The near-limit gaseous detonation behavior of three different methane–oxygen mixtures was investigated. Experiments were performed in transparent tubes of three different inner diameters (d). Due to the relatively large tube length l ($$\frac{l}{d} > 2500$$ except $$\frac{l}{d} > 1000$$ for the largest diameter), the tube was arranged in a spiral configuration for the convenience of testing. Photodiodes were spaced at uniform intervals along the tube to provide a high-resolution velocity measurement, such that up to eight cycles of the galloping mode were registered. From the velocity histogram and the probability distribution function, a bimodal behavior was observed in all galloping regimes for different unstable mixtures, with dominant modes near 70% of the Chapman–Jouguet detonation velocity ($$0.7D_{\mathrm{CJ}}$$) and $$D_{\mathrm{CJ}}$$. With decreasing pressure, the lower-velocity mode became more prevalent until the failure of detonation. The range of initial pressures, within which galloping detonations were observed, decreased rapidly with increasing tube diameter and with increasing mixture stability. These results suggest that both the instability and the boundary effect influence the existence of galloping detonations. The normalized wavelength of the galloping cycle ($$\frac{L}{d}$$) was in the range of 200–450 for the three different mixture compositions and exhibited a general trend that the wavelength increased with decreasing initial pressure.

中文翻译：

---

长细管中甲烷-氧气混合物的接近极限爆炸

研究了三种不同的甲烷-氧气混合物的近极限气态爆轰行为。实验在三种不同内径 (d) 的透明管中进行。由于管长 l 相对较大（$$\frac{l}{d} > 2500$$ 除了 $$\frac{l}{d} > 1000$$ 为最大直径），管被安排在一个螺旋配置，方便测试。光电二极管沿着管子以均匀的间隔排列，以提供高分辨率的速度测量，从而记录多达八个循环的疾驰模式。从速度直方图和概率分布函数中，在不同不稳定混合物的所有疾驰状态中都观察到双峰行为，主要模式接近查普曼-朱盖爆炸速度的 70%（$0.00 美元）。7D_{\mathrm{CJ}}$$) 和 $$D_{\mathrm{CJ}}$$。随着压力的降低，低速模式变得更加普遍，直到爆炸失败。随着管径的增加和混合物稳定性的增加，在其中观察到飞驰爆轰的初始压力范围迅速减小。这些结果表明，不稳定性和边界效应都会影响飞驰爆轰的存在。对于三种不同的混合物组成，奔马循环的归一化波长（$$\frac{L}{d}$$）在 200-450 的范围内，并且表现出波长随着初始压力降低而增加的总体趋势。在其中观察到飞驰爆轰，随着管直径的增加和混合物稳定性的增加而迅速下降。这些结果表明，不稳定性和边界效应都会影响飞驰爆轰的存在。对于三种不同的混合物组成，奔马循环的归一化波长（$$\frac{L}{d}$$）在 200-450 的范围内，并且表现出波长随着初始压力降低而增加的总体趋势。在其中观察到飞驰爆轰，随着管直径的增加和混合物稳定性的增加而迅速下降。这些结果表明，不稳定性和边界效应都会影响飞驰爆轰的存在。对于三种不同的混合物组成，奔马循环的归一化波长（$$\frac{L}{d}$$）在 200-450 的范围内，并且表现出波长随着初始压力降低而增加的总体趋势。