Abstract
This study investigates the stability and combustion features of premixed oxy-propane flames in a dry low emission (DLE) model combustor for clean fuel/oxidizer-flexible combustion applications in gas turbines. The stability of the oxy-propane flame is characterized by its blowout and flashback limits over ranges of equivalence ratios (phi) from 0.1 to 1.0 and oxygen fractions (OF: volumetric concentration of O-2 in the O-2/CO2 oxidizer) from 15 to 70%. For better understanding of the physics behind the flame extinction mechanisms, the stability limits were plotted within the phi-OF space against the contours of adiabatic flame temperature (T-ad), inlet Reynolds number (Re), mixture mass flow rate ((m)over dot(mix)), and combustor power density (PD). The flame speed (FS) was also estimated at selected operating conditions. It was observed that the FS is contingent to T-ad only. A correlation of T-ad-FS was developed for better characterization of premixed oxy-propane flames. It was also found that the blowout curve follows a constant T-ad contour on the stability map, whereas the flashback curve does not. This implies that T-ad is a more relevant controlling parameter choice of combustor stability near the blowout limit, whereas the reaction rate is a suitable indicator of the flame stability limit near flashback. The stability map of the present oxy-propane flame was compared with that of an oxy-methane flame on the same combustor. It was found that, at the same OF, the blowout and flashback limits of the propane flame occur at leaner phi, compared to those of methane flame, which was expected for a higher hydrocarbon fuel like propane. Flame shapes at different sets of operating conditions were investigated for inferring key information on the flame behavior and macrostructure while varying phi, OF, and hence, T-ad. Similar flame shapes were obtained at the same T-ad regardless of phi and OF values. Flames of similar T-ad also demonstrated similar temperature distributions near the flame core. The findings confirm the dependence of the FS on T-ad, irrespective of the combinations of phi and OF used to achieve any particular T-ad.