ABSTRACT

Flame acceleration and the deflagration to detonation transition (DDT) are important physical phenomena in combustion theories. The main objective of this work is to provide a comprehensive understanding of the effect of the positions of obstacles when a flame propagates in obstructed confined channels, using two-dimensional direct numerical simulations (DNSs) with the detailed chemical kinetics mechanism of H₂. The underlying mechanism for the flame propagation and detonation, affected by the obstacles with the flame-shockwave and flame–vortex interactions, is investigated. In 1000 K cases, two different detonation modes associated with flame propagation are observed, where for the case with obstacles near the ignition kernel, autoignition takes place in the end-gas region as predicted, while for the case with obstacles far away from the ignition kernel, autoignition occurs, instead, in front of the flame and triggers a DDT immediately. Both of two modes consist three processes: flame propagation stages, flame-pressure wave/shockwave interaction, and detonation development. The evolutions of centerline temperature and pressure are employed to explicitly demonstrate the detonation process. The differences in the shockwave formation, peak temperature, and pressure values can be clearly observed. The mechanisms of the different detonation modes induced by different obstacle positions are analyzed in detail for the first time. The results indicate that the compressed and preheated temperature of the unburned mixture determines the detonation combustion mode. The conclusion is further proved in the flame-shockwave number variation and detonation modes transition when initial temperature is changed. This study will provide new insight into the DDT and detonation phenomena in engines.

摘要

火焰加速和爆燃到爆震转变 (DDT) 是燃烧理论中的重要物理现象。这项工作的主要目的是使用二维直接数值模拟 (DNS) 和 H ₂的详细化学动力学机制，全面了解火焰在受阻的受限通道中传播时障碍物位置的影响。. 研究了火焰传播和爆炸的潜在机制，受障碍物与火焰冲击波和火焰涡流相互作用的影响。在 1000 K 的情况下，观察到与火焰传播相关的两种不同的爆震模式，其中对于点火核附近有障碍物的情况，如预测的那样在尾气区域发生自燃，而对于远离点火点的障碍物的情况内核，而是在火焰前面发生自燃并立即触发 DDT。两种模式都包含三个过程：火焰传播阶段、火焰压力波/冲击波相互作用和爆炸发展。中心线温度和压力的变化被用来明确地证明爆炸过程。冲击波形成、峰值温度、并且可以清楚地观察到压力值。首次详细分析了不同障碍物位置诱发不同爆轰模式的机理。结果表明，未燃混合物的压缩和预热温度决定了爆轰燃烧模式。该结论在初始温度变化时火焰-冲击波数变化和爆震模式转变中得到进一步证明。这项研究将为发动机中的 DDT 和爆震现象提供新的见解。该结论在初始温度变化时火焰-冲击波数变化和爆震模式转变中得到进一步证明。这项研究将为发动机中的 DDT 和爆震现象提供新的见解。该结论在初始温度变化时火焰-冲击波数变化和爆震模式转变中得到进一步证明。这项研究将为发动机中的 DDT 和爆震现象提供新的见解。