@article{yuan_frey_wei_2022, title={Fuel use and emission rates reduction potential for light-duty gasoline vehicle eco-driving}, volume={109}, ISSN={["1879-2340"]}, DOI={10.1016/j.trd.2022.103394}, abstractNote={Eco-driving offers potential to reduce fuel use and emission rates for light-duty gasoline vehicles (LDGVs). The objective is to quantify real-world route-level and segment-level fuel use and emission rates reduction potential for LDGV eco-driving. Three million seconds of real-world speed trajectory data were analyzed based on predominantly naturalistic driving of 160 drivers on eight mesoscale routes. The routes were further divided into 199 segments. A Vehicle Specific Power modal model was used to estimate trajectory-average fuel use and emission rates of CO2, CO, hydrocarbons, NOx, and particulate matter and to identify eco-driving trajectories. For route-level eco-driving, fuel use and emission rates reduction potential ranges from 6% to 40%, compared to average fuel use and emission rates estimated based on all trajectories. Eco-driving focused on fuel savings typically reduced air emissions and vice versa. Route-level eco-driving typically but not always concurrently reduces segment-level fuel use and emission rates. These co-benefits and tradeoffs can be used to guide LDGV eco-driving decisions.}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Yuan, Weichang and Frey, Christopher and Wei, Tongchuan}, year={2022}, month={Aug} }
 @article{yuan_frey_2021, title={Multi-scale evaluation of diesel commuter rail fuel use, emissions, and eco-driving}, volume={99}, ISSN={["1879-2340"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85112349776&partnerID=MN8TOARS}, DOI={10.1016/j.trd.2021.102995}, abstractNote={Diesel commuter rail emissions affect populations near rail corridors. An approach is demonstrated to quantify mesoscale and microscale diesel commuter rail fuel use and emission rates (FUERs) of CO2, CO, NOx, particulate matter, and total hydrocarbons based on two U.S. systems. A speed trajectory simulator, an energy model, and an emissions model were calibrated, evaluated, and applied. FUERs and potential reductions from eco-driving were quantified based on simulated trajectories. Hotspots were defined as sections with ≥ 90th percentile of section-average FUERs by species. A few key variables explain 74–80% of variability in mesoscopic and microscopic FUERs. On average, FUERs are 7–8 times greater for hotspots than non-hotspots. Eco-driving was estimated to reduce segment-average FUERs by 3–33% and eliminate 2–11% hotspots. However, mesoscale oriented eco-driving can, at some locations, increase microscopic FUERs. The approach is adaptable to other diesel commuter rail systems.}, journal={TRANSPORTATION RESEARCH PART D-TRANSPORT AND ENVIRONMENT}, author={Yuan, Weichang and Frey, H. Christopher}, year={2021}, month={Oct} }
 @inproceedings{wei_frey_yuan_2020, title={Application of transit bus emissions model to emission estimation: Case study for a wolfline transit bus line at North Carolina State University}, volume={2020-June}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85104853939&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Wei, T. and Frey, H.C. and Yuan, W.}, year={2020} }
 @article{yuan_frey_2020, title={Potential for metro rail energy savings and emissions reduction via eco-driving}, volume={268}, ISSN={["1872-9118"]}, DOI={10.1016/j.apenergy.2020.114944}, abstractNote={Metro rail energy efficiency needs to be improved to compensate for growing capacity demand. Eco-driving aims to reduce energy consumption without affecting safety and passenger comfort. Estimates of energy savings from train eco-driving are typically based on theoretical speed trajectory optimization models. However, achievable energy savings from eco-driving should be assessed based on realistic trajectories. A Markov chain speed trajectory simulator calibrated to measured trajectories was used to simulate realistic inter-run variability in 1 Hz trajectories. The simulator was calibrated and applied to the Washington Metropolitan Area Transit Authority Metrorail system. Estimated energy consumption for each trajectory includes auxiliary loads and tractive effort to overcome resistive forces. Inter-run variability in estimated energy consumption implies opportunities for energy savings via eco-driving. Energy savings was quantified by comparing the lowest and average segment energy consumption. A segment is the one-way rail track between adjacent stations of each line. Simulated trajectories are similar to measured trajectories based on mean absolute error and coefficient of determination (R2) for the same operation mode sequence. Based on 100 simulations per segment, energy savings ranging from 5% to 50% among segments and from 14% to 18% at the system level can be achieved without modifying travel time. Energy savings lead to reduced electricity consumption and, therefore, reduced power generation emissions. The method demonstrated here to quantify opportunities for metro train energy conservation and emissions mitigation is broadly applicable to electric metro and commuter trains and rail segments. Implications for energy-efficient passenger rail planning and operation are discussed.}, journal={APPLIED ENERGY}, author={Yuan, Weichang and Frey, H. Christopher}, year={2020}, month={Jun} }
 @inproceedings{yuan_frey_2020, title={Potential for subway energy savings and emissions reductions based on inter-run variability in speed trajectories: A case study of Baltimore subway}, volume={2020-June}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85104829385&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Yuan, W. and Frey, H.C.}, year={2020} }
