Large Eddy Simulation of Combustion Characteristics of Non-premixed Methane Jet with Pilot Diesel in High-Pressure Direct Injection Mode

The high-pressure direct injection (HPDI) mode can effectively reduce knock occurrence and improve engine thermal efficiency for the natural gas (NG)-diesel dual-fuel (DF) engine. To further understand the ignition process and flame stabilization, a large eddy simulation (LES) framework coupled with a detailed chemistry solver was conducted with variations in the pilot diesel mass and methane (CH₄) injection timing. Different combustion regions are identified in the temperature versus equivalence ratio space. Results show that the pilot diesel-fuel mass ratio has a significant influence on the high-temperature diffusive combustion of CH₄. By slightly increasing the pilot fuel mass, less CH₄ is consumed in the non-premixed combustion mode. In addition, numerical results also imply that by prolonging the injection timing of CH₄, more low-temperature species are produced by CH₄ rather than by diesel. Besides, results show that methyl (CH₃) can serve as a marker for high-temperature combustion of CH₄ based on the formation region of CH₃ and OH.