A numerical study on the mixing characteristics and mechanisms of (H2+CH4)/air in a miniature combustor

Abstract

In the present study, the influences of three operating parameters on the mixing performance of H2/CH4 blends and air in a miniature combustor with a rectangular cross section were numerically investigated. The results show that: (1) The mixing process of H2 and air is faster than CH4 and air. (2) The mixing process of H2 and air is diffusion-dominated under low velocities, while convection-dominated under medium and high velocities; However, the mixing of CH4 and air is diffusion-dominated under both low and high average velocities, but dominated by convection under medium velocities. (3) An increase in the nominal equivalence ratio creates a larger fuel concentration gradient perpendicular to the mainstream, which leads to an increase in the diffusion rate. (4) A larger hydrogen blending ratio intensifies the fuel stratification at the combustor entrance, which deteriorates the mixing performance. (5) An empirical correlation is established between the mixing performance evaluation criterion and the three parameters. The nominal equivalence ratio is the most significant factor to the mixing performance.