 @article{zhang_ma_wang_song_li_yuan_zhang_2020, title={The increasing district heating energy consumption of the building sector in China: Decomposition and decoupling analysis}, volume={271}, ISSN={["1879-1786"]}, DOI={10.1016/j.jclepro.2020.122696}, abstractNote={The district heating system accounts for 40% energy consumption of the building sector in China and still has tremendous growth potential due to the urbanisation. However, few studies have conducted explicit quantification on the drivers and the sustainable development of the district heating energy consumption of the building sector (DHEB) in China, although previous aggregation analysis on whole building energy service could convey implications on the district heating systems. This study investigates the driving factors of the DHEB in China between 2004 and 2016 using a decomposition analysis that incorporates effects of energy mix, heat production technology structure, energy intensity, heating area, and population. The decoupling status between the DHEB and gross domestic product (GDP) in China is then analyzed based on the Tapio decoupling index, along with the contributions of each driving factor to the decoupling. The results show that the effects of district heating area and population dominate the increase in the DHEB, while the heating energy intensity is the strongest factor reducing the DHEB. In addition, the shares of coal and heating boilers positively contribute to the increase in 2004–2008, and have a negative effect in 2008–2016. The complete reverse trend is found in the shares of gas and combined heat and power (CHP) during the same period. These results are largely associated with the implementation of “coal to gas” and the “elimination of old boilers” pushed by the Chinese government. Furthermore, a weak decoupling effect is mainly found between China’s DHEB and GDP from 2004 to 2016. The heating energy intensity is the strongest factor promoting the decoupling, while the growth of the district heating area and population leads to a weak decoupling.}, journal={JOURNAL OF CLEANER PRODUCTION}, author={Zhang, Linghui and Ma, Xin and Wang, Yixuan and Song, Rui and Li, Jiaojiao and Yuan, Weichang and Zhang, Shushen}, year={2020}, month={Oct} }
 @article{yuan_frey_wei_rastogi_vandergriend_miller_mattison_2019, title={Comparison of real-world vehicle fuel use and tailpipe emissions for gasoline-ethanol fuel blends}, volume={249}, ISSN={["1873-7153"]}, url={https://doi.org/10.1016/j.fuel.2019.03.115}, DOI={10.1016/j.fuel.2019.03.115}, abstractNote={Differences in fuel use and emission rates of carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), nitrogen oxide (NOx), and particulate matter (PM) were quantified for three gasoline-ethanol blends and neat gasoline measured for one flexible-fuel vehicle (FFV) and four non-FFVs using a portable emission measurement system (PEMS). The purpose was to determine if non-FFVs can adapt to a mid-level blend and to compare the fuel use and emission rates among the fuels. Each vehicle was measured on neat gasoline (E0), 10% ethanol by volume (E10) “regular” (E10R) and “premium” (E10P), and 27% ethanol by volume (E27). Four real-world cycles were repeated for each vehicle with each fuel. Second-by-second fuel use and emission rates were binned into Vehicle Specific Power (VSP) modes. The modes were weighted according to real-world standard driving cycles. All vehicles, including the non-FFVs, were able to adapt to E27. Octane-induced efficiency gain was observed for higher octane fuels (E10P and E27) versus lower octane fuels (E0 and E10R). E27 tends to lower PM emission rates compared to E10R and E10P and CO emission rates compared to the other three fuels. HC emission rates for E27 were comparable to those of E10R and E10P. No significant difference was found in NOx emission rates for E27 versus the other fuels. Intervehicle variability in fuel use and emission rates was observed. Lessons learned regarding study design, vehicle selection, and sample size, and their implications are discussed.}, journal={FUEL}, publisher={Elsevier BV}, author={Yuan, Weichang and Frey, H. Christopher and Wei, Tongchuan and Rastogi, Nikhil and VanderGriend, Steven and Miller, David and Mattison, Lawrence}, year={2019}, month={Aug}, pages={352–364} }
 @article{yuan_frey_rastogi_2019, title={Quantification of Energy Saving Potential for A Passenger Train Based on Inter-Run Variability in Speed Trajectories}, volume={2673}, ISSN={["2169-4052"]}, DOI={10.1177/0361198119838516}, abstractNote={Passenger train energy consumption is dependent on speed trajectories. The variability of passenger train energy consumption owing to the variability in speed trajectories can help identify ways to reduce train energy use via improved operations. Empirical fuel use data from a portable measurement emission measurement system (PEMS) and empirical speed trajectories measured using a global positioning system (GPS) receiver were used to verify and quantify real-world energy consumption variability and the variability in empirical speed trajectories, respectively. To identify potential realistic speed trajectories that can lead to energy saving (i.e., eco-driving), a Markov chain based speed trajectory simulator was used to simulate inter-run variability in speed trajectories. An energy index model (EIM) was used to compare energy consumption among different speed trajectories. The results show inter-run variability in fuel use associated with inter-run variability in the empirical speed trajectories. There is also inter-segment variability in fuel use related to the segment length and grade. The Markov chain based speed trajectory simulator can simulate realistic inter-run variability in speed trajectories based on calibration using empirical speed trajectories. The number of empirical speed trajectories used for simulator calibration affects the range of simulated inter-run variability. The EIM provides an accurate estimation of the empirical fuel use. Eco-driving, such as reducing the peak speed, can reduce energy consumption without compromising travel time. The methodology shown in this study is not system-specific and can be applied to other passenger train systems.