Hybrid Bus Research Articles

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.

Impact of Spanish electricity mix, over the period 2008–2030, on the Life Cycle energy consumption and GHG emissions of Electric, Hybrid Diesel-Electric, Fuel Cell Hybrid and Diesel Bus of the Madrid Transportation System

In spite of the advanced research in automotive technology, and the improvement of fuels, the road transport sector continues to be an environmental concern, since the increase in transport demand is offsetting the effects of these technological improvements. Therefore, this poses the following question: what combination of technology and fuel is more efficient in terms of energy consumption and green house gas (GHG) emissions? To fully address this question it is necessary to carry out a Life Cycle Assessment (LCA). This paper presents a global LCA of 4 buses that run on the following fuel types and technologies: (1) Fuel Cell- Hybrid Bus, (2) Hybrid Diesel-Electric Bus (series configuration), (3) Battery Electric Bus and (4) Combustion Ignition Engine Bus. The impact categories assessed are: primary energy consumption, fossil energy and GHG emissions. Among the principal results, we can conclude that the Global LCA of buses (3) and (1) (which are the more sensitive pathways to the electricity mix variation) have for the 2008–2030 period a room for improvement of 25.62% and 28.16% in terms of efficiency of fossil energy consumption and a potential GHG emission reduction of 28.70% and 30.88% respectively.

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.

동적 계획법을 이용한 직렬형 및 병렬형 하이브리드 버스 시스템 연비 비교

There are lots of studies about hybrid electric vehicles (HEVs) because of the global warming and energy problems. Series and parallel HEVs are the common types of many developing hybrid vehicle types. Series HEV uses engine only as the generator for the battery but parallel HEV utilizes engine for driving and generating of the vehicle. In this paper, backward simulations based on dynamic programming were conducted for the fuel economy analysis of two different types of hybrid transit buses depending on driving cycles. It is shown that there is a relation between the type of HEV and the characteristics of driving cycles. Regarding the aggressiveness, the series hybrid bus is more efficient than the parallel system on highly aggressive driving cycle. On the other hand, the parallel hybrid bus is more efficient than the series system on low aggressive driving cycle. Based on this results of the paper, it is expected to choose more efficient type of the hybrid buses according to the driving cycle.

Urban Transportation Greenhouse Gas Emissions and Their Link with Urban Form, Transit Accessibility, and Emerging Green Technologies

A greenhouse gas (GHG) emissions inventory is estimated at the household level from disaggregated trip data considering all emitting modes. Trip-level GHG emissions are estimated by combining data sources (e.g., origin–destination surveys, vehicle fleet characteristics, transit rider ship data) and by using modeling tools (traffic assignment and GHG models) developed for Montreal, Quebec, Canada. A simultaneous equation model framework is implemented to investigate links between urban form, transit supply, sociodemographics, and travel GHGs, taking into account the issue of residential self-selection. The potential impacts of land use and transit supply strategies with emerging green technology scenarios are then compared with each other. Findings are consistent with the literature; built environment attributes are statistically significant (10% increase in density, transit accessibility, and land use mix results in 3.5%, 5.8%, and 2.5% GHG reductions, respectively), and the number of workers and retirees make important contributions to GHG emissions at the household level (102% increase from adding one worker and 51% decrease from adding one retiree). Also, if the current transit fleet were replaced with electric trains and hybrid buses, transit GHGs would decrease by 32%. If current trends persist in the private motor vehicle fleet, continued improvements in car fuel economy are estimated to reduce car GHGs 7% by 2020. The two most effective strategies for reducing regional and household GHGs appear to be to improve the fuel efficiency of the private motor vehicle fleet and to increase transit accessibility.

HYBRID MODELLING OF AN URBAN BUS

Sophisticated virtual prototyping methods have become a standard in the modern vehicle design process. Unfortunately, in many cases automobile manufacturers (in particular bus manufacturers) still do not take advantage of numerical de­sign techniques, basing instead on intuition and experience. In this paper hybrid modelling of an urban bus is presented. A hybrid bus model links different types of modelling that can be used to perform a wide range of virtual analyses of vehicle static and dynamic behaviour. The major objective of development and usage of a complex model is to reduce a time and cost of vehicle design process improving vehicle quality at the same time. The main advantage instead is a possibility to exploit a model for different performances of vehicle subsystems. A hybrid model representing real vehi­cle behaviour consists of three modelling techniques commonly used in automotive industry: multibody modelling, finite element modelling and multi- port (block) modelling. A full model has been developed via commercial software which ensures its availability among automotive engineers.

