Performance analysis of a novel SOFC-HCCI engine hybrid system coupled with metal hydride reactor for H₂ addition by waste heat recovery

Abstract

A novel SOFC-HCCI engine hybrid power generation system fueled with alternative fuels is proposed and modeled in this paper. The steady-state modeling shows that it is feasible to use SOFC anode off-gas as the downstream HCCI engine fuel for additional power generation under certain fuel utilization and operating temperature. Through parametric and exergy analyses, it is found that the hybrid system without additional H2 can achieve a net electrical efficiency of approximately 59% and an exergy efficiency of 57%, slightly higher than the SOFC-GT hybrid system. In this hybrid system, the components of HCCI engine and its exhaust gas dominate the exergy destruction, which contributes nearly 75% but has a relatively low contribution to the total power. Based on this, the methods of recycling exhaust gas waste heat to drive hydrogen desorption of metal hydride as H2 addition for HCCI engine and H2 recirculation for SOFC anode off-gas are suggested to significantly improve the system overall efficiency due to the consideration of thermal efficiency. The high overall efficiency up to 79.54% and fuel flexibility demonstrate that the novel hybrid system is a promising energy conversion system.