Quantitative Measurements of Soot Volume Fractions in Diesel Engine Using Laser-Induced Incandescence Method

Laser-induced incandescence (LII) is an optical diagnostic method used to measure the soot volume fraction in a flame. In this paper, the principle of LII and the calibration methods normally used are introduced. Based on two-color LII theory, a quantitative test system for determining the in-cylinder soot volume fraction was established. A dual imaging setup was used, which can achieve multipoint calibration and full field-of-view quantification of soot in a diesel engine chamber. An investigation was carried out on an optical diesel engine with the conditions 1200 r.min(-1) and 21 mg fuel injection per cycle, with various injection pressures (60, 100, and 140 MPa). The results show that the natural soot incandescence emerged after the peak rate of combustion heat release. With increasing injection pressure, the duration of natural soot incandescence shortened and the natural soot luminosity decreased. The range of soot volume fractions in the test zone was (0-50) x 10(-6). The mean soot volume fraction at the initial soot stage, soot peak, and soot oxidation stage were in the ranges (5 9) x 10(-6), (15-20) x 10(-6), and (14-16) x 10(-6), respectively, depending on the injection pressure. With increasing injection pressure, the distribution area of the soot particles increased, the mean soot volume fraction decreased, and the distributicin of the soot volume fraction in space tended to be more uniform in combustion flames.