Exergetic sustainability off-design analysis of variable-cycle aero-engine in various bypass modes

Abstract

For next generation aircraft, Variable Cycle Engine (VCE) is a candidate to fulfil the multi-mission requirements of flight. This new concept is promising to complete deficiencies of conventional low by-pass mixed turbofan engines because the VCE model incorporates different thermodynamic cycles (turbojet and turbofan) on the same system. Namely, having single by-pass (SBM) and double by-pass modes (DBM), these engines can modulate by-pass ratio, ranging from 0.3 to 1.8 during flight with respect to operating condition requirements. In this study, parametric equations for components of the developed VCE model are determined by means of cycle equations of a mixed-flow turbofan with afterburner. The first aim is to compare energetic performance results of the developed VCE with the results of F100-PW-100 (as called F100) used on F-15 or F-16 for SBM and DBM. Secondly, the main goal of this study is to perform second law analysis for the VCE model and compare it with the results of the F100 engine for off-design, at which flight altitude (9–20 km) and Mach number (0.3–1.9) changes. For this aim, thermodynamic data (pressure, temperature, mass flow etc.) of this engine main components are obtained from GasTurb program for above stated flight conditions. On the other hand, exergy analysis along with five sustainability parameters is carried out at SBM and DBM as comparing with those of F100 engine. Off-design analysis shows that the specific fuel consumption (SFC) varies from 19.97 g/kN.s to 28.25 g/kN.s for VCE and from 23.91 g/kN.s to 31.14 g/kN.s for F100 at DBM. Moreover, at SBM, SFC changes from 52.68 g/kN.s to 59.19 g/kN.s for VCE and from 58.04 g/kN.s to 63.57 g/kN.s for F100 throughout the entire flight conditions. As for exergy-based sustainability analysis, exergetic sustainability index (ESI) of the whole VCE is found to be in the range of 0.14 and 0.51 for DBM and to be in the range of 0.26 and 0.38 for SBM. For F100 engine, ESI is calculated to be in the range of 0.10 and 0.39 for DBM and to be in the range of 0.15 and 0.34 for SBM. It is thought that this study can help in understanding the effect of the working cycle on engine performance and sustainability parameters.