The effect of concentration gradients on deflagration-to-detonation transition in a rectangular channel with and without obstructions – A numerical study. (8th March 2019)

• Record Type: Journal Article
• Authors: Khodadadi Azadboni, Reza; Heidari, Ali; Boeck, Lorenz R.; Wen, Jennifer X.
• Is Part Of: International journal of hydrogen energy. Volume 44:Number 13(2019)
• Page Start: 7032
• Page End: 7040
• Publication Date: 2019-03-08
• Subjects: DDT -- Detonation -- Explosions -- Hydrogen -- Inhomogeneous mixture; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2019.01.157
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Explosions in homogeneous reactive mixtures have been widely studied both experimentally and numerically. However, in accident scenarios, mixtures are usually inhomogeneous due to the localized nature of most fuel releases, buoyancy effects and the finite time between release and ignition. It is imperative to determine whether mixture inhomogeneity can increase the explosion hazard beyond what is known for homogeneous mixtures. The present numerical investigation aims to study flame acceleration and transition to detonation in homogeneous and inhomogeneous hydrogen-air mixtures with two different average hydrogen concentrations in a horizontal rectangular channel. A density-based solver was implemented within the OpenFOAM CFD toolbox. The Harten–Lax–van Leer–Contact (HLLC) scheme was used for accurate shock capturing. A high-resolution grid is provided by using adaptive mesh refinement, which leads to 30 grid points per half reaction length (HRL). In agreement with previous experimental results, it is found that transverse concentration gradients can either strengthen or weaken flame acceleration, depending on average hydrogen concentration and channel obstruction. Comparing experiments and simulations, the paper analyses flame speed and pressure histories, identifies locations of detonation onset, and interprets the effects of concentration gradients. Highlights: DDT in homogeneous and inhomogeneous H2 -air mixtures was studied numerically. A density-based solver was developed, and results compared to experiments. Numerical simulations enabled additional analyses beyond experimental observations. Gradients in unobstructed channels increase explosion hazards and promote DDT. The effect of gradients in obstructed channels depends on the mean H2 concentration.