The effects of addition of carbon dioxide and water vapor on the dynamic behavior of spherically expanding hydrogen/air premixed flames

Abstract

The effects of addition of carbon dioxide and water vapor on the dynamic behavior of spherically expanding hydrogen/air premixed flames Abstract experimental data under a certain condition but also to create the mathematical model for the prediction of flame propagation velocity under various conditions. Thus, it is significant to understand the characteristics of dynamic behavior of hydrogen/air premixed flames and to elucidate the effects of addition of inert gas, i.e. carbon dioxide CO 2 and water vapor H 2 O. We performed the experiments of hydrogen explosion in two types of closed chambers to observe spherically expanding flames using Schlieren photography. Wrinkles on the flame surface were clearly observed in low equivalence ratios. Analyzing the Schlieren images, the flame propagation velocity depending on the flame radius was obtained. Increasing the addition of inert gas, the propagation velocity decreased, especially in the case of CO 2 addition. The propagation velocity increased monotonically as the flame radius became larger. The appearance of flame acceleration was found, which was caused by the evolution of wrinkles on the flame surface. Moreover, the Markstein length decreased as the concentration of inert gas became higher, indicating that the addition of inert gas promoted the instability of hydrogen flames. Furthermore, the wrinkling factor, closely related with the increment in propagation velocity, decreased as the inert-gas concentration became higher. The wrinkling factor normalized by the propagation velocity of flat flame increased, on the other hand, under the conditions of high inert-gas concentration, except for near the quenching conditions. This indicated that the addition of CO 2 or H 2 O promoted the unstable motion of hydrogen flames, which could be due to the enhancement of the diffusive-thermal effect. Based on the characteristics of dynamic behavior of hydrogen flames, the parameters used in the mathematical model on propagation velocity including flame acceleration was obtained, and then the flame propagation velocity under various conditions was predicted.

Effects of inert-gas addition on the dynamic behavior and propagation characteristics of spherically expanding hydrogen-air flames

“…The obtained results indicate that the addition of inert gas promotes the instability of hydrogen flames, which is due to the reduction of thermal diffusivity of premixtures. The model of propagation velocity is written as follows (Katsumi et al, 2021):…”

“…To mitigate the influence of hydrogen explosion, the addition of inert gas is well-known to be one of possible approaches. We have several reports which experimentally studied the effects of inert-gas addition on the combustion characteristics of hydrogen premixtures (Qiao et al, 2007;Bane et al, 2011;Zhang et al, 2012;Cheikhravat et al, 2015;Duan and Liu, 2017;Li et al, 2018;Li et al, 2019;Yan et al, 2020;Gong et al, 2020;Katsumi et al, 2021;Morovatiyan, et al, 2021). The addition of inert gas has the effects of decreasing the burning velocity and reducing the maximum pressure in explosion.…”