Numerical study on hydrogen heterogeneous reaction characteristic in a micro catalytic combustor with blunt body

Abstract

A numerical investigation has been conducted to explore the effect of an inserted blunt body on the heterogeneous reaction (HTR) characteristics in a micro-catalytic combustor operating with premixed hydrogen/air. The two-dimensional numerical model incorporates a comprehensive heterogeneous reaction mechanism of hydrogen employed by experimental verification. The influences of blockage ratio at various inlet velocities have been investigated to obtain optimized design parameters of the combustor. The findings of this research highlight analysis of the positive influence of an inserted blunt body within the combustor, including enhancement of chemical reaction rate and hydrogen conversion ratio. Numerical results shows that the gaseous mixture between the blunt body and catalytic surface noticed a considerable velocity increase, leading to a greater adsorption–desorption of bulk species on the catalytic surface. At the same inlet velocity, the hydrogen conversion ratio gradually increases with higher blockage ratios. When the blockage ratio is less than or equal to 0.6, the average inner wall temperature is positively affected by the increased blockage ratio. However, the effect becomes negative at higher blockage ratios (0.8). The Pr (Prandtl number) number near the gas–solid interface adjacent to the blunt body initially decreases and then increases, while Nu/Nu0 (Nusselt number) and Pe (Peclet number) exhibit an initial increase followed by a decrease. The presence of the blunt body leads to a reduction in the cross-sectional area of the channel, causing an acceleration in fluid velocity near the blunt body and exerting an impact on the boundary layer near the gas–solid interface. This indicates that the addition of the blunt body reduces the boundary layer thickness and enhances the mass and heat transfer characteristics in the region. The study reveal that as the blockage ratio increases, the overall field synergy of the combustor initially increases and then decreases. The peak field synergy is attained at an optimal blocking ratio of 0.6. The findings of this study have important implications for the design of micro-scale combustors.