Species and temperature measurements of methane oxidation in a nanosecond repetitively pulsed discharge

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https://royalsocietypublishing.org/doi/10.1098/rsta.2014.0333

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Abstruct

• 低温でのNRPDフローリアクタ
• ヘリウムによって希釈された当量比１のメタン空気予混合気
• tunable diode laser absorption spectroscopyによる温度とホルムアルデヒドCH2Oの計測
• ガスクロによる下流での安定な化学種組成の計測
• ZDPlasKinとCHEMKINをコンバイン
• CH2Oの組成は解析と一致しなかった
• その原因はO(1D)とCH3O2の反応っぽい

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Introduction

• メタン空気の希釈混合気で非反応性から反応性までの連続的な遷移が明らかにされた
• その反応過程も数値モデルによって説明されている．
• しかし，温度と他成分の同時計測はまだ行われていない

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CH2Oを選んだ理由

CH2O was identified to be a major intermediate species directly produced by plasma-generated O atoms [4,11,12], and is thus an ideal candidate to determine the fidelity of the initial oxidation reactions.

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Measurement

(b) Mid-IR laser absorption spectroscopy system

absorption line for methane and tepmerature: 1343.56 and 1343.63 cm−1 absorption line for CH2O: 1726.79 cm−1

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Numerical modeling

放電が発生している間はZDPlasKinが電子温度と反応速度を計算する． During the discharge processes,ZDPlasKin employs a Boltzmann equation solver [44] to calculate the electron temperature andreaction rates based on the input list of electron impact reaction cross sections. 放電の終了後には．ZDPlasKinのアウトプットにおける，熱力学特性と反応速度をCHEMKINが計算する．化学種と温度はVODEを用いて統合する After each discharge pulse, CHEMKIN is used to calculate the thermal properties and chemical reaction rates at the conditions output by ZDPlasKin, and the species and temperature equations are integratedusing a VODE [45] solver.

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Energy equation in CHEMKIN

ガラス壁への熱電動が主要な熱の損失らしいので，それを考慮している Adamovichet al.[47] reported that the energy loss is primarily due to conduction to thequartz channel walls. In this zero-dimensional model, the heat loss is described by incorporatinga conduction heat transfer term into the energy equation,

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Results

ホルムアルデヒドの主要な生成経路

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[汐除]KUCRSを用いてO原子を繰り返し投入したときには，O2との反応で生成されている結果だった．この反応機構とは結果が違う？

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化学種組成

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[汐除]反応物と生成物は良好な一致を示している．時間に対するグローバルな燃焼反応の進行度合い（活性化学種の生成速度）はだいたいあっているとみてよさそう．中間生成物については，生成量があっていない．どの反応経路に多くのエネルギーが供給されているのかについては，まだまだ発展途上という感じか

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Path flux

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%は上流の化学種がその反応経路でどれだけ消費されたか [汐除]

• O(1D)が主要なCH4の消費経路（53%）であることはわかる
• ほとんどそれだけを伝えるための図
• 中間生成物とO(1D)の反応速度など報告されているわけがないので，結局，イニシャルの分解がどの経路で行われるかで議論するしかない．

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続編 @article{ROUSSO20195595, title = "Kinetic studies and mechanism development of plasma assisted pentane combustion", journal = "Proceedings of the Combustion Institute", volume = "37", number = "4", pages = "5595 - 5603", year = "2019", issn = "1540-7489", doi = "https://doi.org/10.1016/j.proci.2018.05.100", url = "http://www.sciencedirect.com/science/article/pii/S1540748918301019", author = "Aric Rousso and Xingqian Mao and Qi Chen and Yiguang Ju", keywords = "Plasma assisted combustion, Non-equilibrium plasma, Low temperature oxidation, Pyrolysis, Chemical kinetics", abstract = "The present study explores the chemical kinetics of low temperature oxidation and pyrolysis of pentane/O2/He mixtures in a nanosecond repetitively-pulsed DBD discharge. Time-dependent TDLAS measurements and steady state GC sampling are conducted to quantify species evolution in a plasma discharge. An improved kinetic model of plasma assisted combustion and pyrolysis of pentane is developed with updated electron impact dissociation reactions and low temperature reactions involving excited species. This kinetic model is then validated against the experimental data. The results show that a nanosecond plasma discharge causes significant low temperature fuel pyrolysis and oxidization as well as fast gas heating. The original kinetic model fails to predict many intermediate species such as CH4, C2H2, and CH2O due to missing corresponding reaction pathways and inaccuracies in electron impact cross section areas. The new model shows a dramatic improvement in modeling both pentane pyrolysis and oxidation, with good prediction of the time histories of pentane, CH2O, C2H2 and H2O, and slight under-prediction of CH4. There is still a large discrepancy in OH prediction and measurement in fuel oxidation. The results show that direct electron impact dissociation pathways play a critical role in plasma assisted fuel pyrolysis and oxidation and that plasma generated radicals and excited species such as O and O(1D) enhance low temperature fuel oxidation." }

