Finite-time energy conversion in a hybrid cycle combining electrochemical, combustion and thermochemical recuperation processes

Conversion of fuel chemical energy into electrical and mechanical work in a hybrid cycle combining electrochemical, combustion and thermochemical recuperation (TCR) processes is numerically analyzed. Finite-time thermodynamics is employed to account for the different efficiency dependency on energy conversion rate of each process involved in the cycle. Fuel cell (FC) zero-dimensional (0D) model is employed to simulate the electrochemical reaction in a solid-oxide FC (SOFC), and a finite-speed finite-time thermodynamics (FST-FTT) model of spark-ignition internal combustion engine (SI-ICE) is created for the combustion process simulation. The prediction results show that without TCR, in the range of cycle efficiencies between 50% and 60% there is a potential of power gain by the hybrid cycle compared to the FC. The achievable efficiency levels are much higher if waste heat recovery through TCR is employed. In such a case, the cycle efficiency can reach values above 70% with a significant power gain compared to FC operating along. However, in almost any conditions, a maximal specific power is inferior compared to the ICE.