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Abstract
Employing a novel microwave plasma-assisted combustion (PAC) facility, we conducted a comparative study on PAC of premixed and nonpremixed methane/air mixtures. Results showed that three different reaction zones (plasma zone, hybrid plasma-flame zone, and flame zone) exist, regardless of the fuel injection patterns of the premixed or nonpremixed. Different fuel injection patterns had different optical emission spectra for the hybrid zones and flame zones, with a major difference being the presence or absence of emissions from CH and C2. A U-shaped ignition curve of plasma power versus fuel equivalence ratio was observed in the premixed PAC, whereas an approximately linear increasing line was in the nonpremixed PAC. Pulsed cavity ringdown spectroscopy was also utilized to measure absolute number densities of the ground state OH(X) radicals in the flame zones for both fuel patterns. Results showed different number density profiles along the flame propagation direction between the premixed and nonpremixed PAC.