Effects of ignition position and hydrogen concentration on the flame propagation characteristics of hydrogen–air deflagration

Abstract

In this study, the effects of hydrogen concentration and ignition position on the flame propagation characteristics of hydrogen–air deflagration in a pipe were investigated using a visual explosion propagation system. The change laws of propagation characteristics were analyzed at the microscopic level using free radical spectroscopy. The results indicated that the hydrogen flame had a lower velocity but higher explosion temperature and pressure under central ignition than under bottom ignition. However, the effect of ignition position weakened at higher hydrogen concentrations. As the hydrogen concentration was increased from 13 to 17 vol%, the differences in the maximum flame velocity, maximum temperature, and maximum pressure between central and bottom ignition decreased from 60.4%, 25.3%, and 17.8%, respectively, to 24.9%, 1.1%, and 4.6%, respectively. In addition, the maximum relative intensity and duration of the OH· spectral peak were more than 14% lower and shorter, respectively, under central ignition than under bottom ignition. As the hydrogen concentration was increased, the OH· spectral peak appeared earlier, the duration of this peak was shortened, and the explosion reaction was accelerated. OH· was consumed in the explosion reaction, which resulted in the release of heat; thus, the temperature and explosion pressure increased.