Università degli studi di Modena e Reggio Emilia

Hydrogen-fueled fuel cells are considered one of the key strategies to tackle the achievement of fully-sustainable mobility. The transportation sector is paying significant attention to the development and industrialization of proton exchange membrane fuel cells (PEMFC) to be introduced alongside batteries, reaching the goal of complete de-carbonization. In this paper a multi-phase, multi-component, and non-isothermal 3D-CFD model is presented to simulate the fluid, heat, and charge transport processes developing inside a hydrogen/air PEMFC with a serpentine-type gas distributor. Model results are compared against experimental data in terms of polarization and power density curves, including an improved formulation of exchange current density at the cathode catalyst layer, improving the simulation results’ accuracy in the activation-dominated region. Then, 3D-CFD fields of reactants’ delivery to the active electrochemical surface, reaction rates, temperature distributions, and liquid water formation are analyzed, and critical aspects of the current design are commented, i.e., the inhomogeneous use of the active surface for reactions, limiting the produced current and inducing gradients in thermal and reaction rate distribution. The study shows how a complete multi-dimensional framework for physical and chemical processes of PEMFC can be used to understand limiting processes and to guide future development.

The recent trend towards the decarbonization of the energy system has renewed the scientific community's interest in fuel cells. These devices have the potential to eliminate, or greatly reduce, the production of greenhouse gases. Polymeric Electrolyte Membrane Fuel Cells (PEMFC) are among the most promising technologies in this regard, being suited for various applications in stationary power plants, vehicles, and portable power devices. The critical issues in PEMFC are the limitation of oxygen transport through the air cathode and water management at high current density operation, which could be largely limited by modifying the design of the reactant supplier channels. In this paper, a three- dimensional CFD approach is used to compare straight and interdigitated flow fields, focusing on the increased current density and improved water management in the diffusion and catalyst layers for the interdigitated design. The simulation results show that the fluid is forced to flow through the porous layers, promoting a convection-type transport, leading to better water removal from the porous layers as well as to increased transport rates of reactants/products to/from the catalyst layers. This leads to reduced concentration overpotentials, and it shows the potential of simulation-driven design for high energy density PEMFC systems.

The growing energy demand is inevitably accompanied by a strong increase in greenhouse gas emissions, primarily carbon dioxide. The adoption of new energy vectors is therefore seen as the most promising countermeasure. In this context, hydrogen is an extremely interesting energy carrier, since it can be used as a fuel in both conventional energy systems (internal combustion engines, turbines) and in Fuel Cells (FC). In particular, PEM (Polymeric Electrolyte Membrane) FC are given growing attention in the transportation sector as a Life-Cycle viable solution to sustainable mobility. The use of 3D CFD analysis of for the development of efficient FC architectures is extremely interesting since it can provide a fast development tool for design exploration and optimization. The designer can therefore take advantage of a robust and accurate modelling in order to define and develop fuel cell systems in a more time-efficient and cost-efficient way, to optimize their performance and to lower their production costs. So far, studies available in the scientific literature lack of quantitative validation of the CFD simulations of complete PEM fuel cells against experimental evidence. The proposed study presents a quantitative validation of a multi-physics model of a Clearpak PEM cell. The chemistry and physics implemented in the methodology allow the authors to obtain both thermal and electrical results, characterizing the performance of each component of the PEM. The results obtained, compared with the experimental polarization curve, show that the model is not only numerically stable and robust in terms of boundary conditions, but also capable to accurately characterize the performance of the PEM cell over almost its entire polarization range.

The ever-increasing quest for sustainable mobility is pushing the automotive sector towards electric-based technologies, allowing the reduction of localized emission sources in highly populated urban areas. Among the many possible solutions, Proton Exchange Membrane Fuel Cells (PEMFC) have the potential to de-carbonise the automotive sector without the range anxiety of present and future batteries. The interaction between physical and chemical processes in PEMFC is crucial to their maximum attainable efficiency, albeit the complexity of such interplay still limits a complete understanding of the governing processes. In this paper a canonical PEMFC from literature is simulated using 3D-CFD, and results are compared against experiments. A Eulerian multi-phase/multi-physics non-isothermal framework is used to account for both fluid (gas channels, porous gas diffusion layers) and solid (bi-polar plates, membrane), as well as for electrochemical and sorption reactions. The model is also able to account for the heat balance and for the liquid water formation at cathode catalyst layer, as well as to predict the water transport and the membrane hydration state fundamental for high-efficiency operation. Simulations are compared with measurements and polarization curves are analysed for two membrane thicknesses and rib/channel spacing. The study presents the investigation possibilities given by 3D-CFD in the field of PEMFC and how this can be used to design high efficiency fuel cells. The presented numeric analysis shows how the virtual design of high-efficiency PEMFC for the automotive sector can be guided by simulations amongst multiple degrees of freedom, thus aiding the development of innovative PEMFC.

In the optimization of GDI engines, fuel injection plays a crucial role since it can affect the combustion process and, thus, fuel efficiency and pollutant emissions. The challenging task is to obtain the required fuel distribution and atomization inside the combustion chamber over a wide range of engine operating conditions. To achieve such goals, flash-boiling can be exploited. Flash-boiling is a phenomenon occurring when fuel temperature exceeds saturation temperature or, similarly, when ambient pressure is lower than saturation one. Under these conditions, which can occur inside the injector or directly in the combustion chamber, the fuel undergoes extremely accelerated breakup and quickly evaporates. The proposed manuscript shows the application of an alternative flashboiling model, recently implemented by Siemens-PLM in STAR-CD V.2019.1, to be applied in 3D-CFD Lagrangian simulations of GDI sprays. Results are validated against experimental data, provided by the SprayLAB of the University of Perugia, on a single-hole research injector. The new flash-boiling model consists of three main parts: an atomization model able to compute droplet initial conditions and the overall spray cone angle; an evaporation model and, finally, a droplet break-up model; the last two models are designed to simulate all the physical events occurring when droplets are injected into the combustion chamber. As for the investigated operating condition, vessel pressure and temperature are 40 kPa and 293K, respectively; as for the fuel (n-Heptane) temperature, it ranges from 303.15 K to 393.15 K, on equal injection pressure (10 MPa). The numerical-experimental comparison is carried out in terms of liquid penetration, imaging, and droplet sizing.