In view of increasing concern over diesel particulates and tightening legislation to control their emission, much work has been done to develop diesel particulate filters (DPFs) and systems to allow them to work reliably. Although a filter will effectively trap solid particles, any material in the vapour phase, such as unburned hydrocarbons, may pass through the filter and subsequently condense. The use of a catalytic wash coat, either on the DPF itself or on a separate substrate, has been proposed to oxidise these hydrocarbons and thus reduce the total material emitted.
The use of fuel borne catalysts to aid the regeneration of trapped material within the DPF is also well documented. Such catalyst will also catalyse the oxidation of any hydrocarbons bound up within the particulate. The oxidation of such hydrocarbon occurs at a lower temperature than that of carbon itself, thus allowing lower temperature regeneration of the DPF. The question thus arises; can low temperature regenerations and high filtration efficiencies for particulate mass be achieved by combining the use of a fuel borne catalyst and a catalytic wash coat with the diesel particulate filter.
This paper describes work conducted on a test bench, using fuel treated with a fuel borne catalyst, to assess the emissions and regeneration performance of a DPF preceded or followed by an oxidation catalyst and the regeneration performance of a catalytically coated DPF. The results of fitting a car with a catalytically coated DPF and running on treated fuel are also reported.