Combustion Instability Suppression in Gaseous Oxygen/Hydrogen Combustors Using Methane Dilution

Abstract

Combustion stability characteristics of a turbulent diffusion flame established between a center jet of gaseous oxygen and coflowing jets of gaseous hydrogen blended with different amounts of gaseous methane are studied in a rectangular combustor operating under atmospheric pressure conditions. A compression driver, mounted near the injector, is used to acoustically excite the flame from a transverse direction. Resulting flame perturbations are studied using chemiluminescence imaging, dynamic pressure measurements, and high-speed flow visualizations. Both steady-state perturbations and perturbations as the acoustically forced flames transition from one fuel blend to another are studied. Simultaneous measurements of pressure oscillations and heat release oscillations are used to obtain local Rayleigh indices showing locations that drive or dampen the instability. Transient measurements associated with real-time in situ methane blending are used to obtain timescales associated with the suppression process. Interesting intermittencies in heat release oscillations driven by acoustic forcing and local hydrodynamics are explored. Heat release oscillations, which drive combustion instability, are substantially reduced when gaseous methane is blended with gaseous hydrogen while holding ignition characteristics relatively constant. The reduction appears to result from a lowering of the density difference between the propellant streams upon methane dilution fuel–oxidizer density ratio. The approach could potentially be used in shear-coaxial combustors where instability from similar flame–acoustic interactions are common.