UC San Diego

Laser-induced incandescence (LII) is used to obtain soot particle size measurements in laminar premixed ethylene flames. The LII signals are calibrated by comparing with the particle diameters measured with scanning mobility particle sizer (SMPS). Issues related to the calibration of LII with SMPS are discussed, such as the effects of equivalence ratio and laser fluence. LII and SMPS have similar sensitivities to equivalence ratio in terms of total surface area and total volume, but the equivalence ratio needs to be carefully controlled as it highly affects the results. High laser fluence affects LII results by vaporizing soot particles, which reduces particle size. The effect of high laser fluence is particularly noticeable in the flame positions near the surrounding air such as at high flame heights and the outer combustion zone of nonpremixed flames where particle oxidation takes place. Overall, the comparison between LII and SMPS data yields encouraging results as they exhibit similar trends. The correspondence of LII and SMPS implies that SMPS could be applied as a valuable tool to calibrate LII signals and avoid the necessity of developing complex LII models