Automobile catalysts have been mandatory on new cars in the European Union since 1993 and approximately 70% of the 200 million car fleet in the EU today are nowadays equipped with them[1]. Because of increasingly stringent emission regulations and a growing number of vehicles in the EU, aftertreatment technologies for automobile emissions represent a rapidly growing market and Diesel engines are steadily expanding their market share. Current exhaust aftertreatment concepts for Diesel engines use extruded ceramic substrates with a honeycomb structure for the diesel oxidation catalyst (DOC) as well as the diesel particulate filter (DPF). The turbulent exhaust flow upstream the substrate is converted to laminar flow after entering the single channels of the DOC. The inlet velocity profile in the cross-section of the oxidation catalyst is strongly dependent on the upstream piping geometry and pressure distribution and is similar downstream in the exit cross section, due to the absence of any momentum and mass transfer among the monolith channels perpendicular to the main flow direction.
In the concept evaluated in this paper, catalytic converters will not be implemented as laminar-flow honeycomb-type substrates, as in current systems, but as turbulent-flow ceramic foam substrates. Turbulent-flow foam structures homogenize the flow over its cross-section improving exhaust gas mixing, flow distribution and conversion efficiency by increasing the wall contact of the exhaust gas. Moreover, the ceramic foam based substrate has been functionalized with a specific catalytic coating based on DOC and LNT (lean NOx trap) technologies in order to implement in a single brick both the functionalities and comply with the forthcoming Euro 6 emission limits. The design and development process of the catalyzed foam based substrates is strongly influenced by the macroscopic properties of microscopically heterogeneous materials; therefore, the novel catalytic system has been experimentally evaluated from lab-scale up to vehicle level and, in parallel to the experimental work, a specific software tool has been developed in order to simulate all relevant physical phenomena occurring in porous structures thus satisfying both demands: i) detailed analysis of the exhaust gas flow and diesel particulate motion/deposition phenomena occurring inside the porous structure, ii) design and development of global devices/processes.