To Analyze The Influence Factors on Energy Saving of Hybrid Bus

In order to discuss the different factors, influence on hybrid bus energy saving, we analyzed the collected data information which got when the hybrid bus driving. Discussing the situation that energy consumption and energy recovery when the hybrid operation. At last get the best operational condition when the hybrid bus can play a energy-saving role by analyze the factors such as recovery energy condition, different elevations and different starting ways

Transportation Greenhouse Gas Emissions and its Relationship with Urban Form, Transit Accessibility and Emerging Green Technologies: A Montreal Case Study

This research aims at estimating a GHG emission inventory at the household level using completely disaggregate trip data and taking into account all emitting modes. The impact of urban form (UF) and transit accessibility (TA) characteristics on household level GHG emissions is then quantified and compared to the impact of the introduction of emerging green technologies. Using a large and representative sample of household diaries, trip-level GHG emissions are estimated by combining different sources of data (origin-destination (OD) survey data, vehicle fleet characteristics, transit ridership data, etc.) and by using modelling tools (traffic assignment and GHGs models). Moreover, UF and TA indicators are developed and combined to generate neighbourhood typologies. A simultaneous equation modelling framework is then implemented to investigate the link between UF, TA, socio-demographics, and travel GHGs, taking into account the well known “self-selection” issue. The potential impact of land use and transit supply strategies with emerging green technological scenarios is then compared. Our findings are consistent with the literature, more specifically we have found that the built environment (BE) attributes are statistically significant (10% increase in density, transit accessibility and land-use mix, results in 3.5%, 5.8% and 2.5% reduction in GHG respectively), number of workers and retirees at the household level play an important role in the contribution to GHG emissions (102% increase by adding one worker and 51% decrease by adding a retiree to the household). Moreover, neighbourhood types represented by the combined effects of UF and TS have important effects on GHGs. Also it is found that by replacing transit fleet by electric trains and hybrid buses, the share of transit GHGs would decrease by 32%. With respect to the private motor-vehicle fleet, if current trends persist, the constant improvement of car fuel consumption economy would reduce car GHGs by 7%. According to our results, the two most efficient strategies to reduce GHGs at the regional and household level seem to be the continuous fuel-efficiency improvement of the private motor-vehicle fleet and the increase of transit accessibility.

Parameter Design for the Energy-Regeneration System of Series Hydraulic-Hybrid Bus

This paper simplifies the energy recovery process in the series hydraulic hybrid bus’ energy regeneration system into a process in which the main axle’s moment of inertia drives the secondary element variable delivery pump/motor and brings hydraulic oil from the oil tank to the accumulator. This process enables braking of the vehicle and also allows recovery of energy to the accumulator. Based on the flow equation for the secondary element variable delivery pump/motor and the torque equilibrium equation for its axle, the force equilibrium equation for vehicle braking and the pressure variation and flow continuity equations for the accumulator, simulation studies are conducted to analyze the effects of various system parameters, such as accumulator capacity, displacement of the secondary element variable delivery pump/motor, initial operating pressure of the system, etc. on system performance during regenerative braking. DOI: http://dx.doi.org/10.11591/telkomnika.v10i6.1420

Evaluation of Battery Requirements for Hybrid and Electric City Buses

This paper presents an evaluation of battery requirements for hybrid and electric city buses. Technical specifications of recently developed lithium based batteries and vehicle simulation results are used as basis for the evaluation. The battery requirements are evaluated in terms of power and energy capacity, calendar and cycle life as well as costs. Conventional diesel, parallel and series hybrid, plug-in hybrid, and electric city bus were chosen as different bus applications. The simulation results of the diesel powered city bus were used as reference for performance requirement and a point of comparison in operation cost analysis. Simulations were carried out in four different types of driving cycles. The evaluation shows that lithium based batteries offer sufficient specific power and energy capacity meanwhile requirements for costs and cycle life durability are dependent on the bus application, the driving cycle, and the operation schedule. Especially a power intensive driving cycle can be challenging for the high energy batteries in terms of cycle life. There are also noticeable differences in performance between different battery chemistries. For plug-in hybrid and electric city buses, fast recharge capability can increase significantly the costeffectiveness in bus fleet operation. The operation cost analysis also indicates that the battery cost is more important for the plug-in hybrid and electric buses whereas the initial cost of the bus is a major factor for the charge sustaining parallel and series hybrid buses.

