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

Abstract

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 mounted inside the hot-gas exhaust nozzle (recuperator). Through the operation of the system of heat exchangers, 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 heat exchangers 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 heat exchanger efficiency on the aero engine performance especially the engine’s overall efficiency and the specific fuel consumption. More specifically, two different hot-gas exhaust nozzle configurations incorporating modifications in the system of heat exchangers are examined. The results show that significant improvements can be achieved in overall efficiency and specific fuel consumption hence contributing into the reduction of CO2 and NOx 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 LEMCOTEC (Low Emissions Core engine Technologies).

Investigations of the synergy of Composite Cycle and intercooled recuperation

“…This concept is based on the integration and use of a number of heat exchangers, comprising a recuperator system, carefully mounted inside the hot gas exhaust nozzle, in order to avoid induced pressure losses, and an intercooler mounted between the compressor stages, so as to reduce the required compressor work. This concept has been mostly developed by MTU Aero Engines AG and investigated in large European funded research projects such as: CLEAN (Component vaLidator for Environmental-friendly Aero-eNgine), AEROHEX (Advanced Exhaust Gas Recuperator Technology for Aero-Engine Applications), NEW Aero engine Core concepts (NEWAC) and Low Emissions Core-Engine Technologies (LEMCOTEC) [10,11,12].…”

“…The intercooled recuperative engine concept is schematically shown in The heat exchanger consisting the recuperator's installation [10].…”

“…3together with the MTU developed state-of-the-art tubular heat exchanger (HEX) of elliptic tube profile. ISABE 2017 The IR turbofan engine concept, developed by MTU Aero Engines[10].…”

Investigation of the pressure drop inside a rectangular channel with a built-in U-shaped tube bundle heat exchanger

“…As recuperative heat exchangers operate under conditions involving high temperatures and pressure, their thermalmechanical performance is very important (Schonenborn, Ebert, Simon, & Storm, 2006). Also, the additional pressure drops and weights due to the presence of recuperators affects the potential benefit of an innovative thermodynamics cycle; therefore, a lightweight and lowloss compact heat exchanger is essential in the practical application of intercooled recuperative aero-engines (Goulas et al, 2015;Xu, Kypianidis, & Grönstedt, 2013). One of the most promising heat recuperators used in aero-engines is the double-U-shaped tube bundle heat exchanger (Min, Jeong, Ma, & Kim, 2009).…”

Optimization of Heat Exchangers for Intercooled Recuperated Aero Engines

“…Furthermore, the imposed pressure losses affect the potential benefit of the aero engine thermodynamics cycle while the heat exchanger's own weight reduces a part of the thermodynamic cycle efficiency improvement. For these reasons, the optimization of the recuperation system is of critical importance for the beneficial operation of the IRA engine concept, as pointed out in [11][12][13].…”