Responses of OH (X²Π) and OH (A²Σ⁺) to high-energy electrons of dielectric barrier discharge in plasma-assisted burner flame

Abstract

We examined the responses of OH(X2Π) and OH(A2Σ+) in a premixed CH4 flame to high-energy electrons produced by a dielectric barrier discharge. The density of OH(X2Π) did not respond to the pulsed production of high-energy electrons; however, we observed a pulsed increase in the density of chemically produced OH(A2Σ+). In addition, we observed that OH(A2Σ+) produced at the same time as high-energy electrons had a lower rotational temperature. We discussed possible key reactions in plasma-assisted combustion on the basis of the experimental observation showing the production of cold OH(A2Σ+).

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

“…In other words, the optical emission intensity of OH at 1.0 ≤ r ≤ 1.4 mm indicates the production of OH(A 2 Σ + ) by chemical reactions. As reported in the previous paper, 29) the reaction that produces OH(A 2 Σ + ) is estimated to be CHO + O → OH(A 2 Σ + ) + CO. Since atomic oxygen on the left-hand side of this reaction is provided by the effect of high-energy electrons, the optical emission intensity of OH or the density of OH(A 2 Σ + ) has a sensitive response to the pulsed current, as described in the previous paper.…”

“…In a previous work, we examined the temporal variation of the OH radical density in a premixed burner flame with the superposition of dielectric barrier discharge (DBD). 29) As a result, we observed a slight increase in OH radical density by the superposition of DBD.…”

“…29) Let us assume that the optical emission intensity of OH or the density of OH(A 2 Σ + ) in the DBD-assisted flame has two origins and is given by…”

“…Since atomic oxygen on the left-hand side of this reaction is provided by the effect of high-energy electrons, the optical emission intensity of OH or the density of OH(A 2 Σ + ) has a sensitive response to the pulsed current, as described in the previous paper. 29) 8/? ?…”

Transient change in the shape of premixed burner flame with the superposition of pulsed dielectric barrier discharge

“…3,[26][27][28] In our recent works, we also pointed out the importance of atomic oxygen produced in the preheating zone of a premixed burner flame. 29,30) The understanding on the importance of atomic oxygen is insufficient to optimize practical systems of plasma-assisted combustion. Our recent work shows the importance of atomic oxygen in a limited part of the flame (the preheating zone), but we observe changes in combustion characteristics in a larger volume of the flame.…”