Detailed Kinetic Mechanism for the Oxidation of Ammonia Including the Formation and Reduction of Nitrogen Oxides

This work introduces a newly developed reaction mechanism for the oxidation of ammonia in freely propagating and burner-stabilized premixed flames as well as shock-tube, jet-stirred reactor, and plug-flow reactor experiments. The paper mainly focuses on pure ammonia and ammonia–hydrogen fuel blends. The reaction mechanism also considers the formation of nitrogen oxides as well as the reduction of nitrogen oxides depending upon the conditions of the surrounding gas phase. Doping of the fuel blend with NO₂ can result in acceleration of H₂ autoignition via the reaction NO₂ + HO₂ ⇋ HONO + O₂, followed by the thermal decomposition of HONO, or deceleration of H₂ oxidation via NO₂ + OH ⇋ NO + HO₂. The concentration of HO₂ is decisive for the active reaction pathway. The formation of NO in burner-stabilized premixed flames is shown to demonstrate the capability of the mechanism to be integrated into a mechanism for hydrocarbon oxidation