Empirical Analysis of Electric Vehicle Fast Charging Under Cold Temperatures
7/1/2018
This paper presents an empirical analysis of the effects of temperature on direct current fast charger (DCFC) charging rate and discusses the impact of such effects on wider adoptions of electric vehicles. The authors conducted statistical analysis on the effects of temperature and constructed an electric vehicle charging model that can show the dynamics of DCFC charging process under different temperatures. The results indicate that DCFC charging rate can deteriorate considerably in cold temperatures. These findings may be used as a reference to identify and assess the regions that may suffer from slow charging.
Authors: Motoaki, Y.; Yi, W.; Salisbury, S.
Notes: This Energy Policy article (Vol. 122 (2018): pp. 162-168) is copyrighted by Elsevier B.V. and only available by accessing it through Elsevier's website.
Cooperative and Integrated Vehicle and Intersection Control for Energy Efficiency (CIVIC-E2)
6/28/2018
Recent advances in connected vehicle technologies enable vehicles and signal controllers to cooperate and improve the traffic management at intersections. This paper explores the opportunity for cooperative and integrated vehicle and intersection control for energy efficiency (CIVIC-E2) to contribute to a more sustainable transportation system. We propose a two-level approach that jointly optimizes the traffic signal timing and vehicles' approach speed, with the objective being to minimize total energy consumption for all vehicles passing through an isolated intersection. More specifically, at the intersection level, a dynamic programming algorithm is designed to find the optimal signal timing by explicitly considering the arrival time and energy profile of each vehicle. At the vehicle level, a model predictive control strategy is adopted to ensure that vehicles pass through the intersection in a timely fashion. Our simulation study has shown that the proposed CIVIC-E2 system can significantly improve intersection performance under various traffic conditions. Compared with conventional fixed-time and actuated signal control strategies, the proposed algorithm can reduce energy consumption and queue length by up to 31% and 95%, respectively.
Authors: Hou, Y.; Seliman, S.M.S.; Wang, E.; Gonder, J.D.; Wood, E.; He, Q.; Sadek, A.W.; Su, L.; Qiao, C.
Assessing Energy Impacts of Connected and Automated Vehicles at the U.S. National Level - Preliminary Bounds and Proposed Methods
6/26/2018
Connected and automated vehicles (CAVs) can have tremendous impacts on transportation energy use. Using published literature to establish bounds for factors impacting vehicle demand and vehicle efficiency, we find that CAVs can potentially lead to a threefold increase or decrease in light-duty vehicle energy consumption in the United States. Much of this uncertainty is due to possible changes in travel patterns (in vehicle miles traveled) or fuel efficiency (in gallons per mile), as well as future adoption levels and patterns of use. This chapter details the factors which go into these estimates, and presents a methodological approach for refining this wide range of estimated fuel consumption.
Authors: Stephens, T.S.; Auld, J.; Chen, Y.; Gonder, J.; Kontou, E.; Lin, Z.; Xie, F.; Mohammadian, A.; Shabanpour, R.; Gohlke, D.
Notes:
This copyrighted publication can be accessed through Springer International Publishing's website.
Clean Cities Alternative Fuel Price Report, April 2018
6/14/2018
The Clean Cities Alternative Fuel Price Report for April 2018 is a quarterly report on the prices of alternative fuels in the U.S. and their relation to gasoline and diesel prices. This issue describes prices that were gathered from Clean Cities coordinators and stakeholders between April 1, 2018 and April 16, 2018, and then averaged in order to determine regional price trends by fuel and variability in fuel price within regions and among regions. The prices collected for this report represent retail, at-the-pump sales prices for each fuel, including Federal and state motor fuel taxes.
Table 2 reports that the nationwide average price (all amounts are per gallon) for regular gasoline has increased 17 cents from $2.50 to $2.67; diesel increased 7 cents from $2.96 to $3.03; CNG increased 1 cent from $2.17 to $2.18; ethanol (E85) increased 15 cents from $2.06 to $2.21; propane remained the same at $2.83; and biodiesel (B20) increased 3 cents from 2.84 to $2.87.
