Abstract: To study the effect of initial parameters on homogeneous charge compression ignition(HCCI) combustion performance of CH4-H2 mixtures with different hydrogen ratios, numerical research was carried out through combustion software Chemkin, and the rate of production (ROP) analysis method was used to study the influence of hydrogen mixing ratio and excess air coefficient on the dominant mechanism of NO emission. The result shows that hydrogen ratio, compression ratio, inlet temperature and air excess coefficient affect NOx emission by affecting the temperature in the engine, and the NOx emission can be controlled by reducing the compression ratio and inlet temperature properly and increasing the air excess coefficient at high hydrogen ratios. The analysis shows that the contribution rate of thermodynamic mechanism increases with the increase of hydrogen ratios and decreases with the increase of the excess air coefficient, while the contribution rate of N2O intermediate mechanism increases with the increase of the excess air coefficient. When the excess air coefficient is 2.5, the dominant position of the two mechanisms is approximately the same.

Key words: methane-hydrogen mixed fuel, homogeneous charge compression ignition, rate of production (ROP) analysis