Flame Acceleration, Detonation Limit and Heat Loss for Hydrogen-Oxygen Mixture at Cryogenic Temperature of 77 K

Experiments are performed in hydrogen-oxygen mixtures at the cryogenic temperature of 77 K with the equivalence ratio of 1.5 and 2.0. The optical fibers, pressure sensors and the smoked foils are used to record the flame velocity, overpressure evolution curve and detonation cells, respectively. The 1st and 2nd shock waves are captured and they finally merge to form a stronger precursor shock wave prior to the onset of detonation. The cryogenic temperature will cause the larger expansion ratio which results in the occurrence of strong flame acceleration. The stuttering mode, the galloping mode and the deflagration mode are observed when the initial pressure decreases from 0.50 atm to 0.20 atm with the equivalence ratio of 1.5, and the detonation limit is within 0.25-0.30 atm. The heat loss effect on the detonation limit is analysed. In addition, the regularity of detonation cell is investigated, and the larger post-shock specific heat ratio !"" and the lower normalized activation energy # at lower initial pressure will cause the more regular detonation cell. Also, the detonation cell width is predicted by a model of = ($) ⋅ Δ#, and the prediction results are mainly consistent with the experimental results.