Assessment of planar laminar flame speed of Hythane generated in-situ from non-thermal plasma reforming of Methane : Flame tube based experiments and thermo-chemical analysis

Abstract

The article addresses the characterization of laminar flame speed of Hythane generated from non thermal plasma reforming of Methane using a dielectric barrier discharge reactor. Hythane with 5%, 10% and 15% Hydrogen fraction is generated by controlling the Methane residence time in the plasma zone. Planar laminar flame speed for the Hythane so generated is estimated using a flame tube and compared with flame speed of bottled Hythane over a range of operating stoichiometry. It is observed that Hythane from plasma reforming of Methane has substantially higher laminar flame speed as compared to bottled Hythane. At the peak flame speed equivalence ratio of ϕ=1.1, Hythane generated from plasma activation of Methane has laminar flame speed higher than corresponding bottled Hythane to the extent of 13.3%, 34.1% and 38.9% for 5%, 10% and 15% Hydrogen in Hythane respectively. It is also observed that flame speed difference is muted for lean mixtures as compared to rich mixtures. Thermo-chemical analysis indicates that the enhanced flame speed can neither be addressed based on thermal effects nor due to the presence of neutral intermediate species and non thermal reforming of Methane to generate Hythane potentially results in additional reaction kinetics influences which accelerate the combustion process. Such influences could arise from presence of long lived species formed (charged or otherwise) not detected in conventional analysis and changes to the energy levels of the reaction species, principally Methane and Hydrogen. In terms of terminal utility, non thermal plasma reforming of Methane can have path breaking influence considering that enhanced flame speeds can significantly improve the thermodynamic efficiency of a spark ignited engine with lower than pure thermo-chemical Hydrogen requirement in Hythane.