Experimental study on the diffusive flame stabilization mechanism of plasma injector driven by AC dielectric barrier discharge

Abstract

A plasma injector element was designed to experimentally study the mechanism of methaneair diffusive flame stabilized by a discharge plasma. The air plasma was generated within the annulus gap of the injector by alternating current dielectric barrier discharge. The discharge voltage, current and photographs were recorded first. Three internal effects of the plasma on combustion were later investigated separately through several diagnostic methods, including optical emission spectrometry (OES), infrared thermography, thermocouple, infrared thermometer, schlieren imaging, photos and CH * chemiluminescence. Finally, the return on investment (ROI) was calculated. The results showed that a large number of filamentary micro discharge paths occur within the discharge gap. These discharge paths rotate anticlockwise at high speed and act as a virtual 'fan' to induce the flow jet. The velocity of the induced jet increases with increasing discharge voltage. The original jet expansion angle is enlarged by the radial velocity component of the induced jet, resulting in the mixing enhancement of the air and methane. The plasma rotational temperature (the first negative system) obtained from OES is close to the discharge gas temperature measured by infrared thermography, indicating that the discharge gas temperature can be approximately represented by the rotational temperature. According to the measured temperature of the injector and the jet, the impact of the thermal effect of the plasma on flame stabilization is negligible. Due to the plasma, the height of the flame center and its representative length are generally reduced as the voltage rises, and the methane-air mixture becomes ignitable, and a stable flame can be reached under the conditions in which direct ignition fails. The combustion is enhanced with increasing heat release rate of the flame by the plasma. This finding revealed that the ROI of plasma-assisted flame stabilization is lower under a higher flowrate and a larger equivalence ratio for unstable flame situations.

Discharge characteristics and reactive species production of unipolar and bipolar nanosecond pulsed gas–liquid discharge generated in atmospheric N2

“…However, in figures 7(b) and (c), the emission intensities of OH(A-X, 309 nm) and O(3p-3s, 777 nm) enhance firstly with rising the gas flow rate from 100 to 200 ml min −1 , and then decrease when gas flow rate exceeds 200 ml min −1 . The weaker emission intensities of N 2 (C-B) caused by higher gas flow are also found in atmospheric pressure dielectric barrier discharge reported by Zhou et al [27]. It should be noted that the plasma is generated in a confined quartz tube in this study, the turbulence can be formed in the tube by the gas.…”

Continuous gas temperature measurement of cold plasma jets containing microdroplets, using a focussed spot IR sensor

“…In nonthermal equilibrium APPs there is generally a desire to maintain temperatures as low as possible. However, there is also an understanding that gas temperature can be sensitive to many factors that are rarely well-characterised or controlled, 1 Author to whom any correspondence should be addressed.…”

The Discharge Heated Channel Region Visualization based on Thermal Imaging Registration

“…Later, the convective heat exchange process occurs between the dielectric material layer and the heated air. To study the temperature fields during the nanosecond dielectric barrier discharge (NS-DBD) initiation [4], the results obtained based on IR thermography and optical emission spectroscopy were compared. An analysis of the results showed that the plasma rotational temperature obtained using optical emission spectroscopy turned out to be close to the temperature measured using IR thermography, which means that the gas temperature in the used discharge can be approximately represented by the rotational temperature.…”