Study On The Optimization Design And Emission Analysis Method For Civil Aircraft Engine

The aircraft engine performance optimization is a hot issue in the design of civil aircraft engines.The whole optimization design should be a complete process which includes aircraft mission requirements,engine overall performance scheme design and the scheme evaluation.However,aircraft mission requirements,the engine overall performance scheme design and the scheme evaluation are relatively independent which is unable to make the aircraft engine design an integrated design system.With the "Green Aviation" as a new trend in the civil aviation industry development,the engine scheme evaluation is not only limited to the engine performance itself,but also includes the calculation and analysis of pollution emissions.In this paper,a civil aircraft engine optimization design and emission analysis simulation system which based on the engine design process is developed to investigate the problem above.According to disciplinary relationships in the design process and the concept of modular integration,the design system includes five modules,which consist of the aircraft performance module,the engine performance module,the integration design module of aircraft and engine,the modern optimization algorithm module and the pollution emission calculation and analysis module.Aircraft Performance Module: A lift-drag characteristic calculation model based on the aircraft geometry parameters and airfoil parameters is established in order to make the aircraft engine design system more targeted and accurate.The calculated lift-drag characteristic with and without the high lift device are compared with the reference values.The results demonstrated the accuracy of lift-drag characteristic calculation model,which also made the lift-drag characteristic more easily to be acquired.In order to simulate the aircraft flight and evaluate the fuel consumption and pollution emissions on the route in detail,the calculation model of civil aircraft engine performance and pollution emissions on route,which is based on the flight mechanics model and the typical mission of civil aircraft,is established by using the proportional integral control method.Engine Performance Module: An engine thermodynamic mathematical model is established according to the processes of compression,combustion,expanding power,flow expanding acceleration and blending.The engine thermodynamic mathematical model is used to analyze the performance cycle parameters by combining with rules of the power extraction and the air bleed of the air system.Six engine operation states(maximum takeoff,maximum continuous,maximum climb,maximum cruise,flight idle and ground idle)are calculated and analyzed based on the typical control laws of civil aircraft engine.The study on the problem of preventing the booster surge when the high bypass turbofan is operating at a low rotation speed is also carried out.The constant surge margin control calculation has been achieved by the method of inverse calculation of the air bleeding value behind the booster.The installed losses of the inlet and exhaust system have been investigated by the method of combining experimental characteristics and correction for the engine installed performance.The engine installed performance in the flight envelope is also calculated and analyzed.Aircraft and Engine Integration Design Module: This module is established based on the aircraft constraint analysis and mission analysis.The relationships between the wing loading and takeoff thrust to weight ratio are obtained firstly by the constraint analysis model.The constraint analysis solution domain is also established.Then,the design point of the constraint analysis is determined by the rule of low takeoff thrust to weight ratio and high wing loading.Finally,the preliminary aircraft takeoff weight and thrust requirements are determined according to the mission analysis.Modern Optimization Algorithm Module: The differential evolution algorithm,which is used in present work,is mainly discussed based on the comparison of modern and traditional optimization algorithm.The population initialization method based on the average entropy,keeping elitism strategy,the improved penalty function and self-adaptive three times variation evolution method are applied to the new differential evolution algorithm,which improved the global search ability and calculation efficiency.Pollution Emission Calculation and Analysis Module: The current calculation methods of emissions have been analyzed first.Methods of correlation models and multi-reactors model which are adopted to engine overall performance model are used in present work.The SAGE model and AERO2 k model are introduced in the method of correlation models in detail.The multi-reactors model includes fuel atomization and fuel droplet evaporation model,combustion chemical reaction equilibrium model,simplified flame front model and mechanisms of NO_x,CO,UHC and smoke.The smoke number and emission indexes of NO_x,CO and UHC of CF6-80C2B1 are calculated at the reference sea level static condition.The emission results of CF6-80C2B1 are also compared with the measured values from ICAO.The results show that the results are in good agreement with measured values,which demonstrated the accuracy of multi-reactors model.These three emission calculation models above are also compared to each other in this paper.The comparison results show that the same tendencies is obtained by the three models,but deviation degrees of the calculation results are different according to the types of pollution emission and engine operation statuses.In this paper,the optimization design of the civil aircraft engine is presented by using the civil aircraft engine optimization design and emission analysis simulation system.The B767-200 ER is chosen as the installed object and the 250 kN grade takeoff thrust civil aircraft engine is investigated.The lift-drag characteristic of B767-200 ER is calculated first by the lift-drag characteristic model in the aircraft performance module,and the result is used in the aircraft and engine integration design module to determine the preliminary aircraft takeoff weight and thrust requirements.Then,the preliminary values calculated above are used in the performance cycle parameters optimization model.The optimized engine scheme is solved by using multiple constraints engine performance optimization and engine/aircraft integration design.The installed performance of the optimized engine scheme in the flight envelope is calculated by using the engine performance model and the typical control law of the civil aircraft engine.Finally,the installed performance is applied to the civil aircraft engine performance and pollution emissions calculation models to evaluate the performance and pollution emissions of the optimized engine scheme by using the emission calculation methods.The evaluation results show that the maximum aircraft takeoff weight reduced about 2.7% when the original payload remains the same and the requirement of each mission segment is satisfied.The optimized engine scheme has a better acceleration and climbing performance than the PW4056.The fuel consumption of the optimized engine is also less than PW4056,which improves the economic efficiency.The main pollution emissions such as NO_x and UHC are reduced when RQL(Rich Quench Lean)combustor is installed,which enhances the environmental friendliness.