Static Stability and Combustion Characteristics of Oxy-Propane Flames in a Premixed Fuel-Flexible Swirl Combustor

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 (ϕ) from 0.1 to 1.0 and oxygen fractions (OF: volumetric concentration of O2 in the O2/CO2 oxidizer) from 15 to 70%. For better understanding of the physics behind the flame extinction mechanisms, the stability limits were plotted within the ϕ–OF space against the contours of adiabatic flame temperature (Tad), inlet Reynolds number (Re), mixture mass flow rate (ṁmix), 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 Tad only. A correlation of Tad–FS was developed for better characterization of premixed oxy-propane flames. It was also found that the blowout curve follows a constant Tad contour on the stability map, whereas the flashback curve does not. This implies that Tad 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 ϕ, 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 ϕ, OF, and hence, Tad. Similar flame shapes were obtained at the same Tad regardless of ϕ and OF values. Flames of similar Tad also demonstrated similar temperature distributions near the flame core. The findings confirm the dependence of the FS on Tad, irrespective of the combinations of ϕ and OF used to achieve any particular Tad.