Enhua Wang

Metal-supported solid oxide fuel cells (MS-SOFCs) hold considerable promise for load-fluctuating applications, yet their internal transient multiphysics mechanisms remain poorly understood. Herein, a high-fidelity 3D transient multiphysics model incorporating realistic structural features is developed to investigate the dynamic response under voltage step perturbations. The results reveal a multi-timescale behavior involving ultrafast electrochemistry, mass-transfer hysteresis, and thermal decoupling. This distinct behavior drives a highly direction-dependent spatiotemporal evolution. Specifically, the rib–channel geometry dominates the width direction through a current-focusing effect, stabilizing the response instantly at the step change. In contrast, mass-transfer consumption prevails axially, decreasing the overpotential difference by >15% during the slow tail; downstream weak diffusion forces lengthen the relaxation time from 50 ms to 260 ms, exposing the region to local mass-transfer limitations. Crucially, within the anode outlet (8–10 cm), the metallic support concurrently buffers gas and homogenizes potential, forming an overpotential saturation plateau that fundamentally decouples overpotential from concentration changes. These findings establish the metallic support as a dual, competing constraint on transport dynamics and spatial coupling, suggesting that tailoring its porosity and thickness is a promising route to mitigate downstream mass-transfer limitations.

Solid oxide fuel cells (SOFCs) are an effective and sustainable energy conversion technology. As operating temperatures decrease, metal interconnects and supports are widely employed in SOFCs. It is critical to apply a protective coat on ferritic stainless steel (FSS) to suppress Cr evaporation and element interdiffusion under high temperatures. Electrophoretic deposition (EPD) is a promising approach for depositing metal oxides on FSS substrate. Here, a method based on 3D multi-physical simulation and orthogonal experimental design was proposed to optimize deposition parameters, including applied voltage, deposition time, and electrode distance. The EPD process to deposit Mn_1.5Co_1.5O₄ particles in a suspension of ethanol and isopropanol was simulated and the effects of these three factors on the film thickness and uniformity were analyzed. The results indicate that applied voltage has the greatest impact on deposition thickness, followed by deposition time and electrode distance. Meanwhile, deposition time exhibits a more significant effect on film unevenness than applied voltage. Additionally, the particle-fluid coupling phenomenon was analyzed during the EPD process. In practice, these deposition parameters must be selected appropriately and the deposition time must be controlled to obtain a uniform coating. The proposed method can reduce cost and shorten the design period.

The high‐efficiency turbine design is of great importance for small‐scale power systems with a high expansion pressure ratio (EPR). A two‐stage counter‐rotating impulse turbine is optional, with the advantages of a high efficiency and a compact size. However, few experimental investigations were reported. The performance characteristics incorporating power output and turbine efficiency against operation parameters need to be revealed. In this study, the off‐design performance of a two‐stage counter‐rotating impulse turbine with a rated power of 1.5 kW is investigated experimentally. The internal flow is analyzed based on a 3D numerical simulation. First, a test rig is set up for the small‐scale Rankine cycle. The performances are estimated under various rotational speeds and mass flow rates. Then, a 3D CFD simulation is employed to investigate the internal flow inside the supersonic nozzle and the flow passages of the two rotors. The effect of the second counter‐rotating impeller is analyzed. The results indicate that the mass flow rate increases almost linearly from 7.2 to 18.5 kg/hr as the inlet pressure rises from 200 to 540 kPa. The isentropic efficiency of the turbine increases as the EPR descends, and the superheated degree ascends and is correlated as a linear function of the reciprocal of EPR and superheated degree. The measured maximum efficiency is 0.574. When the turbine speed ascends, the power proportion of the first impeller increases while the second impeller declines. Because the increment of the impeller 1 is more prominent, the overall power output is enhanced. Meanwhile, the second impeller can improve the power output apparently under the off‐design conditions with a high EPR and a low rotational speed. The power proportion of the second stage reaches 32.59% when the EPR is 52.34 and the speed is 17,201 r/min. In this novel two‐stage counter‐rotating impulse turbine, the exit energy of the first rotor can be recovered effectively by the second rotor thanks to a compact structure because of no stator between the two rotors.

The evolution of Co coating in solid oxide fuel cells (SOFCs) under low and medium temperatures (3O₄ spinel layer formed in the initial exposure of 5 min, which improved the oxidation resistance of 441 steel. After oxidation at 650 °C for 120 h, a Cr₂O₃ layer with a thickness of 0.2–0.4 μm was observed on the surface of bare 441 steel, while the surface oxide scale of Co-coated 441 steel samples was composed of an inner Cr₂O₃ and Fe₂O₃ solid solution (0.1–0.3 μm thick), an intermediate (Fe, Co)₃O₄ layer and an outer Co₃O₄ spinel layer, respectively. The Co-coated 441 steel sample exhibited better electrical properties. After oxidation at 650 °C for 120 h, the area-specific resistance (ASR) of the Co-coated steel was 3.73 mΩ·cm², which was 25.4% lower than that of bare 441 steel as 5 mΩ·cm². Furthermore, the thermal growth process and protection mechanism of Co coating at 650 °C were discussed.

