Filter wall-scale experiments to evaluate the impact of particle morphology on capture efficiency in a ceramic particulate filter
Sandeep Viswanathan, University of Wisconsin-Madison
Spark-ignition direct-injection (SIDI) engines are prone to higher engine-out particle number emissions due the formation of rich pockets in-cylinder, driving the need for gasoline particulate filters (GPFs). A combination of factors can result in extended operation of GPFs in the deep-bed filtration regime, where capture efficiency can be sensitive to filter micro-structure and particle morphology. The exhaust filtration analysis (EFA) system, developed at the University of Wisconsin-Madison, was used to perform filtration experiments focusing on just the walls of ceramic particulate filters using PM from an SIDI engine operated at different steady-state points. An advanced characterization system that comprised of a scanning mobility particle spectrometer (SMPS), centrifugal particle mass analyzer (CPMA), differential mobility analyzer (DMA), and a single particle mass spectrometer (SPLAT II) was used to obtain a wide range of information on the SIDI PM emissions. The filter loading process was paused multiple times to evaluate the filtration performance in the partially loaded state using the combined CPMA/DMA/SPLAT system. The change in vacuum aerodynamic diameter (dva) distribution of mass-selected particles was examined during the filtration process to identify whether particles of certain shapes were captured preferentially. The impact of inlet particle size distribution on mobility size-resolved capture efficiency was also studied. Results indicated that under the current experimental conditions diffusion was potentially the dominant capture mechanism and the range of particle shapes did not impact the mobility size-resolved capture efficiency within the filter walls. The methodology explored in the current study serves as proof-of-concept for future experiments focusing on catalyzed samples at higher filtration temperatures.