1995-10-01

An Evaluation of the Long Term Effects of Gasoline Sulphur Level on Three-Way Catalyst Activity 952421

A test programme has been conducted to study any potential long term effects of gasoline sulphur on catalyst performance, using a newly developed transient engine-bed ageing cycle. The ageing cycle, which was based on repeated European Extra Urban Drive Cycles, was chosen to ensure that the catalyst experienced a realistically wide range of temperatures and space velocities, together with transients, idle and periods of overrun.
Two nominally identical platinum/rhodium catalysts (manufactured from the same batch) with matched lambda sensors, were aged for a period of 80,000 km each, one being aged using a gasoline containing 50 mg/kg (ppm wt) sulphur, the other being aged on the same fuel doped to 450 ppm wt S. The emissions performance of both catalysts was measured after 6,000, 40,000 and 80,000 km ageing, by fitting the catalysts to a test vehicle, and performing emissions tests over the European test cycle at both sulphur levels. In addition, post-catalyst emissions were measured on the engine-bed at regular intervals during the ageing cycles.
Results from the programme indicated that the performance of both catalysts deteriorated to similar degrees during the ageing process. Fuel sulphur level, therefore, did not have a significant impact on long term performance of the catalyst. There were, however, differences in the ageing of the lambda sensors which, in the case of ageing on higher sulphur fuel, led to lower NOx emissions but higher CO. The previously reported instantaneous effects of sulphur on conversion efficiency were also observed, with reductions in fuel sulphur content leading to lower THC, CO and NOx.

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