Fuel Cell Stack and Fuel Cell Powertrain for Automotive Application

<div class="section abstract"><div class="htmlview paragraph">Sustainable mobility is a pressing challenge for modern society. Electrification of transportation is a key step towards decarbonization, and hydrogen Fuel Cell Hybrid Electric Vehicles (FCHEVs) offer a promising alternative to Battery Electric Vehicles (BEVs), especially for long-range applications: they combine a battery system with a fuel cell, which provides onboard electric power through the conversion of hydrogen. Paramount importance is then given to the design and sizing of the hybrid powertrain for achieving a compromise between high performance, efficiency, and low cost.</div><div class="htmlview paragraph">This work presents a Hardware-in-the-Loop (HIL) platform developed for designing and testing the powertrain layout of an FCHEV. The platform comprises two systems: a simulation model reproducing the dynamics of a microcar and a hardware system for the fuel cell hybrid electric powertrain. The former simulates the vehicle's behavior, while the latter is composed of a 2kW real fuel cell stack and a 100Ah Li-ion battery pack. This element is used for real-time testing of the hybrid powertrain, using a programmable power supply that emulates the vehicle and motor load request.</div><div class="htmlview paragraph">Two fuel cell stack configurations have been analyzed by applying a linear scale-up approach (2kW and 4kW) and tested on an acceleration and deceleration driving cycle, representative of the microcar application; a simple fuzzy logic control strategy has been chosen for the test.</div><div class="htmlview paragraph">The system's performances have been evaluated and deeply analyzed in terms of component behavior and energy efficiency. The results demonstrate that the 4kW stack configuration scores a nearly 5% higher efficiency than the 2kW stack, mainly operating in the lower current regions corresponding to higher efficiencies. The improvements can then be translated into an increase in the vehicle's estimated range, more than balancing the increased weight burden of nearly 10kg. By enabling the possibility to consider and test the real behavior of powertrain components, the HIL platform has proven to be an effective tool for design purposes.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Faced with one of the greatest challenges of humanity – climate change – the European Union has set out a strategy to achieve climate neutrality by 2050 as part of the European Green Deal. Life Cycle Assessment (LCA), which among other aspects identifies climate change effects, is an important tool to assess the environmental characteristic of sustainable technologies or products to fulfill this ambitious target.</div><div class="htmlview paragraph">In this context, research is presented that examines the ecological sustainability impacts of a metallic vs a composite bipolar plate made of innovative graphite-compound based foils for fuel cell applications. A bipolar plate is a central component of the fuel cell stack to ensure efficiency and durability. For this purpose, a LCA is performed for both bipolar plate materials. This assessment follows the methodology of DIN EN ISO 14040/44 and the EU Product Environmental Footprint framework. Focusing on cradle-to-gate system boundary conditions, the research emphasizes the manufacturing processes with the relevant material and energy flows. Dealing with uncertainties in the energy supply chain, a comprehensive sensitivity analysis is conducted defining current and future energy scenarios with various shares of renewable and fossil energy carriers. Furthermore, the impact of different material production locations on the outcome of the LCA is investigated, considering changing geopolitical conditions. To assess also the effect on a fuel cell stack, the study continues with a cradle-to-gate evaluation of the fuel cell system. Afterwards, to also consider the complete lifetime of a fuel cell vehicle, the study is extended to cradle-to-grave system boundary conditions for a C-segment SUV. Besides the evaluation of the global warming reduction potential, the study deals with the impact of the production processes of both bipolar plates on other impact categories like freshwater eutrophication or acidification. The investigations have shown that the use of foil-based graphite-compound bipolar plates can reduce the global warming potential by up to 75% compared to conventional steel bipolar plates.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the quest for reduced cost and shorter development times for fuel cell systems in industrial applications, two major issues arise. First, the electrochemical behavior of fuel cell systems is inherently difficult to predict. Second, testing fuel cell systems is resource intensive. These issues compound: Setting up an accurate model of a fuel cell system incurs long testing periods for model validation. Further, it does not guarantee acceptable results outside the tested range or for other membrane electrode assembly compositions.