DATA obtained with a cylinder of passenger-car-engine size are discussed. Compression ratios of from 5.7 to 15 to 1 have been explored rather completely with four types of combustion chamber. The investigation of this compression ratio range has included the determination of fuel economy at 1200 and 3000 rpm, with particular emphasis on part-load economy.
In order to make it possible to compare results over a wide range of compression ratios, fuel economy data are presented in terms of relative thermal efficiency. Knocking data are presented in terms of air density in the combustion chamber and in terms of an empirical equivalent of air density. It is shown that, over a considerable compression ratio range, the knock-limited combustion-chamber air density on isooctane or 80 octane-20 heptane is independent of compression ratio.
It is shown that turbulence has rather considerable effects in improving part-load economy and knock-limited performance. Turbulence is also shown to reduce engine severity.