Browsing by Author "Nagui M. Rouphail, Committee Co-Chair"

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    On-board Measurement and Analysis of On-Road Vehicle Emissions
    (2002-11-17) Unal, Alper; Chritopher H. Frey, Committee Chair; Nagui M. Rouphail, Committee Co-Chair; E. Downey Brill, Committee Member; Montserrat Fuentes, Committee Member
    Recent developments in on-board instrumentation enable measurement of vehicle activity and emissions under real-world conditions as opposed to laboratory tests. Variability in vehicle emissions as a result of variation in vehicle operation, roadway characteristics, or other factors can be represented and analyzed more reliably than with other measurement methods. The primary purpose of this dissertation is to develop methodologies for on-board vehicle activity and emissions data collection and data screening. Successful application of the developed methodology resulted at data collected in two signalized corridors in Cary, North Carolina. Eight gasoline fueled light-duty vehicles and four drivers were tested, resulting in a total of 824 one-way runs representing approximately 1,000 vehicle-hours and 2,020 vehicle-miles of simultaneous second-by-second vehicle activity and emissions data. A priori modal definitions were developed based upon vehicle speed and acceleration. It was found that modal definitions yield statistically significantly different emission rates for idle, acceleration, cruise, and deceleration. A secondary, but equally important, purpose was to utilize vehicle activity and emissions data collected to tackle real-world problems related to vehicle emissions. One of these problems is to investigate emissions hotspots along roadways. Methods were developed to identify hotspot locations and applied to two example case studies to illustrate the types of insights obtained from this analysis. Based upon statistical and graphical analysis, hotspots were attributed most typically to stop-and-go traffic conditions which result in sudden changes in speed and accelerations. The sensitivity of different emissions factor estimation methods (i.e., distance-based, time-based, and fuel-based) was evaluated with respect to vehicle operation modes. The effect of changes in signal timing and coordination on vehicle emissions was also investigated. For the example case study it was found that coordinated signal timing improved traffic flow on Walnut Street, which lead to a reduction in vehicle emissions. For Chapel Hill Road, emissions of NO, CO, and HC were lower in the uncongested case compared to the congested case. It was found that differences in emissions were highly associated with differences in quantitative measures of traffic flow such as average speed, average control delay, and average number of stops per mile.
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    Regional On-Road Mobile Source Emissions Characterization for Conventional and Alternative Vehicle Technologies
    (2008-03-20) Zhai, Haibo; Daniel Rodríguez, Committee Member; Donald van der Vaart, Committee Member; Nagui M. Rouphail, Committee Co-Chair; H. Christopher Frey, Committee Chair
    The development of alternative fuels and vehicle technologies could lead to reductions in emissions and reduced reliance on petroleum fuels. The objectives of this study are to evaluate the potential reductions in air pollutant emissions associated with real world operation of future vehicles that utilize advanced fuels or technologies in comparison to conventional vehicles. For light duty vehicles, the fuels or energy sources considered are gasoline, ethanol (E85), compressed natural gas, hydrogen, and electricity. The technologies considered are internal combustion engines, hybrids, fuel cell, and electric vehicles. For heavy duty vehicles, biodiesel is considered for trucks and compressed natural gas is considered for buses, in addition to conventional diesel fuels and technologies. For most of the vehicle fuel and technology combinations, modal fuel use and emissions models were developed based on available second-by-second portable emission measurement system (PEMS) or dynamometer tailpipe emissions data. Link-based average emission rates were estimated for different link-based average speeds and roadway types based upon second-by-second speed profiles measured on the road as part as previous PEMS measurements, supplemented by data from the literature in some cases. The results enable comparison of different vehicle technologies and fuels for each of several link-based average speeds and roadway facility types. The linked-based emissions factors are coupled with the outputs of a transportation demand model for emission inventory estimation and assessment of the potential changes in emissions that can accrue from technology and fuel use. The results will provide support for decision making regarding alternative fuels, adoption of new vehicle technologies, and air quality management.