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Robinson, Mitchell K.

Civil and Environmental Engineering

2011

MS

Recent studies indicate exposure to high particle number concentrations contribute to numerous acute and chronic illnesses, especially particles in the ultrafine (<100 nm) and nanoparticle (<50 nm) range. Vehicles are major contributors to ambient particle number concentrations, and due to the health concerns associated with ambient particles, recent vehicle studies have focused on quantifying particle number, not mass despite the fact that the EPA regulates on a mass basis. Although many studies have been conducted, there is no conclusive evidence relating operational or environmental factors to high emissions. Further, very few studies have been performed on light-duty gasoline hybrid-electric vehicles. This thesis work focused on quantifying second-by-second particle number distributions and emission rates from a hybrid and comparable conventional vehicle while highlighting the differences in particle number emissions between the vehicle types.
The On-board Tailpipe Emissions Measurement System (TOTEMS) was assembled and utilized to quantify real-world, on-board emissions directly from the tailpipe on a 2010 model year Toyota Camry hybrid (5 runs) and the comparable Toyota Camry conventional vehicle (6 runs). This provided uniquely rare real-world, high resolution (I-Hz) emissions data. TOTEMS also recorded vehicle operating parameters via the OBD-II scantool port, the spatial location of the vehicle using GPS, and ambient conditions such as relative humidity and ambient temperature (range: -5°C and 9°C). For this thesis work, total particle number concentrations, emission rates and size distributions were analyzed graphically, spatially and statistically. Particle number data from the city driving portion (5.1 miles) of a longer route was analyzed, where the hybrid vehicle studied had the greatest fuel efficiency over the conventional vehicle. Road grade along the route -spatially joined to the data -ranged from -6.3 to +10.3%. Two particle instruments were operated side-by-side: a TSI Model 3090 Engine Exhaust Particle Sizer (EEPS) counted and sized particles (5.6 om to 562 nm, 32 size bins) and a TSI Model3025A Ultrafine Condensation Particle Counter (UCPC) counted particles (3 to 3000 nm).
The planetary-combination hybrid design used on the Toyota Camry hybrid allowed the ICE to tum off during low load, low speed operation resulting in the hybrid vehicle's internal combustion engine (ICE) being off 16 to 57% of the run duration. The average UCPC total particle number (3 to 3000 nm) emission rates measured for the hybrid vehicle were two times higher than that of the conventional vehicle. Number distributions measured by the EEPS were statistically different between vehicles (alpa=0.05), with the hybrid having a smaller mode at 10 nm and a larger mode at 50 nm. When hybrid restart data were separated from stabilized ICE data, the restart number distributions lacked a 10 nm mode. Spatially, the hybrid restart behavior resulted in high emissions events (HEE, defined as total particle number emission rate [less or equal to] 90th percentile of combined particle number emission rate data from both vehicles) located primarily at intersections where the vehicle was forced to stop. Compared to the conventional vehicle, the hybrid vehicle produced HEEs 62.5% more frequently. In all analyses, the hybrid ICE restart behavior appeared to be directly related to increased emissions, HEEs and differences between vehicle number distributions. The hybrid ICE-off time therefore did not fully account for increased emissions at restart. The results may indicate increased human exposure to particle numbers in city environments as hybrid popularity continues to increase. Further studies are needed to confirm the results as it is likely that different hybrid technologies and vehicle types will produce different results.