Effects of vitiation on the shock-induced combustion of hydrogen-air mixtures

Abstract

In order to achieve a more thorough understanding of the impacts of vitiation on supersonic combustion, a series of numerical simulations are performed to investigate the shock-induced combustion of hydrogen-air mixtures. Direct comparisons are made between electric heating, in which the mixture is brought up to the designated temperature without modifying its composition, and vitiated heating, in which the mixture is heated by the products of hydrogen-air combustion. While the cases with electric heating have much higher thermicities than the cases with vitiation at a given condition, vitiated heating tends to have smaller induction lengths than electric heating for lower temperatures and richer mixtures. At reasonable residence times, this decrease in induction length is primarily caused by the presence of nitric oxide in the vitiated mixture and not by hydroxyl or hydrogen radicals, which implies that nitrogen chemistry cannot easily be neglected in studies of supersonic ignition and detonation.