Retrofitting of Diesel Particulate Filters - Particulate Matter and Nitrogen Dioxide

A diesel particulate filter (DPF) is a crucial weapon in the fight to control the downsides traditionally associated with diesel engined vehicles. The DPF not only produces the benefits required from an environmental standpoint but also has the consumer benefit of eliminating the visible black smoke associated with diesel engines. Thus DPFs have now become a reality, both for series production vehicles and as a retrofit application.

Inevitably there are a number of alternative types of DPF and alternative techniques are used for ensuring they continue to function in an acceptable manner. Due to the complexity of the diesel combustion process and the emissions produced it is only to be expected that a device intended primarily to control one parameter would have some effect on other parameters.

This paper looks at some different DPF technologies and how they effect emissions, with the emphasis on particulate emissions and the speciation of oxides of nitrogen. The conclusions drawn are that whilst a DPF will significantly reduce PM mass and ultra-fine particulate numbers the use of a Pt catalyst can have a negative effect on NO₂ emissions. The use of an iron based fuel borne catalyst, to regenerate the DPF, significantly reduces NO₂ emissions.