To increase system efficiency and power density, the cathode air path of Polymer Electrolyte Membrane Fuel Cells (PEM FCs) is supercharged using electrically driven air bearing centrifugal ...compressors. To maximize system efficiency, the cathode air supply system must be designed to optimally fulfill the requirements of the PEM FC system while obeying the design constraints imposed by the electric compressor drive and the air bearing system. This article proposes a dedicated design process for PEM FC cathode air compressors. Using physically based component models, the impact of varying cathode stoichiometry and operating pressure on PEM FC system performance is assessed to derive the system efficiency optimal compressor operating strategy. The centrifugal compressor stage is subsequently designed to achieve optimum efficiency on this operating line using meanline performance models and three-dimensional computational fluid dynamics simulations. Novel test procedures and measurement equipment are employed to validate the compressor design. The design process is demonstrated using a PEM FC passenger car application as an example. It is shown that significant performance and efficiency gains are achievable when tailoring the cathode air supply system to the application at hand. In the given example, effective compressor efficiency is increased by Δηeff = 12%. Along with an optimized compressor operating strategy, an overall PEM FC system efficiency gain of Δηsys = 2.7% is achieved.
Proton exchange membrane fuel cells are a promising technology for future transportation applications. However, start-up procedures that are not optimized for low temperatures can lead to the early ...failure of the cells. Detailed CFD models can support the optimization of cold start procedures, but they often cannot be solved in a stable way due to their complexity. One-dimensional (1D) models can be calculated quickly but are simplified so that the behavior of the cells can no longer be determined accurately. In this contribution, a coupling between a 2D CFD model of the gas channels and a 1D model of the Membrane Electrode Assembly (MEA) is realized. This method allows not only to determine the location and amount of the condensed water but also to calculate the exact concentration of the reactant gases along the channels. The investigations show that the concentrations of the gases and the relative humidities in the gas channels are strongly influenced by the current density. It has been found that it is not possible to avoid the formation of liquid water at low operating temperatures by controlling the current density.
To fulfil the CO2 emission reduction targets of the European Union (EU), heavy-duty (HD) trucks need to operate 15% more efficiently by 2025 and 30% by 2030. Their electrification is necessary as ...conventional HD trucks are already optimized for the long-haul application. The resulting hybrid electric vehicle (HEV) truck gains most of the fuel saving potential by the recuperation of potential energy and its consecutive utilization. The key to utilizing the full potential of HEV-HD trucks is to maximize the amount of recuperated energy and ensure its intelligent usage while keeping the operating point of the internal combustion engine as efficient as possible. To achieve this goal, an intelligent energy management strategy (EMS) based on ECMS is developed for a parallel HEV-HD truck which uses predictive discharge of the battery and adaptive operating strategy regarding the height profile and the vehicle mass. The presented EMS can reproduce the global optimal operating strategy over long phases and lead to a fuel saving potential of up to 2% compared with a heuristic strategy. Furthermore, the fuel saving potential is correlated with the investigated boundary conditions to deepen the understanding of the impact of intelligent EMS for HEV-HD trucks.
•Direct use of renewable hydrogen and conversion to methane, methanol, or dimethyl ether.•Large-scale steady-state fuel production using carbon dioxide from biogas.•Simultaneous environmental, ...economic, and technical evaluation.•All four fuels enable significant greenhouse gas and pollutant reductions.•Combustion engine fuels considered result in similar emissions and costs.
Hydrogen (H2) production through water electrolysis is widely discussed as a means of storing renewable electricity in chemical bonds. Hydrogen can be used for transportation in fuel cell vehicles, but it can also be reacted with carbon dioxide (CO2) to form other fuels. While many concepts have been proposed, detailed comparisons of different pathways are still scarce. Herein, we present a technical, environmental, and economic comparison of direct H2 use in fuel cells, and production of methane, methanol, and dimethyl ether (DME) for use in internal combustion engines for light-duty vehicle applications. The scenario considered uses renewable electricity for water electrolysis, and CO2 which is supplied continuously from biogas upgrading. All four fuels enable significant reductions (79–93%) in well-to-wheel greenhouse gas emissions as well as pollutant formation compared to fossil fuels, but they require very cheap H2 to be competitive to fossil fuels, confirming intuitive expectations. While direct use of H2 has obvious advantages (no conversion losses, high efficiency of fuel cells compared to internal combustion engines) in terms of overall electricity consumption, emissions, and fuel cost, its drawbacks compared to the other fuels are the need for an H2 infrastructure, the high fueling pressure, and lower driving range. Among the three combustion engine fuels, DME has the lowest fuel cost and electricity consumption per distance driven because of the more efficient use of H2 in its production, as well as the highest volumetric energy density, while methane has slightly lower greenhouse gas emissions. Cost and energy demand are dominated by H2 supply, meaning that integrated solutions could be more attractive than separate electrolysis and fuel production.