A two-way relationship between multi-level technological change and organisational characteristics-cases involving the development of heavy hybrid buses

This paper analyses inter- and intra-organisational interaction in cases of product development, which involves significantly new technologies that affect core product sub-systems. The analysis shows that in such cases, there is a need to collaborate with suppliers to learn about the new technology. Moreover, provided that the firm's existing technology is still relevant, there is a need to integrate the new technology with existing technologies. Therefore, close supplier interaction has to be associated with close intra-organisational interaction. However, even a case where there is a limited need to integrate the new technology with existing technologies, there is a need to justify the new technology internally and negotiate the process of adopting it within the organisation. The paper thus demonstrates a two-way relationship between organisational characteristics and multi-level technological change. On the one hand, different types of technological changes demand different kinds of R&D organisations and supplier relationships. On the other hand, decisions to implement technological changes are influenced by existing organisational structures and product development philosophies.

Hardware-in-the-loop simulation for the design and verification of the control system of a series–parallel hybrid electric city-bus

Hybrid electric buses have been a promising technology to dramatically lower fuel consumption and carbon dioxide (CO2) emission, while energy management strategy (EMS) is a critical technology to the improvements in fuel economy for hybrid electric vehicles (HEVs). In this paper, a suboptimal EMS is developed for the real-time control of a series–parallel hybrid electric bus. It is then investigated and verified in a hardware-in-the-loop (HIL) simulation system constructed on PT-LABCAR, a commercial real-time simulator. First, an optimal EMS is obtained via iterative dynamic programming (IDP) by defining a cost function over a specific drive cycle to minimize fuel consumption, as well as to achieve zero battery state-of-charge (SOC) change and to avoid frequent clutch operation. The IDP method can lower the computational burden and improve the accuracy. Second, the suboptimal EMS for real-time control is developed by constructing an Elman neural network (NN) based on the aforementioned optimal EMS, so the real-time suboptimal EMS can be used in the vehicle control unit (VCU) of the hybrid bus. The real VCU is investigated and verified utilizing a HIL simulator in a virtual forward-facing HEV environment consisting of vehicle, driver and driving environment. The simulation results demonstrate that the proposed real-time suboptimal EMS by the neural network can coordinate the overall hybrid powertrain of the hybrid bus to optimize fuel economy over different drive cycles, and the given drive cycles can be tracked while sustaining the battery SOC level.

Fault-Tolerant Fuel Cell Hybrid Bus Powertrain Integration

Focusing on Polymer Electrolyte Membrane (PEM) Fuel Cell hybrid Bus (FCB) powertrain integration, this paper presents a quasi-parallel dual-powertrain topology that can enhance powertrain reliability and extend optimization of energy distribution. This paper analyzes the redundancy of three practical topological structures for a dual-powertrain FCB, including a full-parallel structure, a quasi-serial structure, and a quasi-parallel structure. By calculation and comparison, the reliability of the quasi-parallel dualpowertrain structure and its corresponding fault redundancy is shown to be the highest. This paper also carries out an optimization design of FCB powertrain parameters by analyzing the power index and typical Chinese bus cycle. Furthermore, the innovative method of designing power sources is discussed in this paper. Not only power characteristics but also energy characteristics of batteries are fully taken into consideration in this paper. Off-board and on-board experiments verify the feasibility and redundancy of the quasi-parallel dual-powertrain. This research is of reference value for the study of FCB powertrains.

Application of CAN bus hybrid scheduling algorithm in HEV control system

Application of CAN bus hybrid scheduling algorithm in HEV control system

Comparison of In-Use Operating Costs of Hybrid-Electric and Conventional School Buses

Hybrid-electric school buses became available in the US through a national consortium designed to bring hybrid-electric school buses to market by creating enough demand among school districts to encourage manufacturers to invest in development of the technology. A number of school districts in the US joined the HESB project to purchase plug-in hybrid-electric school buses. Sixteen hybrid-electric school buses were purchased and piloted in 11 states. Two of the hybrid-electric school buses were purchased by the Nevada and Sigourney school districts in the state of Iowa, US. In-use fuel economy and electricity operating costs were monitored for the two Iowa hybrid school buses and two control buses (one in each district). Fuel consumption and other operational metrics were calculated and compared for each school district. The hybrid buses were deployed in January 2008 and data were recorded through May 2010. Valuation of the data indicated that the Nevada HESB had 29.6% better fuel economy than the control bus and the Sigourney HESB had 39.2% better fuel economy than the control bus. Electrical costs per mile were also calculated for the two hybrid-electric school buses. Total operating costs per mile were calculated based on fuel use per mile for all buses and electrical costs for the hybrid-electric school buses. The cost to operate the hybrid bus in Nevada was 37 cents/mile while the control bus cost 42 cents/mile, making the hybrid bus 13% less expensive to operate. The hybrid bus in Sigourney was 27 cents/mile while the control bus was 34 cents/mile, making the hybrid bus 21% less expensive to operate. All values are in US dollars.

