Examination of ionic wind and cathode sheath effects in a E-field premixed flame with ion density measurements

Abstract

The effect of the ionic wind on a premixed methane-air flame under a DC electric field is studied via mapping of the ion density with Langmuir probes. Ion densities were observed to increase near the burner with increasing electrode voltage up to 6 kV. Past this electrode supply voltage, ion densities ceased increasing and began to decline in some locations within the premixed flame. The increased ion density is caused by an increase in ionic wind force and cathode sheath thickness. The plateau in density is due to the cathode sheath fully encompassing the flame front which is the ion source, thereby collecting all ions in the flame. The spatial density data support the ionic wind hypothesis and provide further explanation of its limits based on the plasma sheath.

Electric Field Modified Bunsen Flame with Variable Anode Placement

“…At high enough voltages, all ions produced in the flame front are attracted to the cathode and collected, thereby preventing further increase in current flux. Jacobs and Xu confirmed this behavior with ion density measurements inside a quasi-onedimensional flame under a dc electric field [30]. They found that the increase in ion density plateaued at 6 kV, and further increase in voltage caused no change in the ion density and current.…”

“…The small and medium anodes all have exponential current profiles, which indicate an asymptotic upper limit on the current, which means an upper limit on the effect of the electric field on the flame, without gas breakdown. The cause for this upper limit is usually current saturation of the cathode as seen and described by other works [16,[29][30][31][32]. At high enough voltages, all ions produced in the flame front are attracted to the cathode and collected, thereby preventing further increase in current flux.…”

“…If the flame had a uniform plasma density everywhere, then the same field strength at different distances should produce the same results. The plasma density along centerline for the 0 kV flame has been measured using single Langmuir probes following the method used by Jacobs and Xu [30]. Briefly, a 2-mm-long, 0.13-mm-diam tungsten filament protruding from a 1.6-mm-diam alumina tube was inserted into the flame.…”

“…The probe voltage was varied with a source meter, and the resulting current to the filament was measured. The ion density was calculated using the measured ion saturation current at −5 V using the equations for Langmuir probes in high-pressure plasmas [30,39]. The total duration of the probe exposure was kept under 6 s to limit carbon deposition.…”

Deformation Study of Lean Methane-Air Premixed Spherically Expanding Flames under a Negative Direct Current Electric Field

“…The Langmuir probe, which was made of carbon steel, was a plate to plate type with a diameter of 4 mm and a spacing of 5 mm for the measuring head, and the rest part of the probe was covered with PTFE. The power supply for the Langmuir probe was 400 V, which was in the linear voltage-current region [32], and series resistance was 150 kΩ.…”