Today's Li-ion battery stringent requirements include high electric currents, large format cells and possibly the use of carbon based current collectors, which would enhance the ...electrochemical-thermal non-uniformities in the cell. Although a number of models have been implemented in order to study such non-uniformities, no efforts have been made to describe the distribution of side reaction rates and their effect on aging distribution. To fill that gap, we developed a pseudo-3D porous electrode electrochemical model that incorporates via first principles the solid-electrolyte interphase (SEI) growth on the anode, which is thought to be a dominant aging mechanism. The model was used to simulate the cyclic behavior of a large format (40 Ah) Li-ion polymer pouch cell with the assumption of a carbon based positive current collector. It was found that SEI growth localization would form in the electrode thickness and planar dimensions during discharging, but would be destroyed during the subsequent charging, so that the associated aging would be uniform upon cycling. This suggests that computationally efficient lumped models could be used to describe the cell aging process associated with the SEI growth on the graphitic anode, which would be ideal for onboard implementations such as in electric vehicle applications.
Hydrogen as carbon-free fuel is a very promising candidate for climate-neutral internal combustion engine operation. In comparison to other renewable fuels, hydrogen does obviously not produce CO2 ...emissions. In this work, two concepts of hydrogen internal combustion engines (H2-ICEs) are investigated experimentally. One approach is the modification of a state-of-the-art gasoline passenger car engine using hydrogen direct injection. It targets gasoline-like specific power output by mixture enrichment down to stoichiometric operation. Another approach is to use a heavy-duty diesel engine equipped with spark ignition and hydrogen port fuel injection. Here, a diesel-like indicated efficiency is targeted through constant lean-burn operation. The measurement results show that both approaches are applicable. For the gasoline engine-based concept, stoichiometric operation requires a three-way catalyst or a three-way NOX storage catalyst as the primary exhaust gas aftertreatment system. For the diesel engine-based concept, state-of-the-art selective catalytic reduction (SCR) catalysts can be used to reduce the NOx emissions, provided the engine calibration ensures sufficient exhaust gas temperature levels. In conclusion, while H2-ICEs present new challenges for the development of the exhaust gas aftertreatment systems, they are capable to realize zero-impact tailpipe emission operation.
The transport sector faces two critical issues: a limited supply of fossil fuels and high greenhouse gas (GHG) emissions. Additionally, the demand for freight transport is steadily increasing, ...ultimately leading to higher GHG emissions. Since these emissions promote climate change, reducing the GHG emissions from the transport sector is necessary. Renewable drop-in fuels can play an essential role in this regard as those are CO2 neutral. Since these fuels come from so-called renewable sources, this represents a way to reduce carbon dioxide emissions from the current vehicle fleet to meet the EU’s Green Deal goals to become climate neutral by 2050. The drop-in fuels from renewable sources and later the purely renewable fuels serve as a bridging technology in this context.
With this in mind, experiments were conducted with a Heavy-Duty Single Cylinder Engine (HD-SCE). The effects of four different renewable fuels or fuel blends – 93% RF/7% UCOME, 60% B0-Diesel/40% RF blend, 70% Diesel/30% Octanol blend and 100% Octanol – on engine performance and raw emissions were studied in comparison to fossil Diesel fuel. The investigations were conducted at three different load points — Rated Power (RP), best Brake Thermal Efficiency (BTE) and Cruise Point, covering all the relevant load points for HD engines. For all load points, the use of renewable fuels resulted in lower carbon dioxide (CO2), hydrocarbon (HC), carbon monoxide (CO) and FSN compared to fossil Diesel due to the fuel-borne oxygen and the lower C/H ratio of these alternative fuels. The blend of 60% B0-Diesel-40% RF shows the highest efficiency due to the paraffinic fuel structure, the fuel-borne oxygen, the higher calorific value, and the high cetane number. 100% Octanol resulted in a reduction in FSN by a factor of 3. All renewable fuels show a GHG emission reduction potential of around 2.5% to 5.5% in the Tank-to-Wheel (TtW) analysis.
