Study on optimization of ammonia-methanol reformed/ cracked gas combustion mechanism and nonlinear relationship between laminar burning velocity and NO generation

Blending methanol reformed (MSR) or cracked (MC) gases with ammonia enhances the laminar burning velocity (SL) but also exacerbates nitrogen oxide emissions. In this work, the SL of NH3/H2/air blends with CO2 and N2 dilution was measured in a constant volume combustion chamber (CVCC) at equivalence ratios ranging from 0.5 to 0.9, temperatures of 400 and 450 K, and pressures of 0.3 and 0.6 MPa. The kinetic parameters for the reaction H + HO2 = H2 + O2 were optimized to accurately predict the SL with CO2 dilution based on the previous mechanism. The optimized mechanism was then applied to investigate the chemical kinetics of SL and NO generation for blended fuels of ammonia with fully methanol reformed/cracked gases, and hydrogen under lean-burn conditions. The results indicated that the sum of peak mole fractions of O, H, OH, and HNO, (O + OH + H + HNO)max, is strongly correlated with SL and NO generation, without being limited by fuel type and equivalence ratio. There is a significant quadratic correlation between SL and NO generation. As the (O + OH + H + HNO)max increases, SL increases monotonically, whereas NO emissions increase and then decrease. This is due to the low concentration of radicals at high ammonia energy ratios and the insufficient ammonia at low ratios, which limit NO generation. At an equivalence ratio of 0.5, the three blends improve combustion and NO emissions performance, with the NH3/MSR blends showing the most significant improvement.