Date

2018

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Environmental Engineering

First Adviser

Fox, John T.

Abstract

The dissertation mainly focused on the process development of Diesel emission after treatment system and these substrate materials including cordierite and silicon carbide. As mobile sources, including highway and non-road vehicles combined to be the second leading anthropogenic source of particulate matter (Both PM2.5 and PM10) in the US, the on road and off road vehicles have required to equipped diesel particulate filter (DPF) and diesel oxidation catalyst (DOC) in order to meet the ever more stringent environmental regulations. DPF are made from artificial ceramics, especially cordierite which accounts for over 90% of the market in US. However, the DPF premature failures have been observed and reported widely. And the currently DPF regeneration technologies suffer thermal damage due to excessive temperature peaks, which occur due to exothermic combustion of soot embedded in DPF. Thus, the focus of the work herein focuses on understanding fundamental science relate to DPF premature failure, developing novel regeneration technology to protect the DPF and material technology to advance the use of DPF.The fundamentally understanding of DPF premature failure has been demonstrated with first appraise and classified the DPF premature by monitoring the exhausted DPF provided by Hunsicker Emission Services, LLC, Earlington, PA. The surface elemental analysis of these premature failure area has been conducted by XPS, SEM-EDS. Results indicated an extraordinary high concentration of Na, K, Zn, Ca and Fe around the area of premature failures. XRD analysis of the failed DPF section indicated complex crystalline phases which are different from the intact cordierite crystalline phase. In order to further understanding the failure mechanism, lab scale tests have been carried out to simulate the DPF premature failure process happened during the commercial use. Results indicated the alkaline metals Na, K in the ash compositions contribute most towards the premature failures, followed by Fe. Despite the concentrations in the DPF ash, the Ca and Zn are not the leading contaminants cause the vitrification of the substrate, further leading to the cracking failure. The corrosion pathway has been revealed through the temperature elevated tests and the corrosion mechanisms were demonstrated by XRD analysis.In order to prolong the lifetime of DPF, a novel water based regeneration process has been developed. This water based regeneration process demonstrated significant higher regeneration efficiency by removing several times more soot and ash, reducing 50% more engine back pressure than the conventional calcination process. And this water based regeneration process can not only remove carbon soot, but also remove majority metallic ash embedded in the DPF channel. Long term observation by Hunsicker Emission Services (HES) give a good consistence on the wash process for both high and low soot, ash loading DPF.Further, a highly purity silicon carbide nanowire matrix (SCNW) has been manufactured by environmental friendly precursors: guar gum and silicon powder. The SCNW has advantages of higher porosity, higher chemical resistance and low thermal expansion coefficient compared to cordierite. When using guar gum/silicon powder ratio of 10 to 3, the substrate gives the most SiC nanowires. Iron acted as catalyst by leading the growth of nanowire under temperature of 1400oC. The nanowires generated with highly crystallized face center cubic structures followed by the growing direction of (112). And the nanowires have core/shell structures with SiC acted as core and covered by SiO2. The nanowires have diameters around 40-60nm and could grow several micrometers in length. The Vicky hardness analysis indicated the SCNW matrix has much higher hardness 467 HV/kg compared to commercial cordierite substrate of 280 HV/kg. The SCNW matrix can be potential substrate materials for DPF and DOC in the future.In addition, the highly porous carbon soot collected from the exhausted DPF could be employed to adsorb the heavy metals (Cu, Cr and Cd). The adsorption capacity of carbon soot was compared with a commercial activated carbon and results indicated much higher adsorption capacity due to the abundant of surface functional groups and larger surface area. The reuse of DPF soot can be a potential absorbent besides the widely used activated carbon.

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