}, number={5}, journal={TRANSPORTATION RESEARCH RECORD}, author={Yuan, Weichang and Frey, H. Christopher and Rastogi, Nikhil}, year={2019}, month={May}, pages={153–165} }
 @inproceedings{yuan_christopher frey_2018, title={An algorithm to simulate segment speed trajectories of a metrorail segment for energy consumption estimation}, volume={2018-June}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85056337873&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Yuan, W. and Christopher Frey, H.}, year={2018} }
 @article{yu_yuan_liu_xu_ruan_2017, title={Asymmetry of the free-standing polyelectrolyte multilayers}, volume={422}, ISSN={["1873-5584"]}, DOI={10.1016/j.apsusc.2017.05.085}, abstractNote={Free-standing polyelectrolyte multilayers (PEMs) triggered an intense research effort to develop functional capsules and membranes, nevertheless, the comprehensive understanding of the surface distinctions between the two sides of the free-standing PEMs has been rarely studied. In this paper, we demonstrate the asymmetric surface morphologies, compositions, surface charge and wetting properties of the free-standing PEMs made of alternating deposition of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrenesulfonate) (PSS) on uncharged trimethoxy (octyl) silane modified silicon wafer (TMOS-Si) substrates. The growth behaviors (e.g., linear or exponential growth) of the (PDDA/PSS)n PEMs deposited on TMOS-Si substrates are similar to those deposited on negatively charged substrates except a slower evolution in morphology and thickness, evidenced by atomic force microscopy (AFM) and ellipsometry. The surface charge of the two sides can be tuned as +/+, −/-, and +/− by selecting the first and the terminate layer of the polyelectrolyte during the deposition process, indicated by X-ray photoelectron spectroscopy (XPS) and the surface zeta potential measured by spinning disk method. Further, water contact angle measurements exhibit a strong difference between the back side (the bottom side that was initially contacted with the substrate) (74 ± 4°) and front side (33 ± 2° and 48 ± 3° for PDDA and PSS as the outmost layer, respectively) of the PEMs. The larger water contact angle of the back side is probably resulted from the orientation of the alkyl chains of the polyelectrolytes as the hydrophobic–hydrophobic interactions played significant roles in deposition of a polyelectrolyte onto an uncharged substrate. This paper may gain new insights on understanding surface properties of the PEMs.}, journal={APPLIED SURFACE SCIENCE}, author={Yu, Li and Yuan, Weichang and Liu, Xiaokong and Xu, Xintong and Ruan, Shuangchen}, year={2017}, month={Nov}, pages={46–55} }
 @inproceedings{yuan_frey_sun_2017, title={Quantification of transit train activity data for energy consumption estimation}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85039168169&partnerID=MN8TOARS}, booktitle={Proceedings of the Air and Waste Management Association's Annual Conference and Exhibition, AWMA}, author={Yuan, W. and Frey, H.C. and Sun, Y.}, year={2017} }
 @article{confined flocculation of ionic pollutants by poly(l-dopa)-based polyelectrolyte complexes in hydrogel beads for three-dimensional, quantitative, efficient water decontamination_2015, url={http://dx.doi.org/10.1021/acs.langmuir.5b01084}, DOI={10.1021/acs.langmuir.5b01084}, abstractNote={The development of simple and recyclable adsorbents with high adsorption capacity is a technical imperative for water treatment. In this work, we have successfully developed new adsorbents for the removal of ionic pollutants from water via encapsulation of polyelectrolyte complexes (PECs) made from positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly(l-3,4-dihydroxyphenylalanine) (PDopa), obtained via the self-polymerization of l-3,4-dihydroxyphenylalanine (l-Dopa). Given the outstanding mass transport through the hydrogel host matrixes, the PDopa-PAH PEC guests loaded inside can effectively and efficiently remove various ionic pollutants, including heavy metal ions and ionic organic dyes, from water. The adsorption efficiency of the PDopa-PAH PECs can be quantitatively correlated to and tailored by the PDopa-to-PAH molar ratio. Because PDopa embodies one catechol group, one carboxyl group, and one amino group in each repeating unit, the resulting PDopa-PAH PECs exhibit the largest capacity of adsorption of heavy metal ions compared to available adsorbents. Because both PDopa and PAH are pH-sensitive, the PDopa-PAH PEC-loaded agarose hydrogel beads can be easily and completely recovered after the adsorption of ionic pollutants by adjusting the pH of the surrounding media. The present strategy is similar to the conventional process of using PECs to flocculate ionic pollutants from water, while in our system flocculation is confined to the agarose hydrogel beads, thus allowing easy separation of the resulting adsorbents from water.}, journal={Langmuir}, year={2015}, month={Jun} }