Thermokinetic Instabilities for Ammonia-hydrogen Mixtures in a Jet Stirred Flow Reactor

Abstract

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 NH3-O2-N2 instabilities in a Jet Stirred Flow Reactor. Oxidation regimes were consequently reassumed in Tin-?? (preheating temperature Tin, and equivalence ratio ?) maps. Second, the effect of H2 as a fuel “enhancer” on the identified NH3-O2-N2 oxidation regimes was numerically investigated, parametrically changing the H2 concentration itself. Results suggested that small concentrations of H2 strongly enhance the system reactivity and tighten the Tin-? windows where instabilities occur. Kinetic analyses suggested that H2 strongly interacts with NH2 radicals, enhancing the overall NH3 oxidation chemistry, thus, suppresses the instabilit