The Influence of Chemical Kinetics on the Structure of Hydrogen-Air Detonations

Abstract

Two-dimensional simulations of a detonation propagating through a 4 cm wide channel filled with a stoichiometric hydrogen-air mixture using two different models for the chemical kinetics are presented: a single-step model calibrated to compute deflagrationto-detonation transitions in hydrogen-air mixtures and a 9-species, 27-reaction mechanism specially constructed for high-pressure combustion. The detonations in both cases are qualitatively similar. Shock triple points that form along the leading edge of the front cause it to be highly corrugated and non-uniform. The trajectories of these triple points are recorded by storing the maximum pressure at each location in space. The cellular patterns formed on these numerical smoke foils are found to differ from those recorded in past experiments. The single-step model produces a hierarchy of cell structures in which the largest structures are comparable in size to experimental ones, but incomplete. Cells are incomplete at the largest scale and over an order of magnitude too small at the smallest scale. While the 27-reaction mechanism produces more regular cells, they are a factor of 3-4 smaller than those found in experiments. Agreement between the present simulation results and others found in the literature suggests that there may be a problem with using detailed thermochemical models for the extreme pressures and temperatures encountered when simulating an unstable detonation. Modifications to the single-step model parameters are presented that produce a one-dimensional detonation structure and constant volume ignition delay times that are similar to those computed using the detailed thermochemical mechanism. The two-dimensional cellular structure computed using this modified single-step reaction model is also similar to that of the 27-reaction mechanism.

2-D Simulation with OH* Kinetics of a Single-Cycle Pulse Detonation Engine

“…Furthermore, 2-D CFD coupled to chemical kinetics resulted in a cell detonation width of 1 mm. In spite of being higher than the experimental values, these findings are usual for H2-air detonation (Gamezo et al, 1999) and other 2-D simulations with chemical kinetics had the same results (Taylor et al, 2012(Taylor et al, , 2013. Simulated reaction and induction zones with thickness around 2 mm and 0.5 mm, respectively, were found.…”

“…The Green-Gauss node-based the second-order implicit method for transient formulation were applied. The setting of time-space discretization follows the works on H2-air detonation simulations (Srihari et al, 2015;Taylor et al, 2012Taylor et al, , 2013Sugiyama and Matsuo, 2012). Figure 1 shows the computational domain for the two-dimensional H2-air detonation simulation in an ideal PDE, where two regions are considered.…”

“…Ignition of stoichiometric H2-air detonation was provided by a narrow rectangular region of high pressure and temperature with circular regions in front of it, all regions are composed by H2O, as the Oran research group has applied (Tangirala et al, 2003;Taylor et al, 2012). The detonation ignition is improved by collisions from the shock front produced in the hot and compressed regions (Taylor et al, 2012). Figure 2 shows the ignition method adopted.…”

High resolution numerical simulation of triple point collision and origin of unburned gas pockets in turbulent detonations

“…In refs. [60,61] the structures obtained using detailed kinetic was not in good agreement with experimental results and it was commented that the problem in using detailed kinetic for extreme pressure and temperature caused this discrepancy. They reported that chemical kinetic mechanisms for combustion systems, in general, are not calibrated for simultaneous extremes of high pressure and temperature, such as those that occur in detonations.…”

Verified and validated calculation of unsteady dynamics of viscous hydrogen–air detonations

“…Much of detonation modelling has neglected diffusive processes, as their effects are thought to be small in comparison with advection and reaction (Shepherd 2009), cf. Fickett & Davis (1979), Oran et al (1998), Hu et al (2004Hu et al ( , 2005, Tsuboi, Eto & Hayashi (2007), Deiterding (2009) and Taylor et al (2012). However, Singh, Powers & Paolucci (1999) and Powers (2006), in a two-dimensional study of detonation patterns using a one-step kinetics model, † Email address for correspondence: cromick@nd.edu demonstrated that for the reactive Euler equations detonation patterns were griddependent.…”