High-Pressure Oxidation of an Ammonia–Methanol Mixture: An Experimental and Modeling Study

Abstract

Mole fraction profiles of key species were measured to determine the effect of equivalence ratios on the oxidation of an ammonia–methanol mixture under low to intermediate temperatures and high-pressure conditions. Experiments were conducted in a flow reactor at 5.0 MPa between 650 and 1250 K under different equivalence ratios. A detailed mechanism for the oxidation of the NH₃/CH₃OH mixture was established; this new model was consistent with the experimental measurements and was adopted for further kinetic analysis. The experimental data also revealed that the equivalence ratio had little effect on the initial reaction temperatures of both NH₃ and CH₃OH, while the kinetic analysis revealed that the dehydrogenation of CH₃OH by O₂, which triggers the oxidation of the fuel mixture, starts at the same temperature and has the same rate of production regardless of the equivalence ratio. In addition, the concentrations of NO and N₂O were found to change nonmonotonically with temperature, especially under fuel-lean conditions, with peak NO and N₂O concentrations increasing with oxygen content. H₂NO plays a dominant role in NO production and reacts as a chain carrier that converts NH₂ to NO. Under fuel-rich conditions, the lack of OH radicals inhibits the oxidation of NH₃ and the production of NH₂. Furthermore, the C–N interaction between CH₃OH or CH₂O and NH₂ is favored, resulting in the reduction of NH₂ back to ammonia. This decrease in the level of NH₂ and H₂NO radicals results in less NO generation.