Autoselective regeneration of gelcast ceramic foam
thesisposted on 17.06.2013 by Andrew M. Williams
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
This thesis describes the development and application of an electric discharge for regenerating gelcast ceramic foam diesel particulate filters (DPF) for effective and efficient reduction of particulate matter (PM) emissions from diesel fuelled IC engines. The combustion in diesel compression ignition engines generates a number of unwanted by-products including PM. The PM from diesel engines is believed to be potentially carcinogenic when inhaled into the lungs and, therefore, needs to be controlled. Emission legislation has made it increasingly difficult for engineers to reduce PM emissions whilst meeting NOx targets by combustion optimisation alone, leading to the requirement for exhaust gas aftertreatment, most notably exhaust gas filtration. Filtration and regeneration (filter cleaning) technology must be robust, filter high amounts of PM, be compact, energy efficient and cost effective. A large number of published solutions do not meet all of these criteria. This research has developed a compact, efficient, robust and cost effective solution: The Autoselective regeneration of gelcast ceramic foam DPFs. Gelcast ceramic foam geometry can be optimised on a microscopic and macroscopic scale with a large number of material characteristics. This thesis develops and applies new methodology for rapid optimisation of gelcast ceramic foam DPFs. The optimum foam geometry is found to be highly application-dependent. Filters with >95% filtration efficiency and a low filtration volume have been demonstrated, although are limited in their PM mass holding capacity. It was found that filters with higher PM mass holding capacity require larger pore sizes and filtration volume. Design maps were produced to allow rapid optimisation of gel cast ceramic foams with a novel methodology that can be applied to all forms of deep bed filtration, saving both time and cost in future filter development. Investigation and optimisation of Autoselective regeneration demonstrated that the regeneration system is most effective when the electric discharge is active within the filter volume. Using modelling and novel methods for measuring heat flux from electrical discharges, thermal optimisation of the heat flows in the system were achieved. Rig tests increased the robustness of the regeneration system and developed profiled mesh electrodes to maximise the effective regeneration volume. An engine test programme demonstrated regeneration effectiveness of -12 g kW·1 h-I which is equivalent to -333 W for a typical 56 kW heavy duty diesel engine. Alternatives such as fuel burners and electrical resistance heaters typically consume between I and 5 kW of fuel energy for filter regeneration. Multiple electrode prototypes are presented and evaluated for efficient and effective on-engine and on-vehicle PM control.
- Mechanical, Electrical and Manufacturing Engineering