RELIABLE predictions of the improvements in efficiency that can be obtained by raising the compression ratio of spark-ignition engines are of obvious value in the long-range planning of both the automotive and petroleum industries.
New equipment and techniques were developed to measure indicated power by obtaining accurate pressure-volume measurements in each cylinder, thus permitting true friction to be determined as the difference between the indicated power of all cylinders and the simultaneously measured brake power. Tests were conducted on a 4-cylinder engine at compression ratios of 7/1 and 12/1.
Results demonstrate the inaccuracies of the conventional “motoring test” method of measuring friction, reveal the effect of changes in compression ratio on true friction, yield conclusive evidence that the potential gains in thermal efficiency from increased compression ratios are greater on both an indicated and brake basis than earlier studies indicated; and establish empirical thermodynamic relationships which provide a convenient and accurate means of predicting these potential gains in efficiency.
