Time Scale Model for the Prediction of the Onset of Flame Flashback Driven by Combustion Induced Vortex Breakdown (CIVB)

Abstract

Flame flashback driven by Combustion Induced Vortex Breakdown (CIVB) represents one of the most severe reliability problems of modern gas turbines with swirl stabilized combustors. Former experimental investigations of this topic with a 500 kW burner delivered a model for the prediction of the CIVB occurrence for moderate to high mass flow rates. This model is based on a time scale comparison. The characteristic time scales were chosen following the idea that quenching at the flame tip is the dominating effect preventing upstream flame propagation in the center of the vortex flow. Additional numerical investigations showed that the relative position of the flame regarding the recirculation zone influences the interaction of flame and flow field. The recent analysis of turbulence and chemical reaction of data acquired with high speed measurement techniques applied during the CIVB driven flame propagation by the authors lead to the extension of the prediction model. As at the flame tip the corrugated flames regime prevails at low to moderate mass flow rates, a more precise prediction in this range of mass flow rates is achieved using a characteristic burnout time τb∼1/Sl for the reactive volume. The paper presents first this new idea, confirms it then with numerical as well as experimental data and extends finally the former model to a prediction tool that can be applied in the full mass flow range of swirl burners.