A Simulation Study of Introduction of Plug-in Electric and Hybrid Buses to an Actual City Route

A Simulation Study of Introduction of Plug-in Electric and Hybrid Buses to an Actual City Route

Design and management of high-performance, reliable and thermal-aware 3D networks-on-chip

Increasing the number of cores over a 2D plane is not efficient in hyper-core systems due to long interconnects. As a viable alternative over the 2D planar chip, 3D integrated technology offers greater device integration and shorter interlayer interconnects. 3D networks-on-chip (NoC)–bus hybrid mesh architecture, which is a hybrid between packet-switched network and a bus, was proposed to take advantage of the intrinsic attributes of 3D ICs. Even though this architecture was proposed as a feasible one to provide both performance and area benefits, the challenges of combining both media (NoC and bus) to design 3D NoCs have not been addressed. In this study, an efficient 3D NoC architecture is proposed to optimise performance, power consumption and reliability of 3D NoC–bus hybrid mesh system. The mechanism benefits from a congestion-aware and bus failure tolerant routing algorithm called ‘AdaptiveZ’ for vertical communication. In addition, the authors propose thermal-aware scheduling strategy in order to mitigate temperature by herding most of the switching activity closer to the heatsink. To estimate the efficiency of the proposed architecture, the system has been simulated using uniform, hotspot 10% and negative exponential distribution traffic patterns. In addition, a videoconference encoder has been used as a real application for system analysis. Compared with a typical stacked mesh 3D NoC, our extensive simulations demonstrate significant power, performance and peak temperature improvements.

Design and characterization of an electronically controlled variable flow rate ejector for fuel cell applications

A variable flow ejector is presented to address the challenge of providing cost-effective recirculation of hydrogen in fuel cell systems. The ejector uses supersonic flow to provide sufficient pressure rise for the Ballard Mark 9 SSL stack used in the University of Delaware’s fuel cell hybrid buses. Details of geometry optimization via computational fluid dynamic simulation, control system design, electronic control implementation, and mechanical design are discussed. Results from testing in the final application are included, showing the ejector’s excellent performance compared to Ballard’s specifications for recirculation flow rate.

Power and area optimisation in heterogeneous 3D networks-on-chip architectures

Three dimensional Network-on-Chip (3D NoC) architectures have evolved with a lot of interest to address the on-chip communication delays of modern SoC systems. However, the vertical interconnections between layers is more power and area hungry compared to 2D interconnections. In this paper we propose area efficient and low power heterogeneous NoC architectures, which combines both the power and performance benefits of 2D routers and 3D NoC-bus hybrid router architectures in 3D mesh topologies. Experimental results show a negligible penalty of up to 5% in average packet latency of 3D homogeneous NoC with bus hybrid routers. The heterogeneity however provides superiority of up to 67% and 19.7% in power and area efficiency of the NoC resources, respectively.

Fleet operator risks for using fleets for V2G regulation

Future fleets of vehicles may include electric vehicles (EVs) or hybrid electric vehicles (HEVs) because of potential fuel savings. Recent demonstration of diesel parallel hybrids in a delivery fleet led to fuel economy improvements, and hybrid bus demonstrations exhibited twice the fuel economy of the conventional bus. Fleet ownership may include management of a fleet of vehicles as small as 10 units and as large as hundreds or thousands. In addition to fuel savings, the newer extended range electric vehicles (EREVs) and pure EVs permit vehicle to grid (V2G) opportunities. These V2G opportunities may present additional revenue for fleets by providing ancillary services to local grid independent system operators (ISOs), provided that the burden of driving and V2G services do not accelerate the degradation of the battery systems in these vehicles. The subject of this study is to determine the financial risks associated with accelerated battery degradation in a V2G-enabled EREV fleet expected to perform ancillary service duty while charging in addition to the normal loads of drive cycle duty. We determine that battery cycle life during V2G duty is a critical parameter, which can determine whether or not the business model is viable.