Experimental Test Bench Showcasing an X in the Loop Strategy for Fuel Cell Testing

<div class="htmlview paragraph">Hyundai has developed a Santa Fe fuel cell vehicle (FCV) in which methanol fuel processor is installed and integrated with PEM fuel cell system. Pure hydrogen is produced from the mixture of methanol and water by steam reforming followed by metal membrane purification and is then fed to fuel cell system to generate electrical energy. This system has the advantage of simplifying the integration of fuel cell subsystem and fuel processor subsystem. The operation of brassboard system has been carried out for performance evaluation and the development of fuel cell controller. And then the methanol reforming fuel cell system has been incorporated into electric drive train in the vehicle.</div> <div class="htmlview paragraph">AC induction motor is powered by the hybrid system using fuel cell and a nickel metal hydride battery as energy sources to improve the system efficiency and the acceleration response of the vehicle. The traction motor is connected with the battery and fuel cell that are connected with each other via DC/DC Booster in parallel. This paper summarizes the current status on development of various system components, their integration and vehicle.</div>

<div class="htmlview paragraph">The purpose of this system study was to compare the performance and fuel consumption of a pure fuel cell vehicle (<i>i.e.</i> with no battery included) with an internal combustion engine (ICE) vehicle of similar weight in different drive cycles. Both light and heavy duty vehicles are studied.</div> <div class="htmlview paragraph">For light duty vehicles, the New European drive cycle, NEDC [70/220/EEC], the FTP75 [EPA] and a Swedish driving pattern from the city of Lund [<span class="xref">Ericsson, 2000</span>] are utilised. The fuel consumption for these drive cycles was compared with ICE vehicles of similar weight, an Ibiza Stella 1.4 (year 2000) from Seat and a Volvo 960 2.5 E sedan (year 1995). For heavy duty vehicles, urban buses in this study, two drive cycles were employed, the synthetic CBD14 and the real bus route 85 from Gothenburg, Sweden.</div> <div class="htmlview paragraph">It can be concluded that marked improvements in fuel economy can be achieved for hydrogen-fuelled light and heavy duty vehicles. The fuel consumption of a small fuel cell vehicle was 50% less than the corresponding ICE vehicle in both the NEDC and the FTP75. With proper dimensioning of the system components, e.g. the engine, further reductions in fuel consumption can be achieved. The range of more than 500 km with 5 kg of hydrogen in a 345 bar fuel tank was comparable to an ICE vehicle. If the pressure is raised to 690 bar, a driving range of 600 km could be achieved. As the auxiliary system counteracts the increase in fuel cell efficiency, raising the minimum operating voltage from 0.6 to 0.75 V in a 50 kW fuel cell system, provides only a 5% reduction in fuel consumption. A fuel cell bus operated in the CBD14 and the bus route 85, compared with diesel-fuelled urban bus of similar weight, demonstrates a reduction in fuel consumption of 33 and 37 % respectively.</div>

