Flame propagation enhancement by plasma excitation of oxygen. Part II: Effects of O2(a1Δg)

Abstract

a b s t r a c tThe isolated effect of O 2 (a 1 D g ) on the propagation of C 2 H 4 lifted flames was studied at reduced pressures (3.61 kPa and 6.73 kPa). The O 2 (a 1 D g ) was produced in a microwave discharge plasma and was isolated from O and O 3 by NO addition to the plasma afterglow in a flow residence time on the order of 1 s. The concentrations of O 2 (a 1 D g ) and O 3 were measured quantitatively through absorption by sensitive off-axis integrated-cavity-output spectroscopy and one-pass line-of-sight absorption, respectively. Under these conditions, it was found that O 2 (a 1 D g ) enhanced the propagation speed of C 2 H 4 lifted flames. Comparison with the results of enhancement by O 3 found in part I of this investigation provided an estimation of 2-3% of flame speed enhancement for 5500 ppm of O 2 (a 1 D g ) addition from the plasma. Numerical simulation results using the current kinetic model of O 2 (a 1 D g ) over-predicts the flame propagation enhancement found in the experiments. However, the inclusion of collisional quenching rate estimations of O 2 (a 1 D g ) by C 2 H 4 mitigated the over-prediction. The present isolated experimental results of the enhancement of a hydrocarbon fueled flame by O 2 (a 1 D g ), along with kinetic modeling results suggest that further studies of C n H m + O 2 (a 1 D g ) collisional and reactive quenching are required in order to correctly predict combustion enhancement by O 2 (a 1 D g ). The present experimental results will have a direct impact on the development of elementary reaction rates with O 2 (a 1 D g ) at flame conditions to establish detailed plasma-flame kinetic mechanisms.

Origin of activated combustion in steady-state premixed burner flame with superposition of dielectric barrier discharge

“…In addition, combustion in speedy flow becomes possible by the superposition of a plasma. [7][8][9][10][11][12] The increase in burning velocity [13][14][15][16][17][18][19][20][21] and the improvement of ignition characteristics [22][23][24][25][26][27][28] have been observed in plasma-assisted combustion.…”

Localized pulsed nanosecond discharges in a counterflow nonpremixed flame environment

“…Localized pulsed nanosecond discharges in a counterflow nonpremixed flame environment through the creation of more stable intermediate species [9]. The temperature increase is due to a rapid heating of the gas, which depends primarily on the reduced electric field.…”

“…For electric fields ∼100 Td, the main source (∼10-15% of the total deposited energy) has been explained as self-quenching reactions of excited nitrogen ( ) Σ + A N u 2 3 [15,16]. More specifically, when the non-thermal plasma is created in the oxidizer stream, the main energy paths that produce flame enhancement are the excitation of molecular oxygen to O ( ) ∆ a g 2 1 and O ( ) Σ + b g 2 1 [9,17], and the creation of ozone [18]. If the oxidizer is air, NO x will also be generated and is a well-known promoter for oxidation reactions [19].…”

“…They can be used to mitigate thermoacoustic instabilities, facilitating the use of otherwise unstable ultra-lean flames [6]. More generally, plasmas can extend lean flammability limits [7], blow-out limits [8], increase flame speeds [9], and enable a more complete combustion [10].…”

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

“…Present techniques in this field are based on the application of direct current/alternating current (DC/AC) electrical potentials on various flames. Using these techniques, flames could be stabilized [1], propagation speed and burning velocity could be enhanced [2][3][4], and low soot formation can be achieved by using this technology in lean combustion techniques [5][6][7].…”