</div><div class="htmlview paragraph">To mitigate these two major issues an X in the Loop concept is proposed. Essentially, this is the direct integration of the test sample, here a single fuel cell, into the modelling environment of the whole system. In practice, two strategies with different levels of integration are defined.</div><div class="htmlview paragraph">The first strategy consists of initially deducing the operating parameters of the sample cell from the fuel cell system model. Then, setting them to the sample cell in the test bench. The response of the test sample is finally used to validate the designed system or update the parameters of the fuel cell model.</div><div class="htmlview paragraph">The second strategy is a step further towards the integration of the test sample into the model. Here, the core model of the fuel cell inside the fuel cell system model is completely replaced with the test sample, reducing the need for an accurate electrochemical model while improving the prediction of the behavior of the fuel cell system.</div><div class="htmlview paragraph">Compared to previously proposed testing concepts, here the balance of plants is directly integrated through a digital emulator, leading to a closer representation of the complete system. Furthermore, the test bench results are looped back to the model at run-time leading to a closer match between testing conditions and the real world as well a reduced impact of inaccuracies in the modelling of the fuel cell.</div><div class="htmlview paragraph">On the way to realizing this goal, an experimental test bench capable of showcasing working prototypes of the proposed operating strategies has been built.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper addresses challenges in current Fuel Cell Stack Buses and presents a novel Fuel Cell Electric Vehicle Bus (FCEV-Bus) powertrain that combines fuel cells, ultra-capacitors, and batteries to enhance performance and reliability. Existing Fuel Cell Stack Buses struggle with responsiveness, power fluctuations, and cost-efficiency. The FCEV-Bus powertrain uses a Fuel Cell stack as the primary power source, ultra-capacitors for quick power response, and batteries for addressing power variations. Batteries also save costs in certain cases. This combination optimizes power management, improves system efficiency, and extends the FCEV-Bus's operational life. In conclusion, this paper offers an innovative solution to overcome traditional fuel cell system limitations, making FCEV-Buses more efficient and reliable for potential wider adoption.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Increasing concerns due to global warming have led to stringent regulation of greenhouse gas (GHG) emissions from diesel engines. Specifically, for GHG phase-2 regulation (2027), more than 4% improvement is needed when compared to phase-1 regulation (2017) in the light heavy-duty (LHD) diesel engine category. At the same time, California Air Resources Board (CARB) and Environmental Protection Agency (EPA) have proposed the new Low NOx standards that require up to 90% reduction in tailpipe (TP) NOx emissions in comparison to the current TP NOx standards that were implemented in 2010. In addition, CARB and EPA have proposed new certification requirements – Low Load Cycle (LLC) and revised heavy-duty in-use testing (HDIUT) based on the moving average window (MAW) method that would require rigorous thermal management. Hence, strategies for simultaneous reduction in GHG and TP NOx emissions are required to meet future regulations.</div><div class="htmlview paragraph">This paper presents potential pathways to achieve the GHG phase-2 and the ultra-low NOx (ULN) regulations with minimum changes in engine design, while meeting the constraints that need to be considered for engine performance stability, component durability, and vehicle drivability. Experimental evaluations were performed focusing on transient cycles such as heavy-duty Federal Test Procedure (hereafter referred as FTP), LLC, and custom transient cycles for HDIUT assessment. We used a model-year (MY) 2021 production Isuzu diesel engine and an advanced dual-dosing aftertreatment system comprising of a close-coupled SCR (ccSCR), diesel oxidation catalyst (DOC), diesel particulate filter (DPF), selective catalytic reduction (SCR), and Ammonia Slip Catalyst (ASC). Conventional thermal management techniques such as multi-injection, intake, and exhaust throttling were implemented to achieve the emissions targets. In addition to the proposed system design, this paper presents following test results from a full-scale system evaluation: <ol class="list nostyle"><li class="list-item"><span class="li-label">1</span><div class="htmlview paragraph">Achieve rapid and sustained turbine-out exhaust temperatures (>200°C) while meeting the engine-out emissions constraints for soot and total hydrocarbon (THC) emissions.</div></li><li class="list-item"><span class="li-label">2</span><div class="htmlview paragraph">A summary of TP NOx, TP N2O and GHG emissions over a composite FTP and LLC.</div></li><li class="list-item"><span class="li-label">3</span><div class="htmlview paragraph">HDIUT assessment results and observations for LLC and custom transient cycles.</div></li><li class="list-item"><span class="li-label">4</span><div class="htmlview paragraph">Robustness evaluation of TP NOx emissions for composite HDT, LLC and custom transient cycles by imposing component variations.</div></li></ol></div></div>

