Study on explosion characteristics of premixed hydrogen/biogas/air mixture in a duct

Abstract

Hydrogen addition into biogas can improve the combustion performance. However, hydrogen addition will also pose higher explosion severity. In order to study the influence of hydrogen addition on the biogas explosion, the deflagration characteristics of premixed hydrogen/biogas/air mixtures with the unity equivalence ratio were evaluated in a 10 L transparent duct. The hydrogen fractionλH2in the blended fuel and the methane fraction in biogas θCH4were varied 0.1–0.6 and 0.4–1.0, respectively. The results show that when the mixture was less reactive, the low flame velocity facilitated the flame front deformation, leading to the more salient tulip flames. The profiles of the reduced flame velocity V/ESL (i.e., laminar burning velocity SL and expansion ratio E) could be divided into three patterns, depending on the combination of λH2 and θCH4. As the reactivity of the mixture increased, the flame velocity profile would shift from the first pattern to the second pattern then to the third one. However, the V/ESL was linearly scaled with the flame position Ztip irrespective of the biogas composition before the flame touched the sidewall, indicating that the effect of flame instability and acoustic wave on flame propagation was insignificant. The explosion parameters (e.g., the maximum flame velocity Vm and the maximum overpressure Pm) were more sensitive to the hydrogen fraction than to the methane fraction. In addition, hydrogen addition was more effective in augmenting the explosion parameters for biogas with low methane fraction. For a fixed methane fraction, the Vm and Pm showed the linearly dependence on the hydrogen fraction defined by Yu et al. (Yu and Law 1986). Moreover, the increasing hydrogen fraction would gradually moderate the effect of the methane fraction in biogas on the explosion parameters. There was a good linear nexus between the Pm and the Vm irrespective of the composition of the mixtures. The Vm was well scaled with the ESL or the maximum H radical [H]max in the reaction zone of laminar flame. Therefore, the (ESL) and [H]max provide the good indicators to predict the explosion parameters of the hydrogen/biogas fuel.