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As legislation tightens in the Heavy Duty Diesel (HDD) area it is essential to develop systems with high activity and excellent durability for both Particulate Matter (PM) and NOx control. The Continuously Regenerating Trap (CRT™) system controls hydrocarbon (HC), CO and PM emissions from HDD vehicles with efficiencies of over 90%, and has demonstrated very good field durability over distances exceeding 700,000 km. The system is widely used in Europe, and is demonstrating the same high performance and excellent durability within field applications in North America. The Continuously Regenerating Trap (CRT™) system has been developed and patented by Johnson Matthey [1]. Throughout this paper this system will be referred to as the Continuously Regenerating Diesel Particulate Filter, CR-DPF. The CR-DPF comprises an oxidation catalyst, optimised for NO2 generation from the engine-out NOx, and a downstream DPF.

The tightening NOx and particulate matter (PM) emission standards for heavy duty diesel powered vehicles are stimulating the development of aftertreatment systems to reduce NOx and PM emissions from such vehicles. Here we present data on a new system which combines NO2-based continuously regenerative trap particulate removal technology with urea-based Selective Catalytic Reduction (SCR) NOx removal technology. There are a number of beneficial synergistic effects associated with combining these two technologies, including a significant improvement in the low temperature NOx removal performance of the SCR system. The development of this PM/NOx control system is described, and the main features of this novel strategy are outlined. The PM/NOx control system has been evaluated on a number of different engines and over a number of different drive cycles.

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.