Developing ultra thin wall ceramic substrates is necessary to meet stricter emissions regulations, in part because substrate cell walls need to be thinner in order to improve warm-up and light-off characteristics and lower exhaust system backpressure.
However, the thinner the cell wall becomes, the poorer the mechanical and thermal characteristics of the substrate. Furthermore, the conditions under which the ultra thin wall substrates are used are becoming more severe. Therefore both the mechanical and thermal characteristics are becoming important parameters in the design of advanced converter systems.
Whereas square cells are used world-wide in conjunction with oxidation and/or three-way catalysts, hexagonal cells, with features promoting a homogeneous catalyst coating layer, have found limited use as a NOx absorber due to its enhanced sulfur desorption capability.
This paper is intended to clarify the structural advantages of both square and hexagonal cells, including mechanical and the thermal characteristics, to securely use ceramic substrates in severe conditions while meeting future stricter emissions regulations.