Composite Cycle Engine Concept with Hectopressure Ratio

The investigated concept targets a significant increase in core engine efficiency by raising the overall engine pressure ratio to over 100 (hectopressure ratio) by means of discontinuous cycles allowing for closed volume combustion. To this end, piston engines enable isochoric combustion and augment the conventional Joule/Brayton cycle, thereby producing a composite cycle. An engine concept is chosen based on idealized parametric studies of simplified representations of the cycle as well as qualitative measures embracing weight, size, efficiency, emissions, operational behavior, and the life cycle. The most beneficial mechanical representation of the composite cycle engine in this study features crankshaft-equipped piston engines driving separate piston compressors, a high-pressure turbine driving an axial intermediate pressure turbocompressor, and a low-pressure turbine driving the fan. The powerplant performance calculations show radical improvements in thrust-specific fuel consumption of 17.5% during cruise. Although engine weight increases correspondingly by 31%, a fuel burn reduction of 15.2% can be shown for regional operations at aircraft level relative to year-2025 engine technology. The concept is capable of meeting the emission reduction targets for carbon dioxide and nitrogen oxides aspired to by the Strategic Research and Innovation Agenda targets for carbon dioxide in 2035 and for nitrogen oxides in 2050.