Measurements and modeling of laminar burning velocities and chemical kinetics analysis of CH3OH blended with NH3 and H2, with and without CO2 addition

Abstract

Methanol (CH₃OH), a carbon-neutral fuel, blended with ammonia (NH₃) cracked gas, has significant potential for efficient combustion. Additionally, the use of CO₂-enriched exhaust gas recirculation (EGR) systems can effectively reduce NO_x emissions. However, experimental data on the laminar burning velocity (LBV) of CH₃OH blended with NH₃ cracked gas under CO₂ dilution conditions are scarce. In this study, the LBV of low-carbon ternary fuels with different fuel blending ratios and CO₂ dilution ratios was measured at elevated temperatures and pressures. The previously developed CH₃OH/NH₃/H₂ combustion mechanism was optimized and then used to analyze the combustion characteristics of a mixture with high-proportion NH₃ cracked gas combined with CH₃OH. The results showed that the optimized mechanism accurately predicted the LBV and NO emissions of the CH₃OH/NH₃/H₂/CO₂ blends. With increasing NH₃ cracking ratios, the co-combustion of CH₃OH with cracking NH₃ significantly enhanced the LBV and reduced NO emissions. The reduction in NO emissions followed a nonlinear relationship with the NH₃ cracking ratio, with more significant reductions observed at cracking ratios of 90–99%, compared to the 50–90% range. At NH₃ cracking ratios of 90–99%, most NH₃ in the mixture is cracked, leading to sharp reductions in NH and HNO concentrations. Meanwhile, the cracking of NH₃ produces substantial amounts of H₂, which accelerates combustion and shortens the duration of NO formation. Additionally, a significant correlation was observed between LBV and NO. Using the NO and LBV of pure NH₃ at an equivalence ratio of 1 as a baseline, four distinct regions were delineated. It was found that X70CR99 (30% CH₃OH/70% NH₃ with 99% cracking ratio), X70CR98, and X30CR99 were located in the high LBV and low NO region.