Investigations of the synergy of Composite Cycle and intercooled recuperation

Abstract

The synergistic combination of two promising engine architectures for future aero engines is presented. The first is the Composite Cycle Engine, which introduces a piston system in the high pressure part of the core engine, to utilise closed volume combustion and high temperature capability due to instationary operation. The second is the Intercooled Recuperated engine that employs recuperators to utilise waste heat from the core engine exhaust and intercooler to improve temperature levels for recuperation and to reduce compression work. Combinations of both architectures are presented and investigated for improvement potential with respect to specific fuel consumption, engine weight and fuel burn against a turbofan. The Composite Cycle alone provides a 15.6% fuel burn reduction against a turbofan. Options for adding intercooler were screened, and a benefit of up to 1.9% fuel burn could be shown for installation in front of a piston system through a significant, efficiency-neutral weight decrease. Waste heat can be utilised by means of classic recuperation to the entire core mass flow before the combustor, or alternatively on the turbine cooling bleed or a piston engine bypass flow that is mixed again with the main flow before the combustor. As further permutation, waste heat can be recovered either after the low pressure turbine – with or without sequential combustion – or between the high pressure and low pressure turbine. Waste heat recovery after the low pressure turbine was found to be not easily feasible or tied to high fuel burn penalties due to unfavourable temperature levels, even when using sequential combustion or intercooling. Feasible temperature levels could be obtained with inter-turbine waste heat recovery but always resulted in at least 0.3% higher fuel burn compared to the non-recuperated baseline under the given assumptions. Consequently, only the application of an intercooler appears to provide a considerable benefit for the examined thermodynamic conditions in the low fidelity analyses of various engine architecture combinations with the specific heat exchanger design. Since the obtained drawbacks of some waste heat utilisation concepts are small, innovative waste heat management concepts coupled with the further extension of the design space and the inclusion of higher fidelity models may achieve a benefit and motivate future investigations.

Aero Engine Concepts Beyond 2030: Part 3—Experimental Demonstration of Technological Feasibility

“…The framework features high flexibility with regards to the synthesis and simulation of unconventional thermodynamic cycles and novel power plant system architectures. While a basis for the FP-CCE simulation and integration has been established already by conceptual design studies of different variants of the CCE concept in the past [15][16][17][18], numerical simulation of the steam injecting engine concept entails further efforts. Indeed, the steam injecting engine concept requires the implementation of additional specific components like steam generator, condenser, liquid water recovery system and pump.…”

A Review of Pressure Gain Combustion Solutions for Aerospace Propulsion

“…The high-pressure compression the high scavenging efficiency in the piston engine, and the following isochoric combustion can lead to significant improvements in efficiency. Kaiser [45] conducted some initial studies on the FP-CCE concept and reports that the overall pressure ratio of this engine can go up to 32.4 at top of climb condition of the aircraft with a maximum thrust specific fuel ratio of 12.78 g/kN-s. It is also reported that at cruise condition, the piston engine NOx emission index estimate is approximately 139.7 g/kg of fuel, and for the sequential combustor, it is 1.3 g/kg of fuel This concept is still in its early stages of development and further studies are required to solve issues of mechanical and scavenging losses, lubrication, mass and size, control, NOx emissions, pulsating flow, and vibrations.…”