Numerical Study of the Mixing Process of Unconfined Diffusion Flame in a Laminar to Transition-to-Turbulent Regime in a Four-Port Array Burner

TL;DR

This study numerically analyzes the mixing process of unconfined diffusion flames in a four-port burner, revealing how jet interactions and turbulence influence flame structure and height in laminar to transitional regimes.

Contribution

It provides a detailed numerical analysis of the mixing mechanisms and turbulence effects in a four-port diffusion flame burner, highlighting the influence of jet interactions on flame development.

Findings

Mixing occurs within a flame cone formed by jet interactions.

Air/fuel mixture reaches flammability limits at two zones.

Flame height depends primarily on fuel mass flow.

Abstract

The mixing process of multiple jets of liquefied petroleum gas and air in a diffusion flame is numerically analysed. The case study considers a four-port array burner where the fuel is injected by four peripheral nozzles and mixed with the surrounding air. Simulations are conducted with the Reynolds-Averaged Navier-Stokes technique, and the turbulence effect is modelled with the realizable k-e model. In addition, the eddy dissipation model is implemented to calculate the effect of the turbulent chemical reaction rate. Results show that the essential mixture mechanism occurs within a flame cone derived from the fuel jets interaction. However, the mixing process is driven by jets drag allowing an air/fuel smooth mixture to reach the flammability limits at two zones: one at a lower location or close to the burner surface and a second before the flame front development. The entire mixing mechanism culminates with the development of the flame necking cone. Any air concentration that falls into the cone radius will be entrained, contributing to the overall flame structure. Since the cone radius reach is limited only by radial distance of the jet array and the nozzles distance, the flame heights, consequently, depend solely on fuel mass flow.