發(fā)布時(shí)間：2018-10-13 13:39

【摘要】：等離子體助燃是近年發(fā)展起來(lái)的強(qiáng)化燃燒的手段,其可以加快化學(xué)反應(yīng)速率、增加活性基團(tuán)的種類和數(shù)量、減小點(diǎn)火延遲時(shí)間、增大燃燒的可燃極限和吹熄極限等從而使其在航空發(fā)動(dòng)機(jī)領(lǐng)域有較好的發(fā)展前景。等離子體火焰的檢測(cè)手段目前主要有探針?lè)ā①|(zhì)譜法和光譜法,但是,這三種方法均無(wú)法獲得等離子體火焰的二維分布圖像。上個(gè)世紀(jì)80年代出現(xiàn)了一種新的過(guò)程層析成像技術(shù)——電容層析成像技術(shù)(Electrical Capacitance Tomography,ECT),其原理是基于被測(cè)物質(zhì)相對(duì)介電系數(shù)不同進(jìn)而獲得其二維物質(zhì)分布圖像。本文利用ECT技術(shù)對(duì)甲烷-空氣等離子體火焰進(jìn)行成像測(cè)量,并結(jié)合實(shí)驗(yàn)和模擬的方法對(duì)等離子體火焰的介電系數(shù)進(jìn)行研究。 等離子體火焰中的極化方式主要有極性分子的偶極轉(zhuǎn)向極化、束縛電子的位移極化、熱轉(zhuǎn)向極化和自由電子位移極化。本文對(duì)等離子體火焰的極化方式進(jìn)行分析,忽略對(duì)相對(duì)介電系數(shù)貢獻(xiàn)較小的極化方式,例如極性分子的偶極轉(zhuǎn)向極化、分子和原子的束縛電子位移極化等。最終確定等離子體火焰中對(duì)相對(duì)介電系數(shù)貢獻(xiàn)最大極化方式為自由電子的位移極化,并借此獲得了相對(duì)介電系數(shù)的表達(dá)式。 等離子體火焰相對(duì)介電系數(shù)表達(dá)式中的未知參數(shù)主要是火焰中自由電子的電子密度和電子溫度,郎繆爾探針是檢測(cè)這兩個(gè)參數(shù)最常用的手段之一,即利用等離子體火焰的伏安特性曲線來(lái)獲得電子密度和電子溫度的值。將兩者代入到相對(duì)介電系數(shù)公式中即可獲得相對(duì)介電系數(shù)的探針實(shí)驗(yàn)值。 利用ECT對(duì)等離子體火焰進(jìn)行測(cè)量就可獲得其二維圖像,圖像中不同像素點(diǎn)的灰度值不同,需要對(duì)不同灰度值代表的相對(duì)介電系數(shù)的大小進(jìn)行標(biāo)定。本文利用MAXWELL軟件進(jìn)行模擬分析,模擬時(shí)所采用的幾何模型與實(shí)驗(yàn)時(shí)一致,實(shí)驗(yàn)時(shí)空標(biāo)定與滿標(biāo)定物質(zhì)的相對(duì)介電系數(shù)同樣成為模擬時(shí)的最小與最大相對(duì)介電系數(shù),并利用相對(duì)介電系數(shù)介于兩者之間工質(zhì)進(jìn)行模擬計(jì)算,借此獲得相對(duì)介電系數(shù)與灰度值的對(duì)應(yīng)關(guān)系。利用此關(guān)系對(duì)ECT圖像進(jìn)行標(biāo)定,獲得等離子體火焰相對(duì)介電系數(shù)ECT實(shí)驗(yàn)值。 對(duì)等離子體火焰相對(duì)介電系數(shù)的探針實(shí)驗(yàn)值與ECT實(shí)驗(yàn)值進(jìn)行分析,獲得了相對(duì)介電系數(shù)的探針實(shí)驗(yàn)值與ECT實(shí)驗(yàn)值的誤差來(lái)源。同時(shí),利用相對(duì)介電系數(shù)公式對(duì)火焰溫度場(chǎng)進(jìn)行了標(biāo)定。
[Abstract]:Plasma combustion is a recently developed means of intensified combustion, which can accelerate the chemical reaction rate, increase the type and number of active groups, and reduce the ignition delay time. By increasing the combustible limit and blowing limit, it has a good prospect in the field of aero-engine. At present, the methods of plasma flame detection mainly include probe method, mass spectrometry method and spectral method. However, none of these three methods can obtain the two-dimensional distribution image of plasma flame. In the 1980s, a new process tomography technique, electrical capacitance tomography (Electrical Capacitance Tomography,ECT), emerged. Its principle is to obtain two-dimensional material distribution images based on the difference of relative dielectric coefficient of measured matter. In this paper, ECT technique is used to measure the methane air plasma flame, and the dielectric coefficient of the plasma flame is studied by means of experiment and simulation. The polarization modes in plasma flame mainly include dipole shift polarization of polar molecule, displacement polarization of bound electron, thermal turn polarization and free electron displacement polarization. In this paper, the polarization modes of plasma flame are analyzed, ignoring the polarization modes which contribute little to the relative dielectric coefficient, such as the dipole shift polarization of polar molecules, the bound electron displacement polarization of molecules and atoms, etc. The maximum contribution to the relative dielectric coefficient in the plasma flame is determined to be the displacement polarization of the free electron and the expression of the relative dielectric coefficient is obtained. The unknown parameters in the expression of relative dielectric coefficient of plasma flame are mainly electron density and electron temperature of free electron in flame. Langmuir probe is one of the most commonly used methods to detect these two parameters. The values of electron density and electron temperature are obtained by using the volt-ampere characteristic curve of plasma flame. The probe experimental data of the relative dielectric coefficient can be obtained by inserting them into the formula of relative dielectric coefficient. The two-dimensional image of plasma flame can be obtained by using ECT to measure the plasma flame. The gray values of different pixels in the image are different, so the relative dielectric coefficient represented by different gray values should be calibrated. The geometric model used in the simulation is the same as that in the experiment. The relative dielectric coefficient of the spatio-temporal calibration and the full calibration is the minimum and the maximum relative dielectric coefficient in the simulation. The corresponding relation between relative dielectric coefficient and gray value is obtained by simulating the relative dielectric coefficient between them. The relative dielectric coefficient of plasma flame is obtained by calibrating the ECT image with this relation. The experimental values of the relative dielectric coefficient of plasma flame were analyzed by using probe and ECT, and the error sources between the probe and ECT were obtained. At the same time, the relative dielectric coefficient formula is used to calibrate the flame temperature field.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TK16

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