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•Renewable fuels meet one or more global fuel standards.•Renewable fuels achieve better efficiency and lower CO2, CO, HC, and smoke emissions.•Smoke emission reduced by a factor of 3 with 100% Octanol fuel.•In the Tank-to-Wheel (TtW) analysis, all the renewable fuels have a GHG reduction potential of around 2.5% to 5.5%.•Renewable fuels could help achieve the EU’s 2050 CO2 emission reduction target without significantly changing the existing vehicle fleets.
Freeze start is a challenge in the commercialization of PEM fuel cells. In this study, ice formation in cell layers is investigated through experiments and simulations. Segmentation of the fuel cell ...on the test bench allows to determine the local distributions of current density and high frequency resistance over the active cell area. The location and timing of ice formation are analyzed in the experiments. It is shown that the formation of ice lenses can be detected by local measurements of the high frequency resistances. Then, a multiphysical CFD model is built and validated with the measurements and the commonalities and differences between the model results and the experiments are studied. It is shown that the model determines the freeze start behavior very well in wide operating ranges. Together with the findings from the experimental investigations, the model will finally be used to investigate local ice formation in detail.
Mechanics plays a crucial role in the performance and lifespan of lithium-ion battery (LIB) cells. Thus, it is important to address the interplay between electrochemistry and mechanics in LIBs, ...especially when aiming to enhance the energy density of electrodes. Accordingly, this work introduces a framework for a fully coupled electro-chemo-mechanical heterogeneous 3D model that allows resolving the inhomogeneities accompanied by electrochemical and mechanical responses of LIB electrodes during operation. The model is employed to numerically study the mechanical degradation of a nickel manganese cobalt (NMC) cathode electrode, assembled in a half-cell, upon cycling. As opposed to previous works, a virtual morphology for a high-energy electrode with low porosity is developed in this study, which comprises distinct domains of active material (AM) particles, the carbon-binder domain (CBD), and the pore domain to resemble real commercial electrodes. It is observed that the mechanical strain mismatch between irregularly and randomly positioned AM particles and the CBD might lead to local contact detachment. This interfacial gap, in combination with the diminishing contact strength over cell cycling, continuously deteriorates the electrode performance upon cycling by impedance rise and capacity drop. In agreement with previous experimental reports, the presented simulation results exhibit that the contact loss mostly takes place in the regions closer to the separator. Eventually, the resulting gradual capacity drop and change in impedance spectrum over cycling, as the consequence of interfacial gap formation, are discussed and indicated.
Within the Cluster of Excellence “Tailor-Made Fuels from Biomass”, a new reaction sequence to transform biomass into 2-methylfuran has been developed. In the present study, the influence of this ...potential biofuel on in-cylinder spray formation and evaporation as well as engine performance is studied experimentally using a direct-injection spark-ignition single-cylinder research engine. The results obtained for 2-methylfuran are benchmarked against investigation on the same engine using conventional research octane number (RON) 95 fuel and ethanol. The in-cylinder spray formation and evaporation process is characterized by high-speed Mie scattering visualizations, indicating quicker evaporation of 2-methylfuran compared to ethanol. Engine experiments support the findings of the optical measurements by revealing excellent combustion stability, especially in cold conditions, combined with a hydrocarbon emission reduction of at least 61 % in the relevant spark timing range compared to conventional fuel. The enleanment capability was also found to be higher by 0.16 units of relative air/fuel ratio. A noticeable drawback resulting from the combustion of 2-methylfuran is higher emissions of nitrogen oxides. The knock resistance of 2-methylfuran at full load is significantly better compared to RON 95, however, worse than ethanol. It allows for a compression ratio increase of more than 3.5 units compared to RON 95. The measured efficiency benefits with a compression ratio increase of 3.5 units range up to 9.9 % at full load.
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