Search Results

PM (Particulate Matter) emitted by vehicles and engines is most often measured quantitatively by collecting diluted exhaust samples on filters that are weighed pre-and post-test. The filter media used have high efficiency for small particles found in vehicle exhaust, but they also collect organic matter from the vapor phase with a lower, but nonzero, efficiency. In the past, organic vapor adsorption was usually negligible compared with PM levels from untreated diesel engine exhaust. For vehicles employing a DPF (Diesel Particulate Filter) and emitting very low PM, that is no longer the case. This paper reports measurements of the organic vapor deposition artifact for different filter media, including the two types (TX40 and Teflo) called for by the 2007 regulations for heavy duty diesel engines. The vapor artifact represents a substantial fraction of the 2007 regulatory standard of 10 mg/mi for light duty vehicles.

The trapping and regeneration behaviors of a diesel particulate filter (DPF), including particle size, are examined via engine dynamometer testing. The exhaust system consists of two active lean NOx (ALN) catalysts in series followed by a catalyzed DPF. Forced regenerations are accomplished by injecting diesel fuel into the exhaust in front of the ALN catalysts to generate an exotherm sufficient to induce soot oxidation. Results are reported for two diesel fuels, one with 340 ppm sulfur, and the other with 4 ppm sulfur, and as a function of DPF regeneration temperature. The results show the DPF to be very effective at removing particulate matter, >99% efficiency. The <1% of particles that escape trapping exhibit a size distribution very similar to engine out soot. During regeneration, particle emissions remain well below engine out levels for the low sulfur fuel, but exhibit a temporary nucleation mode of about ten times the engine out level for the high sulfur fuel.

A direct comparison is made of time-resolved measurements of diesel PM emissions obtained using laser-induced incandescence (LII), an electrical low pressure impactor (ELPI), and a tapered element oscillating microbalance (TEOM). The measurements were made on two diesel passenger vehicles, one of which was equipped with a diesel particulate filter. Both LII and the ELPI performed well for both vehicles, whereas the TEOM lacked the sensitivity required for the filtered vehicle. We estimate that the LII system used has a limit of detection better than 0.2 mg/mi.