Hot surface ignition is relevant in the context of industrial safety. In the present work, two-dimensional simulations with detailed chemistry, and study of the reaction pathways of the buoyancy-driven flow and ignition of a stoichiometric hydrogen-air mixture by a rapidly heated surface (glowplug) are reported. Experimentally, ignition is observed to occur regularly at the top of the glowplug; numerical results for hydrogen-air reproduce this trend, and shed light on this behavior. The simulations show the importance of flow separation in creating zones where convective losses are minimized and heat diffusion is maximized, resulting in the critical conditions for ignition to take place.
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.
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