10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
A Versatile Portable Exhaust Particle Sampling System to Extend Particle Number Measurements below 23 Nanometers
MARKUS BAINSCHAB, Alexander Bergmann, Panu Karjalainen, Jorma Keskinen, Jonathan Andersson, Athanasios Mamakos, Tero Lähde, Christoph Haisch, Oriana Piacenza, Ananias Tomboulides, Zisimos Toumasatos, Leonidas Ntziachristos, Zissis Samaras, Graz University of Technology
Abstract Number: 794 Working Group: Instrumentation
Abstract Modern and near-future combustion engine vehicle technology may emit notable levels of particles below the current particle size threshold (23 nm) of the European Particle Number (PN) emission standards. The Horizon 2020 funded project DownToTen (DTT) is developing a sampling and measurement methodology to characterize exhaust aerosol emissions down to at least ten nanometers. This study presents the first prototype of a portable exhaust particle sampling system (PEPS) developed in the framework of the project.
Laboratory experiments, in which various dilution systems were challenged with aerosols from a variety of sources, showed that a double porous tube dilution (PTD) system is the method offering the lowest detectable size. The radially inflowing dilution air in a PTD reduces thermophoretic and diffusional losses of <23 nm particle sizes and the compact all-metal design facilitates the realization of a heated dilution stage. The first porous tube is supplied with hot (350°C) dilution air. The second PTD operates at room temperature. Dilution may be combined with different conditioning chambers, depending on purpose: an aging chamber to thermodynamically stabilize aerosol, an evaporation tube or a catalytic stripper to isolate non-volatile particles, or a photo-oxidation chamber to address secondary aerosol formation. Sample flowrates and dilution ratios settings are controlled by mass flow controllers.
The system is characterized with laboratory and real exhaust aerosols in terms of particle losses and dilution ratio stability. Computational fluid dynamics (CFD) simulations provide detailed insights on the air flow through the porous medium, and the mixing of the dilution air and the sample flow. Further, the propagation of pressure pulses and their impacts on the dilution ratio is examined. Two different laboratory experiments were conducted to validate the pressure pulsation results of the CFD simulations. The first uses an aerosol source with a controllable pressure level, and uses pressure sensors with high temporal resolutions at various spots in the dilution system to show how pressure pulsations affect the dilution ratio and the performance of downstream particle number measurement devices. The second experiment uses an ultrasonic transit time flow meter to inspect the sample flow downstream of the porous tube diluter to check for high frequency flow fluctuations predicted by the simulations. Finally, the sampling system is employed for engine exhaust measurements on a chassis dynamometer.
The comparison of the developed dilution system with the commercial measurement systems fulfilling current EU PN Regulation demonstrates the feasibility of the DownToTen PEPS for sub 23 nanometer engine exhaust particle number measurements. The versatile tests with laboratory particle sources and the measurements of vehicle exhaust particles suggest that DTT PEPS extends the exhaust particle measurement range down to 10 nm and below reliably.