Experimental and numerical studies on electric field distribution of a premixed stagnation flame under DC power supply

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@article{REN2020103, title = {Experimental and numerical studies on electric field distribution of a premixed stagnation flame under DC power supply}, journal = {Combustion and Flame}, volume = {215}, pages = {103-112}, year = {2020}, issn = {0010-2180}, doi = {https://doi.org/10.1016/j.combustflame.2020.01.028}, url = {https://www.sciencedirect.com/science/article/pii/S0010218020300407}, author = {Yihua Ren and Wei Cui and Heinz Pitsch and Shuiqing Li}, keywords = {Premixed stagnation flame, Electric field measurement, Charge transport model, Flame stabilization mode}, abstract = {In this work, we achieve a sub-breakdown electric field measurement in a premixed stagnation flame by electric-field-induced second-harmonic generation (ESHG) using a nanosecond laser. Under the application of a DC voltage, the premixed flame can transit from a flat substrate-stabilized mode to a conical nozzle-stabilized mode due to the two-way interaction between the electric and hydrodynamic responses of the flame. The average electric fields along the laser pathway for these two flame modes are measured at different heights above the burner. Combining the measurement and the numerical simulation of a charge transport model, we further elucidate that the flame affects the electric field distribution in two different ways. For the flat flame mode, the electric field strength is shielded at the flame front and then quickly increases both upstream and downstream, reaching the maximum at the electrodes. The charge transport model reveals that the electrostatic shielding effect of the flame front can be attributed to the charge redistribution in the chemi-ionized conductive layer. For the conical flame mode, the electric field strength has a large gradient near the conical tip and remains almost zero downstream. The conical flame front then serves as a conductive layer to guide the charge transport under the application of the electric field. The positive and negative charges are separated at different radial positions because of the inclined asymmetric flame front. Thus, the largest electric field gradient is generated upstream of the flame conical tip, where the net charge and the electric body force maximize and create a virtual flame stabilization mode.} }

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電界強度分布の計測結果

• 火炎上流側に行けば行くほど高くなる
• 火炎下流側は一定値

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Abstract

• a sub-breakdown electric field measurement in a premixed stagnation flame by electric-field-induced second-harmonic generation (ESHG) （電界誘起第二高調波生成 (ESHG) による予混合よどみ火炎のサブブレイクダウン電界計測）
• For the flat flame mode, the electric field strength is shielded at the flame front and then quickly increases both upstream and downstream, reaching the maximum at the electrodes. （平面火炎モードでは，電界強度は火炎面でシールドされていて，上流と下流側で急峻にぞうかし電極で最大値をとる）
• For the conical flame mode, the electric field strength has a large gradient near the conical tip and remains almost zero downstream.（円錐火炎モードでは，電界強度は円錐の頂点付近で大きな勾配を持ち下流でほとんどゼロになる）
• The conical flame front then serves as a conductive layer to guide the charge transport under the application of the electric field. （円錐状の火炎面は，電界の印加条件において，電荷輸送のガイドのための導通層となる）

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Introduction

• However, less attention has been paid to the electric field itself, especially from an experimental perspective.（しかしながら，特に実験の観点からは，電界それ自身についてはあまり注目されていない）
• While all those studies were performed under the breakdown condition, the weak sub-breakdown electric field distribution, as an intrinsic electrical property of a flame playing an essential role in electric field-assisted combustion, has not been measured before yet.（ESHGについての研究はすべてブレイクダウン条件で行われてきたが，電界支援燃焼で重要な役割を果たす固有の電気的特性としての弱いサブブレイクダウンの電界分布はいまだ計測されていない．）
• According to this theory, the electric field distribution inside a one-dimensional chemi-ionization layer can be divided into the linear space-charge and saturation regimes depending on the induced space charge. （（1960年に提案された）理論によると，1次元の化学電離層の中の電界分布は，有機された空間電荷によって，線形空間電荷と飽和領域に分離できる．）
• Our recent work reported that the electric field of the flame can suddenly transit from the space-charge regime to the saturation regime, accompanied by the changes of flame stabilization modes [29].（（しかしながら，）私たちの最新の研究では火炎の電界は，火炎の安定モードの変化を伴いながら，空間電荷領域から飽和領域に急激に変化することを報告している．）