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Abstract: In this work, an accurate and computationally fast model for liquid water transport within a proton exchange membrane fuel cell (PEMFC) electrode is developed by lumping the space-dependence of the relevant variables. Capillarity is considered as the main transport mechanism within the gas diffusion layer (GDL). The novelty of the model lies in the coupled simulation of the water transport at the interface between gas diffusion layer and gas flow channel (GFC). This is achieved with a phenomenological description of the process that allows its simulation with relative simplicity. Moreover, a detailed two-dimensional visualization of such interface is achieved via geometric simulation of water droplets formation, growth, coalescence and detachment on the surface of the GDL. The model is useful for optimization analysis oriented to both PEMFC design and balance of plant. Furthermore, the accomplishment of reduced computational time and good accuracy makes the model suitable for control strategy implementation to ensure PEM fuel cells operation within optimal electrode water content. [Copyright &y& Elsevier]

Abstract: It has been well documented that water production in PEM fuel cells occurs in discrete locations, resulting in the formation and growth of discrete droplets on the gas diffusion layer (GDL) surface within the gas flow channels (GFCs). This research uses a simulated fuel cell GFC with three transparent walls in conjunction with a high speed fluorescence photometry system to capture videos of dynamically deforming droplets. Such videos clearly show that the droplets undergo oscillatory deformation patterns. Although many authors have previously investigated the air flow induced droplet detachment, none of them have studied these oscillatory modes. The novelty of this work is to process and analyze the recorded videos to gather information on the droplets induced oscillation. Plots are formulated to indicate the dominant horizontal and vertical deformation frequency components over the range of sizes of droplets from formation to detachment. The system is also used to characterize droplet detachment size at a variety of channel air velocities. A simplified model to explain the droplet oscillation mechanism is provided as well. [Copyright &y& Elsevier]

Abstract: The main aim of the paper is to propose hierarchical modeling as a suitable methodology to perform control-oriented analysis of planar solid oxide fuel cells (P-SOFC). At the high level of the hierarchical structure is a one-dimensional, steady-state model, developed referring to the state of the art in the field of SOFC modeling. Validation is conducted via comparison with both experimental tests and standard references derived from literature. In the proposed modeling structure, at the low-level is the control-oriented model, developed on the basis of the information provided by the higher level model and assuming the SOFC behaves as a first-order system. The thermal dynamics is considered dominant with respect to both electrochemistry and mass transfer dynamics. Therefore, SOFC transients are modeled applying the conservation of energy principle (heat balance) to a lumped control volume, including interconnect, electrolyte and electrodes. Due to the lack of suitable experimental data, model accuracy is verified by comparing the simulated fuel cell response to similar data available in literature, generated by means of a physical comprehensive model. Extensive simulations of the fuel cell dynamic behavior are performed to analyze in detail the SOFC dynamics with respect to load changes. Furthermore, an application example is given, dealing with the development of a PI controller to limit temperature rise across the cell within a safe range. [Copyright &y& Elsevier]

Abstract: A control architecture for air to fuel ratio (AFR) control of gasoline engines designed to work with switching and/or wide range oxygen sensors, with the goal of minimizing calibration effort while meeting performance requirements, is described. A high bandwidth, dithered inner-loop reference tracking controller with pre-catalyst oxygen sensor feedback coupled with a low bandwidth setpoint tracking outer-loop with post catalyst oxygen sensor feedback, is used to control engine exhaust and O2 storage in the three-way catalyst (TWC), respectively. A total synthesis inspired design ensures that significant non-linearity in the system is handled through a coordinated and corrective action and expected response blocks in the open-loop, without burdening the closed loop controller. Calibration is achieved offline, through closed loop optimization using genetic algorithms, while simultaneously meeting performance and stability criteria with significantly reduced need for in-vehicle tuning. Experimental results show comparable emissions performance with the stock OEM AFR controller under warmed up conditions over a standard drive cycle. [Copyright &y& Elsevier]