Effect of Thermal Mass and Aging on CO-NOx Crossover and Light Off Behavior

The tightening of emissions regulations has required changes in many areas of vehicle systems, including calibration strategies, catalytic converter strategies and exhaust configurations. Engine calibration strategies can be engineered to complement the performance parameters of the converter. Knowledge of the precise window of converter performance for different substrates can therefore provide guidance in targeting engine calibration strategies as well as selecting compatible converter systems within calibration constraints.

In a previous paper [5], we explored the effect of thermal mass on emissions performance in the context of the FTP. This paper expands on the previous work and explores the effect of the aging cycle and thermal mass differences on CO-NOx crossover and light-off profiles. This analysis provides a tool to assist in design by defining a window of performance in the converter to be used in matching to a window of operation in the calibration.

The substrate configurations studied in the analysis are 400/4, 900/2 and 900/1. These represent a direct comparison of constant cell density on the one hand and constant bulk density on the other. The air/fuel sweeps and light-off ramps were performed at steps throughout the aging cycle, yielding information not only on the comparison between the products but also on how their relative performances change over the life of the converter. Emissions and temperature were examined to evaluate the performance.