THE EFFECT OF MIXING IRREGULARITIES ON MIXED-REGION CRITICAL LENGTH FOR DEFLAGRATION-TO-DETONATION TRANSITION

Deflagration-to-detonation transition (DDT) may occur through the Zel' dovich or shock wave amplification by coherent energy release (SWACER) gradient mechanism when spatial nonuniformities in temperature and co mposition are formed through turbulent mixing of reaction products wit h unburned gas. If the gradient region is large enough, a spontaneous reaction wave will form and strengthen into a detonation that may prop agate into the unburned mixture. Such gradient regions formed by turbu lent mixing are likely to be highly irregular, containing disturbances with a wide range of magnitudes and length scales. One-dimensional ca lculations in which a sinusoidal disturbance is superimposed on a line ar gradient are used to examine the effect of disturbance amplitude an d frequency on the size of a mixed region necessary for DDT. The resul ts suggest that disturbances caused by turbulent mixing may increase t he critical length by more than order of magnitude as compared to an u ndisturbed linear gradient. Disturbances of intermediate frequency inc rease the critical length more than those of very low or very high fre quency. Large-amplitude disturbances increase the critical length by e ffectively dividing the gradient into subregions. (C) 1998 by The Comb ustion Institute.