Passive Control of Combustion Instability in Lean Premixed Combustors

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Abstract
A Solar fuel injector that provides lean premixed combustion conditions has been studied in a combined experimental and numerical investigation. Lean premixed conditions can be accompanied by excessive combustion driven pressure oscillations which must be eliminated before the release of a final combustor design. In order to eliminate the pressure oscillations the location of fuel injection was parametrically evaluated to determine a stable configuration. It was observed that small axial changes in the position of the fuel spokes within the premix duct of the fuel injector had a significant positive effect on decoupling the excitation of the natural acoustic modes of the combustion system. In order to further understand the phenomenon, a time-accurate 2D CFD analysis was performed. 2D analysis was first calibrated using 3D steady-state CFD computations of the premixer in order to model the radial distribution of velocities in the pre mixer caused by non-uniform inlet conditions and swirling flow. 2D time-accurate calculations were then performed on the baseline configuration. The calculations captured the coupling of heat release with the combustor acoustics, which resulted in excessive pressure oscillations. When the axial location of the fuel injection was moved, the CFD analysis accurately captured the fuel time lag to the flame-front, and qualitatively matched the experimental findings.

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