Visualization Of Micro-combustion Using Electrical Capacitance Tomography And Simulation Analysis

In recent years, micro dynamic device has fast development because of its widespread application prospect in many domains. But micro-combustion chamber has received more and more attention as the most importand and complicated part of micro dynamic device. Because of the limits of the traditional measurements in micro-scale conditions, the process of micro-scale combustion can not be measured accurately and effectively in recent years. This seriously obstructed the in-depth research of complex combustion phenomenon in micro-combustion chamber.The technology of electrical capacitance tomography can provide real-time and continuous visual measurement. It has many advantages such as non-intrusive, multi point and fast in response. All these have unique advantages for solving many problems of micro-combustion.In the dissertation, the ECT system is used to visualize the flame distributions at the micro-combustion chamber, expanding the flame examination to the multi-dimensional space. The methodology of this study provides a novel method for the investigation of micro-combustion.The main contributions of this dissertation are as follows:(1) The dissertation reviewed the image reconstruction algorithms of ECT and analyzed their characteristics and limitations. The electric nature of combustion is expored, analyzing the plasma characteristics of flame and the dielectric properties when existing ECT external AC excitation. The relationship between the dielectric permittivity of flame and the internal interelectrode capacitance and temperature are derived. The conclusion that the dielectric permittivity of flame and the internal interelectrode capacitance will increase with the increase of temperature is conclused.(2) The flame signals in microtubule are real-time measured by the spectrum method. The gas combustion stability is judged by analysing the time and frequency domain signals of flame signals. At last, the conclusion is conclused that combustion stability is better when stoichiometric ratio changes between 1 and 2 by analyzing the specific variance of flame intensity and flame flicker frequency. The comclusion will provide an experimental basis for the rational organization of micro-combustion.(3) A novel high temperature endurable electrical capacitance sensor was designed and made to overcome the shortcomings of ECT sensor that cannot measure flames in high-temperature, testing the responsing feature for flame. The relationship between the dielectric permittivity of flame and the internal interelectrode capacitance is verified by demarcation experiment. An experiment plat for micro-combustion visualizing measurement was built up to achieve real-time micro-scale flame measurement. The instability and incompletely of micro-combustion by ECT images were demonstrated. The flame images change more obviously and the flame extinguishs more easily when combustion is instable.(4) Numerical simulation is conducted using Fluent software. To under the micro-scale combustion chamber different combustion condition's temperature field, the velocity field and various components density field has carried on the numerical simulation. The results shows that in the wall surface adiabatic condition, the changes of combustion chamber structure and inlet velocity has the influence to the micro combustion combustion efficiency and the stability and in the wall surface radiation situation, radiates to the combustion stability and the combustion efficiency has the quite tremendous influence, chooses the rich fuel burning atmosphere to be helpful to the combustion stability.(5) Comparing the flame images by ECT with the results of numerical simulation, the results show that the different images of flame distributions have anastomosis and the ECT method may effectively visual measure the flame distributions of micro-combustion.