This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50 kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different dilution levels of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the first harmonic of the combustor’s natural frequency. As the temperature is reduced, the combustor jumps to fundamental mode and then to a low-frequency mode whose value is well below the combustor’s natural frequency, before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.

This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different fractions of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the five-quarter wave mode. As the temperature is reduced, the combustor jumps to the three quarter mode and then to the quarter wave before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.