<div class="section abstract"><div class="htmlview paragraph">In the future, conventional powertrains will increasingly be supplied by sustainable energy sources. Long-haul freight transport requires efficient energy storage and the ability to refuel quickly. For this reason, hydrogen-powered PEM fuel cells are being discussed as a future energy source for long-distance vehicles. However, there are numerous challenges in packaging, system cooling and service life. Above all, the dissipation of the fuel cell’s heat losses places high demands on the design of the cooling system due to the relatively low operating temperature.</div><div class="htmlview paragraph">In the presented study, a complete generic drive train of a long-distance commercial vehicle was set up within a suitable simulation environment to investigate the required sizes of the fuel cell stack, the HV battery, the hydrogen tanks, and the cooling circuit. The thermodynamic and electrochemical data that was necessary to describe the stack, the BoP components, the battery, the coolers, and the drivetrain components were taken from the literature or similar applications.</div><div class="htmlview paragraph">Afterward, the requested propulsion power, fuel consumption, and cooling demand were analyzed for constant vehicle speed and representative driving cycles. Mountainous highway passages, as typically occurring in the Alpes, were investigated for different ambient temperatures. Detailed loss analyses were carried out for the whole powertrain and visualized in Sankey diagrams.</div><div class="htmlview paragraph">The results revealed challenging thermal management at high ambient temperatures that may result in degrading fuel cell power when crawling uphill with low vehicle speed. However, the potential and suitability of PEM fuel cells for sustainable long-haul transport could be clearly demonstrated.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the face of the pressing climate crisis, a pivotal shift towards sustainability is imperative, particularly in the transportation sector, which contributed to nearly 22% of global Greenhouse Gas emissions in 2021. In this context, diversifying energy sources becomes paramount to prevent the collapse of sustainable infrastructure and harness the advantages of various technologies, such as Fuel Cell (FC) Hybrid Electric Vehicles. These vehicles feature powertrains comprising hydrogen FC stacks and battery packs, offering extended mileage, swift refueling times, and rapid dynamic responses. However, realizing these benefits hinges upon the adoption of a rigorously validated simulation platform capable of accurately forecasting vehicle performance across diverse design configurations and efficient Energy Management Strategies. Our study introduces a comprehensive microcar hybrid prototype model, encompassing all subsystems and auxiliaries. This model incorporates a validated FC stack Digital Twin, alongside an experimentally characterized Li-Ion Battery Pack, thus faithfully representing the real prototype. Moreover, the integration of this model has proven indispensable for design optimization, enabling precise performance estimation across various powertrain configurations. After the analysis of the experimental Pulse Discharge test and the calibration of the battery equivalent circuit with three RC branches, we comprehensively examined both single (2-kW) and parallel (4-kW) architectures, utilizing two FC stacks, on a reference driving cycle. Notably, the combination of two parallel stacks emerged as the most promising, yielding a 6% increase in estimated range. Our findings underscore the significance of this innovative approach in advancing sustainable transportation solutions.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In this paper, a comparison of three different hybrid powertrains is analysed. The numerical model is used to simulate powertrain behaviour in rail application, on a pre-set drive cycle, composed of many acceleration and decelerations, in order to test the components features.</div><div class="htmlview paragraph">The numerical model is dynamic and it is implemented in Matlab-Simulink environmental.</div><div class="htmlview paragraph">A proton exchange membrane fuel cell (FC) is used; it is the most used in transport applications, thanks to its lower temperature compared to the other fuel cell types, which allows fast start up operation and rapid demand changes. A standard supercapacitor (SC), given by higher power density, is utilized as the energy storage system (ESS), Regarding the battery (B), two types are considered, because the battery is used both as prime mover and main component of the ESS; Li-ion batteries are chosen, owing to their good trade-off between specific power and energy.