Kinetic insights into nanosecond pulsed plasma assisted NH 3 /O 2 /Ar ignition with R-matrix cross section

This work experimentally and numerically studied the kinetic roles of non-equilibrium nanosecond pulsed discharge in the oxidation and ignition of NH 3 /O 2 /Ar mixture at low temperatures. Electron ionization molecular beam mass spectrometry (EI-MBMS) was used to qualify and quantify the species pool in NH 3 /O 2 /Ar plasma, involving NH 3 , O 2 , H 2 O, N 2 , NO, and N 2 O. A complete set of electron scattering cross sections of NH 3 , including elastic, rotational, vibrational excitation, electronic excitation, dissociation, and ionization, calculated via the Rmatrix method was included in the developed plasma assisted NH 3 /O 2 /Ar oxidation kinetic mechanism. Rate constants of reactions involving vibrational and electronic excited ammonia, NH 3 (v) and NH 3 (e), were calculated with the Fridman-Macheret alpha-model and Modified Method of Vibronic Terms (MMVT), respectively. The corresponding rate constants were expressed in the Arrhenius equation and featured decreased active energy barriers or increased pre-exponential factors compared to the reactions involving ground state NH 3 . Key reactions that activated NH 3 consumption, e + NH 3 -> e + NH 3 (e), and NH 3 (e) + X -> NH 2 + XH were included based on the newly-calculated cross sections. The concentrations of reactants and main products predicted by the proposed model were consistent with the experimental measurements in the wide range of inlet O 2 mole fractions and applied voltages. Model analysis revealed that the electron impact reactions and plasma reactions involved excited species such as O( 1 D), Ar*, and electrons played key roles in the initial oxidation of NH 3 . A nonmonotonic relationship between ignition delay time and O 2 mole fractions was observed in the lowtemperature plasma assisted NH 3 ignition due to the competitive reaction channels between O( 1 D) reactions with NH 3 and O 2 . This work provided kinetic insight into low-temperature plasma assisted NH 3 oxidation and ignition for future engine applications.