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Abstract: Lean premixed (LP) combustion systems are currently used for most modern power generation gas turbines. Though this method reduces emissions, specifically nitrogen oxides, and is more efficient than non-premixed systems, LP systems are susceptible to blowoff. The goal of this study is to find out how centerbody geometry plays a role in the lean blowoff process for swirl-stabilized flames. We find that cylindrical centerbodies have higher lean blowoff equivalence ratios than tapered centerbodies. We also find that the dominant flame shape for both centerbodies is M-shape when not anchored and tulip shaped when anchored, though the tapered centerbodies induce V-shape flames as well. The blowoff equivalence ratio and blowoff process are strongly coupled ith the flame shape. 

Swirl-stabilized flames are used in many gas turbine combustor configurations due to their enhanced static stability. The effects of combustor geometry, fuel composition, and bulk velocity on flame stability in swirling flows are well studied, but the effects of centerbody temperature have not been rigorously considered. The purpose of this study is to understand the impact of centerbody temperature on flame shape and dynamics. A newly instrumented variable-angle swirl-stabilized combustor was used to perform a repeatability study, and blowoff equivalence ratio was measured at centerbody temperatures ranging from 150 to 350°C and bulk velocities ranging from 16 to 55 m/s. Blowoff equivalence ratio generally decreases with centerbody temperature. Two structures were observed during blowoff: a cone shape and flame chugging. Blowoff equivalence ratio was consistently lower when the cone structure occurred, though the mechanism that excites these behaviors is still under investigation. 

This work focused on understanding how swirl influences the blowoff limit and process in lean-premixed, swirl-stabilized flames. Two initial equivalence ratios (Ф0 = 0.8 and 1.0) were used to study the effect of swirl number (S = 0.80, 0.95, 1.15, and 1.43) on the lean blowoff limits. It was seen that at higher Ф0, the blowoff equivalence ratio of flames with lower swirl levels was typically more sensitive to bulk flow velocities than flames stabilized at lower Ф0. The blowoff Ф of flames stabilized at higher swirl levels did not vary much with an increase in bulk flow velocity. Global CH* chemiluminescence was done to study the lean blowoff process further. At lower Ф0 and swirl levels, the occurrence of the extinction/reignition events in the shear layers seemed more prominent.