<div class="section abstract"><div class="htmlview paragraph">The reliability and durability of vehicles are crucial for the acceptance of new technologies by customers. Realistic test methods are necessary to validate or ensure the lifespan of vehicles and their components, particularly regarding specific conditions such as freeze start. This article provides an overview of the current state of research on the effects of freeze starts on the degradation of fuel cells. With this knowledge, relevant operating and boundary conditions for potential damage of the fuel cell are identified (e.g. start temperature, duration in subzero operation, dehydration). The field data from the BMW demonstrator fleet of iX5 Hydrogen Next were analyzed to gain insights into realistic freeze start related stress to the fuel cells. The dynamics of heating rates and the influence of the operating strategy are best represented on a Fuel Cell System (FCS). An experimental setup for a stack centered test on a FCS was developed including a climatic chamber and a subzero coolant supply in this study. The identified automotive conditions could be implemented similarly and reproducibly for the stack. In total of 140 freeze starts with the start stack temperatures between - 7 °C and - 18 °C were performed. These test results and the vehicle data were compared, and the limitations of this accelerated stress test are stated. The advantage of this method is the feasibility to validate the lifetime regarding freeze starts within a period of 1-2 month in 24/7 operation. The occurred problems during test development and their solutions are also described, and suggestions for improvement for less damaging freeze starts process are given.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Fuel cell electric vehicles are expected to support the effort to overcome the economic and ecological challenges in the automotive sector. Just as battery electric vehicles, fuel cell electric vehicles also offer locally emission free mobility. The drive system of fuel cell electric vehicles consists of a fuel cell system, an electric motor, power electronics, a hydrogen storage system as well as a rechargeable energy storage system, typically a battery. The quantified power ratio between the fuel cell system and the rechargeable energy storage system is referred to as the degree of hybridization, although inconsistent definitions are used. As these existing definitions of the degree of hybridization of fuel cell electric vehicles don’t support a distinct differentiation and characterization of the vehicles, a new definition of the degree of hybridization is proposed considering the ratio of the energy contents of the hydrogen storage system and the rechargeable energy storage system, effectively adding a second dimension. The degree of hybridization is then evaluated for existing fuel cell electric vehicles using the proposed definition and enables the characterization and clustering of the different vehicles. While this two-dimensional degree of hybridization can be used as optimization criteria during the design and optimization of fuel cell drive systems, the aforementioned clusters can be assigned to already established qualitative degree of hybridization definitions used to describe types of hybrid electric vehicles. This supports customers to be able to more easily distinguish between different types of fuel cell electric vehicles while also increasing the suitability of the degree of hybridization as an optimization criterion in drive system development.</div></div>

<div class="section abstract"><div class="htmlview paragraph">This paper focuses on the virtual integration and test approach used for the evaluation of an automation system developed for the multifunctional operation of fuel cells in commercial aircraft. In order to accomplish the virtual integration a model of the overall automation system is linked with a dynamic model of the complete fuel cell system. For this purpose a modeling approach for complex physical systems is described in this paper. During virtual testing various simulation runs are executed based on automatically generated test cases, which cover a complete flight mission. For this reason a flight mission is modeled as a Statechart that includes next to time- based flight phases also potential events and malfunctions (e.g. engine flame-out, cargo fire). An algorithm is described, which can find all possible state combinations including parallel event sequences. Afterwards test cases are automatically generated using segmented flight profiles in order to integrate atmospheric pressure and temperature as well as airspeed. During each simulation run so-called evaluation agents analyze and compare certain operational states with corresponding specifications. The global results are visualized using three-dimensional plots. The presented approach is illustrated in this paper using a simple example of a fuel cell system that operates multiple functions during a flight mission.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the context of aviation sector decarbonization, fuel cell hybrid electric aircrafts are a promising alternative to conventional fuels, presenting opportunities for more sustainable and efficient flight. Hence, the present work is focused on an alternative powertrain architecture, wherein a proton exchange membrane fuel cell system cooperates with a lithium-ion battery to fulfil the electrical power demand of a turboprop-based aircraft. Particularly, a mathematical tool is proposed to evaluate both the components size and performance, while a degradation aware rule-based control strategy guarantees an effective power split between the hybridizing components. Such an energy management approach introduces an idling level and a rate limiter to mitigate degradation associated with start-up/shut-down and transient phases, respectively. Moreover, to have a reliable estimation of the vehicle’s fuel economy, while also guaranteeing the correct components dimensioning, the fuel cell system efficiency model accounts for the recent targets on the achievable power density. The methodology has been applied to a realistic mission profile and the validity of the proposed rule-based strategy, which relies on versatile control maps, has been confirmed via benchmarking against dynamic programming results. The use of such a reference optimal controller for validation purposes represented a novelty in the aviation field. Specifically, when considering an electrical degree of hybridization of 0.79, the dynamic programming outputs a fuel consumption 2% lower than the rule-based strategy, ensuring the effectiveness of the latter.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The temperature management of the proton exchange membrane fuel cell cooling system is very important to the stability and life of the engine. The size and cycle switching of the cooling system and the rapid temperature rise of the system are inseparable from the thermostat. In this paper, a simulation model of the fuel cell cooling system is built for a 30KW fuel cell system, and its accuracy is verified by experiments. The temperature fluctuation of the system in the confluence mode is mainly studied, and the error is about 0.9 °C. The influence of the converging mode of the thermostat on the temperature of the cooling system is researched through the simulation platform. Based on the simulation model, the influence of thermostats with different external environments and opening degrees on the size cycle switching of cooling system is predicted, which provides optimization and guidance for the system control strategy.</div></div>

