Dynamic behavior of detonation waves in millimeter-scale tubes: unraveling the influence of tube diameter, initial pressure, and mixture

This study investigates the flame propagation behaviors of three different mixtures (C₂H₄ + 3O₂, C₃H₈ + 5O₂, and C₂H₂ + 2.5O₂ + 3.5Ar) in millimeter-scale tubes, unraveling their distinct propagation characteristics at the flame front. The experiments consider variations in mixture, initial pressure, and tube diameter, revealing shared features among them. The results indicate that, for a stable mixture, the experimentally calculated velocity deficits closely align with the theoretical predictions. However, when dealing with an unstable mixture, the velocity deficit calculated using Fay’s theory is found to be significantly overestimated. With decreasing tube diameter and initial pressure, the propagation of detonation waves exhibits periodic oscillations, such as galloping and stuttering. Additionally, the relationship between initial pressure and detonation cell width is explored, introducing the parameter (d/λ) to characterize detonation propagation capability. The experimental results demonstrate that for unstable mixtures, as the tube diameter decreases, the value of (d/λ) gradually increases, indicating that smaller tube diameters facilitate unstable detonation propagation. However, for stable mixtures, the value of (d/λ) exceeds the expected theoretical value, suggesting a higher initial pressure requirement compared to unstable mixtures for achieving detonation propagation.