Hybrid Transit Bus Research Articles

A Comparative Study of Lithium-Ion Cathode Chemistry Correlations with Emissions Initiated by Nail Penetration Abuse in the Presence of an Immersive Coolant

<div class="section abstract"><div class="htmlview paragraph">Internal short-circuit in cells/batteries is a phenomenon where there is direct electrical contact between the positive and negative electrodes leading to thermal runaway. The nail penetration tests were used to simulate an internal short circuit within the battery, where a conductive nail was used to pierce the battery cell separator membrane which provided direct electrical contact between the positive and negative electrodes. The batteries tested during this work were common batteries used in existing automotive applications, and they included a nickel manganese cobalt (NMC) battery from a Chevrolet Bolt, a lithium manganese oxide (LMO) battery from a Chevrolet Volt, and a lithium iron phosphate (LFP) battery in a hybrid transit bus. The battery abuse and emissions tests were designed to intentionally drive the three different battery chemistries into thermal runaway while measuring battery temperatures, battery voltages and gaseous emissions. During this testing, the batteries were submerged in an immersive coolant, NOVEC 7300, in order to judge how effective, the immersive coolant was in preventing additional thermal propagation. The emissions data collected from FTIR (Fourier Transform Infrared Spectroscopy), GC-FID (Gas Chromatography and Flame Ionization Detection) and AES (Atomic Emission Spectroscopy) are reported in appropriate units flagging any transgression of health-related safety limits. The emissions collected during the nail penetration testing are summarized in tabular and graphic formats. The NMC showed a higher thermal runaway intensity; it was the only chemistry that continued to have thermal propagation after the initial nail penetration and it had marginally higher temperatures recorded. In contrast, the LFP produced the least number of harmful emissions while the LMO recorded the lowest temperatures.</div></div>

A Comparative Study of Lithium-Ion Cathode Chemistry Correlations with Emissions Initiated by Nail Penetration Abuse in the Presence of an Immersive Coolant

<div class="section abstract"><div class="htmlview paragraph">Internal short-circuit in cells/batteries is a phenomenon where there is direct electrical contact between the positive and negative electrodes leading to thermal runaway. The nail penetration tests were used to simulate an internal short circuit within the battery, where a conductive nail was used to pierce the battery cell separator membrane which provided direct electrical contact between the positive and negative electrodes. The batteries tested during this work were common batteries used in existing automotive applications, and they included a nickel manganese cobalt (NMC) battery from a Chevrolet Bolt, a lithium manganese oxide (LMO) battery from a Chevrolet Volt, and a lithium iron phosphate (LFP) battery in a hybrid transit bus. The battery abuse and emissions tests were designed to intentionally drive the three different battery chemistries into thermal runaway while measuring battery temperatures, battery voltages and gaseous emissions. During this testing, the batteries were submerged in an immersive coolant, NOVEC 7300, in order to judge how effective, the immersive coolant was in preventing additional thermal propagation. The emissions data collected from FTIR (Fourier Transform Infrared Spectroscopy), GC-FID (Gas Chromatography and Flame Ionization Detection) and AES (Atomic Emission Spectroscopy) are reported in appropriate units flagging any transgression of health-related safety limits. The emissions collected during the nail penetration testing are summarized in tabular and graphic formats. The NMC showed a higher thermal runaway intensity; it was the only chemistry that continued to have thermal propagation after the initial nail penetration and it had marginally higher temperatures recorded. In contrast, the LFP produced the least number of harmful emissions while the LMO recorded the lowest temperatures.</div></div>

Preliminary Design, Drive-Cycle Simulation and Energy Analysis of a Hybrid Transit Bus

Preliminary Design, Drive-Cycle Simulation and Energy Analysis of a Hybrid Transit Bus

Design and Optimization of Fuel Injection of a 50 kW Micro Turbogas

The present article deals with the design of a micro turbogas turbine suitable for on board applications, e.g., as a power generator on hybrid transit bus, characterized by a simple constructive approach. Deriving the machine layout from an existing KJ-66 aircraft model engine, the authors propose a theoretical design of a compact, lightweight turbogas turbine, by investigating the technical possibility and limits of the proposed design. In particular, a different combustion chamber layout has been proposed, and fuel adduction channels for different swirler designs have been simulated via ANSYS Fluent in order to identify a satisfactory fuel spreading. As a result, the complete characterization of the design parameters and geometries has been performed, and a series of RANS simulations has been used in order to identify an optimal swirler configuration.

