Temporal and Spatial Evolution of OH Concentration in a Lean Premixed Propane-Air Flame Assisted by Nanosecond Repetitively Pulsed Discharges

Planar laser-induced fluorescence (LIF) has been used to study the evolution of the OH concentration in a weakly turbulent lean premixed flame both spatially and temporally, when applying Nanosecond Repetitively Pulsed (NRP) discharges. A 2-kW turbulent leanpremixed propane-air flame is stabilized by a cylindrical bluff-body. The discharge is created by voltage pulses of amplitude 7 kV, duration 10 ns, applied at a frequency of 30 kHz between two pin electrodes placed in the recirculation zone downstream of the bluffbody. The average electric power deposited by the plasma is up to 20 W, typically less than 1% of the thermal power of the flame. LIF images of the recirculation zone are recorded starting from 15 microseconds after discharge initiation. CH* chemiluminescence images of the flame are also recorded to trace the location of the flame. The results show that OH is produced in the plasma region and is then convected towards the shear layer. The key mechanism of the reduction of flame lift-off height by NRP discharges is the continuous ignition of the fresh combustible mixture in the shear layer, where it comes in contact with the active species produced by the NRP discharges.

[1]  D. Lacoste,et al.  Experimental study of the hydrodynamic expansion following a nanosecond repetitively pulsed discharge in air , 2011 .

[2]  Skip Williams,et al.  Flame propagation enhancement by plasma excitation of oxygen. Part I: Effects of O3 , 2010 .

[3]  Xiaolong Gou,et al.  A dynamic multi-timescale method for combustion modeling with detailed and reduced chemical kinetic mechanisms , 2010 .

[4]  B. Cetegen,et al.  Blowoff dynamics of bluff body stabilized turbulent premixed flames , 2010 .

[5]  D. Lacoste,et al.  Atmospheric pressure plasma diagnostics by OES, CRDS and TALIF , 2010 .

[6]  D. Pai,et al.  Nanosecond Repetitively Pulsed Plasmas in Preheated Air at Atmospheric Pressure - The Diffuse Regime , 2008 .

[7]  D. Veynante,et al.  Stabilization of a Turbulent Premixed Flame Using a Nanosecond Repetitively Pulsed Plasma , 2006, IEEE Transactions on Plasma Science.

[8]  Nikolay Popov,et al.  Investigation of the mechanism for rapid heating of nitrogen and air in gas discharges , 2001 .

[9]  D. Lacoste,et al.  Dynamic response of a weakly turbulent lean-premixed flame to nanosecond repetitively pulsed discharges , 2013 .

[10]  C. Carter,et al.  Kinetic effects of non-equilibrium plasma-assisted methane oxidation on diffusion flame extinction limits , 2012 .

[11]  Skip Williams,et al.  Flame Propagation Enhancement by Plasma Excitation of Oxygen. Part 2. Effects of O2(a1 Delta sub g) , 2010 .

[12]  W. Lempert,et al.  Mechanism of plasma assisted oxidation and ignition of ethylene–air flows by a repetitively pulsed nanosecond discharge , 2009 .

[13]  Guillaume Pilla.  Etude expérimentale de la stabilisation de flammes propane-air de prémélange par décharges nanosecondes impulsionnelles répétitives , 2008 .

[14]  Ronald K. Hanson,et al.  High-temperature ethane and propane decomposition , 2005 .

[15]  E. Zukoski.  Flame stabilization on bluff bodies at low and intermediate Reynolds numbers , 1954 .

[16]  J. P. Longwell,et al.  Flame stabilization by bluff bodies and turbulent flames in ducts , 1953 .

[17]  H. C. Hottel,et al.  Flame stabilization and propagation in high velocity gas streams , 1948 .