According to Table 3, CNG is $.49 less than gasoline on an energy-equivalent basis, while E85 is $0.20 more than gasoline on an energy-equivalent basis.
Authors: Bourbon, E.
Airport Analyses Informing New Mobility Shifts: Opportunities to Adapt Energy-Efficient Mobility Services and Infrastructure: Preprint
6/12/2018
An airport is one of the most important assets for a region's economic development and connectivity with the rest of the nation and world. Key aspects for investigation of energy efficient mobility at airports is ground transportation including factors ranging from the infrastructure, mobility services, and associated revenues. Data is critical to understand the maturity of new mobility services that can inform both cities and airports on how to respond, approach, manage, and adapt to the challenges, opportunities, and uncertainties associated with shifts in new mobility that influence human behavior, energy-efficiency and sustainability strategies. One key question identified in this article is how quickly we are adapting to new mobility options - such as app-based ride-hailing and 'pooling' services - that may provide an opportunity to influence energy efficiency of ground transportation to and from airports. By starting with airports in the regions of four smart city finalists in the U.S. DOT Smart City Challenge, this paper focuses on key observability aspects of new modes and the rate of shifts in mobility patterns across San Francisco, Portland, Denver, and Kansas City. With the emerging megatrend of rising urbanization and rising air travel demand (a predicted doubling in demand by 2035), airports are expected to increasingly be on the front lines of adaptation to new transportation technology and services in terms of infrastructure investments, policies, and revenues. As airports have demonstrated the most potential and capability of any public institution to implement fees for new ride-hailing services, they are also a prime resource for collecting important data to help understand smart mobility transitions. Results focused on the shifts in revenues for ground transportation at airports offer one vantage point into the pace of transitions and adaptations in the new emerging mobility landscape, and present an opportunity to analyze how future adaptations could support more energy-efficient scenarios.
Authors: Henao, A.; Sperling, J.; Garikapati, V.; Hou, Y.; Young, S.
Total Thermal Management of Battery Electric Vehicles (BEVs). SAE Paper No. 2018-37-0026
5/30/2018
The key hurdles to achieving wide consumer acceptance of battery electric vehicles (BEVs) are weather-dependent drive range, higher cost, and limited battery life. These translate into a strong need to reduce a significant energy drain and resulting drive range loss due to auxiliary electrical loads the predominant of which is the cabin thermal management load. Studies have shown that thermal subsystem loads can reduce the drive range by as much as 45% under ambient temperatures below -10 degrees C. Often, cabin heating relies purely on positive temperature coefficient (PTC) resistive heating, contributing to a significant range loss. Reducing this range loss may improve consumer acceptance of BEVs. The authors present a unified thermal management system (UTEMPRA) that satisfies diverse thermal and design needs of the auxiliary loads in BEVs. Demonstrated on a 2015 Fiat 500e BEV, this system integrates a semi-hermetic refrigeration loop with a coolant network and serves three functions: (1) heating and/or cooling vehicle traction components (battery, power electronics, and motor) (2) heating and cooling of the cabin, and (3) waste energy harvesting and re-use. The modes of operation allow a heat pump and air conditioning system to function without reversing the refrigeration cycle to improve thermal efficiency. The refrigeration loop consists of an electric compressor, a thermal expansion valve, a coolant-cooled condenser, and a chiller, the latter two exchanging heat with hot and cold coolant streams that may be directed to various components of the thermal system. The coolant-based heat distribution is adaptable and saves significant amounts of refrigerant per vehicle. Also, a coolant-based system reduces refrigerant emissions by requiring fewer refrigerant pipe joints. The authors present bench-level test data and simulation analysis and describe a preliminary control scheme for this system.
Authors: Chowdhury, S.; Leitzel, L.; Zima, M.; Santacesaria, M.; Titov, G.; Lustbader, J.; Rugh, J.; Winkler, J.; Khawaja, A.; Govindarajalu, M.
State of the States: Fuel Cells in America 2017, 8th Edition
5/23/2018
This January 2018 report, the eighth in a series, provides a comprehensive analysis of state activities supporting fuel cell and hydrogen technology, including profiles of all 50 states with a catalog of recent installations, policies, funding, and deployments around the country.
