The influence of heat transfer and friction on the impulse of a detonation tube

In the present study, we experimentally and numerically investigated the influence of heat transfer and friction on the performance of a single-shot detonation tube open at one end. Two kinds of specific impulse measurement were carried out with various tube lengths and levels of surface roughness, one by using a ballistic pendulum arrangement and the other by integrating the pressure history measured at the thrust wall. These measurements revealed the degree to which potential impulse can be exploited by the detonation tube after the impulse losses due to various wall loss mechanisms such as heat transfer and friction. The detonation tube obtained 89%, 70%, and 64% of the theoretical ideal impulse for electro-polished tubes at a ratio of tube length to diameter (L/D) of 49, 103, and 151, respectively. The impulse losses due to shear stress on the side wall of the detonation tube were found to have a dominant influence on the performance of the detonation tubes of L/D = 103 and 151, but the loss was remarkably small for L/D = 49 relative to that of the longer tubes. In addition to the experiments, a simplified one-dimensional gas-dynamic model was developed by considering heat transfer and friction as wall loss mechanisms and validated by the experimental results. This simplified model was found to predict the experimental results very well, especially in the range of L/D 103-151. (C) 2011 The Combustion Institute. Published by Elsevier Inc. All rights reserved.