Direct observations of reaction zone structure in propagating detonations

Abstract

We report experimental observations of the reaction zone structure of self-sustaining, cellular detonations propagating near the Chapman-Jouguet state in hydrogenoxygen-argon/nitrogen mixtures. Two-dimensional cross sections perpendicular to the propagation direction were imaged using the technique of planar laser induced fluorescence (PLIF) and in some cases, compared to simultaneously acquired schlieren images. Images are obtained which clearly show the nature of the disturbances in an intermediate chemical species (OH) created by the variations in the strength of the leading shock front associated with the transverse wave instability of a propagating detonation. The images are compared to two-dimensional, unsteady simulations with a reduced model of the chemical reaction processes in the hydrogen-oxygenargon system. We interpret the experimental and numerical images using simple models of the detonation front structure based on the "weak" version of the flow near the triple point or intersection of three shock waves, two of which make up the shock front and the third corresponding to the wave propagating transversely to the front. Both the unsteady simulations and the triple point calculations are consistent with the creation of keystone-shaped regions of low reactivity behind the incident shock near the end of the oscillation cycle within the "cell".

Numerical Investigation on Detonation Control Using a Pulse Hot Jet in Supersonic Combustible Mixture

“…When the hot jet is shut down, the contractive passway produced by the hot jet vanishes gradually. As shown in Fig.10, the slopes of the two curves both decrease after the shutdown of the hot jet, Fig.11, and the detonation structures are quite similar to the experimental images of CJ detonation for H 2 /O 2 /Ar mixture presented by Pintgen et al (Pintgen et al, 2003) As shown in Fig.12, when the hot jet is injected into the channel again at 900 μs t  , the CJ detonation changes to overdriven detonation once again because of reformation of the contractive passway. It is indicated that the newly formed overdriven detonation in stage D has almost the same overdrive degree as stage A, because the same contractive passway is generated in the flowfield after the re-injection of the same hot jet.…”

Hydrodynamic Instabilities in Gaseous Detonations: Comparison of Euler, Navier–Stokes, and Large-Eddy Simulation

“…Therefore, in this work L ≅ 50 HRL was chosen for a mixture with E a ∕RT o 20. Table 1 shows the thermophysical properties of the mixture considered in the present work also used in other investigations (e.g., [16,46,47] [15,[54][55][56]. The activation energy corresponds to the mixtures such as hydrogen-oxygen, acetylene-oxygen, and methane-oxygen at low pressures (see [7,10,15,54,[57][58][59]).…”

Adaptive simulations of viscous detonations initiated by a hot jet using a high-order hybrid WENO–CD scheme

“…Previous investigations indicate that the large-scale characteristics of a KH instability are visible when the shear layer is highly unstable [33] and the effect of viscosity and diffusion on the large-scale 12 characteristics of a RM instability is negligible [34]. It may be concluded that diffusion effect can easily suppress the small-scale vortices produced by KH instability, but only play a minimal role in the suppression of the large-scale vortices associated with highly unstable shear layers and driven by RM instability.…”