Cellular stability of hydrogen–oxygen detonation

Abstract

A detonation cellular stability mechanism based on the dynamics of reactive decaying blasts is examined through detailed analyses of two-dimensional (2D) numerical simulations of hydrogen-oxygen detonations. Different from previous blast-based examinations, we resolve the transient process of decoupling between shock and reaction fronts in decaying blasts, and correlate the size of unburnt gas mixtures behind decaying shocks to that of the subsequent blast kernels. The impact on the stability mechanism of (1) chemical kinetics, (2) diffusive processes, and (3) boundary conditions are examined through a series of simulations. At a dopant level, ozone is known to reduce ignition delay without altering thermodynamic properties of the mixture, enabling investigation of the impact of ignition kinetics on the cellular stability. The addition of ozone leads to a stronger coupling between shock and reaction fronts and stabilizes the blast kernel to a smaller size. The resulting global cell size reduction in the ozonated detonation is well described by the stability analysis and in agreement with experimental cell measurements reported in Crane et al., Combust. Flame 200 (2019) 44–52. The inclusion of diffusive physics marginally affects the detonation cellular structure, but causes a global propagation speed deficit. Results from two channel heights show that cell size increases in the smaller channel due to mode-locking. A detailed grid convergence study is performed, which examines both kinetic and macroscopic structural features as a function of grid resolution. The results of the stability analysis is independent of numerical grid resolution.

Novelty and Significance Statement

This work develops a novel theory for detonation cellular stability, enabling the prediction of detonation cell size and instabilities. Theory validation leverages the statistical analysis of blast propagation and decoupling, which is an entirely new way of post-processing detonation simulation. This work also presents the first time, to our knowledge, the link between molecular viscosity and cellular structure has been isolated, accomplished through a set of simulations using both Navier-Stokes and Euler equations, and several boundary conditions. This work is impactful because it enables and validates the modeling of detonation propagation behavior using a blast-based construct. This blast-based construct is many orders of magnitude less expensive as compared to conventional CFD.