Estimate from fuel-air cycle results the indicated fuel conversion efficiency, the indicated mean effective pressure, and the maximum indicated power (in kilowatts) at wide-open throttle of these two four-stroke cycle spark-ignition engines:
A six-cylinder engine with a 9.2cm bore, 9-cm stroke, compression ratio of 7, operated at an equivalence ratio of 0.8
A six-cylinder engine with an 8.3-cm bore, 8-cm stroke, compression ratio of
10, operated at an equivalence ratio of 1.
Assume that actual indicated engine efficiency is 0.8 times the appropriate fuel-air cycle efficiency. The inlet manifold pressure is close to 1 atmosphere. The maximum permitted value of the mean piston speed is 15 m/s. Briefly summarize the reasons why:
(a) The efficiency of these two engines is approximately the same despite their different compression ratios.
(b) The maximum power of the smaller displacement engine is approximately the same as that of the larger displacement engine.