Impact of Design Constraints on Noise and Emissions of Derivative Supersonic Engines

The propulsion systems used in commercial supersonic transport (SST) aircraft, such as the Concorde, have used repurposed engines or derivative engines based on cores from existing donor engines rather than purpose-designed clean-sheet engines. A similar approach is currently being adopted in the development of new SSTs. Turbomachinery components and cooling mass flow rates in derivative engines are sized by the design cycle of the donor engine and constrain the design of the derivative engine cycle. Here, we identify the constraints imposed by the donor engines and quantify their impact on the specific fuel consumption (SFC), certification noise, and NOx (oxides of nitrogen) emissions index [EI(NOx)] relative to purpose-designed clean-sheet engines. We design and optimize a clean-sheet and derivative engine for a notional 55 metric ton SST proposed by NASA. A clean-sheet engine optimized for SFC results in an approximately 4.5% reduction in SFC, an approximately 2.5-fold increase in EI(NOx), and a 1.2 EPNdB increase in certification noise relative to the derivative engine. Applying a constraint on EI(NOx) to the clean-sheet engine results in an approximately 0.5% reduction in SFC relative to the derivative engine. The work provides a quantitative comparison of clean-sheet purpose-built engines and derivative engines from an environmental perspective that can inform policy makers as they develop updated environmental standards for civil supersonic aircraft.