Comparison of PM Measurement Methods for Catalyst-out Diesel Exhaust

摘要

Recent concerns and new EPA rulemaking about the health effects of ambient particulate matter (PM) smaller than 2.5 #mu#m (PM_(2.5)) have focused attention on the importance of combustion aerosols, particularly those from diesel engines. The mass of PM from on-road diesels has declined dramatically since the late 1980's due to higher injection pressures and oxidation catalysts. However, the number concentrations have continued to increase due to the much smaller size of the PM generated. This presentation and the companion presentation discuss results of particle-size measurements on a vehicle and the vehicle's engine with and without an oxidation catalyst. A micro-orifice uniform deposit impactor (MOUDI) is used to sample diluted siesel exhaust. Ten size fractions between 0.054 #mu#m and 10 #mu#m are collected. Results show a weak bimodal distribution with the majority of the particles centered at 100-150 nm with another weak mode at 1-2 #mu#m. While it has been known for some time that diesel particles are all less than 2.5 #mu#m, the distribution from modern engines is less well understood. Higher injection pressures in direct injection engines have resulted in much less mass emission of particulate; however, the number concentrations of ultrafine particles are greater than with earlier engine designs. Particle size is critical to the understanding of the performance of catalysts for modern dieselscatalysts that further increase the number concentrations of ultrafine aerosols may not be desirable.