An Experimental Study Of Laser Measurement For Ultrafine Carbonaceous Particulates In Complex Media

The ultrafine particles (PM2.5) in atmosphere include primary particles discharged into the atmosphere directly, and secondary particles generated from gas precursor through the photochemical role. PM2.5come from soil wind dust and power plants, motor vehicle emissions, etc. PM2.5can enrich all sorts of heavy metal elements and organic pollutants (polycyclic aromatic hydrocarbon), which not only can cause human health negative effect, such as respiratory system disease, lung function decline and cancer, but also can make the greenhouse effect enhancement, the destruction of the ozone layer and reduce atmospheric visibility as well as other environmental problems. In order to limit emissions of PM2.5, our country will formulate PM2.5emissions standards implemented in2016, i.e less than35μg/m3average annual and less than75μg/m3average day. The aim of this paper is an experimental study of rapid laser measurement for ultrafine particle concentration and size under high temperature environment, which can provide scientific proof for the research about combustion mechanism, the combustion optimization operation and solid particle emission control and so on.In the paper, the measurement of carbon ultrafine particles concentration and size in different combustion media using laser-induced radiation technology was investagted. The concentration and size of soot particles in propane flame were calibrated using single wavelength light extinction and Transmission Electron Microscope, respectively. The volume concentration of nanoscale particles was verified with two-color light extinction at different flows of hydrogen in the coal flame.Fitstly, the effect of detecting condition on the measurement results was studied in the propane turbulence flame. The discussions focus on the effects of laser signals trigger source and tested signals of particles trigger source on laser-induced radiation signals.Then, the two-colour laser induced radiation technology was used to determine the soot volume concentration at different propane diffusion flame heights. The light extinction method was used to validate the results. The size of soot particle in propane combustion flame was determined using the time-division average fitting method. The obtained mean diameter of soot particles in the propane flame was validated using Transmission Electron Microscope.At the end, different carbon particles from pulverized coal combustion in the pure hydrogen flame were heated by a high-power pulse laser beam to measure the relative content and size of different carbon particles. The size distribution of carbon particles was obtained using a multistage index function method to fit time-resolved radiation emitted by the laser-heated particles, where the flow zone was determined by Kn. The size of different carbon particles in coal combustion was determined with the laser energy fluence and flame height. The coefficient Ai was determined too. The volume concentration of nanoscale particles was verified with double wavelength light extinction for different flow of hydrogen in the coal flame.