Experimental investigation of near-blowout instabilities in a lean, premixed step combustor

An experimental characterization of combustion instabilities in a lean, premixed backwardfacing step combustor was performed. Specifically, the instabilities of interest were those encountered as the equivalence ratio was reduced to levels approaching the combustor's lean extinction limit. High-response measurements of static wall pressures, inlet velocity and local combustor heat release rate were acquired. In addition, the unstable flow field was visualized using high speed cinematography and a focused shadowgraph system. The results indicate that the magnitude of a longitudinal acoustic disturbance grows with decreasing equivalence ratio, until it eventually triggers a lower-frequency, high amplitude instability. This low frequency instability is visible as a flapping of the flame and increases in severity with decreasing equivalence ratio until it causes combustor blowout