Lifecycle cost assessment and carbon dioxide emissions of diesel, natural gas, hybrid electric, fuel cell hybrid and electric transit buses

This paper evaluates the lifecycle costs and carbon dioxide emissions of different types of city buses. The simulation models of the different powertrains were developed in the Autonomie vehicle simulation software. The carbon dioxide emissions were calculated both for the bus operation and for the fuel and energy pathways from well to tank. Two different operating environment case scenarios were used for the primary energy sources, which were Finland and California (USA). The fuel and energy pathways were selected appropriately in relation to the operating environment. The lifecycle costs take into account the purchase, operating, maintenance, and possible carbon emission costs. Based on the simulation results, the energy efficiency of city buses can be significantly improved by the alternative powertrain technologies. Hybrid buses have moderately lower carbon dioxide emissions during the service life than diesel buses whereas fully-electric buses have potential to significantly reduce carbon dioxide emissions, by up to 75%. The lifecycle cost analysis indicates that diesel hybrid buses are already competitive with diesel and natural gas buses. The high costs of fuel cell and battery systems are the major challenges for the fuel cell hybrid buses in order to reduce lifecycle costs to more competitive levels.

Simulations of the Fuel Economy and Emissions of Hybrid Transit Buses over Planned Local Routes

We present simulated fuel economy and emissions city transit buses powered by conventional diesel engines and diesel-hybrid electric powertrains of varying size. Six representative city drive cycles were included in the study. In addition, we included previously published aftertreatment device models for control of CO, HC, NOx, and particulate matter (PM) emissions. Our results reveal that bus hybridization can significantly enhance fuel economy by reducing engine idling time, reducing demands for accessory loads, exploiting regenerative braking, and shifting engine operation to speeds and loads with higher fuel efficiency. Increased hybridization also tends to monotonically reduce engine-out emissions, but trends in the tailpipe (post-aftertreatment) emissions involve more complex interactions that significantly depend on motor size and drive cycle details.

Comparison of on-road emissions for hybrid and regular transit buses

Hybrid technology offers an attractive option for transit buses, since it has the potential to significantly reduce operating costs for transit agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Laboratory tests have indicated that hybrid transit buses can have significantly lower emissions compared with conventional transit buses. However, the number of studies is limited and laboratory tests may not represent actual driving conditions, since in-use vehicle operation differs from laboratory test cycles. This paper describes an on-road evaluation of in-use emission differences between hybrid-electric and conventional transit buses for the Ames, Iowa transit authority, CyRide. Emissions were collected on-road using a portable emissions monitoring system (PEMS) for three hybrid and two control buses. Emissions were collected for at least one operating bus day. Each bus was evaluated over the same route pattern, which utilizes the same driver. The number of passengers embarking or disembarking at each stop was collected by an on-board data collector so that passenger load could be included. Vehicle emissions are correlated to engine load demand, which is a function of factors such as vehicle load, speed, and acceleration. PEMS data are provided second by second and vehicle-specific power (VSP) was calculated for each row of data. Instantaneous data were stratified into the defined VSP bins and then average modal emission rates and standard errors were calculated for each bus for each pollutant. Pollutants were then compared by bus type. Carbon dioxide, carbon monoxide, and hydrocarbon emissions were higher for the regular buses across most VSP bins than for the hybrid buses. Nitrogen oxide emissions were unexpectedly higher for the hybrid buses than for the control buses. Implications: The main reason agencies consider hybrid transit vehicles is fuel savings and reduced emissions. Hybrid electric buses offer an attractive option and have the potential to significantly reduce operating costs and emissions for transit agencies. However, purchase of hybrid buses cost 50–70% more than regular buses. As a result, agencies require more quantitative information about the on-road costs and benefits of hybrid buses. This study assessed on-road emissions for in-use transit buses. The resulting information can be used by transit agencies in assessing the likely emission reduction benefits for hybrid buses.

