Comparative study on the onset of detonation in methane–oxygen mixtures: initiation in a smooth tube and re-initiation downstreamof a single orifice plate

An experimental comparative study of the detonation re-initiation downstream of an orifice plate and the typical deflagration-to-detonation transition in a smooth tube is carried out. In this study, two tube configurations are employed to study the onset of detonation in stoichiometric methane–oxygen mixtures, i.e., a smooth tube and a tube with a single orifice plate placed in the entrance of the self-sustained detonation transmission. Combustion wave velocity measurement and soot-foil visualization are used to characterize the initiation of detonation. The dimensionless parameters correlated with cell size, tube diameter, and orifice diameter are introduced to analyze the detonation initiation process. The results indicate that the dependence of the detonation initiation distance on the initial pressure as a whole is close to inverse proportionality, and the fitting degree is higher for the detonation re-initiation downstream of the orifice plate. The effect of inherent instability of CH\(_{4}\)–2O\(_{2}\) on the onset of detonation is significantly enhanced when the cell size is smaller than the characteristic dimension of an unobstructed tube, either for deflagration-to-detonation transition in a smooth tube or for the detonation re-initiation downstream of an orifice plate.