<div class="htmlview paragraph">It is well known how local and global environment issues as well as the consumption and supply of energy are major challenges for the future of our planet.</div> <div class="htmlview paragraph">Just to give an example, transports in Europe today rely for 98% on oil.</div> <div class="htmlview paragraph">Internal combustion engines today are a major cause of global warming and local pollution that causes the closing of most city centres in Europe.</div> <div class="htmlview paragraph">Fuel cells have the potential to replace the conventional power generation technologies mainly promising efficiency improvements which could lead to energy saving and reduction of greenhouse gas emission.</div> <div class="htmlview paragraph">In 2001, CRF (FIAT research center) started together with Nuvera Fuel Cells europe Srl a project to evaluate the exploitation of FC inside the Seicento car, studying different levels of hybridisation: from an APU range extender to a full power fuel cell.</div> <div class="htmlview paragraph">The objective of this paper is to give an overview of the performance evolution of the fuel cell powertrain used in the Seicento prototypes and their integration inside the vehicle power plant. In particular the paper highlights the effectiveness and robustness of the system mainly related to the air and water management developed by CRF and NUVERA. The paper also reports comparison of the Seicento fuel cell vehicle with road testing results among different electric vehicles developed by CRF.</div>

<div class="section abstract"><div class="htmlview paragraph">The growing demand for air transport requires efficient and sustainable power systems to meet the pressing need for decarbonizing the sector. A hybrid unit, consisting of a proton exchange membrane fuel cell system and a lithium-ion battery, is a suitable option due to the advantages of reduced gravimetric and volumetric impacts, along with the flexibility of energy management strategies. This work addresses, using a model-based approach, the issue of integrating these electrochemical devices into the aircraft’s electrical architecture considering both design and energy management aspects. A literature derived DC-DC converter bi-dimensional power map is exploited to investigate scenarios differentiated by the fuel cell system power rating and number of stacks working in parallel such that the DC bus line voltage requirements can be respected. These maps relate the converter’s maximum deliverable power to the input and desired output voltage. The combined design and energy management problem is tackled via a multi-objective optimization supported by a design space exploration based on a full factorial parametric analysis. Therefore, a Pareto front is derived by considering the hydrogen consumption and overall hybrid unit mass as objective functions. As additional contributions, the auxiliaries’ power absorption, heat generated by the stack and resulting cooling load are also estimated, thus providing information for the preliminary sizing of the thermal management system. For the mission profile under consideration, the hydrogen consumption exhibited a variation ranging from 7 kg to 6.7 kg as the fuel cell system rated power increased. On the other hand, a smaller fuel cell system lowers the hybrid unit’s total mass. Particularly, when considering a configuration featuring a 70.5 kW fuel cell system, a single stack and two DC-DC converters, the total mass is estimated to be approximately 237 kg. Therefore, for the reduced impact on the aircraft’s maximal mass, the latter design choice is deemed as the most suitable option to be installed on hybrid aircraft with more electric onboard systems.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the next years, the upcoming emission legislations are expected to introduce further restrictions on the admittable level of pollutants from vehicles measured on homologation cycles and real drive tests. In this context, the strict control of pollutant emissions at the cold start will become a crucial point to comply with the new regulation standards. This will necessarily require the implementation of novel strategies to speed-up the light-off of the reactions occurring in the after-treatment system, since the cold start conditions are the most critical one for cumulative emissions. Among the different possible technological solutions, this paper focuses on the evaluation of the potential of a burner system, which is activated before the engine start. The hypothetical burner exploits the lean combustion of an air-gasoline mixture to generate a high temperature gas stream which is directed to the catalyst section promoting a fast heating of the substrate. In this work, an experimental test bench has been adopted to characterize the thermal transient of the after-treatment system when the burner-like system is activated, monitoring the temperature of the gas flow and the temperature of the metallic walls at different locations. Moreover, a CFD model has been developed to investigate the light-off of the reactions during the initial operation of the burner and the subsequent start of the engine. The model, developed on the basis of the OpenFOAM code, resorts to a multi-region approach, where different meshes are employed to describe the fluid domain and the solid regions, namely the catalytic porous substrates and the metallic walls constituting pipes and canning. Specific submodels are implemented to consider flow resistance, heat transfer, mass transfer and catalytic reactions occurring in the catalyst region. The CFD framework has been initially validated on the experimental data acquired on the test bench. The methodology has been then applied to the preliminary analysis of the catalyst light-off at engine cold start, considering a full exhaust line equipped with burner-like system.</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>