</div><div class="htmlview paragraph">Therefore, three configurations, FC-SC, FC-B and B-SC, are analysed.</div><div class="htmlview paragraph">The vehicle model takes into account other components. The regenerative brake system is used to recover energy during the deceleration phases, and the auxiliary system is modelled in order to consider the consumption due to lighting, air conditioning, etc. The DC/DC converter is used to connect energy sources and load; it is unidirectional for the FC and bidirectional for the other sources. This is because the ESS provides power for the drive cycle and it stores energy provided by the FC (when the power demand is low) and recovered by the regenerative brake (in deceleration operation).</div><div class="htmlview paragraph">In addition, a control system is implemented, able to manage the entire system and set the power output of each source at each instant of time. It works in order to achieve good performance for each energy source, in terms of high efficiency and long lifetime. This means low power variations for the FC and a pre-set interval for the ESS state of charge.</div><div class="htmlview paragraph">At the end, the results achieved by the simulations (such as efficiency, state of charge, and hydrogen consumption) are discussed and analysed for the different configurations.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Transport sector decarbonization is a key requirement to achieve Green House Gases emissions reduction. Future regulations and the large deployment of Low Emission Zones (LEZ) will lead to deep changes in this sector. The green hydrogen appears as a promising fuel, containing no carbon. H2 Internal combustion engine (H2 ICE) offers the opportunities of quick refueling, known reliability, relative low total cost of ownership. It is based on mature manufacturing processes and tools. Hence this solution can be commercialized in a near future, offering a short term pathway to decarbonization and a H2 market growth accelerator.</div><div class="htmlview paragraph">However, hydrogen combustion in air generates NOx emissions, which should be reduced close to zero to fulfill future requirements.</div><div class="htmlview paragraph">The HyMot project gathers seven public and industrial partners to develop an H2 engine for Light Commercial Vehicle (LCV) application offering the same performances as the replaced Diesel Engine. Target is intercity use with access to LEZ. The consortium develop an H2 engine almost from blanksheet which will be integrated in a demonstrator. The minimum air fuel ratio target will be 2.5 on the whole engine map, so that NOx emissions stay at a very low level. This requires a specific air path to reach performance targets, with H2 and vehicle constraints.</div><div class="htmlview paragraph">This paper presents the 0D/1D model developed to design this new air path, define its architecture and choose the most efficient components. We will present the assumptions, the used methodology and the management of the different actuators. The model was used to build a virtual database to size some mechanical elements and the cooling system, define the valve lift and to supply boundary conditions for the combustion chamber and the after – treatment devices. Both static and transient conditions were studied to give some hints to calibration department in advance.</div><div class="htmlview paragraph">The authors are aware that a purely simulation-based study has significant limitations when it comes to characterize the behaviour of an internal combustion engine. Further research will involve an experimental validation step for the results presented here as soon as real engine data are available.</div></div>

<div class="htmlview paragraph">The scope of the hybrid propulsion systems studies that have been developed by FIAT Research Centre, is the energy consumption evaluation in comparison with conventional traction drives.</div> <div class="htmlview paragraph">After a general study on the hybrid propulsion systems, mathematical models have been developed for the evaluation of performances and energy balance.</div> <div class="htmlview paragraph">The construction of a prototype with parallel hybrid propulsion system has been completed to validate the computer simulation models.</div> <div class="htmlview paragraph">Computer and on road tests results are reported.</div> <div class="htmlview paragraph">Criteria used to select the parameters to the optimization of the system are discussed.</div>

