Numerical Study of Detonation Propagation in a Nonuniform Hydrogen-Oxygen Layer Bounded by an Inert Gas

Abstract

This numerical study investigates the propagation failure and limits of a detonation through stoichiometric hydrogen-oxygen layer stratified above an inert gas with a diffuse interface at atmospheric pressure. The study simulates previously-conducted experiments where the layer is buoyancy driven. Diffusive gravity current simulations are used to generate the initial conditions. Detonation propagation is modeled by solving the two-dimensional reactive Euler equations for a calorically perfect gas with single-step Arrhenius chemistry. To account for acoustic impedance gradients under the limitations of the perfect gas assumption, the initial temperature is varied throughout the simulated mixture while pressure and density are held true to the physical experiments, where pressure and temperature were uniform. The simulations are validated using the physical stoichiometric hydrogen-oxygen experiments this numerical study strives to replicate. Numerical soot foils are generated from simulations and are compared to the experiment’s. The study verified Bauwen’s and Dorofeev’s failure criteria for non-uniform reactant mixtures which states a minimum of 5-7 cells are needed for a detonation to sustain itself under the bounds of dλ/dx ≤ 0.1. Two models are proposed to investigate the failure in the diffuse layer reported in experiments. Both consist of tailoring the activation energy of the mixture spatially based on the inert gas dilution; one accounts for the non uniform temperature within the domain calculated by the numeric code, the other maintains the correct constant volume ignition time. Re-initiation of the detonation in the diffuse layer was seen through regeneration of triple points that seep into the reactive layer. These triple points that generate new detonation cells are credited to inflection zones that occur in the diffuse layer that develop because of the local increase in detonation strength.