Flow, mixing, and flame stabilization in bluff-body burner with decreased central jet velocity

Abstract

The flame stabilization is a complex problem, especially when reducing the fuel supply, as it involves complicated interactions of turbulence, mixing, and chemistry. In this study, the flamelet progress variable combined with large eddy simulation has been used to simulate a bluff-body non-premixed flame to reveal the mechanisms of flow, mixing, and flame stabilization during the central fuel jet velocity reduction. The two flow patterns of jet dominant and coflow dominant are first analyzed by the concept of persistence of decay similarity of jet. The results show that this concept is informative to interpret whether and where the flow is jet dominant and understand the competition between two flows in detail, not only for flow but also for mixing. The results further show that the jet–coflow interaction, which has a pronounced impact on flame topology, has a minimal impact on flame stabilization for the bluff-body stabilized non-premixed flames over a wide range of fuel jet velocities, because of approximately close ignition delay time and flow convection velocities. In addition, it is observed that a ribbon-like structure of formaldehyde forms upstream of the hydroxyl. This phenomenon is caused by autoignition which is favored by high temperature in the recirculation zone and takes place far upstream of the flame. That would particularly facilitate flame stabilization in bluff-body burners.