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Measurement of soot distribution in two cross-sections in a gasoline direct injection engine using laser-induced incandescence with the laser extinction method

An approach based on regression was developed to reveal the soot volume fraction (SVF) distribution of a horizontal cross-section in an optically accessible gasoline direct injection engine, based on the quantitative data in vertical images from planar laser-induced incandescence, which was calibrated by the laser extinction method (LEM). The approach used the matching of the corresponding pixels in the vertical and the horizontal images to solve the problem of visible range that limited the use of the LEM in measuring SVFs of the horizontal plane. Local SVFs of as low as 0.05 ppm can be detected. Analysis of both the horizontal and vertical image results showed that the case of ϕa = 0.7 (equivalent air–fuel ratio) resulted in significantly rich soot regions with a peak SVF approximately three times higher than that of the case with ϕa = 0.8.