<div class="htmlview paragraph">Delphi Automotive Systems and BMW are jointly developing Solid Oxide Fuel Cell (SOFC) technology for application in the transportation industry primarily as an on-board Auxiliary Power Unit (APU). In the first application of this joint program, the APU will be used to power an electric air conditioning system without the need for operating the vehicle engine.</div> <div class="htmlview paragraph">The SOFC based APU technology has the potential to provide a paradigm shift in the supply of electric power for passenger cars. Furthermore, by supplementing the conventional fuel with reformate in the internal combustion engine, extremely low emissions and high system efficiencies are possible. This is consistent with the increasing power demands in automobiles in the new era of more comfort and safety along with environmental friendliness.</div> <div class="htmlview paragraph">Delphi Automotive Systems and BMW were successful in demonstrating an Auxiliary Power Unit (APU) based on Solid Oxide Fuel Cell (SOFC) technology in February, 2001. A SOFC APU generates power using hydrogen and carbon monoxide reformed from fuels such as gasoline, diesel, or natural gas. The proof-of-concept unit and the advantages of using a SOFC APU will be activities in the development of a second generation APU. This development has been targeted towards resolving the fundamental issues with the following key subsystems: fuel cell stack, fuel reformers, and energy and thermal management. Major focus has also been directed at system integration challenges to make a more robust and efficient product.</div>

<div class="section abstract"><div class="htmlview paragraph">Zero emission vehicles are essential for achieving sustainable and clean transportation. Hybrid vehicles such as Fuel Cell Electric Vehicles (FCEVs) use multiple energy sources like batteries and fuel cell stacks to offer extended driving range without emitting greenhouse gases. Optimal performance and extended life of the important components like the high voltage battery and fuel-cell stack go a long way in achieving cost benefits as well as environmental safety. For this, energy management in FCEVs, particularly thermal management, is crucial for maintaining the temperature of these components within their specified range. The fuel cell stack generates a significant amount of waste heat, which needs to be dissipated to maintain optimal performance and prevent degradation, whereas the battery system needs to be operated within an optimal temperature range for its better performance and longevity. Overheating of batteries can lead to reduced efficiency and potential safety hazards, while low temperatures can decrease battery performance and range. The multiple temperature control loops in the thermal system design of the current FCEVs require significant energy for continuous heating and cooling. This is due to the fact that each of them exchanges energy directly with an external source or sink without redistributing energy among themselves. This can lead to energy losses during the heat exchange process. Our goal is to optimize thermal energy usage while maintaining the same performance and efficiency of both battery electric system and the fuel cell stack in a vehicle. In this paper, an analysis of thermal energy utilization of a single system is compared to the exchange of thermal energy across multiple systems, considering various heating and cooling scenarios. We compare our proposed strategy (with redistribution) with the existing strategy (without redistribution) quantitatively with respect to controller effort/ energy spent in achieving thermal target.</div></div>

<div class="htmlview paragraph">While the ZEV program's electric vehicles did not become successful market-driven products, many of the technical advantages of electric vehicles were validated by enthusiastic California consumers. Yet, battery technology has been and continues to be the limiting factor in terms of cost, functionality (range) and durability of EV systems.</div> <div class="htmlview paragraph">The automotive industry has largely moved on to research and development of other approaches to extremely low emissions and reduced fossil fuel consumption. PZEV gasoline vehicles, Hybrid electric vehicles, clean (EPA Tier 2) diesel vehicles and Proton Exchange Membrane (PEM) fuel cell electric vehicles (FCEVs) are the focus of attention.</div> <div class="htmlview paragraph">The purpose of this paper is to explore another possible solution: a battery electric vehicle with a relatively small fuel cell auxiliary power unit (APU) to recharge the battery pack during driving. The attraction of this configuration is the use of a relatively small battery pack (to allow 65 - 110 km of ZEV range) while increasing vehicle range and functionality to be equivalent to conventional vehicles (400 - 650 km). Another key attraction is that a majority of km could be efficiently refueled from the grid allowing low or zero CO<sub>2</sub> power generating technology to be deployed in private transportation without the enormous cost and inefficiency of the H<sub>2</sub> infrastructure.</div> <div class="htmlview paragraph">The combination of Solid Oxide Fuel Cell (SOFC) APU and advanced Lithium Ion battery systems appears to make the fuel cell range extender EV an attractive system in terms of efficiency, weight and (in the midterm) cost. This paper will discuss the product attributes and advantages that such a system would bring to the customer and society and compare SOFC to Proton Exchange Membrane (PEM) fuel cell and other competing APU technologies. This paper will present system level assessment and analysis of the SOFC/Lithium Ion range extender EV applied to a GM EV1 platform.</div>

