Lagrangian mechanisms of flame extinction for lean turbulent premixed flames

Flame extinction is a critical impediment invariably limiting the performance of modern turbulent combustion technology. Combustion systems operating at lean conditions are highly susceptible to dynamic flame stability induced by local flame extinction. This stimulates flame blow-out and inevitably termination of the combustion process. The present study focuses on understanding the driving mechanisms which lead to flame extinction. A Lagrangian flame-vortex model is developed and used to study the flame extinction mechanisms. The model dynamically simulates the turbulent reacting flow exploiting a Lagrangian vortex element scheme and detailed strained kinetics. This systematic modeling strategy effectively encapsulates the dynamics of premixed turbulent flames in terms of stability and extinction. Two extinction modes of flame blow-out are analyzed using the model, the first of which is induced by decreasing equivalence ratio primarily resulting in diminishing strain rate limit of the flame. The alternate mode is focused on inflow-velocity induced extinction which is caused principally by increased hydrodynamic strain in the flow-flame field. The mechanics of both modes are examined utilizing the model's unique Lagrangian tracking capability for extinction-inducing fluid element clusters. This technique enables isolation and detailed analyses of flame and fluid properties leading to blow-out, demonstrating the crucial driving mechanisms of flame extinction.