Characterization Of A Burner Flame Using Non-Intrusive Electrostatic Sensor Arrays

The accurate detection of combustion state,combustion efficiency and the changes of combustion state of the fuel in boiler are of great importance for the safety and economy of boiler operation.The flame has weak electrical conductivity as the combustion is a complex and rapid exothermic chemical reaction where a large number of soot particles,ions and electrodes are generated.In this paper,the electrostatic sensor is proposed to measure the dynamic characteristics of soot particles and ions flow through inducing the charge of these charged species in the flame.The electrostatic sensing method has the advantages of simple structure,low cost,high sensitivity and less interference of the external environment.The main contribution of the research is as follows.Firstly,the available flame detection technologies and the research background of the electrostatic sensing method are reviewed and summarized in detail in this paper.Secondly,the principle of electrical conductivity of flame and the distribution characteristics of charged species are discussed and analyzed.Last,the detailed analysis of the performance of electrostatic sensors is conducted.Finally the electrostatic sensor array and sensor unit are designed to full the experimental requirements based on these theoretical basis.In this paper,the electrostatic signal from the electrostatic sensor is processed by calculating its root mean square,power spectrum density,Hurst index and cross-correlation.The root mean square represents the concentration of soot particles and ions.The oscillation frequency is calculated based on the power spectrum density of electrostatic signal.The Hurst index is used to characterize the motion complexity of soot particles and ions.The flow velocity is obtained through the cross-correlation velocimetry.It is essential to analyze these characteristics for the better understanding of the combustion state.Experiments were conducted with a fixed fuel flow rate and a fixed air flow rate in flame root region,middle region and upper region,respectively.The results indicate that the concentration,oscillation frequency and motion complexity reach the maximum in the middle region.Moreover,all parameters increase with the air flow rate when the fuel flow rate is fixed.In addition,the result shows that the flow velocity decreases along the flame propagation direction.It can be concluded that the flow velocity is mainly influenced by the air and fuel flow velocity.