Effects of autoignition mode induced by periodic thermal stratification on deflagration-to-detonation transition

In this study, the partially stirred reactor model is utilized to simulate the turbulent–chemical interactions involved in deflagration-to-detonation transition (DDT). Jet-A/air is used as the reactant to simulate flame propagation within an inhomogeneous temperature field with periodic thermal stratification. The results reveal that autoignition induced by periodic thermal stratification plays a crucial role in the DDT. Two autoignition modes are identified: diffusion autoignition, driven by molecular thermal diffusion, and critical autoignition, triggered by shock waves inducing new hot kernels. The occurrence of autoignition considerably increases the flame surface area, expediting the propagation of deflagration flame and shortening the time until DDT onset. By varying the amplitude and wavelength, the characteristics of periodic thermal stratification are adjusted. At appropriate amplitudes, periodic thermal stratification notably promotes DDT, but excessive amplitude leads to multiple autoignition kernels forming simultaneously, hindering the DDT onset. A reduction in wavelength increases the number of diffusion autoignition kernels, delaying DDT onset compared to cases with larger wavelengths. Additionally, detonation wave decoupling is caused by the detonation wave being diffraction by obstacles and the effects of thermal stratification. An analysis of the decoupled detonation and its subsequent re-initiation confirm a shock–detonation re-initiation mode.