This work presents a comparative analysis of hybrid
systems that make use of closed-cycle externally heated
bottoming systems. Two options are considered:
reciprocating (Stirling) engines and supercritical carbon
dioxide turbines. These engines share the common
feature of working on closed cycles with optimised fluids
(H2 and CO2 respectively). However, they differ in their
internal structure: Stirling engines make use of volumetric
machinery whereas the SCO2 system is composed by
turbomachinery. In both cases, the working fluid is
subjected to very high pressure and temperature in the
range of 50-200 bar and 40-650 ºC.
A brief description of both bottoming systems is
provided in the article along with the expected
performance of each case in on-design and off-design
(part load) conditions. The analysis is therefore split into
two stages. First, a comparison is shown for on-design
operation aiming to evaluate the maximum efficiency
attainable by the proposed systems. Second, a
preliminary analysis of off-design operation is presented.
The paper concludes that hybrid systems based on
atmospheric fuel cells and externally heated closed-cycle
bottoming engines have the potential to outperform
conventional pressurised fuel cells and gas turbines
hybrids while preserving the topping system from the
demanding operating conditions of the latter configuratio
