Species and temperature measurements of methane oxidation in a nanosecond repetitively pulsed discharge

Speciation and temperature measurements of methane oxidation during a nanosecond repetitively pulsed discharge in a low-temperature flow reactor have been performed. Measurements of temperature and formaldehyde during a burst of pulses were made on a time-dependent basis using tunable diode laser absorption spectroscopy, and measurements of all other major stable species were made downstream of a continuously pulsed discharge using gas chromatography. The major species for a stoichiometric methane/oxygen/helium mixture with 75% dilution are H₂O, CO, CO₂, H₂, CH₂ O, CH₃OH, C₂H₆, C₂H₄ and C₂H₂. A modelling tool to simulate homogeneous plasma combustion kinetics is assembled by combining the ZDPlasKin and CHEMKIN codes. In addition, a kinetic model for plasma-assisted combustion (HP-Mech/plasma) of methane, oxygen and helium mixtures has been assembled to simulate the measurements. Predictions can accurately capture reactant consumption as well as production of the major product species. However, significant disagreement is found for minor species, particularly CH₂O and CH₃OH. Further analysis revealed that the plasma-activated low-temperature oxidation pathways, particularly those involving CH₃O₂ radical reactions and methane reactions with O(¹D), are responsible for this disagreement.