Thermokinetic instabilities for ammonia-hydrogen mixtures in a jet stirred flow reactor

The oxidation of ammonia and the interaction between ammonia and hydrogen chemistry have been extensively studied at high temperatures for traditional fames, while no experimental evidences have been provided for conditions relevant to MILD (Moderate or Intensive Low-oxygen Dilution) combustion. The high dilution levels and the relatively low working temperatures have been proven to promote thermo-kinetic instabilities, with detrimental effects on pollutant emissions and process efficiency. Given this background, first, this work reports on an experimental characterization of NH-O-N instabilities in a Jet Stirred Flow Reactor. Oxidation regimes were consequently reassumed in T- ? (preheating temperature T, and equivalence ratio ?) maps. Second, the effect of H as a fuel "enhancer" on the identified NH-O-N oxidation regimes was numerically investigated, parametrically changing the H concentration itself. Results suggested that small concentrations of H strongly enhance the system reactivity and tighten the T-? windows where instabilities occur. Kinetic analyses suggested that H strongly interacts with NH radicals, enhancing the overall NH oxidation chemistry, thus, suppresses the instabilities.