Effect of hydrogen addition on the ionization of partially premixed methane flame

Abstract

The flame ionization characteristic is a key point to realize the combustion diagnosis and control of hydrocarbon flame based on electric fields. In this paper the effects of hydrogen addition on the ionization of partially premixed methane flame were investigated experimentally and computationally. The flame current was measured by applying a small electric field across the partially premixed methane flame with different hydrogen addition and the effects of hydrogen addition on the ionization intensity and the flame ionization structure were analyzed. Furthermore, the intrinsic reaction mechanism of hydrogen addition affecting the ionization of partially premixed methane flame was studied based on a comprehensive reaction mechanism, which combines GRI 3.0 for neutral species and an 85-steps flame ionization reaction for 13 kinds of charged species. The results show that hydrogen addition can promote the ionization of partially premixed flame by affecting the chemical ionization process. However, when the hydrogen content reaches 50% of the total fuel amount, the promotion effect will be significantly weakened. Moreover, for partially premixed methane flame, the effect of hydrogen addition on the flame ionization was affected by the amount of primary premixed air. The larger the amount of primary premixed air, the more significant the promotion of hydrogen addition. What’s more, the hydrogen addition mainly affects the concentration of e− in the flame through the reactions H + CH3 (+M) ⇔ CH4 (+M) and H + O2 ⇔ O + OH while affects the concentration of H3O + through the reactions OH + CH3 ⇔ CH2 (S) + H2O and H3O+ + e− ⇔ OH + 2H.