Thermoelectrical-based fuel adaptability analysis of solid oxide fuel cell system and fuel conversion rate prediction

Solid oxide fuel cell (SOFC) has attracted more and more attention for its advantages of high efficiency, low emission, and strong fuel adaptability. However, the fuel adaptability also brings issues for thermoelectric cooperative optimization of SOFC system because different fuel compositions can result in different thermal stresses and system performances. In this paper, the temperature distribution and electrical characteristics of a 1 kW external steam-reforming SOFC system at different power stages are studied based on the 200-hour experimental data obtained from the system fed by hydrogen and methane respectively. The thermoelectric characteristics of SOFC system using hydrogen and methane as fuels with the same output power are further compared. Furthermore, the influences of methane conversion rate (MCR) on the thermoelectric characteristics in SOFC system are analyzed through a mathematical SOFC system model and a Gaussian process regression (GPR) model is constructed to predict the MCR. The results show that, the stack voltage of the SOFC system fed by methane (CH4-SOFC) is lower than that of the SOFC system fed by hydrogen (H-2-SOFC) by 0.59-4.35 V for the hydrogen concentration at the anode is relatively low in the CH4-SOFC system. Meanwhile, the electrical efficiency of the CH4-SOFC system is lower than that of the H-2-SOFC system by 0.85-6.08% in the power range of 300-600 W. In terms of thermal characteristics, the stack temperature gradient on the fuel direction of the CH4-SOFC system is much larger than that of the H-2-SOFC system. Different methane conversion rates (MCRs) in the CH4-SOFC system can shift the stack temperature distribution significantly, and properly increasing the MCR can effectively increase the stack voltage and electrical efficiency. Finally, the GPR model can accurately predict the MCR and the MAPE is 0.030%, which can prevent the deformation and fracture of cells caused by the excessive temperature gradient in the stack when the MCR is too low. This work lays a foundation for system control strategy design in the future, especially SOFC stack thermal management, improving the fuel adaptability of the system and ensuring the safety of the stack temperature.