Influence of Combustion Efficiency on the Operation of Spark Ignition Engines Fueled with Methane and Hydrogen Investigated in a Quasi-Dimensional Simulation Framework

Within the context of widening application of numerical simulations for shortening engine development times, the present work covers the issue of quasi-dimensional simulation of spark ignition engines. Multi-fuel operation was the main goal of the study, with the analysis of methane and its blends with hydrogen; gasoline was also considered as a reference case. Data recorded on two engines with practically the same geometry, was used for calibrating the model. The first power unit was of commercial derivation for small applications, while the second one featured optical accessibility through the piston crown. The relative difference between the two engines allowed the top-land region crevice to be identified as the major contributor to overall combustion evolution, especially during its late stages. Using an in-cylinder pressure based method, compression ratio and blow-by losses were determined, and differences between fuel types were recognized in the sense of oxygen utilization rates. Then, the effects of the latter parameter were investigated with regard to model calibration. It was found that the entrainment coefficient was practically insensitive to combustion efficiency, while the characteristic length was closely linked to its modification. An important decrease was observed in the characteristic length when oxidation completeness was lower. Hydrogen addition to methane was found to improve combustion efficiency, most likely linked to its higher reactivity. These results emphasize the importance of incorporating fuel effects in quasi-dimensional simulation and given insight into how specific properties could be integrated for correct interpretation of results.