Modeling the performance and emissions of a steam injected water recovering turbofan engine

Abstract

The increase in air traffic creates the need for more efficient aircraft. Current design trends of increasing efficiency and reducing fuel consumption also lead to an increase in NOx emissions. Environmental considerations and regulations create a demand for aircraft engine technology with NOx emissions lower than that of current engines. The Steam Injected Water Recovering Turbofan engine is proposed; it injects steam before the combustion chamber and recovers it through condensation in a heat exchanger. Moreover, the cycle recovers more heat from the exhaust gasses, using them as a heat source in a Rankine cycle. The SIWRT was modeled in NPSS in collaboration with GKN Aerospace Sweden AB, to better understand this configuration. A new method was devised to model heat exchanger performance, referred to as a 'variable Cp NTU', capable of taking into account phase change. This new method was verified and partially validated. The engine was studied in a range of water to air of 1% to 7%. It was determined that it is capable of reducing thrust specific fuel consumption by up to 8\% and NOx emissions by up to 66% compared to a conventional future turbofan. Increasing WAR leads to an increase in the fan bypass ratio (FBPR) mostly by reducing the core size. The SIWRT displays design trends similar to conventional turbofan when varying overall pressure ratio, combustor outlet temeperature, and fan pressure ratio. At top of climb the condenser was not able to condense enough water for the engine to self sustain, thus extra water was supplied through an on board reservoir. The research questions were answered, and concluding remarks with suggestions for future work were provided.