Analysis Of The Dielectric Coefficient Of Plasma Flame And Imaging Plasma Flame Using Electrical Capacitance Tomography

Plasma-assited is a new method to intensify combustion which is developed in recent years. It can accelerate the chemical reaction rate, increase the variety and quantity of active group, reduce the ignation delay time, increase the burning flammable and cut-off limit so that it has excellent prospects in the field of aviation engine. The detection means are main the probe, mass spectrometry and spectrophotometry, however, these three methods are unable to obtain two-dimensional images of the plasma flame. Electrical capacitance tomography (ECT) is a kind of process tomography technique which appeared in the last80’s. The principle is based on the relative dielectric coefficient of the measured objects are different to obtain two-dimensional images of material distribution. This paper makes use of ECT imaging measurement of air-methane plasma flame and researches the relative dielectric coefficient combined with the method of theory, simulation and experiment.Plasma flame polarization ways mainly have the polar molecular dipole polarization, bound electron displacement polarization, heat turning direction polarization and free electron displacement polarization.Through the analysis of the polarizational mode, we ignore these modes which make little contribution to the relative dielectric coefficient, for example, dipole polarity molecular orientation polarization, bound electron displacement polarization of atoms and molecules etc. Ultimately determine the free electrons displacement polarization makes maxiium contribution to the plasma flame relative dielectric coefficient and get the expression of relative dielectric coefficient.The unkown parameters are the electron density and electron temperaue. For measuring these parameters generally used the Langmiur probe, namnely the use of plasma flame volt and ampere characteristic curve to obtain the two parameters. We can obtain the probe experimental values of relative dielectric coefficient by substituting the two parameters into the expression.Measurement of the plasma flame can obtain the two-dimensional image using ECT. The different pixels have different gray values, so we need to calibrate the different gray values corresponding to the different relative delectric coefficients. This paper uses the MAXWELL software to do the simulation analysis and the geometric model is the same as the experiment used. The relative delectric coefficient of full and empty calibration can also be the minimum and maximum relative permittivity in the simulation. And we use the value between the minimum and maximum to do the simulation to get the correpoding relationship between relative dielectric and gray value. The ECT images are calibrated using the relationship and we can obtain the relative delectic coefficient ECT experimental values.The plasma flame relative delectric coefficient ECT and probe experimental values were analyzed and obtained the main error source. On the use of the relative delectric coefficient expression to calibrate the flame temperature field is studied.