Gasoline Particulate Filter wall permeability testing

With the introduction of particulate matter emissions regulations for gasoline engines, most car manufacturers are considering using gasoline particulate filters (GPFs). Although very similar to diesel particulate filters (DPFs), GPFs operate at higher temperatures and generally have thinner monolith walls. In order to estimate the pressure loss through the filter, filter wall permeability is needed. This presents a number of challenges since wall losses cannot be efficiently isolated from other losses in a full-scale filter or filter core. Thin wall wafers have been used for DPF characterization. However, GPF wafers are generally thinner, which makes the testing less straightforward. This article presents a novel effective methodology for estimation of GPF wall permeability using thin wafers cut from the filter monolith. Both cold and hot flow permeabilities can be estimated, which allows to account for the change of apparent permeability due to the slip effect. The flow through the wafer is also modeled numerically to assess the effect of the uneven wafer surface resulting from wafer preparation method. A technique for calculating corrected permeability is suggested which is estimated to provide values within 5% of the “nominal” value. Combining experimental results with the applied correction, consistent permeability values have been obtained for seven wafer samples. Maximum variation in the permeability values was 10%, with a standard error of ±2.5% of the mean. Being able to assess filter wall permeability from a simple cold flow pressure testing procedure will allow development of more efficient flow and pressure loss models for GPFs, which in turn will facilitate design of efficient aftertreatment systems with lower back pressure.