The Ideal Performance of Petrol Engines

Abstract

A method of calculating the ideal thermal efficiencies of petrol engines is described which may be of value when thermodynamic charts for the particular fuels and mixture strengths under consideration are not available. Results of such calculations are given for engines running on octane, benzene, and ethyl-alcohol at compression ratios between 4/1 and 9/1 and at various mixture strengths. From the relationships between thermal efficiency, specific fuel consumption, volumetric efficiency, mixture strength, and indicated mean effective pressure, new charts based upon the familiar “consumption loop” diagram are developed. These charts yield information not generally obtained from the consumption loop diagrams, and the volumetric efficiency of the engine may be determined. The ideal consumption loops based upon a standard volumetric efficiency are included on the charts, and these values are readily corrected to the actual engine conditions by a simple construction. This enables a direct comparison between actual and ideal engine performance to be made, from which the relative merits of engines running under widely diverse conditions can be determined.