Propulsion system by-pass ratio impact on derivative or new aircraft's optimisation

Abstract

The purpose of this paper is to present a joint Snecma and Aerospatiale study on propulsion system By-Pass Ratio and its impact on aircraft operation and economics. Snecma have created three engines at different BPR with a consistent set of technology. Aerospatiale have evaluated them on two aircraft applications : a derivative long range quad-engine aircraft, a typical short/medium range twin-engine aircraft optimized around each propulsion system with the same set of specifications. The study was developed by both companies with advanced design tools, which allow the comparison of several engine architectures with a sufficient degree of accuracy to drive the selection toward the most promising solution. 4 @ 1% by the American Institute of Aeronautics and Astronautics, h c . AU rights r e ~ e ~ e d . In the past twenty years, engines and aircraft's manufacturers have dedicated enormous resources to improve powerplant thermal and propulsive efficiencies and to improve aircraft range and fuel burn. Each partners were primarily concentrating their efforts to either engine SFC or drag, weight, operability and cost to approach the truth in defining a product. Once the powerplant and the aircraft were defined, the actual installed impact on the operation and operating economics of a given aircraft were determined. This evolutionary process moved the engine designs in the direction of higher By-Pass Ratio (BPR) and higher Overall Pressure Ratio (OPR) with their corresponding impact on compressor discharge and turbine inlet temperatures. Such thermodynamic improvements were linked to technological barriers : materials, manufacturing processes, development and retention of increased component efficiencies. These include lightweight materials and improved nacelle lines. On the other side this process moved the aircraft toward high lift-drag ratio. Such aerodynamic design 1 American Institute of Aeronautics and Astronautics improvement was also linked to the capacity to handle fuel capacity, wing area, operational empty weight to keep the objective of improved range and fuel burn. Today, to follow on these technologies will require more investment than ever to assure development of robust, highly reliable systems. The benefit will become less important than in the past, due to the high level of achievement of today aircraft and powerplant and to the asymptote trend of the improvements. A source of improvement is a better integration of the powerplant and aircraft optimisation process in order to achieve a global optimum instead of a result of two separates optimizations. This global optimisation needs more resources in the objectives definition process, but the result should be a better understanding of the constraints that each partner has and to find a better way to built the product within these limits at the best bcnefit for the airlines who are the final customers. Aerospatiale and Snecma have associated their Advanced Design teams to evaluate the benefit of Powerplant By-Pass Ratio on a derivative aircraft and on a new aircraft. The Powerplant optimisation was studied using as a first pass derivative to optimize the powerplant on A/C operation criteria. The derivative long range Aircraft was evaluated on operations and economics while the new twin aircraft was reoptimized around each powerplant using thc same specifications and then evaluated on economics. The objective of this joint study was to evaluate the best Aircraft configuration optimized for customer needs 1. Power Plant oDtimisation studies 1.1 Selection of c o r e technological level for the studies The technological level to be considered LO size the engine was evaluated taking into account the component efficiencies achievable including the cooling flow needcd by given materials capability. Separate study was conducted to estimate optimum OPR with given High Pressure Turbine blades cooling techno-logy. Therefore the level of compressor temperature discharge and turbine inlet temperature was selected and gave thc thermal efficiency of the gas generator. According to this objective OPR thc split between the HP compressor and the booster was determined to allow the maximum flexibility of the core to derive a family of engine. The core architecture selected was 11 stages High Pressure Compressor (Pressure ratio at Top of Climb = 26) consistently with Snecma core demonstrator P A T , which is under manufacturing process and will be in test cell i n 1996. This core, with its very high pressure ratio, is capable of advanced OPR engine that will be achievable i n the future with the development of new powder materials for HP Compressor and Turbine disks. It also uses all the two stages HP turbine capability in term of loading. It is a baseline for future commercial engine with high and efficient performances. L Bucket SFCINl YS OPR 1 90