Effects of boundary conditions on premixed CH4+2O2 detonation characteristics
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摘要: 通过实验研究及数字化处理研究了边界条件对CH4预混气体爆轰特性的影响。在内径为63.5、50.8 mm圆柱形管道及长方体管道进行爆轰实验，得到胞格结构和爆轰速度曲线。烟膜数字化处理量化了预混气体的爆轰不稳定性，并计算出胞格尺寸。3种管道内测得的平均爆轰速度与CJ速度接近，边界条件的影响不明显。分析爆轰速度曲线发现，极限压力受到边界条件的影响，Ø50.8和Ø63.5 mm管道内预混气的极限压力分别为5和4.05 kPa，即随着管径增大，爆轰极限压力降低。数字化处理所得不同管道内烟膜轨迹的不规则程度无明显差别，因此可以认为不稳定性是预混气固有的性质。在相同爆轰初始压力下，管径增大，胞格数量变多，表明爆轰传播时爆轰螺旋头数增多以维持传播。Abstract: To find out the exact effects of boundary conditions on premixed CH4+2O2 detonation characteristics, detonation experiments were conducted respectively in two cylindrical tubes with inner diameters of 63.5 mm and 50.8 mm and one rectangle tube. The detonation velocity curves were obtained using a signal detection system, and cellar patterns drawn from the smoked-foil records were obtained using a digital image processing program. Quantitative irregularities of CH4+2O2 detonation and cell size data under different initial pressures in the three tubes were analyzed and compared. It is found that the average velocities in the three tubes always closely resembled vcj, showing that the detonation velocity is mainly determined by the initial detonation pressure and mixture type rather than by the boundary conditions. In addition, judging by the detonation velocity curves, the limit pressures of the tubes with inner diameter of 50.8 and 63.5 mm are 5 and 4.05 kPa, respectively. Therefore, the boundary conditions can influence the limit pressure. Quantitative irregularities exert little significant difference under different boundary conditions of the tubes. Besides, as the detonation needs to compensate for the energy loss with the increase of the tube diameter, there is a greater number of spin heads in the tubes.
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图 1 Ø50.8 mm爆轰管道结构简图
Figure 1. Detonation tube structure with inner diameter of 50.8 mm
图 2 Ø50.8 mm管道内CH4+2O2预混气不同初始压力下爆轰烟膜
Figure 2. Smoked foils of premixed CH4+2O2 in tube with inner diameter of 50.8 mm
图 3 不同初始压力下Ø50.8 mm管道内CH4+2O2爆轰速度曲线
Figure 3. Velocity curves of premixed CH4+2O2 in Ø50.8 mm tube at different initial pressures
图 4 Ø63.5 mm爆轰管道结构简图
Figure 4. Detonation tube structure with inner diameter of 63.5 mm
图 5 Ø63.5 mm管道内CH4+2O2预混气不同初始压力下爆轰烟膜
Figure 5. Smoked foils of premixed CH4+2O2 in tube with inner diameter of 63.5 mm
图 6 不同初始压力下Ø63.5 mm管道内CH4+2O2爆轰速度曲线
Figure 6. Velocity curves of premixed CH4+2O2 in Ø63.5 mm tube at different initial pressures
图 8 矩形截面管道内CH4+2O2爆轰烟膜
Figure 8. Smoked foils of premixed CH4+2O2 in the rectangle tube
图 9 矩形截面管道内CH4+2O2预混气爆轰速度
Figure 9. Velocity of premixed CH4+2O2 in the rectangle tube
图 10 Ø50.8 mm管道内烟膜轨迹线
Figure 10. Trajectory in two sets in tube with inner diameter of 50.8 mm
图 11 Ø63.5 mm管道内烟膜轨迹线
Figure 11. Trajectory in two sets in tube with inner diameter of 63.5 mm
图 12 Ø50.8 mm管道内典型轨迹柱状图
Figure 12. Typical trajectory histograms of tube with inner diameter of 50.8 mm
图 13 Ø63.5 mm管道内典型轨迹柱状图
Figure 13. Typical trajectory histograms of tube with inner diameter of 63.5 mm
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