Authors: Curtin, S.; Gangi, J.
Foothill Transit Agency Battery Electric Bus Progress Report, Data Period Focus: Jan. 2017 through Dec. 2017
5/16/2018
This report summarizes results of a battery electric bus (BEB) evaluation at Foothill Transit, located in the San Gabriel Valley area of Los Angeles. Foothill Transit is collaborating with the California Air Resources Board and the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) to evaluate the buses in revenue service. The focus of this evaluation is to compare the performance and the operating costs of the BEBs to that of conventional technology buses and to track progress over time. Previous reports documented results from April 2014 through December 2016. This report extends the data analysis through December 2017. NREL plans to publish progress reports on the Foothill Transit fleet every six months through 2020.
Authors: Eudy, L.; Jeffers, M.
Electric Trucks: Where They Make Sense
5/1/2018
This report assesses the viability for North American Class 3 to 8 commercial electric vehicles to help the industry understand the many arguments for and against them. This report provides a foundation for understanding the key pro and con discussions of this rapidly evolving technology alternative to diesel powertrains.
Notes:
This copyrighted publication can be accessed through North American Council for Freight Efficiency's website.
Electric School Bus Pilot Project Evaluation
4/20/2018
This report provides an overview of a Massachusetts Department of Energy Resources pilot project to test electric school buses in school transportation operations. Through this project, three electric school buses were deployed at three school districts around the state and bus operations and reliability tracked for approximately one year. The project was designed to understand the opportunities and challenges associated with using electric school buses as a strategy to provide safe, reliable, cost effective school transportation. Key findings and recommendations are also provided.
The Dynamics of PEVs in the Secondary Market and Their Implications for Vehicle Demand, Durability, and Emissions
4/13/2018
California is one of the first markets in the world to have a significant secondary market for plug-in electric vehicles (PEVs). This study examines the status of the nascent secondary PEV market in California. It reviews who purchases these vehicles and how used PEVs are utilized. It also examines the role of PEV purchase incentives via surveys of used PEV buyers and by analyzing the purchase behavior for used vehicles nationwide and in California.
Authors: Turrentine, T.; Tal, G.; Rapson, D.
Determining Off-Cycle Fuel Economy Benefits of 2-Layer HVAC Technology. SAE Paper No. 2018-01-1368
4/12/2018
This work presents a methodology to determine the off-cycle fuel economy benefit of a 2-Layer HVAC system which reduces ventilation and heat rejection losses of the heater core versus a vehicle using a standard system. Experimental dynamometer tests using EPA drive cycles over a broad range of ambient temperatures were conducted on a highly instrumented 2016 Lexus RX350 (3.5L, 8 speed automatic). These tests were conducted to measure differences in engine efficiency caused by changes in engine warmup due to the 2-Layer HVAC technology in use versus the technology being disabled (disabled equals fresh air-considered as the standard technology baseline). These experimental datasets were used to develop simplified response surface and lumped capacitance vehicle thermal models predictive of vehicle efficiency as a function of thermal state. These vehicle models were integrated into a database of measured on road testing and coupled with U.S. typical meteorological data to simulate vehicle efficiency across seasonal thermal and operational conditions for hundreds of thousands of drive cycles. Fuel economy benefits utilizing the 2-Layer HVAC technology are presented in addition to goodness of fit statistics of the modeling approach relative to the experimental test data.
Authors: Jehlik, F.; Chevers, N.; Moniot, M.; Song, Y.; Hirabayashi, H.; Nomura, M.; Wood, E.
