Detonation Propagation in Hydrogen/Methane-Air Mixtures in a Round Tube Filled with Orifice Plates

In this study experiments were carried out in a round tube, 5 800 mm in length and 48 mm in inner-diameter, filled with orifice plates, to investigate the detonation of hydrogen-air mixtures and stoichiometric hydrogen-methane-air mixtures, and the DDT (Deflagration-to-Detonation Transition) limits were determined.The blockage ratio of the orifice plates was 0.56, and the spacing was divided into two, i.e., S=D and S=2D, in which S and D are the obstacle spacing and the tube diameter.The flame velocity was obtained using photodiodes mounted on the tube wall.The results show that the flame regime observed is the quasi-detonation or the choked flame.The flame velocity measured for S=2D is larger than that for S=D, and the velocity fluctuation is more significant.This indicates that the cycle of the detonation failure and re-initiation is longer for S=2D, which is similar to the "galloping detonation".For hydrogen-air mixtures, detonation re-initiation occurs more aptly at S=2D, and the limits correlate well with d/λ≈1.In the case of hydrogen-methane-air mixtures, the DDT limits for S=D and S=2D are both consistent with d/λ≈1, where d and λ are the inner diameter of the orifice plate and the detonation cell size.The results indicate that the obstacle spacing has a significant effect on the propagation of detonation, i.e., detonation propagates more aptly for increased spacing.To generate the quasi-detonation, the opening of the orifice plate has to be large enough to contain at least one cell size while the spacing has to be large enough to form detonation re-initiation.