Effect of hydrogen addition on the dynamics of premixed C1–C4 alkane-air flames in a microchannel with a wall temperature gradient

Abstract

The effect of hydrogen (H2) addition on the flame dynamics of premixed C1–C4 alkane/air mixtures in a microchannel is investigated using a detailed-chemistry model through two-dimensional numerical computations. A detailed computational study have been performed in a 2 mm diameter tube with 120 mm length and a wall temperature gradient along the axial direction of the channel. The numerical simulations are carried out for various stoichiometric hydrocarbon (HC)/H2 mixtures at 0.15 m/s mixture inlet velocity. Flame repetitive extinction and ignition (FREI) flame pattern has been identified for all the fuel mixtures at these channel wall and mixture flow conditions. CH4/air mixture shows a higher HRR than C3–C4 alkane/air mixtures. Flame residence time in microchannel increases with increase in hydrogen addition percentage for all the three hydrocarbon/air mixtures considered in the present study. A non-monotonic behavior of FREI frequency is identified for CH4/air mixture, whereas it decreases monotonically for C3H8/air and C4H10/air mixtures with H2 addition. The amount of HRR and flame propagation velocity decreases with increase in H2 addition for lower-alkanes/air mixtures. The flame bifurcation effect is observed for CH4/air mixture, which disappears due to H2 addition in the mixture. The bifurcation effect is not present for other hydrocarbon/air mixtures investigated in the present study. The addition of H2 in the mixture enhances the flame stability of hydrocarbon/air mixtures in the microchannel.