著者

前田 慎市 吉木 一秀 菅野 祥一郎 冨田 啓太 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

vol.83, no.852, pp.17-00019-17-00019, 2017 (Released:2017-08-25)

参考文献数

26

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Shock-induced combustion around a spherical body was experimentally investigated by launching the projectile at supersonic speed into a combustible mixture. This study focused on occurrence conditions for an unsteady combustion which was characterized as combustion instabilities with an oscillating combustion front. A spherical body of 4.76 mm dimeter was used as the projectile, and its flight Mach numbers were ranged from 3.5 to 7.5. Four types of combustible mixtures, which were stoichiometric hydrogen-oxygen and ethylene-oxygen mixtures diluted with argon or nitrogen (2H2 + O2 + 3Ar, 2H2 + O2 + N2, C2H4 + 3O2 + 12Ar, C2H4 + 3O2 + 2.5N2), were used and their initial pressures were varied between 25 and 100 kPa. The combustion regimes around the projectile were observed by using a schlieren optical system and high-speed camera. The combustion regimes generally varied from the steady combustion with smooth combustion front to the unsteady combustion with oscillating combustion front, when the projectile Mach number or the initial pressure increased. The occurrence conditions for the unsteady combustion were expressed by the two dimensionless parameters; dimensionless heat release rate, q*t* and dimensionless induction length, lind*, which were defined by the post-shock state and flow velocity on the stagnation streamline of the projectile and by assuming the chemical reaction as a constant-volume explosion. The q*t* included a temperature gradient in a reaction zone, and represented the strength of the pressure wave driven by the heat release reaction. The lind* included an induction time, and represented the distance between the shock wave and the location where the heat release reaction started. The unsteady combustion occurred when these two dimensionless parameters were above the critical values, and the trend of occurrence condition of the two combustion regimes could be explained by introducing the parameters.

著者

前田 慎市 菅野 祥一郎 古藤 亮平 小原 哲郎

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 (ISSN:21879761)

巻号頁・発行日

pp.14-00332, (Released:2015-01-16)

参考文献数

26

被引用文献数

1

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The gaseous detonation driven gas gun was developed for accelerating the projectile to a supersonic speed. The gas gun was simply consisted of two straight stainless-steel tubes. The one was the detonation tube and the other was the launch tube. The detonation tube was 50 mm inside diameter with 2180 or 4280 mm long, and the launch tube was 5 mm inside diameter with 1040 mm long. Chapman-Jouguet detonation wave was initiated in the detonation tube, and the projectile was accelerated in the launch tube via combustion products behind the detonation wave. The spherical projectile of 4.76 mm diameter was made of high-density polyethylene with 52 mg mass. The driver mixture was stoichiometric hydrogen-oxygen premixed gas with initial pressure ranging from 120 to 450 kPa. The gas gun was successfully operated, and the maximum projectile velocity of 1400 m/s was obtained for the conditions that the detonation tube was 4280 mm long and the initial pressure of the driver gas was 450 kPa. The results of the longer detonation tube demonstrated that the projectile velocity was 1.15 - 1.25 times higher than the case of shorter detonation tube. This velocity change of the projectile could be explained by the pressure increase at the inlet of the launch tube by using longer detonation tube. The reason of the pressure increase has a possibility that the length of Taylor wave behind the detonation wave becomes longer for the case of longer detonation tube.