Experimental Study on Detonation Initiation and Transmission Across a Mixture

• Main Authors: Jiun-Ming Li, 李俊明
• Other Authors: Wei-Hsiang Lai
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/63590010448412483766

博士 === 國立成功大學 === 航空太空工程學系碩博士班 === 95 === A predetonator concept has been proposed to ensure a success of an airbreathing pulse detonation engine. Decreasing the volume of a predetonator and the diffraction critical diameter to a realistic size prompts this concept into practice. Here the diffraction critical diameter is the minimum tube diameter for the successful transmission of a detonation through an abrupt area expansion. Previous investigations have shown that the diffraction critical diameter decreases with a higher degree of overdrive of overdriven detonations. In the present research, a series of experiments were performed to achieve a strong overdriven state in a less sensitive mixture by propagating an overdriven detonation via a deflagration-to-detonation transition (DDT) process. First, the propane/oxygen mixtures were used to initiate detonations through a deflagration-to-detonation transition (DDT) process with a weak spark. A nonstationary cross-correlation technique is adopted to define the uncertainty of the DDT run-up distance and further derive the minimum length of a predetonator. The subsequent work focuses on the tube diameter effect on the DDT process. The possible mechanisms associated with the DDT process, such as amplification factor, flame acceleration and energy loss, are correlated the experimental results. In addition, the attenuation of overdriven detonations was also addressed. Finally, experiments were performed wherein a propane/oxygen mixture is separated from a propane/air mixture by a thin diaphragm to study the transmission of an overdriven detonation. Based on the characteristic relations, a simple wave intersection model has been developed to calculate the state of the transmitted detonation. The results showed that the rarefaction effect must be included to ensure that the degree of overdrive of transmitted detonation is not overestimated. The experimental results showed that a transmitted overdriven detonation occurs instantaneously with a strong incident overdriven detonation across a mixture. To achieve and maintain a strong overdriven state across a mixture, the mixture interface may be placed between slightly behind DDT transition location and one tube diameter from DDT transition location in propane/oxygen mixtures.