Polymer electrolyte membrane fuel cell (PEMFC) systems for heavy-duty vehicles (HDV) are attracting attention for several reasons including tighter emission regulations and, compared with light duty vehicles (LDVs), possibility of a gradual build-up of hydrogen infrastructure during the market introduction phase, and higher allowable cost (60 $/kWe vs. 30 $/kWe) and Pt loadings.1 However, competing with the incumbent diesel technology requires longer stack lifetimes than for LDVs (30,000 h vs. 8,000 h) and higher efficiencies to compensate for the likely price differential between diesel and hydrogen.2 Heat rejection in fuel cells for HDVs can also be an issue. We conducted simulations to compare radiator heat loads in two propulsion systems for a Class-8 HDV: a 450-hp turbocharged diesel engine, and a hybrid 275-kWe FCS with a 35-kWh battery. The simulations showed that the radiator heat load at rated power is higher for the hybrid propulsion system even though it is 20% more efficient than the diesel engine. Higher heat load combined with lower operating temperature makes heat rejection in an HDV radiator more challenging for the hybrid powertrain. We conducted system analysis to determine the stack operating conditions (cell voltage and temperature) and the radiator fan power required to reject the waste heat in the HDV radiator at rated power. Figure 1 summarizes the important results of the analysis of an FCS with a compressor-expander module (CEM) for air management, 2.5-atm stack inlet pressure, no cathode humidifier, de-alloyed PtCo cathode catalyst supported on a high surface-area carbon, and 0.25 mg/cm2 total Pt loading.3, 4 Figures 1a and 1b show that the heat load and radiator fan power are strong functions of the cell voltage and stack coolant temperature. These indicate a heat transfer limit that sets the minimum coolant temperature which only depends on the cell voltage. For example, at 0.7 V cell voltage, the minimum coolant temperature is 88oC corresponding to 265 kW radiator heat load and 30 kWe fan power. The cell voltage needs to be higher than 0.75 V for stacks that operate below 80oC. Figures 1c and 1d present the net stack power (stack power minus the parasitics including radiator fan power) density and system efficiency (net power produced divided by the lower heating value of H2 consumed) as functions of cell voltage and coolant temperature. Increasing the cell voltage at fixed coolant temperature improves the system efficiency at the expense of lower power density. For a fixed cell voltage, there is an optimum temperature at which the net power density is highest. The net power density is smaller below the optimum temperature because of higher fan power, and above it because of the adverse effects of low relative humidity on Ohmic losses and ORR kinetics. As a reference point, the stack can reach 1200 mW/cm2 gross and 1015 mW/cm2 net stack power density for 0.7 V cell voltage at rated power and 88oC optimum coolant temperature. The projected power density and operating conditions are based on a model formulated using the experimental data for d-PtCo/C cathode catalysts with 0.05, 0.1 and 0.15 mg/cm2 Pt loading. Further work is required to confirm these projections by building and optimizing electrodes with 0.2 mg/cm2 Pt loading. References Marcinkoski, R. Vijayagopal, J Adams, B. James, J. Kopsz, and R. Ahluwalia, DOE Advance Truck Technologies https://www.hydrogen.energy.gov/pdfs/19006_hydrogen_class8_long_haul_truck_targets.pdf L. Borup, A. Kusoglu, K. C. Neyerlin, R. Mukundan1, R. K. Ahluwalia, D. A. Cullen, K. L. More, A. Z. Weber, and D. J. Myers, “Recent Developments in Catalyst-related PEM Fuel Cell Durability,” Current Opinion in Electrochemistry, 21, 192–200 (2020)Ahluwalia, X. Wang and J-K Peng. "Fuel Cell System Modeling and Analysis," 2019 DOE Hydrogen and Fuel Cells Program Annual Merit Review and Peer Evaluation Meeting, Arlington, VA, April 29 - May 1, 2019.K. Ahluwalia, X. Wang, and A.J. Steinbach, “Performance of Advanced Automotive Fuel Cell Systems with Heat Rejection Constraint,” Journal of Power Sources, 309 (2016), 178-191. Figure 1

