High-Pressure\nOxidation of an Ammonia–Methanol\nMixture: An Experimental and Modeling Study

Mole fraction profiles of key species were measured to\ndetermine\nthe effect of equivalence ratios on the oxidation of an ammonia–methanol\nmixture under low to intermediate temperatures and high-pressure conditions.\nExperiments were conducted in a flow reactor at 5.0 MPa between 650\nand 1250 K under different equivalence ratios. A detailed mechanism\nfor the oxidation of the NH<sub>3</sub>/CH<sub>3</sub>OH mixture was\nestablished; this new model was consistent with the experimental measurements\nand was adopted for further kinetic analysis. The experimental data\nalso revealed that the equivalence ratio had little effect on the\ninitial reaction temperatures of both NH<sub>3</sub> and CH<sub>3</sub>OH, while the kinetic analysis revealed that the dehydrogenation\nof CH<sub>3</sub>OH by O<sub>2</sub>, which triggers the oxidation\nof the fuel mixture, starts at the same temperature and has the same\nrate of production regardless of the equivalence ratio. In addition,\nthe concentrations of NO and N<sub>2</sub>O were found to change nonmonotonically\nwith temperature, especially under fuel-lean conditions, with peak\nNO and N<sub>2</sub>O concentrations increasing with oxygen content.\nH<sub>2</sub>NO plays a dominant role in NO production and reacts\nas a chain carrier that converts NH<sub>2</sub> to NO. Under fuel-rich\nconditions, the lack of OH radicals inhibits the oxidation of NH<sub>3</sub> and the production of NH<sub>2</sub>. Furthermore, the C–N\ninteraction between CH<sub>3</sub>OH or CH<sub>2</sub>O and NH<sub>2</sub> is favored, resulting in the reduction of NH<sub>2</sub> back\nto ammonia. This decrease in the level of NH<sub>2</sub> and H<sub>2</sub>NO radicals results in less NO generation.