Mechanism of Combustion Instability in a Lean Premixed Dump Combustor

Results from an experimental study of the mechanism of unstable combustion in a coaxial, optically accessible, bluff-body-stabilizeddumpcombustorwithnaturalgasasthefuelarereported.Aparametricstudywasperformed to investigate the effects of equivalence ratio, inletvelocity, inlet fuel distribution, inlet swirl, and centerbody recess oncombustionstability. It wasfoundthatall of theseparametershadan effectonthestability characteristicsofthis combustor.Atselectedunstableoperatingconditions,phase-resolvedCHchemiluminescenceimageswerecaptured to study the heat-release structure during one period of pressure oscillation. The e ame‐ e owe eld interaction that is depicted in these images indicates that e ame‐ vortex interactions, and the resultant e ame area changes, play a signie cant role in the instabilities that occur when there is no swirl. A simple analysis of these images, however, showedthate uctuatinge ameareaandequivalenceratioe uctuationsbothcontributetotheheatreleasee uctuations that drive the instability. Unstable combustion with swirl appears to be fundamentally different from unstable combustion without swirl in that instabilities with swirl occur near lean blowout and appear to be associated with repeated detaching and reattaching of the e ame from the centerbody.

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