<div class="htmlview paragraph">The effect of atmospheric pressure on the performance characteristics of a crankcase-scavenged spark-ignition two-stroke cycle engine has been investigated. An air-borne, 350 cc opposed 2-piston engine was tested on an experimental test bench where both the pressure at the inlet manifold and the pressure at the exhaust pipe were controlled separately.</div> <div class="htmlview paragraph">The experimental results were analyzed by using a computer program, the MICE Program, which simulates in detail the various processes occurring inside the cylinder of an internal combustion engine. The computer program has been calibrated by using the measured results at sea-level.</div> <div class="htmlview paragraph">An empirical correlation has been proposed for the correction factor of the engine power in the range of 100 to 44 kPa, where the low pressure corresponds to a standard altitude of 21,000 ft (7 km). The present study suggests that the correction factor is proportional to the ambient pressure raised to a power which depends on the engine speed (between 1 for low and 2 for high engine speed). Previous studies have suggested a power of 9/8 (1.125), their validity, however, was limited to low engine speeds and a minimum ambient pressure of 70 kPa which corresponds to an altitude level of up to 10,000 ft (3 km).</div>

<div class="section abstract"><div class="htmlview paragraph">In today’s world, due to fast depletion of fossil fuel and the increasing CO2 emission, the need to switch to alternate energy sources are higher. Stringent norms on exhaust emissions in IC Engine vehicles implies, very complex after treatment systems. Already many OEMs have refined their development strategies towards phasing out of IC Engines and bringing in Fuel Cell vehicles, Battery Electric Vehicles and Hydrogen IC Engine vehicles. Focus is on Hydrogen for Long Haul vehicles. In this paper cooling system design is demonstrated for Fuel Cell, Battery and Power Electronics system in a Heavy Duty Fuel Cell Electric Truck. Radiator and Fans are selected based on the overall heat rejection and Coolant inlet temperature requirements of components. Cooling system circuit and pump is decided to meet the coolant flow rate targets. High temperature cooling system and Low temperature cooling system are explained in detail. Thermal simulation is done using simulation software KULI. Test results signifies good correlation.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Fuel cell electric vehicles offer an attractive option for decarbonizing long-haul on-road transport. However, there are still several barriers to widespread adoption of hydrogen-fueled fuel cells for this application including system durability and total cost of ownership compared to traditional diesel engines. A primary contributor to fuel cell system costs and maintenance requirements is the air management system. It is common for heavy duty fuel cell electric vehicles to use light-duty automotive air management components which are ill-suited for the requirements of larger, long-haul vehicles. This study focuses on the development of a durable and efficient air management system for heavy duty vehicle applications as part of a cooperative research project funded by the Department of Energy’s Hydrogen and Fuel Cell Technologies Office.1</div><div class="htmlview paragraph">The proposed air management design incorporates a novel two stage filtration system, an innovative water-lubricated bearing and electrically-assisted variable turbine geometry turbocharger, charge air cooler, and humidifier. To achieve the ambitious Department of Energy project goals for efficiency and durability, a system-level optimization approach has been employed using a semi-empirical 1D model. Design optimization of the compressor and turbine wheel geometries yielded a large compressor wheel diameter and small trim to reduce mass flow capacity, resulting in a broad efficiency map and a relatively small turbine wheel diameter with non-radial inlet blade angle suitable for the low temperature exhaust. 1D simulations of the optimized system compared to a baseline e-compressor showed a >40% reduction in required e-motor power at steady-state conditions and a >30% reduction in e-motor energy consumption in a transient cycle.</div></div>