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

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.