forward travel of the piston in the cylinder.
Bottom Dead Centre (BDC) is the lowest point of backward travel of the piston in the
cylinder.
Stroke (I) is the distance, between TDC and BDC, travelled by the piston in the cylinder.
One forward and backward strokes of the piston make one revolution of the crankshaft.
Bore id) is the inside diameter of the cylinder.
Throw is the distance between the centre of crankshaft main bearing to the centre of the
crank pin or connecting rod bearing. The throw is the half of the stroke length.
Clearance Volume (vc) is the volume of cylinder above the piston when the piston is at
TDC.
Piston Displacement (dp) is the volume displaced by the piston between TDC and BDC.
Therefore, dp = (7i/4)/d2Z, where d is cylinder diameter, and I is stroke length.
Total Volume (vt) is the volume of the cylinder above piston when the piston is at BDC.
Therefore, vt = vc + dp
Compression Ration (r) is the ratio of total volume of the cylinder to clearance volume,
Therefore, r = vt/vc
