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This thesis presents a numerical and experimental investigation on the characteristics of oxy-fuel combustion utilising CH4 as a fuel. An emphasis is placed on investigating the thermal structure and the impact of the oxidiser diluent on oxy-fuel flames. The numerical portion of this thesis sheds light on off-stoichiometric temperature peaking (OTP), which is a phenomenon whereby the flame temperature does not peak at exactly stoichiometry, but rather near stoichiometry. Specifically, OTP in equilibrium calculations (0D OTP) and opposed-flow diffusion flame simulations (1D OTP) is explored for N2, CO2 and H2O diluted flames examining the significance of reactivity, dissociation, diffusivity, conductivity, finite-rate chemistry, heat release, and specific heats. Results from both 0D OTP and 1D OTP analysis indicate that all investigated flames possess some degree of OTP, with the CO2 diluted oxidiser case displaying the largest degree of OTP. Parametric analysis utilising concepts of imaginary species and post-simulation equilibrium calculations are shown to be valuable tools to determine the dominant mechanism causing OTP for the different simulation results examined. Experimentally, the development and application of a planar hydroxyl radical (OH) laser induced fluorescence thermometry technique to a laminar oxy-fuel counter-flow diffusion flame is presented. The resulting temperature profiles obtained by a spectrally integrated two-line technique are found to agree well with the simulated thermal structure to within a 2% difference. Further, this thesis also presents the detailed design of a counter-flow burner and laser pulse stretcher for the application Raman scattering in oxy-fuel flames for future experiments. |
