Modelling of Gasoline Direct-Injection Compression Ignition Engines

With the development of low-temperature engine combustion strategies, the performance of gasoline-type fuels under compression ignition conditions has attracted extensive research interest. Meanwhile, for the sake of co-optimization of engines and fuels for future ground transportation, identification, and evaluation of general fuel properties should be a core research priority instead of endless testing of specific fuels. In this study, the roles of fuel octane sensitivity in characterizing the ignition performance of gasoline surrogates have been systematically investigated under typical gasoline direct ignition compression ignition (GDCI) engine conditions using 1D and three-dimensional combustion CFD simulation. The results of 1D simulations illustrate the combustion phasing of different fuel surrogates under HCCI conditions. Three-dimensional CFD simulations were employed to investigate the coupled effects of in-cylinder charge stratification and charge cooling. We considered two operating conditions. One is a beyond-RON case that has a high boost pressure and a low boost temperature. The other is a beyond-MON case that has a low boost pressure and high boost temperature. By comparing the three-dimensional CFD results with zero-dimensional chemical kinetic results, the effects of stratification and charge cooling on these combustion processes are highlighted through the analysis of chemical kinetics, fluid dynamics, and mixing. The results showed that due to its lower volatility, the fuel with higher fuel octane sensitivities leads to a slightly higher equivalence ratio stratification and stronger charge cooling. However, the chemical kinetics that depends on the fuel reactivity are still the more dominant factor than the stratification and charge cooling effects in determining combustion phasing.