Control of the flame and flow characteristics of a non-premixed bluff body burner using dielectric barrier discharge plasma actuators

Abstract

Reducing emissions and improving combustion are necessary steps to reach greener combustion systems. In this study, the effect of employing an annular plasma actuator mounted on the surface of a bluff body in a non-premixed burner is numerically investigated. Activating the plasma actuator induces an ionic wind near the surface of the bluff body that modifies the flow features. While the previous relevant studies were mainly focused on volume dielectric barrier plasma discharges, this study investigates the influences of surface plasma discharges. Also, the effect of plasma actuator position, fuel-to-air velocity ratio, and the size of the bluff body are investigated. The characteristics of the flow and temperature fields, the mass fraction of carbon monoxide and carbon dioxide inside the burner in the presence, and the absence of a plasma actuator are analyzed. Also, spatial mixing deficiency (SMD) is used to evaluate the plasma actuator's influence on the reactants' mixing. The results show that among various configurations of annular plasma actuators, positioning the plasma actuator on the bluff body surface acting upwards near the air duct, strengthens the external recirculation region which leads to a favorable change in the characteristics of the flame inside the burner. With the activation of the plasma actuator, the spatial mixing deficiency (SMD) values decrease by an average of 12.75%, showing improvement in mixing, and the flame becomes more uniform compared to the baseline case leading to the reduction of CO concentration. In addition, the root of the flame is strengthened and the height of the body of the flame measured from the bluff body surface is reduced by about 43%. For both low and high fuel-to-air velocity ratios, the presence of a plasma actuator leads to a positive effect on the flame structure. For a high fuel-to-air velocity ratio, the external recirculation area has a favorable size. The created flame is elongated and the root of the flame is entirely away from the burner. When the plasma actuator is active, it causes the flame to get closer to the burner tip. For various diameters of the bluff body, the plasma actuator showed reasonable capability in altering the flame behavior. For larger bluff body diameters, the plasma actuator strengthens both recirculation zones, especially the external recirculation zone, leading to a uniform and shorter flame.