The influence of wall roughness on detonation limits in hydrogen–oxygen mixture

In this study, wall roughness is generated by inserting a Shchelkin spiral with different wire diameter (δ) and pitch (Ls). Roughness is defined as the ratio δ/Ls. The effect of tube wall roughness on the detonation limits in stoichiometric hydrogen–oxygen mixture is systematically examined. The detonation velocity is determined from optical fibers and shock pins spaced at 10 cm intervals along the tube. Smoked foils are employed to record the cellular detonation structure near the limits. The experimental results indicate that detonation in both smooth and rough sections can be self-sustaining and can propagate with a steady velocity as the conditions are well within the detonation limits. However, the detonation velocity decreases as it transmits into the rough-walled tube. The velocity deficit is more significant in tubes with larger roughness due to the interaction of the detonation reaction zone and the boundary layer formed behind the shock. Single-headed spinning structure is observed as the detonation approaches the limits in the rough-walled tube. Below the minimum initial pressure at which single-headed spinning phenomena occur, detonation fails and decays to deflagration, and the minimum velocity is approximately 0.4VCJ. It is found that wall roughness can either promote or prohibit the detonation propagation limits. When the roughness is smaller than 0.231, it is believed the turbulence generated from the roughness facilitates detonation and extends the detonation limits. However, when the roughness is larger than 0.333, low-velocity behavior plays a dominant role in prohibiting the detonation, which indicates that roughness above a certain level has a negative effect on detonation limits.