Numerical investigation of the hybrid pulse–DC plasma assisted ignition and NO_x emission of NH₃/N₂/O₂ mixture

The ignition delay and NO emission characteristics of the NH₃/N₂/O₂ mixture under the influence of pulse–DC hybrid plasma discharges have been studied. The plasma and combustion chemistry mechanisms for NH₃/N₂/O₂ mixture are reviewed, an improved kinetics mechanism is proposed with a well validated electron scattering cross section data. An improved coupled plasma and combustion chemistry code allowing sensitivity/pathway analysis is developed. The role of key species on the ignition delay time and the effects of low E/N discharge over long periods of time (DC stage) on NO_x emission are studied. The results show that, NO emission will be strongly enhanced due to the increased HNO, NH and N density in NH₃ containing mixtures in the DC stage, NO density increases with the E/N value in DC stage due to the reduction of NH and NH₂ species. The role of O₂(a¹Δ_g) in promoting ignition was studied using different rate constant of O₂(a¹Δ_g)+NO→O₂+NO: O₂(a¹Δ_g) mainly reacts with H₂ and H to produce radicals such as O, H and OH instead of quenched by NO. The vibrationally excited NH₃(v2) molecule plays the dominating role in heat release through V–T relaxation with NH₃.