Understanding in-cylinder soot reduction in the use of high pressure fuel injection in a small-bore diesel engine |
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Authors: | Lingzhe Rao Yilong Zhang Sanghoon Kook Kenneth S. Kim Chol-Bum Kweon |
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Affiliation: | 1. School of Mechanical and Manufacturing Engineering, The University of New South Wales, Sydney, NSW 2052, Australia;2. US Army Research Laboratory, Aberdeen Proving Ground, MD 21005, USA |
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Abstract: | This study shows how soot particles inside the cylinder of the engine are reduced due to high pressure fuel injection used in a light-duty single-cylinder optical diesel engine fuelled with methyl decanoate, a selected surrogate fuel for the diagnostics. For various injection pressures, planar laser induced incandescence (PLII) imaging and planar laser-induced fluorescence of hydroxyl (OH-PLIF) imaging were performed to understand the temporal and spatial development of soot and high-temperature flames. In addition, a thermophoresis-based particle sampling technique was used to obtain transmission electron microscope (TEM) images of soot aggregates and primary particles for detailed morphology analysis. The OH-PLIF images suggest that an increase in the injection pressure leads to wider distribution of high-temperature flames likely due to better mixing. The enhanced high-temperature reaction can promote soot formation evidenced by both a faster increase of LII signals and larger soot aggregates on the TEM images. However, the increased OH radicals at higher injection pressure accelerates the soot oxidation as shown in a higher decreasing rate of LII signals as well as dramatic reduction of the sampled soot aggregates at later crank angles. The analysis of nanoscale carbon layer fringe structures also shows a consistent trend that, at higher injection pressure, the soot particles are more oxidized to form more graphitic carbon layer structures. Therefore, it is concluded that the in-cylinder soot reduction at higher injection pressure conditions is due to enhanced soot oxidation despite increased soot formation. |
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Keywords: | Diesel engine Injection pressure PLII PLIF Soot morphology |
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