Abstract
The present work focuses on the impact of dielectric barrier discharge (DBD) plasma actuators (PAs) on non-premixed lifted flame stabilization in a methane CH4-air Bunsen burner. Two coaxial DBD-PA configurations are considered. They are composed of a copper corona, installed on the outer surface of a quartz tube and powered with a high voltage sinusoidal signal, and a grounded needle installed along the burner axis. The two configurations differ in the standoff distance value, which indicates the positioning of the high frequency/high voltage (HV) electrode’s upper edge with respect to the needle tip. Experimental results highlight that flame reattachment is obtained at a lower dissipated power when using a negative standoff distance (i.e., placing the needle upstream with respect to the corona). At 11 kV peak-to-peak voltage and 20 kHz frequency, plasma actuation allowed for reattaching the flame with a very low dissipated power (of about 0.05 W). Numerical simulations of the electrostatic field confirmed that this negative standoff configuration has a beneficial effect on the momentum sources, which oppose the flow and show that the highest electric field extends into the inner quartz tube, as confirmed by experimental visualization close to the needle tip. The modeling predicted an increase in the gas temperature of about 21.8 °C and a slight modification of the fuel composition at the burner exit. This impacts the flame speed with a 10% increase close to the stoichiometric conditions with respect to the clean configuration.
Highlights
Nowadays, the aeroengine industries have addressed the development of low NOx combustion technologies in many ambitious national and international research programs
It is worth underlining that the lean burn is defined by the lean flammability limit (LFL) expressed as percentage by volume of the fuel into the mixture; lean combustion usually occurs below the LFL [3]
Predictions, which were compared with the ones predicted in the absence of plasma actuation, namely at ambient temperature and pure methane
Summary
The aeroengine industries have addressed the development of low NOx combustion technologies in many ambitious national and international research programs. Several DBD-PAs have been investigated to improve the fuel/air mixtures ignition [21,22,23], increase flame propagation [24,25], or enhance flame stabilization by extending flammability limits [26,27,28,29,30,31] Concerning this last aspect, combustion enhancement has been observed when applying a DBD-PA for fuel/oxidizer decomposition [32,33]. DBD-PAs have been widely investigated as fuel reforming reactors with promising results when applied to combustion systems [34,35,36] In this context, the present work provides an investigation of plasma actuation in a coaxial DBD configuration for a non-premixed lean lifted flame stabilization. The analysis of the experimental results is supported by simulations of the electrostatic field, in combination with a one-dimensional spatio-temporal analysis of the plasma chemistry inside the methane tube, aiming to decouple thermal and kinetics effects
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