Historically, a succession of thermodynamic processes has been used to idealize the operating cycles of internal combustion engines. In this study, the 256 possible combinations of four reversible processes—isentropic, isothermal, isochoric, and isobaric—are surveyed in search of cycles promising superior thermal efficiency. Regenerative cycles are excluded. The established concept of the air-standard cycle, which mimics the internal combustion engine as a closed-cycle heat engine, is used to narrow the field systematically. The approach relies primarily on graphical interpretation of approximate temperature-entropy diagrams and is qualitative only. In addition to identifying the cycles offering the greatest efficiency potential, the compromise between thermal efficiency and mean effective pressure is addressed.

Lauck, F., Uyehara, O. A., and Myers, P. S., 1963, “An Engineering Evaluation of Energy Conversion Devices,” SAE Trans., 71, Paper 630466.
Heywood, J. B., 1988, Internal Combustion Engine Fundamentals, McGraw-Hill, New York.
Flynn, P. F., Hoag, K. L., Kamel, M. M., and Primus, R. J., 1984, “A New Perspective on Diesel Engine Evaluation Based On Second Law Analysis,” SAE Paper 840032.
Caton, J. A., 2000, “Operating Characteristics Using the Second Law of Thermodynamics: Effects of Speed and Load,” SAE Paper 2000-01-0952.
Lichty, L. C., 1939, Internal Combustion Engines, McGraw-Hill Book Company, New York.
Jennings, B. F., and Obert, E. F., 1944, Internal Combustion Engines: Analysis and Practice, International Textbook Company, Scranton, PA.
Stone, R., 1999, Introduction to Internal Combustion Engines, Society of Automotive Engineers, Warrendale, PA.
Luria, D., Taitel, Y., and Stotter, A., 1982, “The Otto-Atkinson Engine—A New Concept in Automotive Economy,” SAE Paper 820362.
You do not currently have access to this content.