Numerical Investigation of the Impact of the Diffusion Time on the Transition Mechanisms from a Turbulent Premixed Flame to Detonation in a Hydrogen-Air Mixture

Abstract

Numerical simulations were performed for the investigation of diffusion time on the detonation in premixed hydrogen-air mixtures. Hydrogen-air mixtures containing average hydrogen concentrations of 22.5% and 30% were examined under an initial pressure of 1 atm. Numerical results are presented for accelerated flames within gas mixtures exhibiting vertical concentration gradients in a confined channel obstructed by an obstacle. The employed solution methodology was the finite-volume method incorporating the ??? ??? turbulence model and the Weller flame wrinkling combustion model. The Harten-Lax-Van Leer Contact method was also implemented to capture shock waves. The findings underscore the pronounced influence of vertical concentration gradients on flame acceleration (FA). In the case of the inhomogeneous hydrogen-air mixture with an average hydrogen concentration of 22.5% (lean mixture), detonation occurred in all instances. A comparative analysis of flame-speed profiles revealed that reductions in diffusion time, coupled with heightened mixture inhomogeneity, expedited both flame propagation and the occurrence of the deflagration to detonation transition (DDT) within the channel. For the inhomogeneous hydrogen-air mixture characterized by an average hydrogen concentration of 30% (close to stoichiometric mixture), DDT was observed across all scenarios. However, the presence of mixture inhomogeneity attenuated flame acceleration and led to delays in the DDT phenomenon.