@article{graver_frey_hu_2016, title={Effect of Biodiesel Fuels on Real-World Emissions of Passenger Locomotives}, volume={50}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84994320268&partnerID=MN8TOARS}, DOI={10.1021/acs.est.6b03567}, abstractNote={Few data are available regarding the effect of biodiesel on exhaust emission rates of two-stroke engines used in many passenger locomotives. Using a portable emissions measurement system (PEMS), duty cycle average nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO), particulate matter (PM), and carbon dioxide (CO2) emission rates were measured for three locomotives operating on ultra-low sulfur diesel (ULSD) and soy-based B10, B20, and B40 biodiesel blends. Measurements were conducted in the rail yard (RY) and over-the-rail (OTR) during passenger service. Compared to ULSD, B20 biodiesel had statistically significant average emission rate reductions in the RY of 58% for CO, 45% for PM, and 6% CO2 and OTR of 59% for HC, 50% for CO, 26% for PM, and 5% for CO2. The average differences in NOx emission rates for both the RY and OTR, and HC in the RY, were not statistically significant. The OTR findings typically agreed qualitatively with the RY findings; however, OTR provides a better basis for estimating the real-world impact of fuel switching. The results indicate substantial potential to reduce in-use locomotive emissions for existing older locomotives, with the exception of NOx.}, number={21}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Graver, Brandon M. and Frey, H. Christopher and Hu, Jiangchuan}, year={2016}, month={Nov}, pages={12030–12039} }
 @article{graver_frey_2015, title={Comparison of Over-the-Rail and Rail Yard Measurements of Diesel Locomotives}, volume={49}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84946601235&partnerID=MN8TOARS}, DOI={10.1021/acs.est.5b02497}, abstractNote={Locomotive prime mover engine emission rates are typically measured at steady-state for discrete throttle notches using an engine dynamometer weighted by a standard duty cycle. However, this method may not represent real-world locomotive emissions. A method for in-use measurement of passenger locomotives, using a portable emissions measurement system (PEMS), was developed to estimate duty cycle average emission rates. We conducted 48 measurements of one-way trips between Raleigh and Charlotte, NC, on 7 locomotives and 18 sets of measurements in the rail yard (RY). Real-world duty cycles differed from those used for regulatory analyses, leading to statistically significant lower cycle average NOx and HC emission rates. Compared to RY measurements, notch average NOx emission rates measured over-the-rail (OTR) at the highest two notch settings were, on average, 19% lower for four locomotives. At the highest notch, OTR CO2 emission rates were, on average, 12% lower than RY rates for five locomotives. For a more accurate representation of real-world emission rates, OTR measurements are preferred. However, using steady-state notch average RY emission rates and standard duty cycles may be tolerable for some applications. OTR versus RY cycle average emission rates typically differed by less than 10%.}, number={21}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Graver, Brandon M. and Frey, H. Christopher}, year={2015}, month={Nov}, pages={13031–13039} }
 @article{hu_frey_sandhu_graver_bishop_schuchmann_ray_2014, title={Method for Modeling Driving Cycles, Fuel Use, and Emissions for Over Snow Vehicles}, volume={48}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84904409293&partnerID=MN8TOARS}, DOI={10.1021/es501164j}, abstractNote={As input to a winter use plan, activity, fuel use, and tailpipe exhaust emissions of over snow vehicles (OSV), including five snow coaches and one snowmobile, were measured on a designated route in Yellowstone National Park (YNP). Engine load was quantified in terms of vehicle specific power (VSP), which is a function of speed, acceleration, and road grade. Compared to highway vehicles, VSP for OSVs is more sensitive to rolling resistance and less sensitive to aerodynamic drag. Fuel use rates increased linearly (R2>0.96) with VSP. For gasoline-fueled OSVs, fuel-based emission rates of carbon monoxide (CO) and nitrogen oxides (NOx) typically increased with increasing fuel use rate, with some cases of very high CO emissions. For the diesel OSVs, which had selective catalytic reduction and diesel particulate filters, fuel-based NOx and particulate matter (PM) emission rates were not sensitive to fuel flow rate, and the emission controls were effective. Inter vehicle variability in cycle average fuel use and emissions rates for CO and NOx was substantial. However, there was relatively little inter-cycle variation in cycle average fuel use and emission rates when comparing driving cycles. Recommendations are made regarding how real-world OSV activity, fuel use, and emissions data can be improved.