Effects of Diffusion Fuel and Oxygen Fraction on Macrostructure, Operability Limits, and Emissions of Premixed Natural-Gas Oxy-Flames Over a Perforated Plate Burner

Abstract The stability, macrostructure, and emissions of diffusion-assisted premixed oxy-CNG (compressed natural gas) flames, stabilized over a burner of a perforated plate with a diffusion central hole, were experimentally investigated in a model gas turbine combustor. Four sets of experiments were conducted with the first three sets characterizing stability maps of the combustor, in terms of upper and lower blow-off limits, in the Φ–Reoxidizer domain, over ranges of fuel diffusion percentage (DP: 0%, 5%, 10% and 15%) at different oxygen fractions (OFs) of 29%, 32% and 36%. The fourth set characterizes the combustor near stoichiometry (Φ = 0.85) stability maps, in terms of flashback and blow-off limits, in the OF–Reoxidizer domain over ranges of the same range of DPs. The results showed better flame stability with extended upper and lower blow-off limits at higher DPs and OFs because of the excess CNG ejecting in the burner and high kinetics at high O2 concentrations. Overall flame length was elongated with OF; however, adding a diffusion flame at high DP fades the outer flame of the cone due to high O2 consumption and low reactivity. At Φ = 0.85, close to stoichiometry, operability of the combustor was constrained within the OF range of 25% (at blowout) to 46% (at flashback). The operating OF value should not surpass 36% at a DP of 15% in order to prevent flashback. The developments of concentrations of CO, CO2, and O2 are presented within the combustor domain for better characterization of the flame stratification.