Effect of Rotation on Ignition Thresholds of Stoichiometric Hydrogen Mixtures

Successful transition to a hydrogen economy calls for a deep understanding of the risks associated with its widespread use. Accidental ignition of hydrogen by hot surfaces is one of such risks. In the present study, we investigated the effect that rotation has on the reported ignition thresholds by numerically determining the minimum surface temperature required to ignite stoichiometric hydrogen-air using a hot horizontal cylinder rotating at various angular velocities, ω. Numerical experiments showed a weak but interesting dependence of the ignition thresholds on rotation: the ignition thresholds increased by 8 K, from 931 K to 939 K, with increasing angular velocity (0 ≤ ω ≤ 240 rad/s). A further increase to ω = 480 rad/s resulted in a decrease in ignition surface temperature to 935 K. Detailed analysis of the flow patterns inside the vessel and in close proximity to the hot surface brought about by the combined effect of buoyancy and rotation, as well as of the distribution of the wall heat flux along the circumference of the cylinder, support our previous findings in which regions where temperature gradients are small were found to be prone to ignition.