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Extracts of exhaust emissions from passenger cars equipped with conventional and lean-burn gasoline engines were tested for PAHs, NPAHs and mutagenicity. When installed with an appropriate three-way or oxidation catalyst very large reductions in each of these measurements were observed, alongside reductions in regulated emissions and gaseous aldeyhdes. These beneficial effects were apparent over U.S. and European cycles.

The effective use of a catalyst to initiate regeneration of a diesel particulate trap has traditionally been based on the concept that the catalyst coated onto the trap adsorbs particulate, and activates oxygen in the exhaust causing initiation of particulate combustion. Reported regeneration temperatures generally lie in the range of 350°C and above. This paper reports on a new mechanism of diesel particulate combustion involving activation of oxygen over a catalyst to form NO2, which is then capable of adsorbing on diesel particulate trapped in a filter and initiating combustion at lower temperatures. Diesel particulate has been combusted on a wire mesh trap at temperatures as low as 265°C, and this regeneration capability has been maintained over hundreds of hours of operation. However, the most active catalysts for low temperature activation of diesel particulate are also high sulfate producers.

Proposals to further lower particulate matter standards for heavy duty diesel powered vehicles throughout the world, have prompted further interest in particulate filter based aftertreatment solutions. Continuously regenerating traps have been utilised in Europe as a retrofit technology for more than 6 years and this study summarises that experience. Predominantly the growth in the market for the continuously regenerating trap has been in those countries which have promoted the use of ultra-low sulfur diesel fuel (i.e. less than 50 ppm S) - Sweden, Germany, and the UK, and to a lesser extent in another seven countries. A selection of continuously regenerating traps was taken from the field after high road mileage accumulation, up to 600,000 km, and subsequently tested for performance on diesel engine bench dynamometers; the results of these studies are reported and discussed.