Investigation On Measurement Of Soot By Laser-induced Incandescence (LII)

Laser induced incandescence（LII） is the black body radiation from soot particleswhich are heated by laser light to a temperature above2500K. LII has proven to be apromising tool for soot particle measurement in combustion system, due to itsnon-intrusive detection as well as high spatial and temporal resolution.A LII system for soot diagnostics was established in this thesis, utilizing ICCDdetector for two-dimentional imaging of the soot volume fraction and particle sizedistribution. The quantitative measurement of soot volume fraction was achieved bythe method of two-color LII; Two-dimentional time-resolved LII was applied todetermine the particle size distribution. A plug-in tool for Origin software wascomplied with LabTalk language, for the LII model calculation and LII experimentdatum processing. Different heat conduction sub-model were compared under a widerange of gas pressure, the result shows that a FMR sub-model with aggregatecorrection can be applied to a wide pressure rang of1-30bar, and the accuracy ofparticle size evaluation by this model is acceptable.LII measurement was carried out on a self-designed co-flow partial-premixedburner under atmospheric temperature and pressure, to study on two critical aspectsthat influence soot emission. First, the effect of CO₂addition to premixed gas on thesoot emission was studied, by changing the volumetric percentage of CO₂from0%to20%. The experimental result shows a decline of soot volume fraction with theincreasing CO₂concentration, due to a dramatic reduction in flame temperature thatsuppress the formation of soot, and the lengthened lift-off length is an another reasonfor the soot reduction. Secondly, the effect of oxygenated bio-fuel was discussed.Mixing fuel of n-heptane and toluene was used as a basic case, and oxygenatedbio-fuels of ethanol and n-butanol were added respectively as comparative cases. Theresults show the addition of oxygenated bio-fuel is an effective way to reduce sootemission in the flame, while n-butanol has a better soot-reduction effect than ethanoldue to differences in chemical kinetics reaction path.