THE ASSESSMENT OF ENGINE LOSSES DUE TO FRICTION AND LUBRICANT LIMITATIONS

A major area for improving the efficiency of spark ignition and diesel engines is a reduction of frictional losses. Existing literature on engine friction was used as a basis for estimating possible gains in engine fuel economy which look promising within the constraints of modern practice. The means considered include reduction in oil viscosity, increase in bearing and piston clearances, possible changes in piston and valve gear design, and reduction of pumping losses. Estimates indicate potential fuel consumption improvements of 3 to 4% for Otto-Cycle at wide open throttle, 7 to 9% for Otto-Cycle at road load, 4 to 5% for diesel at wide open throttle, and 6% for diesel at road-load. Much larger gains at road load could be obtained by using a stratified charge system which requires no air throttling. A literature search on techniques for measuring engine friction under firing conditions was also performed and various concepts employing Pressure-Volume Indicator Diagrams were assessed. Balanced pressure and direct pressure measurement in concert with instantaneous measurement of piston position provide the most reliable and repeatable assessment of engine efficiency. Pressure measurements in the range of 1/2 to 1% are achievable with digital processing techniques reducing dramatically the time and effort to generate P-V Indicator Diagrams.