Effect of Flow Parameters on the Acoustic Susceptibility of Shear-Coaxial Flames

The effect of density ratio, velocity ratio, momentum ratio, and fuel composition on the susceptibility of shear coaxial flames to periodic pressure waves is studied experimentally. A GO2-GH2 turbulent diffusion flame, established in an atmospheric-pressure, two-dimensional, shear coaxial combustor, is acoustically forced by a transversely mounted compression driver, and the level of flame acoustic interaction is quantified using OH* chemiluminescence imaging. The parameter of interest is varied by diluting the propellants with helium, argon, or methane by appropriate amounts while holding other parameters relatively constant. Flame response is found to vary exponentially with density ratio, whereas it is found to vary linearly with velocity ratio and fuel composition, at least within the limited ranges tested. Flame response is found to vary exponentially when momentum ratio is varied by varying density ratio, whereas it is found to vary linearly when momentum ratio is varied by varying velocity ratio. Overall, our results support the notions that propellant density ratio is a critical parameter affecting shear coaxial flame–acoustic interactions and that a reduction in propellant density ratio could improve the stability of combustors using such injectors.