Hetero-/homogeneous combustion characteristics of premixed hydrogen-air mixture in a planar micro-reactor with catalyst segmentation

Abstract

Numerical simulation of stoichiometric hydrogen-air premixed flame in a platinum-coated micro channel was performed to investigate hetero-/homogeneous combustion characteristics. An elliptical two-dimensional (2D) Computational Fluid Dynamics (CFD) model with detailed reaction mechanisms for homogeneous (gas phase) and heterogeneous (catalytic) reactions was adopted. The hetero-/homogeneous reaction characteristics with different inlet flow velocities and flame speeds were used to evaluate the effect of heterogeneous reaction on homogeneous reaction in the combustor with 2 mm length of catalyst segmentation. The effect of heat generation of the heterogeneous reaction was also analyzed. The numerical results indicated that the highest temperature in the catalytic combustor was lower than that in the combustor without catalyst. In the presence of heterogeneous reaction, the species (OH) concentration near the catalytic surface decreased significantly due to the dominated heterogeneous reaction at that region. The homogeneous ignition distance increased with increasing inlet flow velocity. The heat transfer from the catalytic surface to the gaseous mixture in the catalytic zone exhibited a high intensity under the large flow velocity, and the preheated incoming flow improved the heterogeneous reaction to inhibit the homogeneous reaction. The decreased flame speed in the catalytic combustor further demonstrated that the homogeneous reaction was suppressed by the heterogeneous reaction.