A Composite Cycle Engine Concept with Hecto-Pressure Ratio

This paper describes research carried out in the European Commission funded Framework 7 project LEMCOTEC (Low Emission Core Engine Technologies). The task involved significant increase in core engine efficiency by raising the overall engine pressure ratio to over 100 (hecto-pressure 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 was 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 turbo compressor, and a low pressure turbine driving the fan. The power plant performance calculations showed radical improvements in thrust specific fuel consumption of 17.5% during cruise. Although engine weight increases correspondingly by 31%, at aircraft level, a fuel burn reduction of 15.2% could be shown for regional operations relative to year 2025 engine technology. The concept is capable of meeting the emission reduction targets for CO2 and NOx aspired to by the LEMCOTEC project and the Strategic Research and Innovation Agenda (SRIA) targets for CO2 in 2035, and for NOx in 2050.