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Detonation Initiation at the Focusing of Shock Waves in Combustible Gaseous Mixture
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gelfand, Boris E. |
| Copyright Year | 1999 |
| Abstract | The detonation initiation under the focusing conditions in a hydrogen air mixture was experimentally investigated. It has been found that the mild ignition inside reflector cavity can lead to detonation initiation. Schlieren pictures of the process were obtained and the dependence of the distance of initiation on the incident shock wave Mach number was established. Introduction The phenomenon of shock waves focusing in the inert medium on a reflector located in a shock tube has been extensively studied during last 20 years. This phenomenon is less investigated in the case of combustible gaseous mixtures. The regions with high pressure and temperature resulting from a collision of a shock wave with a reflector can give birth to different modes of reaction front propagation. The possibility of realization of mild (combustion) and strong (detonation) modes of ignition in the highly sensitive oxyhydrogen mixture dependencies on the Mach number of the incident shock wave [1]. The existence of two modes of ignition was shown for stoichiometric hydrocarbon-air mixtures in [2]. The experimental featuring the focusing in hydrogenair mixtures [3] revealed the different ignition mode that is characterized by the high pressure spikes behind the reflected shock wave. The values of the Mach numbers for this mode of the ignition fall in the range between Mach numbers for mild and strong ignition. In the present work the process of detonation initiation due to the focusing of the shock waves of different intensities was investigated. Experimental The experiments were carried out using a shock tube of 54 mm x 54 mm in cross section, low pressure section of 6.25 m in length and high pressure section of 3.15 m in length. The laser schlieren high-speed photography was used simultaneously with the pressure recording by transducers located on the top and bottom walls of the tube. Lean hydrogen – air mixture (15% vol. H 2) at initial pressure 26.3-40 kPa was used in the experiments. The symmetrical wedge reflector with apex angle of 90 was used for the focusing of shock waves. The Mach number was calculated by processing the instants of the incident shock wave arrival on the pressure transducers with the accuracy about 2%. Results The experiments show that at Mach numbers of the incident shock wave ≥ 2.52 the detonation is initiated in the volume adjacent to the reflector apex. At the beginning of propagation the detonation appears as a cylindrical wave, and after leaving of the reflector cavity transforms into the plane detonation wave. The parameters of this wave correspond well to the parameters of detonation propagating in the mixture compressed by initial shock wave. This case can be classified as an analog of direct detonation initiation by the high energy pulse. Decreasing the Mach number of the incident shock wave to the value of M = 2.47 leads just to the combustion mode behind the reflected shock wave. Detonation in this case is initiating at the some distance L from the edge |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.icders.org/ICDERS1999/PapersICDERS1999/ICDERS1999-050.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
