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Catalysts taken from the lightoff and underfloor converters of two 1986 Corvette exhaust systems which had been vehicle-aged for 100,000+ miles were cut into 1″ thick sections along their axis and characterized for lean lightoff and warmed-up performance using a laboratory reactor. Sections were then treated to remove the poisons, and the characterization was repeated. An axial gradient in both lightoff and warmed-up conversion efficiency for HC and CO was detected within the first 2″ of both lightoff converters for both vehicles. This activity gradient is in agreement with the gradient in the phosphorus and zinc concentrations found in the front 2-3″ sections of the lightoff converters.

Infrared diode laser spectroscopy was used to make the first measurements of carbon monoxide (CO) concentrations in automotive exhaust with a time response fast enough to be useful in the analysis of engine and emission control system dynamics. Currently used measurement techniques are too slow to follow rapidly changing CO levels. Infrared diode laser spectroscopy can selectively measure CO in the presence of large amounts of water vapor, permitting the direct analysis of the full exhaust flow. Carbon monoxide concentrations were measured before and after a three-way catalytic converter. The response time of the laser system (for a change in amplitude of 10%–90% of fullscale) was 25 ms, more than adequate to resolve all CO transients of interest. The instrument was capable of resolving concentration changes on the order of 0.1 vol % before the catalyst and 0.02 vol % after it.