@article{zhai_frey_rouphail_goncalves_farias_2009, title={Comparison of Flexible Fuel Vehicle and Life-Cycle Fuel Consumption and Emissions of Selected Pollutants and Greenhouse Gases for Ethanol 85 Versus Gasoline}, volume={59}, ISSN={["1096-2247"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-70350516518&partnerID=MN8TOARS}, DOI={10.3155/1047-3289.59.8.912}, abstractNote={Abstract The objective of this research is to evaluate differences in fuel consumption and tailpipe emissions of flexible fuel vehicles (FFVs) operated on ethanol 85 (E85) versus gasoline. Theoretical ratios of fuel consumption and carbon dioxide (CO2) emissions for both fuels are estimated based on the same amount of energy released. Second-by-second fuel consumption and emissions from one FFV Ford Focus fueled with E85 and gasoline were measured under real-world traffic conditions in Lisbon, Portugal, using a portable emissions measurement system (PEMS). Cycle average dynamometer fuel consumption and emission test results for FFVs are available from the U.S. Department of Energy, and emissions certification test results for ethanol-fueled vehicles are available from the U.S. Environmental Protection Agency. On the basis of the PEMS data, vehicle-specific power (VSP)-based modal average fuel and emission rates for both fuels are estimated. For E85 versus gasoline, empirical ratios of fuel consumption and CO2 emissions agree within a margin of error to the theoretical expectations. Carbon monoxide (CO) emissions were found to be typically lower. From the PEMS data, nitric oxide (NO) emissions associated with some higher VSP modes are higher for E85. From the dynamometer and certification data, average hydrocarbon (HC) and nitrogen oxides (NOx) emission differences vary depending on the vehicle. The differences of average E85 versus gasoline emission rates for all vehicle models are −22% for CO, 12% for HC, and −8% for NOx emissions, which imply that replacing gasoline with E85 reduces CO emissions, may moderately decrease NOx tailpipe emissions, and may increase HC tailpipe emissions. On a fuel life cycle basis for corn-based ethanol versus gasoline, CO emissions are estimated to decrease by 18%. Life-cycle total and fossil CO2 emissions are estimated to decrease by 25 and 50%, respectively; however, life-cycle HC and NOx emissions are estimated to increase by 18 and 82%, respectively.}, number={8}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Zhai, Haibo and Frey, H. Christopher and Rouphail, Nagui M. and Goncalves, Goncalo A. and Farias, Tiago L.}, year={2009}, month={Aug}, pages={912–924} }
 @article{zhai_frey_rouphail_2008, title={A Vehicle-Specific Power Approach to Speed- and Facility-Specific Emissions Estimates for Diesel Transit Buses}, volume={42}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-55349085068&partnerID=MN8TOARS}, DOI={10.1021/es800208d}, abstractNote={Emissions during a trip often depend on transient vehicle dynamics that influence the instantaneous engine load. Vehicle specific power (VSP) is a proxy variable for engine load that has been shown to be highly correlated with emissions. This study estimates roadway link average emission rates for diesel-fueled transit buses based on link mean speeds, using newly defined VSP modes from data gathered by a portable emissions monitoring system. Speed profiles were categorized by facility type and mean travel speed, and stratified into discrete VSP modes. VSP modal average emission rates and the time spent in the corresponding VSP modes were then used to make aggregate estimates of total and average emission rates for a road link. The average emission rates were sensitive to link mean speed, but not to facility type. A recommendation is made regarding the implementation of link average emission rates in conjunction with transportation models for the purpose of estimating regional emissions for diesel transit buses.}, number={21}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Zhai, Haibo and Frey, H. Christopher and Rouphail, Nagui M.}, year={2008}, month={Nov}, pages={7985–7991} }
 @article{frey_rouphail_zhai_2008, title={Link-based emission factors for heavy-duty diesel trucks based an real-world data}, number={2058}, journal={Transportation Research Record}, author={Frey, H. C. and Rouphail, N. M. and Zhai, H. B.}, year={2008}, pages={23–32} }
 @article{frey_rouphail_zhai_farias_goncalves_2007, title={Comparing real-world fuel consumption for diesel- and hydrogen-fueled transit buses and implication for emissions}, volume={12}, ISSN={["1361-9209"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-34247868934&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2007.03.003}, abstractNote={This paper explores the influence of key factors such as speed, acceleration, and road grade on fuel consumption for diesel and hydrogen fuel cell buses under real-world operating conditions. A Vehicle Specific Power-based approach is used for modeling fuel consumption for both types of buses. To evaluate the robustness of the modeling approach, Vehicle Specific Power-based modal average fuel consumption rates are compared for diesel buses in the US and Portugal, and for the Portuguese diesel and hydrogen fuel cell buses that operate on the same route. For diesel buses there is similar intra-vehicle variability in fuel consumption using Vehicle Specific Power modes. For the fuel cell bus, the hydrogen fuel consumption rate was found to be less sensitive to Vehicle Specific Power variations and had smaller variability compared to diesel buses. Relative errors between trip fuel consumption estimates and actual fuel use, based upon predictions for a portion of real-world activity data that were not used to calibrate the models, were generally under 10% for all observations. The Vehicle Specific Power-based modeling approach is recommended for further applications as additional data become available. Emission changes based upon substituting hydrogen versus diesel buses are evaluated.}, number={4}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Frey, H. Christopher and Rouphail, Nagui M. and Zhai, Haibo and Farias, Tiago L. and Goncalves, Goncalo A.}, year={2007}, month={Jun}, pages={281–291} }