1991-02-01

On-the-Road Durability and Performance of TWC Exhaust Emission Control Under Real Nordic Driving Conditions 910172

The temperature regime of driving conditions in Nordic countries is very wide. This may have some effect on the performance and durability of the emission control systems used in todays vehicles, because normally these are designed with a less rigorous environment in mind. This paper describes durability and cold-start performance results obtained with two current technology TWC-cars in a full 80,000 km's on-the-road test under realistic driving conditions in Finland. The temperature extremes during the 24-month test period ranged from -28° to + 28°C. All vehicles were operated in day-to-day traffic as normal passenger cars without using any predetermined driving pattern. This practice is in contrast to the standardized durability run.
The evaluation of long-term emissions performance showed a reasonable low deterioration over the test. However, at an early stage of the test one of the cars suffered from a mechanical failure in the converter unit leading to reduced performance. Rather than by cold environment, this failure was caused by a strong outside impact breaking down the ceramic substrate, probably in off-road driving. After 80,000 km's both vehicles needed a new oxygen sensor to bring their emissions within the legal conformity limits. In addition to the standardized tests, emissions were measured in proprietary on-the-road cold-start tests. These showed quite high CO emissions. The main cause of this elevation was the heavy enrichment of the air-fuel mixture necessary in cold-start and warm-up operation. This enrichment disturbed the correct composition of the exhaust gases and made the operation of a TWC converter impossible, because it normally works solely on the oxygen contained in the exahausts. Therefore a furher optimization of TWC systems for low ambient temperatures seems necessary.

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