Mixing Enhancement of Inverse Jet Flame with Circumferential Fuel Ports

Abstract

ABSTRACT Despite more than a decade-long effort to understand the flow structure in Inverse Jet flame (IJF) configuration, the performance enhancements on such configurations are sparsely investigated. A passive technique to improve the air-fuel entrainment in IJF configuration is implemented in this study by altering the central-air port geometry with an elliptical port. The flow and mixing characteristics are studied using a three-dimensional Favre-averaged method for the elliptical central air-port IJF compared to its circular counterpart. The numerical model is validated using the standard k-ε turbulence model to capture the complex flow physics and comprehend the mixing characteristics of IJF in this burner configuration. The elliptical central port brought the differences in the spreading and entrainment rates. The present work emphasizes flow dynamics and mixing characteristics, including the features of the recirculation zone, turbulence kinetic energy, and velocity distribution. The (omega) Ω vortex identification method and turbulent kinetic energy distribution provided more profound insights into the role of vortex structures on air-fuel mixing. The vortex structures are prominent in the novel elliptical port IJF compared to the circular counterpart, thus affecting the flame structure. The vortex strength Ω was found to be 0.94 in elliptical IJF and 0.88 for the circular central port IJF. This work further quantifies the enhanced air-fuel mixing as observed with the elliptical inverse jet diffusion flame based on mixture fraction mixing index, which can be applied to any IJF configurations. The mixing index at the axis switching location was greater than 80% for the elliptical IJF compared to 45% in the circular IJF configuration.