Affiliation:
1. University of Salford, Salford 5.
2. Senior Lecturer in Mechanical Engineering, Dept of Mechanical Engineering, University of Manchester Institute of Science and Technology, P.O. Box 88, Sackville Street, Manchester, M60 1QD.
Abstract
This paper reports on the effect of position and timing of gas admission on the performance of a spark-ignition engine using methane. The investigation was aimed at exploring the effect of design limitations experienced with turbocharged medium-speed engines. Performance was judged on the criteria of optimum specific fuel consumption combined with minimum cyclic dispersion. Results were obtained at a fixed fuel consumption and mostly at fixed air/gas ratios and are not, therefore, necessarily directly applicable to commercial engines. For near stoichiometric air/gas ratios, optimum performance was obtained most easily by early and prolonged gas admission. Better thermal efficiency was obtained with weak mixtures, about 80 per cent of stoichiometric, and optimum gas admission was generally less obvious. Performance patterns did not vary consistently with gas admission timing; they improved or deteriorated with late gas admission, depending on the type of air inlet valve—presumably owing to air motion and gas/air mixing in the cylinder. From the results obtained, it seems probable that cyclic dispersion was minimal when the mixture around the spark was at, or near, stoichiometric and was most easily achieved by perfect mixing when the overall mixture was near stoichiometric.