Particle Size-Dependent Filtration of Clean (Non-loaded) Diesel Particulate Filters
Jessica Sheappard, Texas A&M University (CRCL)
Internal combustion engines are used almost ubiquitously in the developed world. These engines produce, as a byproduct of their combustion, exhaust particles which have been shown by the World Health Organization (WHO) to cause cancer . Diesel exhaust particulate filtration is mandated by the United States Environmental Protection Agency (US-EPA) primarily to improve the air quality in urban areas, and is achieved through use of the diesel particle filter. However, other types of internal combustion engine produce qualitatively different particle size distributions . For example, gasoline direct injection engines produce fewer particles overall than diesel, and the particles themselves are smaller on average. This means that a soot cake, which does the majority of filtration in DPFs, will never form. In this work diesel filter models are used as a starting point for modeling and designing an exhaust particle filter for particle size distributions different from those found in diesel exhaust. Since particle laden engine exhaust emissions pose a health hazard, and since gasoline engine particle emissions are currently unfiltered, a need exists for a particle filter suitable for gasoline engines.
In addition, there is a known tradeoff between fuel efficiency and the efficiency of a particle trapâ€™s filtration. Any filter placed in the exhaust stream of an engine will partially obstruct the flow, thus causing a pressure buildup. This pressure difference incurs a penalty on the engineâ€™s performance, and thus on the engineâ€™s fuel-efficiency . Therefore, particle traps with efficient filtration and low pressure drop remains a subject of intense interest.
This work uses an existing filtration model for diesel particulate filters as a starting point to predict design changes that may yield a filter suitable for use on gasoline engine exhaust. The existing model is modified to better fit experimental data of filter samples without a soot cake. These modifications include changes in the pore shape used in the model, and the addition of a thermophoretic mode and a gravity deposition mode of filtration to the already accounted modes of Brownian diffusion, inertial impaction, and direct interception.
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