Experiments on spinning detonations with detailed analysis of the shock structure

Spinning detonations are characteristic of detonation limit phenomena in round tubes. In this work we study experimentally the structure of the transverse wave of single-headed spinning detonations. The flow field is experimentally analysed and an original approach enables us to calculate the overall shock structure. The calculations and experimental results indicate that the actual structure of the spinning detonation tries to match closely to the condition where the state parameters (pressure and temperature) reach their maximum values. This condition corresponds to a spinning head where the Mach stem is normal to the incoming flow and could be readily used as boundary condition by further investigators to determine the structure of spinning detonations

Inhibition of detonation wave with halogenated compounds

The influence of CF3Br, CF2HBr, CF2HCl and CF3H on a benchmark mixture composed of stoichiometric H-2-CO-O-2-Ar is experimentally investigated. Several ratios hydrogen/carbon monoxide are studied. For each benchmark mixture, the initial pressure is adjusted in such a way that the detonation cell sizes are quasi identical. The effect of the additives on the detonation velocity and the detonation cellular structure is analyzed. The experiments show that CF3Br is the best inhibitor and CF2HBr might be substituted for CF3Br. CF3H does not inhibit the detonation wave. Simple chemical kinetics analysis gives us a better understanding of the inhibiting and promoting effect of the halocarbons

Pressure profiles in detonation cells with rectangular and diagonal structures

Experimental results presented in this work enable us to classify the three-dimensional structure of the detonation into two fundamental types: a rectangular structure and a diagonal structure. The rectangular structure is well documented in the literature and consists of orthogonal waves travelling independently front each another. The soot record in this case shows the classical diamond detonation cell exhibiting 'slapping waves'. The experiments indicate that the diagonal structure is a structure with the triple point intersections moving along the diagonal line of the tube cross section. The axes of the transverse waves are canted at 45 degrees to the wall, accounting for the lack of slapping waves. It is possible to reproduce these diagonal structures by appropriately controlling the experimental ignition procedure. The characteristics of the diagonal structure show some similarities with detonation structure in round tube. Pressure measurements recorded along the central axis of the cellular structure show a series of pressure peaks, depending on the type of structure and the position inside the detonation cell. Pressure profiles measured for the whole length of the two types of detonation cells show that the intensity of the shock front is higher and the length of the detonation cell is shorter for the diagonal structures

Preliminary experimental investigation of the pressure evolution in detonation cells

Recently two types of three-dimensional (3D) structure of gaseous detonation have been documented: rectangular and diagonal modes easily distinguishable from soot records. This paper presents pressure measurements recorded along the central axis of the cellular structure. The pressure records are achieved rd by using piezoelectric gauges flush-mounted with respect to the surface of the soot-covered plate located in the detonation tube. The low pressure reactive mixture used (H-2, O-2, Ar; Equivalence ratio = 1) is ignited in a square cross-section tube. The detonation tube is operated in the shock tube mode. The time evolution of the local pressure exhibits several pressure peaks depending on the type of 3D structure and on the position in the detonation cell. The first peak characterizes the leading shock and the subsequent pulses correspond to the elaborate shock structure, The influence of the slapping waves (SW) is documented. The pressure profiles throughout the whole length of the detonation cell ale reported for the individual types of 3D structure. The second pressure jumps can be rationalized in terms of the classical transverse wave structure. (C) 2000 Elsevier Science Inc. All rights reserved

Modeling of Gas-phase Detonation in Complex Reactive Systems

A numerical study of detonations in hydrogen-oxygen-argon mixtures containing CF4 or CF3H is presented. Experiments have established the promoting effect of these additives on the detonation velocity. The Chapman-Jouguet model fails to explain the observed behavior and a numerical approach solving the steady equations of the fluid dynamics provides a first grasp of such an unexpected behavior. In this paper, we use a numerical model that solves the unsteady equations of the fluid dynamics to simulate the detonation wave and to predict the stabilized detonation velocity. The chemical model used is a parametric one that takes into account a temperature and composition dependence of the heat capacity. In a serie of one-dimensional calculations, we describe first the numerical ignition of the detonation wave. In particular, we examine the effect of the pressure in the driving gas section of the numerical domain. Then, we examine the influence of the additives on the detonation wave propagating in a mixture of H-2/O-2/Ar. We compare successfully the results of the modeling to experimental data. The promoting behavior of both fluorocarbons is numerically observed up to about 10% of the additives. Our conclusion is that it is possible to model the overall description of a detonation wave in complex reactive system. Prerequisites are the knowledge of the chemical kinetics to within a reasonable accuracy, robust algorithm for computing the fluid dynamics and attention to coupling

The Influence of the Heat-capacity and Diluent On Detonation Structure

In this article, we investigate the validity of certain common simplifications in the chemical and thermophysical models used as input to multidimensional detonation simulations, derive a more accurate model, and apply the model in two-dimensional studies of the structure detonations in hydrogen-oxygen mixtures diluted with argon and nitrogen. In a series of one-dimensional calculations, we examine the effects of (1) approximation of the temperature dependence of the ratio of specific heat, gamma, (2) varying the amount and rate of heat release, and (3) varying the chemical induction time, and we compare all of these approximations with a computation that uses a detailed model of the chemical kinetics and correct thermophysics. From these, we derive a simple form for the temperature dependence of gamma and show that this gives good results in comparison to the predictions of the detailed calculation for the detonation velocity and the thickness of the induction zone. In a series of two-dimensional calculations, we investigate the effects of using the more accurate simplified chemical models and varying the type of diluent while maintaining the same dilutions. In agreement with experiments, the mixture of hydrogen, oxygen, and argon mixture shows regular detonation structures and clearly formed detonation cells, whereas the mixture of hydrogen, oxygen, and nitrogen shows highly irregular cellular structure