Research On Combustion Stability Of SI Gas Fuel Engine

With the intensification of the global energy crisis, alternative fuels research is more and more critical to our country’s energy security. Therefore, Gas engine has gradually become the new frontier in this field.Unlike gasoline, fuel gas is prone to have combustion stability problems, so a systematic and deep-going research on gas engine combustion characteristics and stability is of very important theoretical significance and practical value to improve fuel-economy, dynamic performance as well as reduce emissions of fuel gas engine.In this paper, gas fuel engine is taken as the study subject, by applying time-average method in the intake process and RANS/LES combination model in the combustion process.an ignition model was well developed. Meanwhile, by using Weller combustion model which describes the structural parameters of the flame front, the three-dimensional simulation model for gas fueled engines was established. On this basis, as for the substantial growth of computing time caused by using large eddy method, a parallel computing platform was built on the supercomputer at the Chinese Academy of Sciences. When performing Domain Decomposition load balancing algorithm, the results show that excessive computing subregions will result in a sharp growth of the communications, which lead to the conclusion that reasonable choice of subregions number can get the higher parallel speedup and parallel efficiency.On the other hand, by taking Fuel gas engine and the constant volume bomb as the study subject, the accuracy of the above-mentioned model characterizing the intake process is verified. On this basis, through numerical simulation, after comparing the characterizations of the eddy and turbulence fields, we find that other than time-average method, large-eddy method can solve the instantaneous value of grid-scale eddies directly, and the resolution of the eddies increased with the decrease of the grid scale. In the meantime, through analyzing the interaction of large-scale eddies and flame structure, we got an ultimate value of eddy strength. When the strength of the eddy is above that value, the local flame surface folds degree will be reduced, while the flame stability increasing. Besides, according to the research on Markstein length and the turbulence strain rate, when Markstein length is less than0, the folds degree of the flame front increases, the increase rate is related to the local turbulence strain rate; when the Markstein length is greater than0,the opposite effect will appear. This paper has also discussed the influences of different ignition parameters, excess air ratio, and speed, intake pressure on the combustion process and flame stability. This article is supported by the National Natural Science Foundation funded project "basic research on low calorific value gas fuel engine combustion stability". Project number:50676008.