Optimising the Low Temperature Performance and Regeneration Efficiency of the Continuously Regenerating Diesel Particulate Filter (CR-DPF) System 2002-01-0428

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 DPF collects the PM, and the NO₂generated over the catalyst combusts this PM (carbon) at temperatures much lower than is the case for combustion with oxygen (250°C for the NO₂-carbon reaction, and 550°C for the O₂-carbon reaction). The oxidation catalyst is also very efficient at converting the engine-out CO (into CO₂) and HC (into CO₂ and H ₂ O).

The current CR-DPF system uses a DPF without a catalytic coating. Within this work we have compared the respective performance of the CR-DPF, a Catalysed Soot Filter (CSF, comprising a Pt-based catalyst coated onto a DPF), and an Oxicat + CSF system. The work presented shows that the low temperature performance of the CR-DPF system is significantly better than that of the CSF, and that the best low temperature regeneration is obtained by using the Oxicat + CSF system. In addition, it is shown that the efficiency of the reaction between NOx and carbon in the filter can be significantly increased by applying a catalytic coating to the filter.

These results demonstrate that it is possible to widen the operating window of the CR-DPF system, and clearly reveal that the preferred PM control system is the Oxicat + CSF system, in which the CSF has an optimised catalytic coating.