Detonation propagation in hydrogen–air mixtures with transverse concentration gradients

Abstract

The influence of transverse concentration gradients on detonation propagation in H 2 -air mixtures is investigated experimentally in a wide parameter range. Detonation fronts are characterized by means of high-speed shadowgraphy, OH* imaging, pressure measurements, and soot foils. Steep concentration gradients at low average H 2 concentrations lead to single-headed detonations. A maximum velocity deficit compared to the Chapman-Jouguet velocity of 9 % is observed. Significant amounts of mixture seem to be consumed by turbulent deflagration behind the leading detonation. Wall pressure measurements show high local pressure peaks due to strong transverse waves caused by the concentration gradients. Higher average H 2 concentrations or weaker gradients allow for multi-headed detonation propagation.

2-D Simulation with OH* Kinetics of a Single-Cycle Pulse Detonation Engine

“…Simulated OH* images (Figs. 8 to 11) exhibit these multicellular structures, as has been recently experimentally observed (Boeck et al, 2013(Boeck et al, , 2016Rankin et al, 2017). Further, the detonation cells verified in OH* images were coincident with the regions of higher heat release simulated, not shown here.…”

“…At 1.25 m, the detonation front seems to be more inclined near the tube bottom wall (Fig. 11), similar experimental OH* images have shown this behaviour for a transition regime (Boeck et al, 2016). In addition, the simulated OH* image at 1.50 m displayed a reduced number of detonation cells compared with those at 1.25 m and the detonation front was straighter.…”

“…In addition, the simulated OH* image at 1.50 m displayed a reduced number of detonation cells compared with those at 1.25 m and the detonation front was straighter. However, the OH* image at the end of the tube did not characterize an unstable propagation regime or a single-head detonation (Boeck et al, 2016). Furthermore, it is supposed to have a dilution effect of the reagents due to the interface of the vacuum region at 10 Pa, where no physical barrier separating it from the fresh mixture was placed in the computational domain.…”

“…8 to 10. OH* images demonstrate stable H2-air multiheaded detonation propagation, in which the detonation front has a height of more than three detonation cells (Boeck et al, 2016). Detonation cells are defined by the shock triple point, where the reaction is very intense and the OH* concentration is high.…”

The effect of concentration gradients on deflagration-to-detonation transition in a rectangular channel with and without obstructions – A numerical study

“…The authors found that DDT propensity is increased by mixture inhomogeneity for globally lean mixtures, and may be correlated with the maximum local hydrogen concentration within the layer. Vollmer et al [6] and Boeck et al [7][8][9] reported a strong effect of concentration gradients on FA and DDT in an entirely closed channel at laboratory-scale. Boeck et al observed that in a channel with obstructions, concentration gradients promoted FA and DDT only in globally lean mixtures with an average hydrogen concentration below about 24%; for richer mixtures, the presence of gradients lead to weaker FA and delayed DDT.…”