NOx formation mechanism of plasma assisted ammonia combustion: A reactive molecular dynamics study

Abstract

The effects of ionization ratio (α) on the reaction rate of NH3 combustion and the formation characteristics of NOx are studied by ReaxFF MD, and the formation mechanism of NOX in plasma assisted NH3 combustion are analyzed from the molecular level. It is found that the maximum growth rate of NOX gradually slows down with increasing reaction system temperature. The plasma promotes NOX formation at the initial stage of NH3 combustion, and when the nitrogen-containing radicals are consumed, the non-nitrogen-containing components will inhibit NO formation. When the α is 25%, the NH3 reaction rate reduces slightly. This is attributed that the proportion of NH2/H is the larger at this lower α. The plasma effect at lower α = 25% enhances the N2 formation path from NH3 by the primary reaction pathway of NH3→NH2→NH→NNH→N2, and the intermediate NH consumes some of the NO to form N2 by NH + NO↔HN2O and HN2O↔N2+OH. As α increases to 50%, the plasma leads to the direct generation of NO from NH by NH + OH↔H2NO and H2NO + O↔H2O + NO, which makes the maximum of NO increase.