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続編２ @article{MAO2019522, title = "Effects of controlled non-equilibrium excitation on H2/O2/He ignition using a hybrid repetitive nanosecond and DC discharge", journal = "Combustion and Flame", volume = "206", pages = "522 - 535", year = "2019", issn = "0010-2180", doi = "https://doi.org/10.1016/j.combustflame.2019.05.027", url = "http://www.sciencedirect.com/science/article/pii/S0010218019302408", author = "Xingqian Mao and Qi Chen and Aric C. Rousso and Timothy Y. Chen and Yiguang Ju", keywords = "Controlled non-equilibrium excitation, Ignition enhancement, Kinetic modeling, Uncertainty analysis, Hybrid nanosecond and DC discharge", abstract = "The present work reports on the effects of controlled non-equilibrium excitation of reactant molecules on low temperature H2/O2/He ignition by numerically modeling a hybrid repetitive nanosecond (NSD) and DC discharge at atmospheric pressure. At first, a detailed plasma-combustion kinetic model of H2/O2/He, including non-equilibrium excitation, is developed and validated by experimental data of a repetitively-pulsed nanosecond discharge. Then, the effects of ignition enhancement by NSD and a hybrid NSD/DC discharge, with controlled electron energy distribution for selective non-equilibrium excitation of vibrationally excited H2(v) and O2(v) as well as electronically excited O2(a1Δg) and O(1D), are compared. The results show that H2(v1) contributes significantly to the H production and OH consumption in the hybrid plasma discharge. Moreover, O2(a1Δg) and O2(v1−4) also contribute to the production O and OH. Uncertainty analysis of H2(v) and O2(a1Δg) elementary reactions on ignition delay time is conducted by using several different kinetic models. The comparison of ignition delay time using different plasma kinetic models indicates the selection of accurate rate constants involving excited species is important for plasma assisted ignition modeling. The results of hybrid discharge assisted H2/O2 ignition show that the optimized ignition enhancement is achieved when both excited species and radicals are produced efficiently at an appropriate DC electric field strength. The present modeling provides useful insight into the plasma-combustion model development and the development of controlled plasma discharge to achieve efficient ignition with optimized non-equilibrium excitation of reactants." }

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類似 @ARTICLE{Eckert2018, author={Eckert, Z. and Tsolas, N. and Togai, K. and Chernukho, A. and Yetter, R.A. and Adamovich, I.V.}, title={Kinetics of plasma-assisted oxidation of highly diluted hydrocarbon mixtures excited by a repetitive nanosecond pulse discharge}, journal={Journal of Physics D: Applied Physics}, year={2018}, volume={51}, number={37}, doi={10.1088/1361-6463/aad2b1}, art_number={374002}, url={https://www.scopus.com/inward/record.uri?eid=2-s2.0-85052624749&doi=10.1088%2f1361-6463%2faad2b1&partnerID=40&md5=53bd51e0508f2cf09ad35d3ebd10cf3d}, abstract={Plasma-assisted oxidation of atmospheric pressure hydrogen- and hydrocarbon-oxygen mixtures diluted in argon is analyzed by kinetic modeling, over a wide range of temperatures. In the experiments, preheated reactant mixtures are excited by a repetitively pulsed, double dielectric barrier ns discharge in plane-to-plane geometry, at near-isothermal conditions. Plasma images and temperature distributions in the discharge indicate that the reactant flow is nearly uniform, justifying the use of quasi-0D approximation in kinetic modeling. The kinetic model is based on a plasma chemistry mechanism combined with a conventional combustion reaction mechanism. The model does not contain adjustable parameters such as reduced electric field in the plasma, used in a number of previous 0D modeling studies. Comparison of the modeling predictions with the experimental data for hydrogen and methane oxidation exhibits good agreement between measured and predicted fuel concentrations over a wide range of temperatures, showing that the yield of primary radicals generated in the plasma is predicted accurately. Concentrations of intermediate hydrocarbon species predicted by the model are also in good agreement with the experiments, with the exception of acetylene below the hot ignition point. For ethylene and propane oxidation, the model overpredicts fuel consumption at low temperatures, also overpredicting concentration of CO, the dominant oxidation product, and underpredicting acetaldehyde concentration. This indicates that low-temperature pathways of formaldehyde formation, a major precursor for CO, as well as low-temperature reactions of several radicals which are precursors for formaldehyde and acetaldehyde, are not represented accurately in both conventional reaction mechanisms used. Although concentrations of intermediate hydrocarbon species in ethylene and propane are predicted relatively well, kinetics of formation and decay of acetylene remains not understood. This may be due to inaccurate branching ratio for dissociative quenching of metastable argon by heavy hydrocarbon species, as well as deficiencies of the conventional reaction mechanisms. © 2018 IOP Publishing Ltd.}, author_keywords={kinetic modeilng; nanosecond pulse discharge; plasma assisted combustion}, }