Flame Enhancement by Microwave-Induced Plasma: The Role of Major Bath Gas N₂ Versus Ar

A novel centralized microwave jet burner system is proposed here that can be used as a test platform to enable studies of plasma-assisted combustion (PAC) under various operation conditions and combustible mixtures. Spectroscopic characterizations of this burner are conducted using optical emission spectrum with methane/O₂/N₂ and methane/O₂/Ar mixtures for comparison to distinguish the effects of the bath gas on flame enhancement and to delineate the flame enhancement mechanism of microwave induced plasma. The results show that the flame enhancement, by applying a nonequilibrium plasma, is more efficient when the dilution inert N₂ in the air is replaced by Ar. The bath gas in the oxidizer stream plays an important role in the flame enhancement mechanism for the PAC system through more efficient direct impact of excited electrons on oxygen in the plasma and resulting in earlier initiation of the chain reactions through branched OH formation reactions in the flame.