A major cause of atmospheric pollution is from mobile sources emitting noxious gases from internal combustion engines. Chief among the pollutants are nitrogen oxides (NOX) and hydrocarbons (HC), carbon monoxide (CO) and volatile organic compounds (VOC). A catalytic converter functions to reduce the levels of NOX and CO, HC and other pollutants in the engine exhaust gases. Catalytic converters render toxic NOX and CO, HC into harmless compounds such as CO2, N2 and water. Catalytic converters are used as emission control devices to reduce toxic exhaust gases emitted from internal combustion engines, such as in automobiles, trucks, diesel-electric “genset” locomotives, agricultural and construction machinery, and marine vessels. Non-linear (non-straight) geometric channels differ from conventional linear (straight) channels because exhaust gases or liquids transport differently to the surface of a solid catalyst coated onto channel walls. Non-linear geometric catalytic converters may have significant beyond just automotive applications in industrial and scientific fields as well, including chemical and petrochemical refinery processes and in producing pharmaceuticals, agrochemicals, fine chemicals, food flavorings, aromatic perfumes and fragrances, and dietary supplements, among other uses.
Most automotive catalytic converters include a honeycomb substrate core that is coated with a known catalyst formulation applied to the substrate core, sometimes containing a metal oxide washcoat. Most ceramic substrate cores contain linear channels with square cross sections. E.g. see U.S. Pat. Nos. 3,790,654 and 5,866,079 Metallic honeycomb substrate cores may have different channel cross sectional shapes because of the malleability of metal. Metal substrate cores may be formed as linear parallel, U-shaped channels with the catalyst embedded in the washcoat on the walls of the channels. The substrate core is wrapped in a retaining mat and is packaged in a protective outer metal shell. E.g., U.S. Pat. No. 8,071,505 issued to Ebener et al. discloses a metallic catalytic converter support body with a longitudinal axis containing a honeycomb body and housing. The honeycomb body has at least three metal layers arranged one above the other, which are wound with their end surfaces in each case starting from a common center into layers lying one above the other in a spiral form in a sleeve of the housing. The metal layers are developed as a corrugated sheath that creates straight and parallel channels through which exhaust flows.
The conventional design of a catalytic converter relies on a substrate core that is composed of hundreds or thousands of thin, narrow, long, and identical-sized duct-like channels or cells in a honeycomb-like structure. Each flow channel is typically several inches long, with channel openings, each roughly 1/20th of an inch (about one millimeter) in diameter. Channel length and channel opening may vary depending on the catalytic substrate selected for a particular application. Exhaust flow through conventional linear channels is predominantly laminar. During exhaust flow, toxic compounds such as CO, NOX, and HC diffuse across the flow and react with the catalyst coated on the channel walls and are detoxified to CO2, N2, and H2O. Diffusion is the dominant mode of species transport across flow streamlines for catalytic reactions in conventional catalytic honeycomb substrate cores. Thus catalytic reactions are rate-limited by overall diffusion coefficients. Furthermore, the reactant concentration gradient in the exhaust flow is generally higher in the bulk flow, especially near the channel centerline, and is lower near the channel walls (i.e., near the catalytic coating). thus imposing a certain limit on catalytic efficiency in linear channels. One may increase catalytic efficiencies inter alia by offsetting the rate-limiting step of diffusion by increasing the length of the honeycomb channels or by increasing the number of flow channels per honeycomb or by increasing the density of catalytic substrate material embedded in the washcoat. However, the downside to these measures would be to increase the weight of honeycomb and increase packaging size, and escalate the overall cost of manufacture. The instant disclosure offers an alternate cost saving approach to increase catalytic efficiencies. The current disclosure aims to increase catalytic efficiencies of converters by utilizing non-linear substrate core channels that can generate flow vortical forces that increase diffusion and convection across flow channels. The current disclosure includes non-linear channel geometries that increase catalytic efficiencies compared to conventional linear substrate channels.