Effects of controlled non-equilibrium excitation on H₂/O₂/He ignition using a hybrid repetitive nanosecond and DC discharge

The present work reports on the effects of controlled non-equilibrium excitation of reactant molecules on low temperature H₂/O₂/He ignition by numerically modeling a hybrid repetitive nanosecond (NSD) and DC discharge at atmospheric pressure. At first, a detailed plasma-combustion kinetic model of H₂/O₂/He, including non-equilibrium excitation, is developed and validated by experimental data of a repetitively-pulsed nanosecond discharge. Then, the effects of ignition enhancement by NSD and a hybrid NSD/DC discharge, with controlled electron energy distribution for selective non-equilibrium excitation of vibrationally excited H₂(v) and O₂(v) as well as electronically excited O₂(a¹Δ_g) and O(¹D), are compared. The results show that H₂(v1) contributes significantly to the H production and OH consumption in the hybrid plasma discharge. Moreover, O₂(a¹Δ_g) and O₂(v1−4) also contribute to the production O and OH. Uncertainty analysis of H₂(v) and O₂(a¹Δ_g) elementary reactions on ignition delay time is conducted by using several different kinetic models. The comparison of ignition delay time using different plasma kinetic models indicates the selection of accurate rate constants involving excited species is important for plasma assisted ignition modeling. The results of hybrid discharge assisted H₂/O₂ ignition show that the optimized ignition enhancement is achieved when both excited species and radicals are produced efficiently at an appropriate DC electric field strength. The present modeling provides useful insight into the plasma-combustion model development and the development of controlled plasma discharge to achieve efficient ignition with optimized non-equilibrium excitation of reactants.