Abstract
dc:description.abstractHealth concerns have led to the widespread application of the diesel particle filter (DPF) in engine exhaust systems to limit emissions of combustion-generated particles. The collection of particulate matter in exhaust after-treatment devices depends on a number of mechanisms for aerosol particle deposition that are analysed in the first part of this thesis. Experiments on a diesel burner designed to reproduce the particle emissions and exhaust conditions of a light-duty engine showed that turbulent deposition of large agglomerates in the channels of flow-through monoliths is likely to make a contribution comparable to that expected for diffusion and gravitational settling. The number deposition efficiency of size-classified particles in the same monoliths was measured at low volume flow rates controlled to achieve similar mass transfer conditions to flow through the pores of a DPF in order to separate the effects of different deposition mechanisms. Results showed close agreement with equations for the diffusion of particles in fully developed laminar flow. Isolation of the action of the Coulombic force in the data implied the presence of weak electric fields generated by static charges on the ceramic wall surface. Models describing the performance of the DPF typically treat deep-bed filtration and cake filtration as two distinct regimes. Since the deep-bed filtration stage causes the rapid initial increase in exhaust back pressure as a clean DPF is loaded, it is of significant advantage to engine operation to minimise particle deposition within the walls and achieve immediate bridging over the pores. The second part of this thesis focuses on the monitoring of this process; successive stages of pore filling were visualised for the first time and in unprecedented detail with scanning electron microscopy. Electron images from repeated filtration in the same wall sample indicated that the profile of a DPF pore entrance does not influence the location of initial particle deposition. Particles from the tail-end of a diesel burner accumulation mode contribute to the growth of dendrites that extend over pores to lengths of several microns and very large agglomerates can cause sudden plugging, which substantially reduces the pre-cake pressure drop penalty. However, particles from a smaller size distribution generated by a medium-duty diesel engine fill pores in a manner that appeared approximately radially uniform. This observation of shrinking pore behaviour was confirmed in a subsequent study using a custom filter wall consisting of tungsten foil laser-drilled with nearly monodisperse circular micro-channels.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2011
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Payne, Simon Daniel
- Advisor dc:contributor.advisor
-
- Collings, Nicholas
Subjects
dc:subject × 2Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.93208
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/345786