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Study of the Deep-Bed Filtration Using Pore Filtration Model (PFM)
Abstract:
To meet stringent emissions regulations, filtration devices are often used in engine exhaust systems to reduce particulate mass (PM) and particulate number (PN). Diesel particulate filters (DPFs) are a well-established means of reducing PM from diesel engines to meet emissions regulations. New emissions regulations will most likely require a similar technology on gasoline engines with direct injection, gasoline particulate filters (GPFs). Due to differences in the exhaust and particulate characteristics, the design and operation of GPFs and DPFs differ. In a DPF filtration is dominated by the buildup of a soot cake. Whereas in a GPF, much of the soot is trapped inside the porous substrate, or filter wall, where deep-bed filtration is dominant. Thus, an accurate model describing the porous filtration properties of GPF substrates is desired.
The pore filtration model (PFM) was developed to more accurately model the deep-bed filtration process that occurs in a GPF. This includes changes in the porous material characteristics which impact the filtration efficiency and pressure drop. The PFM model is based on a constricted tube unit collector rather than the traditional spherical unit collector used in DPF models. This geometry more closely represents the pores in a GPF substrate. In addition, it gives additional geometric parameters for representing different types of substrates. Data from a spark-ignition direct-injection (SIDI) engine was used to validate the model. The PFM can capture with high accuracy both the number-based filtration efficiency and pressure drop under various engine operating conditions and for various filter samples. Of the different geometric parameter used in the PFM, it was found the pore throat diameter had the largest effect on the filtration efficiency.