1 Effects of Non-Equilibrium Plasmas on Low-Pressure, Premixed Flames. Part 1: CH * Chemiluminescence, Temperature, and OH

In this paper, we investigate the effects of nanosecond, repetitively-pulsed, non-equilibrium plasma discharges on laminar, low-pressure, premixed burner-stabilized hydrogen/O2/N2 and hydrocarbon/O2/N2 flames using CH * chemiluminescence and quantitative OH laser-induced fluorescence (LIF) diagnostics. Two different plasma sources, both of which generate uniform, low-temperature, volumetric, non-equilibrium plasma discharges, are used to study changes in chemiluminescence, temperature, and OH concentration when non-equilibrium plasmas are directly coupled to conventional hydrogen/hydrocarbon oxidation and combustion chemistry. Qualitative imaging of CH * chemiluminescence indicates that during plasma discharge, the luminous flame zone is shifted upstream towards the burner surface with little change in the CH* zone thickness. For the same plasma discharge and flame conditions, quantitative results using spatially-resolved OH LIF and multi-line, OH-LIF thermometry show significant increases in ground-state OH concentrations in the preheating zones of the flame. More specifically, for a particular axial position downstream of the burner surface, the OH concentration increases, which can be viewed as an effective “shift ” of the OH profiles towards the burner surface. The increase in OH concentration is conceivably due to an enhancement of the lower-temperature kinetics including O atom, H atom and OH formation kinetics and temperature rise due to the presence of the low-temperature, non-equilibrium plasma