Portable In-Use Reference PM Measurement - Heavy-Duty Vehicle

This page last reviewed February 6, 2012


Background

The European countries have developed new methodologies for the measurement of 'solid' article number above a size cut threshold of 23 nanometers (nm) as an alternative to gravimetric measurements at low particle levels typically found with engines and vehicles equipped with diesel particle filters (DPFs). This methodology provides significant improvements in measurement sensitivity, but should be fully understood in terms of the representativeness of the particles, which are only solid and >23 nm in size, their adverse health effects, and the repeatability of the measurement. The specific objective of this study was to critically evaluate the proposed PMP method for determining 'solid' particle number emissions from heavy-duty vehicles in the laboratory and during over-the-road driving. For this program, testing was conducted on the chassis dynamometer at the CARB heavy-duty vehicle emissions laboratory in Los Angeles and over the road with the CE-CERT mobile emissions laboratory (MEL). One or two PMP compliant dilutions systems for measuring solid particle number were tested and compared directly with filter-based PM measurements on two heavy-duty trucks equipped with a DPF. A full suite of other particle measurements and instruments were also used in conjunction with this testing including a TSI EEPS, a Combustion DMS, and TSI CPCs with lower size cuts ranging from 3 to 23 nm, a Dekati DMM, and a DustTrak. The test cycles included a 50 mph cruise, UDDS, idle, and some European driving schedules. This program was conducted in collaboration with other particle emission experts from Europe and the United States (US), including European counterparts who have direct, hands on experience with the PMP protocol.

The overall combined laboratory and on-road results seem to indicate the potential for particle number to provide a more accurate/repeatable measurements at the emission levels of current DPFs. The variability between the different PMP particle number counts and the PM mass depended on the cycle, sampling location and time, the specific test instrument, and other experimental conditions. Outlier tests were observed for a number of the PMP test scenarios that appear to be real events that may be masked in the mass measurement. Thus, statistical techniques for the removal of outlier tests for particle number need to be used to take advantage of any improvement in repeatability of the particle number measurements. The particle number measurements provided the greatest advantages at typical emission levels for a properly operating DPF, which are often only a small percentage of the certification value. At these levels, the mass measurements typically show greater scatter, are usually below the quantification limit, and can be impacted heavily by artifact formation. At higher mass levels, such as levels closer to the actual limit of the 2007 standard forheavy-duty engines, the quantification accuracy and repeatability of the gravimetric PM measurements improve. Nucleation particles were found to form under a variety of testing conditions when the temperature of the aftertreatment device exceeded a 'critical' temperature, which was typically in excess of 300įC. The level of nucleation increased significantly under the most aggressive, on-road testing conditions. Sulfate was an important portion of the chemical make-up of the nucleation particles, suggesting that SO2 to SO3 conversion over the catalyst played an important role in their formation. In order to better characterize the PMP system, further study is suggested to understand the chemical composition and nature of the particles measured below the PMP, the potential impacts of utilizing a smaller size cut for counting particles below the PMP, and the impacts of the different design elements of the PMP. Testing should also be expanded to include a wider range of vehicles and aftertreatment systems.


References

Publications for Peer-reviewed Journals

  • Kent C. Johnson et al., (2009). Evaluation of the European PMP Methodologies during On-Road and Chassis Dynamometer Testing for DPF Equipped Heavy-Duty Diesel Vehicles. Aerosol Science and Technology. Link

Conference Presentations

  • 29th American Association of Aerosol Research (AAAR) Annual Conference, October 25-29, 2010, Portland, Oregon
  • Barouch Giechaskiel et al., Evaluation of the European Method and the Catalytic Stripper for Particle Number Measurements. Poster (PDF - 192KB)
  • Heejung Jung et al., Measurement of Diesel Solid Nanoparticle Emissions. Poster (PDF - 1,093KB)
  • Western States Section - Combustion Institute Spring Technical Meeting, March 17-18, 2008, Los Angeles, CA
  • Heejung Jung et al., Evaluation of the European PMP Methodologies during On-Road Testing. Presentation (PDF - 1,056KB)

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