Performance of a spark ignition engine under the effect of friction using a gas mixture model

This paper presents the effect of friction on the performance of a spark ignition engine using a gas mixture as the working fluid. The results were compared to a frictionless engine. Engine parameters that were studied include equivalence ratio, engine speed, break mean effective pressure (BMEP), and cycle thermal efficiency. It was found for the frictionless engine operating at 6000 rev min^-1 and stoichiometric air-fuel mixture that BMEP and efficiency were about 14 bar and 36% respectively. On the other hand, when friction is included under the same condition BMEP and efficiency were about 10 bar and 27% respectively. However, at lower engine speed and equivalence ratio, the deviations were much smaller. Therefore, it is more realistic to consider the effect of friction using the gas mixture model instead of air as the working fluid for the analysis of spark ignition engines, especially when running at high speeds and/or rich mixtures.