Micro-scale Experimental Evaluation of PM Filtration with Low Particle Mass Concentrations

Sandeep  Viswanathan, University of Wisconsin-Madison

Micro-scale filtration experiments are being performed at the University of Wisconsin-Madison to develop a fundamental understanding of the filtration of particulate matter (PM), from engine exhaust with low particle mass concentrations, such as those found in the exhaust of spark-ignition direct-injection (SIDI) engines. In order to understand the nature of particles entering the filter, PM characterization studies have been performed, in collaboration with PNNL, to explore the impact of engine operating conditions on particle size distribution, mass mobility relationships, and other morphological parameters such as shape factors and fractal dimensions. Results from these studies have been compared with relevant data obtained from conventional diesel combustion (CDC) on a heavy-duty diesel engine.
Current experiments are aimed at understanding the impacts of relevant parameters on the evolution of filtration performance for different substrate geometries. PM from previously characterized SIDI operating conditions was loaded on micro-scale filter samples to evaluate the filtration performance. Results from filtration of PM using a low porosity filter, showed a continuous decrease in most penetrating particle size (MPPS) as the filter was loaded. During PM loading from low load, stoichiometric conditions, an increase in penetration of small particles was observed. This was not observed for the cases with higher concentration of accumulation mode particles in the exhaust. However, when a higher porosity filter was used, a consistent increase in penetration of smaller particles was seen for all engine operating conditions. The mass-mobility relationships obtained from PM characterization studies was used to estimate the trapped mass within the filter. Subsequently, the filtration data was also evaluated on the basis of PM mass trapped within the filter. This information was used to compare the evolution of filtration performance between filter samples with different substrate properties. The PM penetration data was seen to show consistent overlap between the different operating conditions when compared on a trapped mass basis.

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