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Following concern about the association between adverse health effects and ambient particulate concentrations, there are now an increasing number of heavy-duty Diesel engines fitted with catalysed particulate filters. These filters virtually eliminate carbon particle emissions but there is some evidence suggesting a potential to form a cloud of secondary nucleation particles post trap. This event occurs at high temperature operating conditions and is produced mainly from the increased sulphate production over the catalyst. This paper investigates the measurement of particle emissions from a heavy-duty engine operating over the European legislated cycle, both with and without a filter fitted and investigates how emissions are affected by the use of a sulphur-free Diesel fuel. The work also demonstrates a contribution to the measured nucleation particles from material desorbed not only from the trap, but also from the exhaust system.

Many researchers have reported the measurement of high numbers of emitted particles from gasoline vehicles operating at high speed. To date, in the absence of standard test protocols or analytical techniques, these measurements have all been made from a dilution tunnel set up according to regulatory procedures. Currently, there is great uncertainty relating to the use of the dilution tunnel as a suitable tool for the measurement of automotive particle size and number distribution and also the relevance of the procedure to ambient measurement of the same parameters. Gasoline particle number emissions, as measured on a dilution tunnel, are low at speeds under 120km/h. Beyond this speed, high numbers of very small particles have been measured. There is some evidence to show that these particles may be formed as an artefact within the sampling system, either from the desorption of deposited material or from the pyrolysis of other material in the sampling system itself.