Evaluation of In-Use Fuel Economy for Hybrid and Regular Transit Buses

Fuel costs are a significant portion of transit agency budgets. Hybrid technology offers an attractive option and has the potential to significantly reduce operating costs for agencies. The main impetus behind use of hybrid transit vehicles is fuel savings and reduced emissions. Laboratory tests have indicated that hybrid transit buses can have significantly higher fuel economy and lower emissions compared to conventional transit buses. However, the number of studies is limited and laboratory tests may not represent actual driving conditions since in-use vehicle operation differs from laboratory test cycles. Several initial studies have suggested that the fuel economy savings reported in laboratory tests may not be realized on-road. The objective of the project described in this paper was to evaluate the in-use fuel economy differences between hybrid-electric and conventional transit buses for the Ames, Iowa (USA) transit authority. On-road fuel economy was evaluated over a 12-month period for 12 hybrid and 7 control transit buses. Fuel economy comparisons were also provided for several older in-use bus types. Buses other than the control and hybrid buses were grouped by model year corresponding to US diesel emission standards. Average fuel economy in miles per gallon was calculated for each bus group overall and by season. Hybrid buses had the highest fuel economy for all time periods for all bus types. Hybrid buses had a fuel economy that was 11.8% higher than control buses overall and was 12.2% higher than buses with model years 2007 and higher, 23.4% higher than model years 2004 to 2006, 10.2% higher than model years 1998 to 2003, 38.1% higher than for model years 1994 to 1997, 36.8% higher for model years 1991 to 1993, and 36.8% higher for model years pre-1991. Differences between groups of buses also varied by season of the year.

Integration of batteries with ultracapacitors for a fuel cell hybrid transit bus

Battery electric vehicles and hybrid electric vehicles require electric energy storage systems that exhibit high energy and power density, as well as good cycle life. Batteries possess good energy density, whereas ultracapacitors possess high power density and cycle life. The complementary features of batteries and ultracapacitors can be advantageously combined to create an integrated system that exhibits high performance with low weight and adequate battery lifetime, at an affordable cost. This paper presents simulation studies on the benefits of adding ultracapacitors to a fuel cell battery hybrid transit bus operating on two standardized driving schedules (Manhattan Bus Cycle and UDDS). Simulations were conducted using our LFM powertrain simulator which was developed in MATLAB/SIMULINK. The energy storage systems considered here include battery only, as well as various combinations of batteries and ultracapacitors. Simulation results show that the addition of ultracapacitors greatly improves performance parameters such as battery C-rates, energy throughput, and energy storage heat generation at comparable cost and weight.

In-Use Fuel Economy of Hybrid-Electric School Buses in Iowa

ABSTRACT Although it is much safer and more fuel-efficient to transport children to school in buses than in private vehicles, school buses in the United States still consume 822 million gal of diesel fuel annually, and school transportation costs can account for a significant portion of resource-constrained school district budgets. Additionally, children in diesel-powered school buses may be exposed to higher levels of particulates and other pollutants than children in cars. One solution to emission and fuel concerns is use of hybrid-electric school buses, which have the potential to reduce emissions and overall lifecycle costs compared with conventional diesel buses. Hybrid-electric technologies are available in the passenger vehicle market as well as the transit bus market and have a track record indicating fuel economy and emissions benefits. This paper summarizes the results of an in-use fuel economy evaluation for two plug-in hybrid school buses deployed in two different school districts in Iowa. Each school district selected a control bus with a route similar to that of the hybrid bus. Odometer readings, fuel consumption, and maintenance needs were recorded for each bus. The buses were deployed in 2008 and data were collected through May 2010. Fuel consumption was calculated for each school district. In Nevada, IA, the overall average fuel economy was 8.23 mpg for the hybrid and 6.35 mpg for the control bus. In Sigourney, IA, the overall average fuel economy was 8.94 mpg for the hybrid and 6.42 mpg for the control bus. The fuel consumption data were compared for the hybrid and control buses using a Wilcoxon signed rank test. Results indicate that fuel economy for the Nevada hybrid bus was 29.6% better than for the Nevada control bus, and fuel economy for the Sigourney hybrid bus was 39.2% higher than for the Sigourney control bus. Both differences were statistically significant. IMPLICATIONS The results of the research presented in this paper can be readily used by school districts and policy-makers who are interested in purchasing hybrid school buses. Very little information about actual on-road fuel consumption or costs is available. Because the cost of a hybrid bus can be significantly more than the cost of a conventional bus, the information provided in this paper can be very useful for an agency to determine the costs and benefits of a hybrid bus. The information is also useful to researchers who are studying hybrid school and transit buses.

Design and Simulation of FC Plug-in Hybrid Bus with Ultracapacitors

The plug-in hybrid vehicle has been taken as one of the main streams of electric vehicles world wide with the development of battery technology and the remaining obstacles by the fuel cell to be broken through. Fuel cell plug-in vehicle will follow the engine plug-in vehicle because of the more and more strict control of green house gas emission. At this moment, lithium battery is still expensive and safety problem remains. The performance of ultra capacitor has been significantly improved and the price goes down rapidly because of being used on harbor vehicle and mechanical facilities such like container/cargo cranes in-small-batch. It has become a popular ESS for energy regeneration such like the transit buses. The paper will present the advantage and the performance of a FC plug-in hybrid transit bus with ultracapacitors and NiMH batteries. The design and simulation will be covered in the paper.