Thermodynamics Cycle Analysis, Pressure Loss, and Heat Transfer Assessment of a Recuperative System for Aero-Engines

Aiming in the direction of designing more efficient aero-engines, various concepts have been developed in recent years, among which is the concept of an intercooled and recuperative aero-engine. Particularly, in the area of recuperation, MTU Aero Engines has been driving research activities in the last decade. This concept is based on the use of a system of heat exchangers (HEXs) mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of HEXs, the heat from the exhaust gas downstream the LP turbine of the jet engine is driven back to the combustion chamber. Thus, the preheated air enters the engine combustion chamber with increased enthalpy, providing improved combustion and by consequence, increased fuel economy and low-level emissions. If additionally an intercooler is placed between the compressor stages of the aero-engine, the compressed air is then cooled by the intercooler; thus, less compression work is required to reach the compressor target pressure. In this paper, an overall assessment of the system is presented with particular focus on the recuperative system and the HEXs mounted into the aero-engine's exhaust nozzle. The herein presented results were based on the combined use of CFD computations, experimental measurements, and thermodynamic cycle analysis. They focus on the effects of total pressure losses and HEX efficiency on the aero-engine performance especially the engine's overall efficiency and the specific fuel consumption (SFC). More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of HEXs are examined. The results show that significant improvements can be achieved in overall efficiency and SFC, hence contributing to the reduction of CO₂ and NO_x emissions. The design of a more sophisticated recuperation system can lead to further improvements in the aero-engine efficiency in the reduction of fuel consumption. This work is part of the European funded research program Low Emissions Core engine Technologies (LEMCOTEC).