环形管道内爆轰起爆促进机制及传播特性研究

The operating frequency of the PDE (Pulse Detonation Engine, PDE) is one of the critical indicators to evaluate its performance. For a given the length of the combustor, the frequency is mainly determined by both DDT (Deflagration to Detonation Transition) process and velocity of detonation propagation in a tube. According to previous studies, the strength of the shock wave can be effectively enhanced by the effect of the convergence in annular channels, and hence the DDT process happens earlier. Besides, the velocity of detonation propagating in the annular channel is found to be faster than that in straight channel. Based on these findings, theoretical, numerical and experimental approaches will be adopted to do in-depth and systematic research on the detonation phenomena in annular channels in the present project. Detailed research contents are as follows: (1) the promoted mechanism of DDT process will be investigated; (2) the effect of the geometry of the annular channel and the condition of the mixtures on the stability of detonation will be dissected; (3) the mechanism of the change of detonation propagation modes will be investigated; (4) the parameters of the detonation, such as periodic angle and velocity deficit, will be identified to obtain the criterion for detonability limits. The project is to explore new rules and mechanisms of the initiation and propagation of the detonation wave in annular channels, and its results are expected to provide realistic guidance to the design and optimization of PDE.

脉冲爆轰发动机（Pulse Detonation Engine,简称PDE）运行频率是评估其性能优劣的重要指标之一，对于给定的燃烧室长度，爆轰的产生及管内运行时间决定了脉冲频率的高低。研究发现，环形管道能够有效的增强激波强度，进而加快缓燃向爆轰转捩（Deflagration to Detonation Transition，简称DDT）过程；另外，爆轰波在环形管道内的传播速度大于常规直管。鉴于此，本项目采用实验研究、数值模拟与理论分析相结合的方法对环形管道内的爆轰现象进行深入和系统的研究，具体探究DDT过程的促进机制，剖析燃烧室尺寸及预混气条件对爆轰稳定传播的影响规律，揭示爆轰波传播模式的转变机理，确定临界条件下爆轰参数从而获得爆轰传播极限的判定准则。本项目旨在探索环形管道内爆轰起爆和传播模式的规律和机理，研究结果对PDE的设计和优化具有一定的指导意义。

脉冲爆轰发动机（Pulse Detonation Engine,简称PDE）运行频率是评估其性能优劣的重要指标之一，对于给定的燃烧室长度，爆轰的产生及管内运行时间决定了脉冲频率的高低。研究发现，环形管道能够有效的增强激波强度，进而加快缓燃向爆轰转捩（Deflagration to Detonation Transition，简称DDT）过程；另外，爆轰波在环形管道内的传播速度大于常规直管。鉴于此，本项目采用实验研究、数值模拟与理论分析相结合的方法对环形管道内的爆轰现象进行深入和系统的研究，具体探究DDT过程的促进机制，剖析燃烧室曲率及预混气条件对爆轰稳定传播的影响规律，揭示爆轰波传播模式的转变机理，确定临界条件下爆轰参数从而获得爆轰传播极限的判定准则。对于一个弯曲的通道，在热点点火之前观察到三种火焰形状（球形、郁金香形和舌形）。在舌形火焰和外壁之间形成了一个未反应气体的漏斗，在这个漏斗处最易触发热点。热点的位置在很大程度上取决弯曲通道内的初始压力。当压力相对较低时（p0 < 22 kPa），热点总是在舌形火焰和外壁的交汇处（舌形火焰的根部）点燃，而相对较高的初始压力（p0 > 33 kPa）会导致热点在靠近舌形火焰头部的外壁表面出现。在中间压力下，即22≤p0≤33，热点处于上述两个位置之间。DDT发生后，实验获得了三种爆轰传播模式，即稳定模式、临界模式和不稳定模式。Ri/λ的比率被引入作为敏感参数来描述爆轰传播的能力，其中Ri为环形燃烧室的内径，λ代表爆轰胞格宽度。在本研究中，发现环形管道内的爆轰传播极限在2.6≤Ri/λ≤4.8的范围内。本项目旨在探索环形管道内爆轰起爆和传播模式的规律和机理，研究结果对PDE的设计和优化具有一定的指导意义。