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Typically, the maximum converter skin temperature occurs when the catalytic converter is in the cool down process after the engine is shut-off. This phenomenon is called temperature soaking. This paper proposes a numerical method to simulate this process. The converter skin temperatures vs. time are predicted for the converter cool down process. The soaking phenomenon is observed and the maximum temperature is determined. Temperatures are also predicted for the exhaust gas, substrate, mounting mat and shell of the converter assembly. The numerical results are validated with measurements, and an acceptable correlation is achieved. This study focuses on converters with ceramic substrates; however, this methodology can also be used for converters with metallic substrates.

Single seam stuffed converters are often used to house ceramic substrates due to the simplicity and low tooling cost of the canning process. However, stuffing thinwall substrates requires careful GBD (gap bulk density) control because of their low isostatic strengths. Statistical simulation results indicate that the stuffing process can be performed within the required GBD range of 0.8 to 1.2 g/cm3 using vermiculite mats with the current tolerance specifications. A nominal value of 0.925 g/cm3 is recommended to minimize substrate breakage. Experimental results show that prototypes can be built with a GBD accuracy of 0.05 g/cm3. This paper describes the requirements needed to design and validate single seam stuffed converters.

Fluid flow, temperature prediction, thermal response and light-off behavior of the catalytic converter were investigated using Computational Fluid Dynamics (CFD), combined with a conjugate heat transfer and a chemical reaction model. There are two objectives in this study: one to predict the maximum operation temperature for appropriate materials selection; and the other, to develop a numerical model which can be adjusted to reflect changes in the catalyst/washcoat formulation to accurately predict effects on the flow, temperature and light-off behavior. Temperature distributions were calculated for exhaust gas, catalyzed substrate, mounting mat and converter skin. Converter shell skin temperature was obtained for different mat materials. By changing reactant mass concentrations and noble metal loading, the converter light-off behavior, thermal response and temperature distributions were changed.

A stochastic simulation based on the Monte-Carlo method was developed to study the effect of substrate, mounting mat and converter shell dimensional tolerances on the converter manufacturing process. Results for a stuffed converter with nominal gap bulk density (GBD) 1.00 g/cm3 show an asymmetric probability density function ranging from 0.90 to 1.13 g/cm3. Destructive and non-destructive GBD measurements on oval and round production converters show close correlation with the Monte-Carlo model. Several manufacturing options offering tighter GBD control based on component sorting and matching are described. Improvements ranging from 28% and 64% in GBD control are possible.