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Abstract
A 2-step reaction model is used to analyze the interaction between (i) a fuel-air multi-stratified vortical mixing layer and (ii) strong pressure waves caused by rapid combustion in the mixed region. During the first-stage induction period, where no heat release occurs, a large-scale vortical structure evolves, generating a wide contact surface and extended mixing between fuel and air. During the ensuing second-stage exothermic reaction, the locally premixed fuel-air rapidly burns and produces strong pressure waves. Three different Da numbers are parametrically tested to evaluate the amplitude of generated pressure waves and to find out the possibility to trigger a detonation wave
The results show that the second-stage exothermic reaction starts in the core of each vortex where the “Reactivity Index” is high. The generated strong pressure waves promote the reaction in the outermost stratified region of each vortex, and spot-like flames formed in the premixed region propagate toward the surrounding unburned region, as a standard defragration. Subsequently, delayed combustion starts in the braided region where little mixing takes place. Finally, after the premixed reactants are consumed, a diffusion flame with a low mass consumption rate remains
The highest Da number simulation generated the strongest pressure waves, indicating the possibility of shock wave occurrence and transition to detonation.