Tanner, C., Twiggs, K., Tao, T., Bronfenbrenner, D. et al., "High Porosity Substrates for Fast-Light-Off Applications," SAE Technical Paper 2015-01-1009, 2015, doi:10.4271/2015-01-1009.
Regulations that limit emissions of pollutants from gasoline-powered cars and trucks continue to tighten. More than 75% of emissions through an FTP-75 regulatory test are released in the first few seconds after cold-start. A factor that controls the time to catalytic light-off is the heat capacity of the catalytic converter substrate. Historically, substrates with thinner walls and lower heat capacity have been developed to improve cold-start performance. Another approach is to increase porosity of the substrate. A new material and process technology has been developed to significantly raise the porosity of thin wall substrates (2-3 mil) from 27-35% to 55% while maintaining strength. The heat capacity of the material is 30-38% lower than existing substrates. The reduction in substrate heat capacity enables faster thermal response and lower tailpipe emissions. The reliance on costly precious metals in the washcoat is demonstrated to be lessened. The microstructure of the new substrate material is optimized for washcoat compatibility and to maintain strength. The new materials are confirmed to be thermomechanically robust for service in the harsh exhaust system environment.