Experimental Measurement Of Local Element Ratio Of Hydrocarbon Flame Based On Laser Induced Breakdown Spectroscopy

Combustion is the most important way for human to use energy.However,a large amount of pollutants such as NO_X,SO_X,CO_X and soot are generated during the combustion process,which will cause environmental pollution.Combustion measurement technology can detect the characteristics of combustion flame,such as temperature distribution,component concentration,etc.It is of great significance in combustion diagnosis and pollutant control.Laser-induced breakdown spectroscopy?LIBS?is a typical laser spectrum analysis technology,which can detect samples qualitatively and quantitatively through the spectral information emitted by plasma.It has been widely used in flame detection with high temperature and complex flow field due to the advantages of non-contact,real-time online measurement,etc.In this thesis,Laser-induced breakdown spectroscopy was used to break down the ethylene/air premixed combustion flame to analyze flame plasma spectroscopy information.Firstly,the Laser-Induced Breakdown Spectroscopy system was built.The spectral information of laser-induced breakdown flame was preprocessed to eliminate background noise.The delay receiving time of LIBS spectrometer signal was optimized.Based on the spectral information of characteristic elements C?247.8 nm?,H?656.3 nm?and O?777.2nm?in ethylene/air premixed combustion flame,the laser energy was investigated.The results show that the spectral intensity of characteristic elements in flame increases with the increase of laser energy,and the laser energy has no effect on the spectral intensity ratio C/O and H/O.Then,the LIBS system was used to quantitatively analyze the CO₂/O2 mixtures with different mixing fractions.It was found that there was a linear correlation between the spectral intensity ratio and the atomic number density ratio.On this basis,the relationship between spectral element ratio and equivalence ratio of ethylene combustion flame is analyzed theoretically and experimentally.The results show that the spectral element intensity ratio C/O?H/O are linearly correlated with the equivalence ratio.The C and H spectral intensity were measured along the flame axial height.The results show that the C and H spectral intensity decrease with the flame height,and the C/H spectral intensity ratio increases first and then decreases with the flame height.