Abstract
A combined experimental and numerical study was carried out to investigate thermal ignition by millimeter size (d=6 mm) moving hot spheres in H2-O2-N2 environments over a range of equivalence ratios. The mixtures investigated were diluted with N2 to keep their laminar flame speed constant and comparable to the sphere fall velocity (2.4 m/s) at time of contact with the reactive mixture. The ignition thresholds (and confidence intervals) were found by applying a logistic regression to the data and were observed to increase from lean (Φ=0.39; Tsphere = 963 K) to rich (Φ=1.35; Tsphere = 1007 K) conditions. Experimental temperature fields of the gas surrounding the hot sphere during an ignition event were, for the first time, extracted using interferometry and compared against simulated fields. Numerical predictions of the ignition thresholds were within 2% of the experimental values and captured the experimentally observed increasing trend between lean and rich conditions. The effect of stoichiometry and dilution on the observed variation in ignition threshold was explained using 0-D constant pressure delay time computations.
Highlights
There is a continuing interest in the aircraft, nuclear power, and chemical processing industries to investigate and understand the hazards associated with accidental ignition events [1]
This study aims to provide: (i) new data on the ignition thresholds for hydrogen mixtures by moving hot particles; (ii) quantitative two-dimensional temperature fields of the gas surrounding the hot sphere during ignition; and (iii) numerical modelers with validated experimental ignition thresholds and quantitative two-dimensional temperature fields during an ignition event
The numerical simulations predicted thresholds that were within 2% of the experimentally determined values
Summary
There is a continuing interest in the aircraft, nuclear power, and chemical processing industries to investigate and understand the hazards associated with accidental ignition events [1]. Such events can lead to an explosion or other catastrophic failure of the craft or plant resulting in loss of life and infrastructure and a high environmental impact. This study aims to provide: (i) new data on the ignition thresholds for hydrogen mixtures by moving hot particles; (ii) quantitative two-dimensional temperature fields of the gas surrounding the hot sphere during ignition; and (iii) numerical modelers with validated experimental ignition thresholds and quantitative two-dimensional temperature fields during an ignition event. We comment on the implications of our results to the correlation proposed by Roth et al [9]
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