Exhaust Catalyst Thermal Management
The rate at which the catalyst heats up is an important factor in the control of the start-up emissions of an engine. A number of measures have been used to improve this:
- Moving the catalyst closer to the exhaust valve outlets - close coupled.
- Insulation of the exhaust manifold.
- Insulation of the downpipe.
- Insulation of the catalyst.
- Burch et al looked at vacuum insulation of a catalyst.
- Burch et al looked at a phase change material as a heat store for a catalyst and managed to maintain the temperature of the catalyst for 17 hours compared to 25 minutes for an untreated catalyst.
An exhaust catalyst runs at a high temperature internally and has a high surface temperature that also needs to be accounted for when packaging.
Bauer et al showed that All measures intended to reduce heat output, should be applied to all elements of the exhaust system (manifold, cones, catalytic converter), as otherwise the component’s thermal load is unchanged.
- The influence of the catalytic converter′s surface emissivity on the temperature of the component is greater than the influence of the temperature of the cat surface. Thus, when assessing a component′s thermal load, the surface temperature of the catalytic converter is not the only appropriate measure.
- Despite a rising surface temperature, by reducing the radiation emissivity of the converter mantle, the heat output of the catalytic converter falls.
- Reducing heat loss by using a mantle material with a lower emissivity supplements the insulation on the exhaust system.
- Austenitic mantle material clearly displays a lower emissivity than a ferrite mantle.
- In the positioning of converter and component here, the distance from each other is of practically no importance, as long as a minimum distance is maintained.
- Simple and effective control of the component temperature can be achieved by reducing the emissivity of the component.
Steve D. Burch, Thomas F. Potter, Matthew A. Keyser, "Reducing Cold-Start Emissions by Catalytic Converter Thermal Management", SAE 950409
Hans Bauer, H., G. Haldenwanger, Peter Hirth, Rolf Brück, "Thermal Management of Close Coupled Catalysts" SAE 991231
See also: Exhaust Catalyst.