Experimental Study On The Effect Of Post Injection Schemes On The Microscopic Morphology And Nanostructure Of Particles From A Diesel Engine

It is a common way to achieve clean combustion for diesel engines by the multiple injection technology. The parameters of a post injection have a great influence on soot morphology and nanostructure, which are quite related to its oxidation process. Therefore, detail investigations of the particulates generated from different post injection schemes are necessary for understanding the evolution process of PM and optimizing injection schemes. In this dissertation, soot samples were collected from a Euro IV diesel engine.In the main-post injection conditions, the fuels mass injected after the main injection varied from 2 to 14 mg, while the injection interval varied from 0.7 to 1.9ms.This dissertation studied on the effect of post injection on regulated emissions(CO/HC/NOx/PM), firstly. The results show that CO and HC emission increases with the increasing of the post injection mass and timing, while PM emission decreases.According to the TEM image processing analytical methods, the evolution mechanism of morphology and nanostructure of soot generated at different main-post injection conditions and related single injection conditions was subsequently studied. The results show that most of the typical particulates are in core-shell nanostructures. The fractal dimensions of the main-post conditions are in a range of 1.12~2.21 and show a decreasing trend with the increasing of post injection mass, while the fractal dimensions at single injection condition are in a range of 1.16~1.49.The diameters of primary particles generated at all of the conditions show an unimodal distributions with the peak value in a range of 16~26nm. The fringe separation distances also show a unimodal distribution, with the maximum in a range of 0.35~0.38 nm, and are little influenced by the injection intervals. At certain injection timing, the mean separation distance rises at low post injection mass and then decreases slowly with the increasing of post injection mass, while little difference was observed between at 10 mg and 14 mg conditions. The fringe lengths of primary particles generated at 2mg conditions are the longest, then is the 6mg conditions, and the fringe lengths of primary particles are similar at 10 mg and 14 mg conditions. Meanwhile, the fringe tortuosity distributions correspond with the length distributions.According to Raman spectrum and XPS analytical technology, the effect of post injection parameters on particles graphitization degree and ordering degree were studied. The area ratios AD1/AG of D1-peak to G-peak in Raman spectrum reflect the Graphitization degree of particles. The ratio increases with the increasing of post injection mass. The area of D4-peakincreases with extending the main post interval and this result is consistent with the XPS results, which is used to show the order degree of the particle surface.