Kinetic effects of non-equilibrium plasma on partially premixed flame extinction

A new plasma assisted combustion system was developed by integrating a counterflow burner with nano-second pulsed non-equilibrium discharge. The kinetic effects of plasma assisted fuel oxidization on the extinction of partially premixed methane flames was studied at 60 Torr by blending 2% CH ₄ into the oxidizer stream. The non-equilibrium discharge accelerated dramatically the fuel oxidation. The O production and the products of plasma assisted fuel oxidation were measured, respectively, by using two-photon absorption laserinduced fluorescence (TALIF) method, Fourier Transform Infrared (FTIR) spectrometer , and Gas Chromatography (GC). The product concentrations were used to validate an existing plasma assisted combustion kinetic model. The comparisons showed the kinetic model prediction was poor due to missing reaction pathways, such as those involving carbon formation, H₂ excitation and dissociation, and interactions of excited species with hydrocarbon species. The path flux analysis determined that O was the critical species for kinetic modeling because it was generated by the discharge and dictated the oxidization process. The extinction strain rate measurements showed the non-equilibrium plasma discharge extended the extinction limit significantly. Strong emission from Ar* was observed at high plasma repetition rates and numerical modeling showed that Ar* contributed significantly to the enhancement of extinction limit.