【摘要】：等離子體助燃是近年發(fā)展起來的強化燃燒的手段,其可以加快化學反應速率、增加活性基團的種類和數(shù)量、減小點火延遲時間、增大燃燒的可燃極限和吹熄極限等從而使其在航空發(fā)動機領域有較好的發(fā)展前景。等離子體火焰的檢測手段目前主要有探針法、質(zhì)譜法和光譜法,但是,這三種方法均無法獲得等離子體火焰的二維分布圖像。上個世紀80年代出現(xiàn)了一種新的過程層析成像技術——電容層析成像技術(Electrical Capacitance Tomography,ECT),其原理是基于被測物質(zhì)相對介電系數(shù)不同進而獲得其二維物質(zhì)分布圖像。本文利用ECT技術對甲烷-空氣等離子體火焰進行成像測量,并結(jié)合實驗和模擬的方法對等離子體火焰的介電系數(shù)進行研究。 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。本文對等離子體火焰的極化方式進行分析,忽略對相對介電系數(shù)貢獻較小的極化方式,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相對介電系數(shù)貢獻最大極化方式為自由電子的位移極化,并借此獲得了相對介電系數(shù)的表達式。 等離子體火焰相對介電系數(shù)表達式中的未知參數(shù)主要是火焰中自由電子的電子密度和電子溫度,郎繆爾探針是檢測這兩個參數(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獲得電子密度和電子溫度的值。將兩者代入到相對介電系數(shù)公式中即可獲得相對介電系數(shù)的探針實驗值。 利用ECT對等離子體火焰進行測量就可獲得其二維圖像,圖像中不同像素點的灰度值不同,需要對不同灰度值代表的相對介電系數(shù)的大小進行標定。本文利用MAXWELL軟件進行模擬分析,模擬時所采用的幾何模型與實驗時一致,實驗時空標定與滿標定物質(zhì)的相對介電系數(shù)同樣成為模擬時的最小與最大相對介電系數(shù),并利用相對介電系數(shù)介于兩者之間工質(zhì)進行模擬計算,借此獲得相對介電系數(shù)與灰度值的對應關系。利用此關系對ECT圖像進行標定,獲得等離子體火焰相對介電系數(shù)ECT實驗值。 對等離子體火焰相對介電系數(shù)的探針實驗值與ECT實驗值進行分析,獲得了相對介電系數(shù)的探針實驗值與ECT實驗值的誤差來源。同時,利用相對介電系數(shù)公式對火焰溫度場進行了標定。
[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.
【學位授予單位】：北京交通大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TK16

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