Design and thermodynamic analysis of solid oxide fuel cells–internal combustion engine combined cycle system based on Two-Stage waste heat preheating and EGR

The integrated solid oxide fuel cell (SOFC)-internal combustion engine (ICE) hybrid system has attracted more and more attention due to its advantages of high efficiency and good response ability. Combined with waste heat recovery (WHR) strategy, the system energy conversion efficiency can be further improved. In this study, a new integrated hybrid power system consisting of SOFC and pilot diesel micro-ignition natural gas engine, with WHR strategy was designed and analyzed. Firstly, the mathematical modeling of each component was established and compared with the experimental results to ensure the reliability of the simulation results. Moreover, the effects of key operating parameters and natural gas mixing with an appropriate amount of hydrogen on improving system efficiency and exergy efficiency were also explored. The results showed that the efficiency of the combined system was higher than each component and improved with the increase in the power distribution ratio of the SOFC and ICE, while descended with the decrease of fuel utilization of the SOFC. Anode exhaust of SOFC had a similar effect on the engine as exhaust gas recirculation, which can significantly reduce NOx emissions. In addition, when the SOFC and ICE had equal power distribution with fuel utilization of 0.7, with adding a 25% hydrogen volume ratio, the exergy efficiency and thermal efficiency of the system increased by 6.01% and 5.8% respectively.