Auto-ignition effect in gaseous detonation propagation
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摘要: 基于基元反应模型和单步反应模型，对直管道中H2-air混合气体中爆轰波的传播过程进行了数值模拟，揭示了气相爆轰波传播过程中的自点火效应。利用数值模拟方法计算了不同爆轰模型的点火延迟时间，并得到了爆轰波三波点的传播过程以及所形成胞格结构的尺寸。结果表明，胞格宽度与点火延迟时间成正比；爆轰波诱导区内气体的点火延迟时间与三波点的运动周期基本一致。进一步对结果分析可知，爆轰波的自维持传播取决于点火延迟时间(表征化学反应的特征时间)和三波点的运动周期(表征流动的特征时间)的匹配；当二者相匹配时，经过前导激波压缩后形成的高温高压爆轰气体，在短时间内实现了自点火，同时释放出大量的能量推动了爆轰波的前进，即爆轰波的稳定自维持传播依靠其自点火机制。Abstract: In this paper, the auto-ignition mechanism in the gaseous detonation propagation of the stoichiometric H2-air detonable mixture in a straight tube was numerically studied using an overall one-step chemical reaction model and a detailed chemical reaction model based on the two-dimensional Euler equations. Meanwhile, the ignition delay times predicted by different models under different pressures and at different temperatures were compared and the propagation process of triple-shock points and the cell sizes were investigated. The results demonstrated that the cell sizes are proportional to the ignition delay times, and the ignition delay time in the induction zone is consistent with the average movement period of the triple-shock points. The leading shock compresses the detonable gas and then both the temperature and the pressure of the gas rise. The gas with high temperature and pressure soon finishes the process of auto-ignition, and a lot of heat is released during the ignition to maintain the detonation propagation, which means the auto-ignition mechanism ensures the self-sustained detonation propagation. The ignition delay time is considered as a chemical time scale characterizing the chemical reaction. The period of the movement of the triple-shock points is a characteristic time scale of shock dynamics. The coupling of these two time scales is a principal mechanism in gaseous detonation propagation.
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Key words:
- cellular detonation /
- auto-ignition /
- ignition delay time /
- triple-shock points
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图 2 模型和实验预测的点火延迟时间对比
Figure 2. Comparison of ignition delay times predicted by two models and the experimental data
图 3 不同压力下model-1和model-2的点火延迟时间
Figure 3. Comparison of ignition delay times predicted by model-1 and model-2 at different pressures
图 4 不同化学反应模型预测的点火延迟时间
Figure 4. Comparison of ignition delay times predicted by different chemical reaction models
图 5 采用model-1数值模拟二维爆轰波传播，流场的压力等值线
Figure 5. Instantaneous contours of pressure for a two-dimensional detonation propagation simulated by model-1
图 6 采用model-1数值模拟的一对三波点的压力等值线分布
Figure 6. Movement of triple-wave points shown with the pressure contour maps in the numerical simulation by model-1
图 7 采用model-2数值模拟二维爆轰波传播，流场的压力等值线
Figure 7. Instantaneous contours of pressure for a two-dimensional detonation propagation simulated by model-2
图 8 采用model-2数值模拟的一对三波点运动的胞格结构
Figure 8. Movement of triple-wave points shown with the cellular structure simulated by model-2
图 9 采用model-1数值模拟二维H2-air爆轰波的胞格结构
Figure 9. Cellular structures for a two-dimensional H2-air detonation simulated by model-1
图 10 采用model-2数值模拟二维H2-air爆轰波的胞格结构
Figure 10. Cellular structures for a two-dimensional H2-air detonation simulated by model-2
表 1 单步反应模型的参数取值
Table 1. Parameters of one-step reaction model
ZU ZB γU γB RU/(J·kg-1·K-1) RB/(J·kg-1·K-1) Ea/(J·kg-1) K/s-1 q/(J·kg-1) 1.0 0 1.40 1.24 398.5 368.9 4.794×106 7.5×106 3.5×106 
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