Stringent IC engine PM emission regulation requires development of future filter substrate materials to achieve high filtration efficiency, low filter pressure drop, low cost and highly durable solutions. Monolithic wall flow filters perform well as they achieve high filtration efficiency due to the formation of the PM cake structure while maintaining low substrate face velocities due to the large filtration area. Within the process industry, Micropore™ slotted metallic membrane filters offer both large surface areas and low filter pressure drops while maintaining the durability of metal substrates. The pore structure and pore arrangement can be readily tailored to suit specific applications. This paper characterizes a 300 μm thickness Micropore™ metallic membrane with slots of 10 μm by 400 μm in size in the context of application as an engine exhaust particulate filter.
The investigation was based on single layer of Micropore™ slotted metallic membrane with size of 52 mm in diameter. The pressure drop performance was evaluated experimentally on a cold flow rig capable of face velocities from below 0.01 m s−1 to above 5 m s−1. The filtration efficiency was measured on a 1.9 liter turbocharged diesel engine at face velocities of 0.22 m s−1 and 1.48 m s−1. At low face velocity, the clean metallic membrane filter trapped more than 30% of the emitted particulates by number count. The filtration efficiency then evolved to above 99% as flow passages were blocked by PM deposits. Higher face velocity tests showed an increase of particulate number downstream the filter relative to upstream. The comparison between upstream and downstream particulate numbers revealed that relatively large particles broke down into smaller particles which increased the total particulate number. This phenomenon was due to the high forces on the agglomerates due to the high local flow velocities.
Filter pressure drop performance of the Micropore™ slotted metallic membrane was also compared with two filter substrate layers extracted from two monolithic uncoated cordierite DPFs. The DPFs are 52% porous and have mean pore size of 15 μm, with cell density of 100 cpsi and 300 cpsi respectively. The pressure drop of the slotted metallic membrane is consistently lower than the cordierite layers at comparable face velocities, being ∼70% lower than the 100 cpsi sample and ∼35% lower than the 300 cpsi sample at face velocities of 0.046 m s−1.
The advantage of the low filter pressure drop of Micropore™ slotted metallic membrane and its competitive filtration performance comparing to more conventional cordierite DPF substrates makes it a potential alternative for future particulate filters.