Search Results

The limits on reciprocating engine performance are set by the idealized constant-volume cycle. Heretofore, fuel-air cycles have been computed by tracing them out on thermodynamic charts -- a long and tedious process. By programming the thermodynamic characteristics of the fuel-air media and the cycle processes on a digital computer, it has been possible to compute the characteristics of fuel-air cycles over a wide range of fuel-air ratios, compression ratios, and initial conditions and present the results in graphic form. The results are used to compute equivalent theoretical cycles for comparison with real engine performance. The ratio of actual to ideal thermodynamic performance of engines can be computed using equivalent cycles. The method to evaluate engine performance is illustrated, and a number of actual cycles are compared with their equivalent fuel-air cycles, and losses are considered.

THIS PAPER PRESENTS a theoretical analysis of the ideal adiabatic Otto cycle engine. The analysis was made to examine the influence of compression ratio and dissociation on engine thermal efficiency over an extreme range of compression ratios (that is, 4–300) to see if chemical dissociation could limit Otto cycle engine thermal efficiency. Assuming isooctane, benzene, ethyl alcohol, and nitromethane to be the fuels being consumed, the effects of compression ratio and mixture strength on the thermodynamic properties and equilibrium species concentration of the working fluid at every step in the ideal Otto cycle were computed. The calculations were made using a mathematical model of the ideal adiabatic engine which had been programmed to an IBM 704 digital computer. With the model, the effect of compression ratio on engine thermal efficiency was calculated over a wide range of operating conditions.