| Monitoring the flame state during the combustion process of gas plays an important role in achieving stable operation of gas appliances,improving combustion efficiency,and reducing pollutant emissions.The flame ionization current method,as a representative of invasive flame monitoring methods,is currently mostly applied in practical engineering to monitor the two states of flame extinction and combustion,lacking more detailed applications,such as monitoring specific flameparameters and analyzing the dynamic characteristics of flame current.The study of flame characteristics using flame spectroscopy is extensive,but its application in flame detection is limited.This article is based on the principles of flame ionization current and spectrum,and takes premixed flames as the research object to study the changes in their current and spectral characteristics with flame parameters.Based on these changes,a monitoring method for the air coefficient of premixed flames is obtained,providing a basis for the safe and energy-saving operation of gas combustion appliances.The main content is as follows:(1)Analyze and obtain the ionization current of premixed flames as a function of air coefficient α,the variation pattern of load QIn a partially premixed flame,the current intensity varies with the air coefficient αIncreasing with the increase of load Q.air coefficient α.The change from 0.7 to 0.9 can be monitored by the exponential function of its current intensity I fitting.In a fully premixed flame,the current intensity decreases with an increase in air coefficient and decreases with an increase in load Q.air coefficient α.The change from 1.0 to 1.2 can be monitored using a polynomial function fitted to its current intensity.(2)Analyze and obtain the full spectrum characteristics of the flame.In the full spectrum of premixed flames,the emission intensity is highest in the nearinfrared range,followed by the visible range,and the emission intensity is lowest in the ultraviolet range.The spectral bands of CH*and C2*can be seen in the visible range,while the spectral bands of OH*can be seen in the ultraviolet range.(3)Analyze the dynamic variation of ionization current of premixed flames with air coefficient αWhen the load Q remains constant,as the air flow rate Lair increases,the air coefficient α.As the current increases,the rate of change V increases.At the completion time of the flow regulation action T2,the rate of change V reaches its maximum value.After T2,the rate of change gradually decreases.When the flow rate remains basically unchanged,increasing the gas flow rate LCH4 of a partially premixed flame increases the air coefficient α1 added to α2(or reduce the gas flow rate LCH4 of the fully premixed flame to increase the air coefficient)The corresponding current intensities are I1 and I2,respectively.I1<I2.During the adjustment process,the current first slightly decreases,then rapidly increases to the peak Imax>I2,and then gradually fluctuates and stabilizes to I2.Changing the air coefficient when the flow rate remains constant α,the change of current I is close to step response.(4)Detailed spectral variation with air coefficient of premixed flames obtained through analysis α,The variation pattern of load QIn partially premixed flames,the spectral intensity of free radicals varies with the air coefficient α Increasing with the increase of load Q.The spectral intensity from high to low is CH*,C2*(0,0),OH*,and C2*(1,0).And for the air coefficient α.The sensitivity levels of OH*,CH*,and C2*are in order from strong to weak,with the minimum values of free radical spectral intensity being 80%,70%,and 60%of the maximum values,respectively.The change in air coefficient from 0.7 to 0.9 can be monitored by the ratio of the emission intensity integral in the C2*(1,0)and CH*bands.In a fully premixed flame,the spectral intensity of CH*and C2*varies with the air coefficient α.The spectral intensity of OH*decreases with the increase of air coefficient α The increase first increases and then decreases,with its peak appearing at α=1.05～1.10,the intensity of each fundamental spectrum decreases with the increase of load Q.The spectral intensity from high to low is CH*,C2*(0,0),OH*,and C2*(1,0),which affect the air coefficient α The sensitivity level of C2*(0,0),C2＊(1,0),CH*,OH*from strong to weak.The minimum values of free radical spectral intensity are 60%,50%,40%,and 20%of the maximum values,respectively.The change in air coefficient from 1.0 to 1.2 in a fully premixed flame can be monitored by the integral ratio of the emission intensity of the OH*wave to the CH*band. |
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