著者

Maeda Shinichi Sumiya Satoshi Kasahara Jiro Matsuo Akiko

出版者

Elsevier Inc.

雑誌

Proceedings of the Combustion Institute (ISSN:15407489)

巻号頁・発行日

vol.34, no.2, pp.1973-1980, 2013

被引用文献数

27

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Direct initiations and stabilizations of three-dimensional conical detonation waves were attained by launching spheres with 1.06–1.31 times the C–J velocities into detonable mixtures. We conducted high time-resolution Schlieren visualizations of the whole processes over unsteady initiations to stable propagations of the stabilized Oblique Detonation Waves (ODWs) using a high-speed camera. The detonable mixtures were stoichiometric oxygen mixtures with acetylene, ethylene or hydrogen. They were diluted with argon in a 50% volumetric fraction, and a 75% diluted mixture was also tested for the acetylene/oxygen. The direct initiation of detonation by the projectile and the DDT process like the re-initiation appeared in the initiation process of stabilized ODW. This process eventually led to the stabilized ODW supported by the projectile velocity and the ringed shape detonation wave originating in the re-initiation. We modeled the spatial evolution of stabilized ODW after the re-initiation based on its C–J velocity and angle. The model qualitatively reproduced the measured development rate of stabilized ODW. We also discussed about the detonation stability for the curvature effect arising from the three-dimensional nature of stabilized ODW around the projectile. The curvature effect attenuated the detonation wave below its C–J velocity at the vicinity of projectile. The propagation limits of curvature effect will be responsible for the criticality to attain the stabilized ODWs. By accessing the detailed distributions of propagation velocities and curvature radiuses, the critical curvature radiuses normalized by the cell sizes experimentally revealed to be 8–10 or 15–18 for mixtures diluted with each 50% argon or 75% argon/krypton.

著者

Nagura Yuto Kasahara Jiro Sugiyama Yuta Matsuo Akiko

出版者

Elsevier Inc.

雑誌

Proceedings of the Combustion Institute (ISSN:15407489)

巻号頁・発行日

vol.34, no.2, pp.1949-1956, 2013

被引用文献数

26

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The geometry and characteristic length of diffraction and re-initiation during a two-dimensional detonation propagation were revealed by visualization. C2H4 + 3O2 (unstable), 2C2H2 + 5O2 + 7Ar (stable) and 2C2H2 + 5O2 + 21Ar (stable) were used as the test mixtures. Experiments were performed over the deviation angle range from 30° to 150° and the initial pressure range from 15.8 to 102.3 kPa. By self-emitting photography, we confirmed that the geometry and the characteristic length of diffraction are not different among test gases, with the exception of the fan-like structure of re-initiation that occurred regardless of whether the mixture was unstable or stable. We conducted a compensative experiment by changing the deviation angle and initial pressure, and summarized the detonation diffraction by shadowgraph. At deviation angles larger than 60°, we measured the distances from the vertex of the channel corner to the point where the transverse detonation wave reflected on the under wall (= wall reflection distance) and confirmed that wall reflection distances are approximately in the range of 10–15 times the cell width, whether the mixture is unstable or stable.

著者

Nakayama Hisahiro Kasahara Jiro Matsuo Akiko Funaki Ikkoh

出版者

Elsevier Inc.

雑誌

Proceedings of the Combustion Institute (ISSN:15407489)

巻号頁・発行日

vol.34, no.2, pp.1939-1947, 2013

被引用文献数

61

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The propagation of curved detonation waves of gaseous explosives stabilized in rectangular-cross-section curved channels is investigated. Three types of stoichiometric test gases, C2H4 + 3O2, 2H2 + O2, and 2C2H2 + 5O2 + 7Ar, are evaluated. The ratio of the inner radius of the curved channel (ri) to the normal detonation cell width (λ) is an important factor in stabilizing curved detonation waves. The lower boundary of stabilization is around ri/λ = 23, regardless of the test gas. The stabilized curved detonation waves eventually attain a specific curved shape as they propagate through the curved channels. The specific curved shapes of stabilized curved detonation waves are approximately formulated, and the normal detonation velocity (Dn)−curvature (κ) relations are evaluated. The Dn nondimensionalized by the Chapman–Jouguet (CJ) detonation velocity (DCJ) is a function of the κ nondimensionalized by λ. The Dn/DCJ−λκ relation does not depend on the type of test gas. The propagation behavior of the stabilized curved detonation waves is controlled by the Dn/DCJ−λκ relation. Due to this propagation characteristic, the fully-developed, stabilized curved detonation waves propagate through the curved channels while maintaining a specific curved shape with a constant angular velocity. Self-similarity is seen in the front shock shapes of the stabilized curved detonation waves with the same ri/λ, regardless of the curved channel and test gas.

著者

Uemichi Akane Nishioka Makihito

出版者

Elsevier Inc.

雑誌

Proceedings of the Combustion Institute (ISSN:15407489)

巻号頁・発行日

vol.34, no.1, pp.1135-1142, 2013

被引用文献数

2

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Rotating counterflow twin premixed flame (RCTF) of hydrogen air was numerically simulated with detailed chemistry to explore the possibility of ultra-lean combustion. As a result, it was found that ultra-lean RCTF of equivalence ratio Φ = 0.052, which is far leaner than the generally-recognized flammability limit Φ = 0.10, is realized. It was also found that under ultra-lean conditions the flame temperature of RCTF largely exceeds the adiabatic flame temperature; e.g., at Φ = 0.06 the former is 1171 K, while the latter is 503 K. This increase of burned gas temperature is attributed to the so-called low Lewis number effect within the flammability limit, but under an ultra-lean condition some other mechanism to increase temperature is dominant. The “pseudo local equivalence ratio” of burned gas of RCTF differs largely from that of the unburned gas due to the extraordinarily high concentration of H2O. This suggests the possibility that the local condition at the reaction zone is much richer than the unburned gas, which brings about the large temperature increase.