According to the reactivity gradient theory of Zel'dovich, the non-uniformity in temperature or concentration can lead to detonation development under certain conditions. In the literature, there are many studies on detonation development caused by temperature gradient or hot spot. However, the modes of supersonic reaction front propagation and detonation development regime caused by concentration non-uniformity have not been investigated previously. In this study, one-dimensional simulations were conducted to investigate the transient autoignition and reaction front propagation processes in n-heptane/air mixture with concentration non-uniformity. With the increase of equivalence ratio gradient, three modes (supersonic autoignitive reaction front, developing detonation and subsonic reaction front) of reaction front propagation induced by concentration non-uniformity were identified. The effects of heat conduction and mass diffusion on these three modes were examined and it was demonstrated that molecular diffusion has little influence on the first two modes. The detonation development regime caused by concentration non-uniformity was reported in this paper. This regime was found to be similar to the one caused by temperature gradient. A non-dimensional parameter was proposed to characterize the lower limit of the detonation regime. Furthermore, the effects of initial temperature on the detonation development regime were examined. It was found that the detonation development regime becomes wider as the initial temperature decreases. The initial temperature was shown to only have great impact on the upper limit of the detonation development regime while it has little influence on the lower limit. The influence of initial temperature was explained using the volumetric energy density of the mixture.

根据Zel'dovich的反应梯度理论，温度或浓度的不均匀会导致在特定条件下爆炸的发展。在文献中，有许多关于由温度梯度或热点引起的爆炸发展的研究。然而，由浓度不均匀引起的超音速反应锋面传播和爆轰发展机制的模式以前尚未被研究过。在这项研究中，一维模拟，以调查在瞬态自燃和反应前传播过程Ñ-庚烷/空气混合物，浓度不均匀。随着当量比梯度的增加，确定了浓度不均匀引起的反应前沿传播的三种模式（超音速自燃反应前沿，发展爆轰和亚音速反应前沿）。研究了导热和质量扩散对这三种模式的影响，并证明了分子扩散对前两种模式的影响很小。报道了由浓度不均匀引起的爆轰发展机制。发现该状态类似于由温度梯度引起的状态。提出了无量纲参数来表征爆轰机制的下限。此外，检查了初始温度对爆轰发展机制的影响。已经发现，随着初始温度降低，爆震发展机制变得更宽。结果表明，初始温度仅对爆轰发展机制的上限有很大的影响，而对下限的影响很小。使用混合物的体积能密度解释了初始温度的影响。