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 of the mixed region. During the 1st-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 2nd-stage exothermic reaction, the locally premixed fuel-air rapidly burns and produces strong pressure waves, where 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 (1) the 2nd-stage exothermic reaction starts at the core of each vortex where “Reaction Rate (
YCH4)(
YO2)
2exp(-
Ze/
T*)” is high, (2) then the generated strong pressure waves promote the reaction at the outermost stratified region of each vortex, and (3) spot-like flames formed in the premixed region propagate toward the surrounding unburned region, due to conventional defraglation mechanism. (4) On the other hand, delayed combustion starts in the braid region where mixing is highly inactive. (5) Finally, after the consumption of premixed reactants, a diffusion flame with a low mass consumption rate prevails. The highest
Da number simulation naturally has generated the strongest pressure waves, indicating the possibility of shock wave occurrence and transition to detonation.
抄録全体を表示