<div class="htmlview paragraph">The present work concerns the study of the potentialities of high-boost small-displacement C.R. (Common Rail) diesel engines where the compressor and the expander are mechanically disengaged for the purpose of power cogeneration from the exhaust gas. This objective can be achieved by means of advanced concept electrical devices capable of delivering the energy produced by the expander either to the drivetrain transmission or to the even more power-demanding auxiliary equipment of both the engine and the vehicle.</div> <div class="htmlview paragraph">The performance of a small-displacement boosted diesel engine with a common-rail injection system has been predicted by means of a computational code obtained by integrating different in-house non-commercial codes that simulate the intake, combustion and exhaust processes.</div> <div class="htmlview paragraph">The model validation has been carried out by means of the experimental data obtained at Fiat Research Center on a commercial small-displacement C.R. turbocharged diesel engine. The data related to: in-cylinder pressure time-histories, injection-rate distributions, air- and fuel-flow rates, EGR (Exhaust Gas Recirculation) mass fraction, discharge flow coefficients of the intake and exhaust valves, intake- and exhaust-gas pressures as well as engine performance at different speeds and loads. The computational code requires the heat-release distribution and the heat-transfer coefficients as inputs for the simulation of the engine cycle. Therefore, a heat release analysis of the measured in-cylinder pressure was performed and the heat-transfer coefficients in the model were adjusted so that the computed in-cylinder pressure matched the measured one.</div> <div class="htmlview paragraph">After calibration, the model was applied to the analysis of the engine performance at <b>A/F</b><sup><span class="xref">1</span></sup> of approximately 19 for different boosting and exhaust pressures as well as for different engine speeds and loads. The compressor and the expander were taken as mechanically disengaged and the maximum boost pressure was chosen so as to comply with an in-cylinder pressure limit of ≈ 180 bar. The engine performance were characterized in terms of the following main parameters: engine torque, power and fuel consumption, expander power output and overall system efficiency. This latter was evaluated as the ratio between the available net power of the whole system, including the supercharger, and the energy supplied by the fuel. It was ascertained that an overall efficiency of the system higher than 45% can be achieved. Moreover, an insight was given into the CO2 and pollutant exhaust emissions.</div>

<div class="section abstract"><div class="htmlview paragraph">In contrast to the currently primarily used liquid fuels (diesel and gasoline), methane (CH<sub>4</sub>) as a fuel offers a high potential for a significant reduction of greenhouse gas emissions (GHG). This advantage can only be used if tailpipe CH<sub>4</sub> emissions are reduced to a minimum, since the GHG impact of CH<sub>4</sub> in the atmosphere is higher than that of carbon dioxide (CO<sub>2</sub>). Three-way catalysts (TWC - stoichiometric combustion) and methane oxidation catalysts (MOC - lean combustion) can be used for post-engine CH<sub>4</sub> oxidation. Both technologies allow for a nearly complete CH<sub>4</sub> conversion to CO<sub>2</sub> and water at sufficiently high exhaust temperatures (above the light-off temperature of the catalysts). However, CH<sub>4</sub> combustion is facing a huge challenge with the planned introduction of Euro VII emissions standard, where stricter CH<sub>4</sub> emission limits and a decrease of the cold start starting temperatures are discussed.</div><div class="htmlview paragraph">The aim of the present study is to develop a reliable kinetic catalyst model for MOC conversion prediction in order to optimize the catalyst design in function of engine operation conditions, by combining the outputs from the predicted transient engine simulations as inputs to the catalyst model. Model development and training has been performed using experimental engine test bench data at stoichiometric conditions as well as engine simulation data and is able to reliably predict the major emissions under a broad range of operating conditions. Cold start (-7°C and +20°C) experiments were performed for a simplified worldwide light vehicle test procedure (WLTP) driving cycle using a prototype gas engine together with a MOC. For the catalyst simulations, a 1-D catalytic converter model was used. The model includes detailed gas and surface chemistry that are computed together with catalyst heat up. In a further step, a virtual transient engine cold start cycle is combined with the MOC model to predict tail-pipe emissions at transient operating conditions. This method allows to perform detailed emission investigations in an early stage of engine prototype development.</div></div>