Development of a Diesel/Natural Gas Mechanism Model for the CFD Simulation of Dual-Fuel Engine

Diesel/natural gas (NG) can effectively improve the performance and reduce emissions of the reactivity-controlled compression ignition (RCCI) engine. In this work, n-hexadecane was used to characterize diesel and the methane/ethane/propane mixture was used to characterize NG, and a simplified diesel/NG mechanism containing 645 reactions and 155 species was established. We used brute force sensitivity analysis to optimize the key dynamic parameters of the mechanism and, through the laminar flame velocity, the substance concentration in the jet-stirred reactors and the ignition delay in the shock tube to verify the optimized n-hexadecane/NG mechanism and found that this mechanism can better respond to diesel/NG. Finally, the mechanism was coupled with the computational fluid dynamic (CFD) to study the effect of different diesel injection timings (DITs) on the combustion performance of RCCI engines. The results show that as the DIT advanced, the temperature distribution in the cylinder became uneven. Also, when the temperature was lower, the content of unburned methane in the cylinder increased. When the DIT was 45° crank angle (CA) before the top dead center (BTDC), the temperature and equivalent in the cylinder were more evenly distributed than in the cylinder and the unburned methane content was lower and diesel/NG exhibited a better combustion effect. The diesel/natural gas mechanism model can be better applied to the CFD simulation of dual-fuel RCCI engines.