Experimental and numerical study on different dual-fuel combustion modes fuelled with gasoline and diesel

摘要

In this study, numerical simulation and experiments have been carried out to explore the differences in combustion and emissions characteristics between dual-fuel Highly Premixed Charge Combustion (HPCC, including E-HPCC and L-HPCC) and blended-fuel Low Temperature Combustion (LTC) modes with gasoline and diesel. The results illustrate that, most of the mixture in E-HPCC is uniform in both concentration and reactivity, and there are various degrees of mixture stratification in L-HPCC and LTC. Based on the in-cylinder charge distributions, the combustion occurs in the very center area of combustion chamber and the area closer to the piston bowl wall in the two HPCCs and LTC respectively, and then flame spread to peripheral regions. In the two HPCCs, the substantial heat release is determined by the oxidation of OH radical that derived from the low temperature reaction of diesel fuel, and the staged reaction of diesel and gasoline leads to reasonable MPRR values; the fuel stratification in LTC mode results in a rapid heat release rate and high MPRR because of the coupling combustion reaction of gasoline and diesel taking place in the regions with higher fuel concentration. The observed NO_X and soot reductions of E-HPCC are due to the avoidance of high equivalence ratio and high temperature region in the combustion chamber. Compared to LTC, the two HPCCs produce more incomplete combustion products and consequent lower combustion efficiencies, which can be improved by increasing gasoline ratio.