Advances in Durability and Performance of Ceramic Preconverter Systems 950407

Ceramic preconverters have become a viable strategy to meet the California LEV and ULEV standards. To minimize cold start emissions the preconverter must light-off quickly and be catalytically efficient. In addition, it must also survive the more severe thermomechanical requirements posed by its close proximity to the engine. The viability of the ceramic preconverter system to meet both emissions and durability requirements has also been reported recently^(1,2). This paper further investigates the impact preconverter design parameters such as cell density, composition, volume, and catalyst technology have on emissions and pressure drop. In addition, different preconverter/main converter configurations in conjunction with electrically heated catalyst systems are evaluated. The results demonstrate that ceramic preconverters substantially reduce cold start emissions. Their effectiveness depends on preconverter design and volume, catalyst technology, and the system configuration.

The preconverter durability is evaluated by both on-vehicle testing and hot vibration testing. Eight preconverters, following aging for 160,000 km on 3.0 and 4.0 liter vehicles, showed no significant degradation in their mechanical integrity with only minimal degradation of the catalytic activity. In addition, advanced packaging designs have extended the life of the ceramic preconverter system to nearly 100 hours in limited hot vibration testing at 75 g's, 185 Hz with an inlet gas temperature of 900°C.