The NH <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si3.svg"> <mml:msub> <mml:mrow/> <mml:mn>3</mml:mn> </mml:msub> </mml:math> /NO <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> /O <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> system: Constraining key steps in ammonia ignition and N <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg"> <mml:msub> <mml:mrow/> <mml:mn>2</mml:mn> </mml:msub> </mml:math> O formation
Peter Glarborg
Abstract
Amine/NO2 interactions are important for ignition and N2O emissions in ammonia combustion. In the present work, reported results from batch reactors (580–690 K) and flow reactors (850–1350 K) for the NH3/NO2 system were re-interpreted in terms of the present understanding of the amine chemistry. Furthermore, additional flow reactor results on the impact of O2 on the NH3/NO2 reaction were presented and analyzed. Based on the experimental results and the modeling analysis, it was possible to constrain the rate constants for reactions of NH3 and NH2 with NO2 and for subsequent steps involving H2NO and HNO intermediates. The key reaction is NH2 + NO2, forming H2NO + NO (R2) and N2O + H2O (R3). The results indicate that the yield of N2O in the NH2 + NO2 reaction decreases with temperature in the 850–1350 K range, in agreement with the theoretical study by Klippenstein and coworkers. The fate of H2NO and HNO is important for the overall reactivity. In the absence of O2, formation of chain carriers is controlled by the sequence H2NO + NO2 → HNO + HONO, HNO + NO2 → NO + HONO, HONO (+M) → NO + OH (+M). At higher temperatures, in the presence of O2, the sequence H2NO + O2 → HNO + HO2, HNO + O2 → NO + HO2, NO + HO2 → NO2 + OH enhances radical formation and recycles NO2. The satisfactory agreement between experiments and modeling predictions, both without and with O2, supports the present rate constants for the reactions of H2NO and HNO with NO2 and O2, respectively.