Numerical study of the combustion mechanism of a homogeneous charge compression ignition engine fuelled with dimethyl ether and methane,with a detailed kinetics model. Part 2: the reaction kinetics of dimethyl ether and methane dual-fuel

Abstract

A numerical study was carried out using a zero-dimensional detailed chemical kinetics model to investigate the chemical reaction phenomena encountered in the homogeneous charge compression ignition process of a dimethyl ether (DME) and methane dual-fuel mixture. The results show that the heat release of DME/methane dual-fuel combustion is a typical two-stage process: the first stage is mainly associated with DME oxidation, and the second is mainly the result of methane oxidation. The low-temperature reaction (LTR) of DME is inhibited, the second molecular oxygen addition of DME is restrained, and β-scission plays a dominant role in DME oxidation. Therefore, methane changes the paths of the LTR of DME. Most of the formaldehyde (CH₂O) is produced from H abstraction of methoxy (CH₃O) rather than from the LTR of the DME. The heat release by DME oxidation and the existence of H₂O₂ generated by DME oxidation make methane oxidation occur at a low initial temperature. However, methane oxidation also promotes hot flame reactions of DME. During the second stage of heat release, OH is produced in many different ways rather than only by way of H₂O₂ decomposing in neat DME oxidation; this results in higher OH mole fraction when dual fuel is used compared with DME alone. Finally, the major paths of the DME/methane HCCI reactions occurring in the engine cylinder are clarified.