Flame propagation behavior and ReaxFF molecular dynamics simulation of gasoline surrogate fuel with various oxygen-containing substances

Abstract

The effects of adding oxygen-containing substances, ethanol, methyl tert-butyl ether (MTBE), and 2-methylfuran on the flame propagation characteristics of base gasoline fuel were studied in a constant volume combustion chamber (CVCC) system. The effects were characterized with ignition delay time, flame propagation speed, and Markstein length. Furthermore, the intrinsic combustion chemistry of these fuels were investigated by using ReaxFF molecular dynamics (ReaxFF MD) simulation calculations, including the consumption of fuel and O₂ molecules and the generation of combustion products, as well as the generation, reaction, and evolution of some important intermediates. By combining combustion experiments and computational simulations, the combustion properties and mechanisms of these gasoline surrogate fuels are obtained. The important conclusions are summarized as follows. In the flame propagation experiments, the addition of oxygen-containing substances shortens the ignition delay time and promotes the formation of the flame kernel. During the stable propagation stage of the flame, all the three oxygen-containing gasoline exhibits higher laminar burning velocity (LBV). The contributions to LBV, in order of magnitude, are ranked as 2-methylfuran > MTBE > ethanol. In the ReaxFF MD simulations, the three oxygen-containing substances help achieve complete combustion of the fuel, promote fuel consumption and to some extent reduce CO₂ emission. In particular, the generation evolution and participation of some key reactive radicals can predict evolution trends of macroscopic combustion characteristic parameters at a certain extent, including that a faster generation rate of HO leads to a shorter ignition delay time when the fuel is ignited, and that a higher proportion of H participating in reactions results in a faster flame propagation speed of the fuel. This study reveals the essence of combustion characteristics of oxygenated gasoline fuels from the perspective of chemical kinetics, which provides a theoretical basis for the use of oxygenated biomass as gasoline additives.