To meet ever tightening exhaust emission limits, improved engines and exhaust gas after treatment systems must be developed. The principal trend is to install the catalytic converter as close as practically possible to the engine to hasten light-off performance of the catalyst. A second trend is to reduce the thermal mass of the converter by reducing wall thickness of the substrate, and thirdly, increasing the cell density to improve mass and heat transfer from the bulk gas to the catalyst surface.
At the same time, demands for improved mechanical durability of the converter are required. These improvements most not only withstand higher temperatures but also higher accelerations caused by engine vibration and exhaust gas pulsation.
A new type of metallic substrate is introduced to meet more stringent requirements. The essential feature of the substrate is that flow channel is not straight and is specifically designed to keep the gas flow partly turbulent and mixed instead of the traditional laminar flow pattern. This factor improves heat and mass transfer.
Essentially, using thinner shell material reduces thermal mass and this has become possible with a new shell structure. These improvements mean that the converter can be warmed up to normal operating temperatures very quickly. The new substrate has excellent mechanical durability and superior performance durability compared to that of conventional metallic and ceramic substrates.
Theoretical calculations related to mechanical durability, mass and heat transfer together with practical emission and mechanical durability tests are presented.