Influences on Energy Savings of Heavy Trucks Using Cooperative Adaptive Cruise Control
4/3/2018
An integrated adaptive cruise control (ACC) and cooperative ACC (CACC) was implemented and tested on three heavy-duty tractor-trailer trucks on a closed test track. The first truck was always in ACC mode, and the followers were in CACC mode using wireless vehicle-vehicle communication to augment their radar sensor data to enable safe and accurate vehicle following at short gaps. The fuel consumption for each truck in the CACC string was measured using the SAE J1321 procedure while travelling at 65 mph and loaded to a gross weight of 65,000 lb, demonstrating the effects of: inter-vehicle gaps (ranging from 3.0 s or 87 m to 0.14 s or 4 m, covering a much wider range than previously reported tests), cut-in and cut-out maneuvers by other vehicles, speed variations, the use of mismatched vehicles (standard trailers mixed with aerodynamic trailers with boat tails and side skirts), and the presence of a passenger vehicle ahead of the platoon. The results showed that energy savings generally increased in a non-linear fashion as the gap was reduced. The middle truck saved the most fuel at gaps shorter than 12 m and the trailing truck saved the most at longer gaps, while lead truck saved the least at all gaps. The cut-in and cut-out maneuvers had only a marginal effect on fuel consumption even when repeated every two miles. The presence of passenger-vehicle traffic had a measurable impact. The fuel-consumption savings on the curves was less than on the straight sections.
Authors: McAuliffe, B.; Lamert, M.; Lu, X.-Y.; Shladover, S.; Surcel, M.-D.; Kailas, A.
Range Extension Opportunities While Heating a Battery Electric Vehicle. SAE Paper No. 2018-01-0066
4/3/2018
The Kia Soul battery electric vehicle (BEV) is available with either a positive temperature coefficient (PTC) heater or an R134a heat pump (HP) with PTC heater combination (1). The HP uses both ambient air and waste heat from the motor, inverter, and on-board-charger (OBC) for its heat source. Hanon Systems, Hyundai America Technical Center, Inc. (HATCI) and the National Renewable Energy Laboratory jointly, with financial support from the U.S. Department of Energy, developed and proved-out technologies that extend the driving range of a Kia Soul BEV while maintaining thermal comfort in cold climates. Improved system configuration concepts that use thermal storage and waste heat more effectively were developed and evaluated. Range extensions of 5%-22% at ambient temperatures ranging from 5 degrees C to -18 degrees C were demonstrated. This paper reviews the three-year effort, including test data of the baseline and modified vehicles, resulting range extension, and recommendations for future actions.
Authors: Meyer, J.J.; Lustbader, J.; Agathocleous, N.; Vespa, A.; Rugh, J.; Titov, G.
Effects of Heat of Vaporization and Octane Sensitivity on Knock-Limited Spark Ignition Engine Performance. SAE Paper No. 2018-01-0218
4/3/2018
Knock-limited loads for a set of surrogate gasolines all having nominal 100 research octane number (RON), approximately 11 octane sensitivity (S), and a heat of vaporization (HOV) range of 390 to 595 kJ/kg at 25 degrees C were investigated. A single-cylinder spark-ignition engine derived from a General Motors Ecotec direct injection (DI) engine was used to perform load sweeps at a fixed intake air temperature (IAT) of 50 degrees C, as well as knock-limited load measurements across a range of IATs up to 90 degrees C. Both DI and pre-vaporized fuel (supplied by a fuel injector mounted far upstream of the intake valves and heated intake runner walls) experiments were performed to separate the chemical and thermal effects of the fuels' knock resistance. The DI load sweeps at 50 degrees C intake air temperature showed no effect of HOV on the knock-limited performance. The data suggest that HOV acts as a thermal contributor to S under the conditions studied. Measurement of knock-limited loads from the IAT sweeps for DI at late combustion phasing showed that a 40 vol% ethanol (E40) blend provided additional knock resistance at the highest temperatures, compared to a 20 vol% ethanol blend and hydrocarbon fuel with similar RON and S. Using the pre-vaporized fuel system, all the high S fuels produced nearly identical knock-limited loads at each temperature across the range of IATs studied. For these fuels RON ranged from 99.2 to 101.1 and S ranged from 9.4 to 12.2, with E40 having the lowest RON and highest S. The higher knock-limited loads for E40 at the highest IATs examined were consistent with the slightly higher S for this fuel, and the lower engine operating condition K values arising from use of this fuel. The study highlights how fuel HOV can affect the temperature at intake valve closing, and consequently the pressure-temperature history of the end gas leading to more negative values of K, thereby enhancing the effect of S on knock resistance.
Authors: Ratcliff, M.A.; Burton, J.; Sindler, P.; Christensen, E.; Fouts, L.; McCormick, R.L.