Experimental Study On Laser Induced Incandescence Spectrometry Of Carbon Particles In Complex Combustion Environment

The soot formed during combustion has negative effects on human health,air quality and global and regional climate.Because laser-induced incandescence（LII）technology has the advantages of non-intervention and quantitative field measurement,an experimental system of laser-induced incandescence spectroscopy is designed and built in this paper.The evolution process of carbon particles in ethylene and pulverized coal flame is studied.Besides,the effects of CO₂ addition,pulverized coal type and particle size on the growth process of soot particles are also studied.The main contents are as follows:1.Establishment of an experimental system and method for LII spectrometryThe flame combustion system,laser measurement system and soot particle sampling platform were built.The reliability of pulverized coal burner feeding and the stability of pulverized coal flame are verified,and the pulverized coal combustion enviro nment is close to the combustion enviro nment in the furnace by setting the primary and secondary air conditions reasonably.The laser wavelength of 1064 nm and the detection wavelength of 450 nm are reasonably selected,which ensures the accuracy and reliability of the laser-induced incandescence experiment.The experimental method of measuring soot particle concentration and particle size by LII was established.The volume concentration of soot particles was calibrated by extinction method.The two-dimensional distribution of ethylene flame temperature was measured by ratio pyrometry method.The results were compared with thermocouple temperature measurement and the error of temperature measured by two-color method was within50K.The particle size of soot particles was measured by sampling combined with TEM,which was in good agreement with the LII model.2.LII measurement of soot particles in ethylene flameThe ethylene/air laminar diffusion flame fuel was studied experimentally from three aspects:the optical properties of soot particles,the particle size and concentration of soot particles.With the increase of measurement height,soot particles become more mature,less transparent and more absorbent.The concentration and particle size of soot particles increase first and then decrease,which indicates that soot particles undergo nucleation,growth and oxidation in the flame.With the increase of CO₂ addition on the fuel side,the yellow luminescence height decreases while the dark area height increases,which indicates that adding CO₂ on the fuel side can slow down the nucleation rate and inhibit the formation of primary soot particles.The laser energy curve,particle size and concentration distribution of soot were measured by LII technology.The absorption performance of soot particles decreased slightly due to the mixing of CO₂,which indicated that the maturity of soot particles decreased with the dilution of CO₂.From the measurement results of soot size and concentration,it can be seen that adding CO₂ to the fuel side can reduce soot particle size and change the boundary between the flame surface growth zone and oxidation zone,but has no obvious effect on the oxidation process.3.LII Measurement of carbon particles in pulverized coal flamesThe evolution of carbon-containing particles in pulverized coal flame is studied from three aspects:flame morphology,particle optical properties and LII signal intensity distribution.It is found that the laminar small particle bituminous coal flame has typical single particle homogeneous ignition stage,group ignition stage and coke heterogeneous ignition stage.The measurement results of laser energy curve show that with the increase of laser energy,the LII signal intensity increases first,then decreases slightly,and finally rises again.The effects of pulverized coal type and particle size on the growth of soot particles were studied.The results showed that the larger the particle size of pulverized coal,the lower the soot concentration of pulverized coal flame,and the ignition mode of pulverized coal flame tended to single particle ignition.Among bituminous coal,lignite and anthracite,the soot concentration of bituminous coal flame is the highest;the soot concentration of anthracite flame is very low due to the low volatile content while the lignite particles tend to generate small molecular gases after devolatilization,which is not easy to generate soot.