Effects of adiabatic flame temperature on flames’ characteristics in a gas-turbine combustor

In this study a comparison between the premixed methane oxygen-enriched-air (CH₄/O₂/N₂) and oxy-methane (CH₄/O₂/CO₂) in a gas-turbine model combustor that imitates pre-mixers in operational air-fuel dry low emissions gas turbines is presented. The comparison and analyses that follow in this study are based on the results of experiments conducted. The combustion stability maps were obtained through the estimation of acoustic limits and measurement of blowout limits within the space of equivalence ratio (φ) – oxygen fraction (OF). The stability maps obtained were superimposed on the contour plots of constant adiabatic temperature (T_ad), Reynolds number (Re), and power density (PD) of the combustor. Effects of T_ad on flame macrostructure, flame stability, flame speed, and blowout mechanism were investigated. The temperature distributions were also measured. The study results indicated that blowout of CO₂ as well as N₂ flames occur at constant T_ad. These results are more pronounced in the case of the multi-hole burner because, such burner is not characterized with sporadic nature of flame lifting and reattachment that dominate the occurrence of a blowout in swirl burner; for a given OF, φ at which CO₂ flames blowout is higher than that of N₂ flames due to the poorer resistance of oxy-flames to blowout as compared to air flames; the stable combustion zone of CO₂ flames is larger than that of N₂ flames.