Impact of Liquefied Natural Gas usage and payload size on Hybrid Wing Body aircraft fuel efficiency

Abstract

This work assessed Hybrid Wing Body (HWB) aircraft in the context of Liquefied Natural Gas (LNG) fuel usage and payload/range scalability at three scales: H1 (B737), H2 (B787) and H3 (B777). The aircraft were optimized for reduced fuel burn and airframe noise at approach, based on NASA N+3 goals for the 2030 timeframe. Well-to-wake greenhouse gas emissions for LNG from conventional sources were estimated to be 16% lower than conventional Jet A. Minimally insulated in-wing storage was shown to reduce HWB wing loading and improve fuel burn by 7-12%. Improvements were based on 16% higher fuel specific energy, 17% lower skin friction drag through wall cooling on the wing bottom and 11-16% lower SFC through alternative cycles. Considerations were made for 1% insulation/fuel weight and 39% additional fuel volume but secondary systems and icing issues were not examined. Though technologically viable, significant developmental hurdles, infrastructure demands and safety risks would need to be overcome before these benefits could be achieved. The global optimization framework was presented using a hybrid genetic algorithm for simultaneous optimization of airframe/propulsion/operations. Due to cabin aisle height restrictions, unusable white" space for the H1 designs resulted in excessive empty weight fractions. However the design achieves 45% lower fuel burn than the B737-800 due to its all lifting configuration, advanced propulsion system and assumed structural advancements. The H2 and H3 designs mitigated this drawback by carrying increased payload in a larger, more efficiently packaged centerbody with H3 fuel burn being 52-56% lower than the B777-200LR. However as airport span constraints for the B777 class aircraft were reached, the scaling performance was observed to asymptote with lower improvement from H2 to H3, as compared from H1 to H2.