Spark ignition (SI) engines fueled with kerosene have broad application prospects in unmanned aviation vehicles. The knock phenomenon of kerosene in SI engines is a huge challenge, leading to a much lower power output than gasoline engines. In this context, the combustion characteristics of kerosene blending with hydrogen are analyzed numerically regarding the working conditions of an SI engine. First, the ignition delay time of a kerosene/hydrogen mixture is estimated for temperatures of 600–1000 K and pressures of 15–35 bar using the Tay mechanism. The effects of hydrogen addition are evaluated with a ratio of 0–0.4. The sensitivities of the main reactions that affect the ignition delay time are discussed. Then, the laminar flame speed is predicted using the HYCHEM-SK mechanism, and the effects of hydrogen addition on the net reaction rates of the main reactions are analyzed. The results indicate that the ignition delay time is shortened and the laminar flame speed is increased as the hydrogen addition ratio rises. Meanwhile, the ignition delay time decreases except for the NTC range, and the laminar flame speed increases evidently as the temperature rises. In addition, the ignition delay time decreases obviously as the pressure increases with a temperature greater than 750 K. However, the laminar flame speed declines at 600 K and 800 K, while an opposite trend exhibits at 1000 K as the pressure rises. The laminar flame speed increases by 23.85–24.82%, while the ignition delay time only decreases by 4.02–3.59% at 1000 K as the hydrogen addition ratio rises from 0 to 0.4, which will be beneficial for knock suppression.

Organic Rankine cycle (ORC) is an effective technology to harness low-grade energy. Turbine, as a key component of ORC, takes advantages of its high efficiency and compact size compared with other expanders. Currently, developing suitable turbines with a high performance and a low cost is one of the bottlenecks for wide applications of various ORCs. In this context, technical progress on radial inflow turbines (RITs), axial turbines (ATs), and radial outflow turbines (ROTs) is introduced, and loss models used in the preliminary design are compared, especially for small-scale ORCs. RIT is recommended for medium and small ORCs with an expansion pressure ratio of <10. The power outs and rotational speeds of the designed RITs spanned the ranges of 9.3–684 kW and 3000–114,000 r/min with an efficiency of 56.1–91.75%. In comparison, the power outputs and speeds of ATs were 3–2446 kW and 3000–91,800 r/min with an efficiency of 63–89.1%. AT is suitable for large-scale ORCs with a power output of greater than hundreds of kW. However, AT with impulse stages is feasible for small-scale ORCs when the pressure ratio is high, and the mass flow rate is small. The power outputs of the designed ROTs were relatively small, at 10–400 kW with a speed of 7200–42,700 r/min and an efficiency of 68.7–85%. For organic working fluids with a large expansion pressure ratio, ROT might be employed. Conventional mean-line models may neglect the effects of supersonic flow, which will be encountered in many ORC turbines. Therefore, adequate models for supersonic expansion loss and shock loss need to be added. Meanwhile, a proper multivariable optimization algorithm such as a gradient-based or stochastic search method should be selected. Finally, the challenges and potential research directions are discussed. The outcomes can provide some insights for the development of ORC turbines and the optimization of ORC systems.

Hydrogen as an energy carrier is critical for building a zero-carbon emission society. Solid oxide electrolysis cell (SOEC) is a feasible technology for hydrogen production with a high efficiency. Currently, the durability of SOEC systems still needs to be improved and technical issues need to be overcome. Reducing the working temperature is helpful for the lifetime. A good cell design to avoid delamination is also very important. In this study, the performance of a metal-supported intermediate-temperature SOEC is estimated using gadolinium doped ceria Gd_0.1Ce_0.9O_2-δ (GDC) as the main electrolyte. First, a mathematical model is setup for the metal-supported SOEC. The effects of the porosity and tortuosity of the electrodes are analyzed. Subsequently, the influences of the working temperature, pressure, and steam concentration are estimated. Finally, the partial oxygen pressure inside the multi-layer electrolyte is determined and the risk of delamination is discussed. The results indicate that increasing the operation temperature can decrease the activation, concentration, and ohmic overpotentials simultaneously while increasing the pressure also can enhance the performance. Compared with the conventional design of Ceres Power, the new design using 10Sc1CeSZ as the barrier layer can increase the partial oxygen pressure of the GDC layer close to the cathode such that decomposition of GDC is avoided. Meanwhile, the partial oxygen pressure inside the multi-layer electrolyte close to the anode declines and the risk of delamination is reduced. Hence, the new design of the SOEC is beneficial for the durability of metal-supported SOEC.