EU-PEMS PM evaluation program : second report : study on post DPF/PM/PN emissions

This study evaluated the performance of five in total candidate PEMS-PM systems at diesel exhaust PM levels spanning from 20 mg/kWh (Euro V) to post CRT. The different emission levels were simulated by means of a CRT/bypass configuration. The PEMS-PM systems evaluated included Horiba's On Board System with Transient PM measurement (OBS-TRPM), AVL's Micro Soot Sensor (MSS) and Gravimetric Filter Box (GFB), Control Sistem's micro Particulate Sampling System (m-PSS), Sensors Portable Particulate Measurement Device (PPMD) and Dekati's Mass Monitor (DMM). The correlation between the PM results determined with the PEMS instrumentation and that measured with the laboratory sampling systems was found to depend on the filter media employed. This was attributed to adsorption artefacts that become more important as the PM levels decrease. Teflo filters were found to be less susceptible to gas adsorption artefacts, but were difficult to handle yielding some times even negative masses. Even with Teflo filters, however, more than 99% of the PM at CRT out levels was OC which could not be detected by the real time aerosol instrumentation and therefore is expected to be adsorbed material. Furthermore, background PM levels at all candidate systems utilizing laboratory conditioned dilution air averaged at a level equivalent to 3 mg/kWh which is almost 1/3 of the Euro VI level. The background was even higher (equivalent to ~5 mg/kWh) for the PEMS system that employed ambient air (internally conditioned) for the dilution. The study also evaluated the performance of the real time sensors employed in the different candidate systems using both engine exhaust aerosol and Poly(Alpha)-Olephin spherical particles. The results of these experiments revealed a number of issues related to the calibration of the instruments and cross sensitivities to non PM sources. These findings need to be addressed by the manufacturers as they are expected to significantly affect the accuracy of the measurements in PEMS applications.