}, number={14}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Hu, Jiangchuan and Frey, H. Christopher and Sandhu, Gurdas S. and Graver, Brandon M. and Bishop, Gary A. and Schuchmann, Brent G. and Ray, John D.}, year={2014}, month={Jul}, pages={8258–8265} }
 @article{graver_frey_2013, title={Comparison of Locomotive Emissions Measured During Dynamometer Versus Rail Yard Engine Load Tests}, ISSN={["2169-4052"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84887758744&partnerID=MN8TOARS}, DOI={10.3141/2341-03}, abstractNote={ For environmental emissions certification, locomotive prime mover engines undergo rigorous measurements with the use of federal reference methods (FRMs). However, there are nonregulatory reasons for engine emissions measurement, such as to compare relative differences in fuel use and emissions as a result of engine rebuild or between engines in a fleet. Portable emissions measurement systems (PEMSs) are widely used for highway vehicle and nonroad construction equipment but have had limited locomotive applications. The objectives are to (a) demonstrate an approach for quantifying locomotive emission rates with a PEMS during dynamometer and rail yard engine load tests, (b) compare the emissions measured in dynamometer versus rail yard load tests, and (c) assess the relative change in fuel use and emissions from engine rebuild. Measurements were conducted on 3,000-hp prime movers, including an EMD 16-645 for a GP40 and two EMD 12-710s for F59PHs. Fuel use and PEMS-based emission rates for nitric oxide, carbon monoxide, hydrocarbons, and particulate matter were compared between dynamometer and rail yard load tests and with data from previous literature. Fuel use and oxides of nitrogen (NOx) emission rates after engine rebuild were lower for the GP40 prime mover, and the fuel use and NOx emission rates for the F59PH rebuilt engines were lower than those of the rebuilt GP40 engine. PEMS is not a substitute for locomotive FRMs if compliance certification is needed but provides useful data for comparative assessment. }, number={2341}, journal={TRANSPORTATION RESEARCH RECORD}, author={Graver, Brandon M. and Frey, H. Christopher}, year={2013}, pages={23–33} }
 @article{graver_frey_choi_2011, title={In-Use Measurement of Activity, Energy Use, and Emissions of a Plug-in Hybrid Electric Vehicle}, volume={45}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-80054685657&partnerID=MN8TOARS}, DOI={10.1021/es201165d}, abstractNote={Plug-in hybrid electric vehicles (PHEVs) could reduce transportation air emissions and energy use. However, a method is needed for estimating on-road emissions of PHEVs. To develop a framework for quantifying microscale energy use and emissions (EU&E), measurements were conducted on a Toyota Prius retrofitted with a plug-in battery system on eight routes. Measurements were made using the following: (1) a data logger for the hybrid control system; (2) a portable emissions measurement system; and (3) a global positioning system with barometric altimeter. Trends in EU&E are estimated based on vehicle specific power. Energy economy is quantified based on gasoline consumed by the engine and grid energy consumed by the plug-in battery. Emissions from electricity consumption are estimated based on the power generation mix. Fuel use is approximately 30% lower during plug-in battery use. Grid emissions were higher for CO₂, NO(x), SO₂, and PM compared to tailpipe emissions but lower for CO and hydrocarbons. EU&E depends on engine and plug-in battery operation. The use of two energy sources must be addressed in characterizing fuel economy; overall energy economy is 11% lower if including grid energy use than accounting only for fuel consumption.}, number={20}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Graver, Brandon M. and Frey, H. Christopher and Choi, Hyung-Wook}, year={2011}, month={Oct}, pages={9044–9051} }