Flame lift-off height control by a combined vane-plasma swirler

Abstract

In this study, a swirler combining the vane swirler and the plasma swirler is designed to control the flame lift-off height. The plasma swirler is located near the rim of the injector and the vane swirler is placed upstream of the plasma swirler. The vane swirler is employed to form a divergent flow to sustain the detached flame and the plasma swirler is adopted to control the flame lift-off height. The ionic wind clinging to the inner wall of the injector tube does not penetrate into the center, leaving the main stream flow in the central region largely undisturbed. Characteristics of the flow field are analyzed from the results of laser Doppler anemometry (LDA) measurement and mechanism of the flame lift-off control by the combined vane-plasma swirler is revealed. The flame lift-off locations calculated from the LDA measurement are consistent with those from direct observation. The dielectric barrier discharge (DBD) voltage influences the height of the flame lift-off with a linear relationship observed, which means the flame lift-off height can be controlled precisely by the DBD voltage without any mechanical movement or changing the mass flow rate. The combined vane-plasma swirler has the potential to improve the fuel flexibility, increase flame stability and attenuate the injector overheating. Highlights 1. A combined vane-plasma swirler is designed to control the flame lift-off height. 2. Flame lift-off height can be adjusted by changing the voltage of the dielectric barrier discharge. 3. A linear relationship between flame lift-off height and the dielectric barrier discharge voltage is observed. 4. Flame lift-off control by the combined vane-plasma swirler is mainly associated with the aerodynamic effect. 5. The swirler can improve fuel flexibility, increase flame stability and attenuate injector overheating.

Central recirculation zone induced by the DBD plasma actuation

“…The results show that the swirl as well as the axial adverse pressure gradient are increased because of the plasma actuation and the induced reverse flow is sufficiently strong to result in a CRZ, but the increase is not big enough to cling the CRZ Reacting flow field measured by LDA. The reacting flow experiments carried out are similar to a previous study 29 , but with different flow rates (the methane/air are 225/18 L/min and 150/12 L/min respectively). The effect of plasma excitation is stronger in this study because of the lower inflow velocity.…”

“…However, the effect of plasma is still significant. The DBD actuation not only shifts the position of the flame front but also increases the mean axial stretch rate represented by the steeper slope of the linear velocity decline at downstream locations 29 . The flame axial leading-edge position shifts depending on the voltage, and the flame lift-off height decreases with increased voltage.…”

“…1. The same experimental setup as that in our previous studies 28,29 has been used. Air is supplied by a screw air compressor then stabilized in two tanks of 1.2 cubic meter.…”

“…Flame stability under lean burn conditions is becoming increasingly important because of the needs to mitigate combustion pollutant emissions. Previous experiments show that the plasma swirler is effective in controlling the non-swirling jet flow and flame 26,27 and the lift-off height of the flame 28,29 , but its mechanism is not very clear. Effects of active particles, heat release and aerodynamics are coupled together in the plasma combustion control.…”

“…The LSI was chosen in the study, because the lift-off height is a critical parameter which influences the flame stability and thermal load of the injector. The lifted flame protects the actuators from being burnt-out, in addition to other advantages of the combined vane-plasma swirler 29 . In the experiments, the effects of the plasma actuation can be distinguished through the changes of the lift-off height, flow divergence angle and axial velocity decay rate.…”