【作者】 黄磊；

【导师】 赵荣超； 张磊；

【作者基本信息】 华南理工大学 ， 车辆工程（专业学位）， 2023， 硕士

【摘要】 涡轮复合技术通过回收发动机排气能量,可显著提高发动机燃油经济性。然而,由于涡轮复合系统需工作于多转速、变海拔、脉冲排气等变工况条件下,致使涡轮复合系统性能因偏离设计点而导致性能下降。为了提高变工况下涡轮复合发动机的性能表现,本文针对电涡轮复合系统,研究了不同转速下系统参数对发动机的影响,开展了变海拔下电涡轮复合系统的优化设计和能量管理研究,进行了脉冲来流条件下复合涡轮的三维气动设计研究。首先,建立了电涡轮复合发动机循环耦合模型,采用实验数据对模型进行了可靠性校核与验证。基于数值仿真模型,研究了不同转速下轴承效率、涡轮流通能力MFP和电机功率对电涡轮复合发动机全转速工况性能的影响。结果表明,轴承效率对集成式方案的系统效率影响较大;随着发动机转速上升,串联式方案中动力涡轮最优MFP减小,而集成式方案中涡轮最优MFP则随之增大;串联式方案的最优电机电压随转速上升而增大,集成式方案的电压控制需与发动机的增压需求相匹配,在低转速下电机作为电动机加速压气机旋转,在高转速下电机作为发电机回收多余的排气能量。其次,进行了串联式和集成式涡轮复合发动机的变海拔性能分析和管理。集成式涡轮复合发动机在高海拔工况下通过主动增压缓解了发动机动力下降的问题,串联式涡轮复合发动机由于动力涡轮引起的高背压致使增压能量与空燃比的显著下降,高海拔工况下总功率和油耗显著恶化。针对串联式涡轮复合发动机在高海拔工况出现的动力下降和油耗恶化的问题,研究了不同流通能力的增压涡轮和动力涡轮对发动机变海拔性能的影响,结果表明,采用固定几何的涡轮复合系统不能有效解决高海拔问题。进一步研究了可变几何增压涡轮、可变几何动力涡轮和废气旁通动力涡轮对串联式发动机变海拔性能的影响。可变几何动力涡轮具有最好的表现,与涡轮增压发动机相比,选用可变几何动力涡轮的串联式涡轮复合发动机在4km和1900 r/min下运行时,总功率提高了1.2%,BSFC降低了2.99%;与原有的串联式涡轮复合发动机相比,总功率提高20.1%,BSFC降低了2.1%。最后,针对脉冲来流下电涡轮复合系统的涡轮流动损失增加问题,研究了蜗壳A/R比、蜗壳出口半径、截面形状和导管角度等设计参数对流动损失的影响机理。研究表明增大蜗壳出口半径,可使蜗壳末端的气流补充至蜗舌附近的转子通道,减弱脉冲波峰下蜗舌位置的流动不均匀性。蜗壳出口半径由R₁/R₂=1.062增大到1.154,涡轮平均效率提高4%。此外,蜗壳A/R比对涡轮性能影响较大,而截面形状、蜗壳导管角度对涡轮性能影响较小。更多还原

【Abstract】 Turbocompound technology can significantly improve engine fuel economy by recovering engine exhaust energy.However,the turbocompound system must be operated under variable working conditions,such as different speeds,variable altitudes and pulse exhaust,so the performance of it decreases due to deviation from the design point.In order to improve the performance of turbocompound engines under variable working conditions,this article focuses on the influence of system parameters on the engine at different speeds for electric turbocompound systems.The optimal design and energy management of electric turbocompound systems at variable altitudes were studied,and the three-dimensional aerodynamic design of turbocompound turbines under pulsing flow was studied.Firstly,a cycle coupling model of electric turbocompound engine was established.The reliability of the model was verified using experimental data.Based on the numerical simulation model,the effects of bearing efficiency,turbine flow capacity MFP and motor power on the performance of the electric turbocompound engines at different speeds were studied.The results show that the bearing efficiency has a significant impact on the system efficiency of integrated turbocompound engine.As the engine speed increases,the optimal MFP of the power turbine in the series turbocompound engine decreases,while the optimal MFP of the turbine in the integrated turbocompound engine increases accordingly.The optimal motor voltage of the series turbocompound engine increases with the increase of engine speed,and the voltage control of the integrated turbocompound engine needs to match the turbocharging demand of the engine.The motor acts as an electric motor to accelerate the rotation of the compressor under low-speed conditions,while the motor acts as a generator to recover excess exhaust energy under high-speed conditions.Secondly,the variable altitude performance analysis and management of series and integrated turbocompound engines were conducted.The integrated turbocompound engine can alleviate the problem of engine power decline through active turbocharging at high altitudes.The series turbocompound engine significantly reduces turbocharging energy and air fuel ratio because of high back pressure caused by the power turbine,resulting in a significant deterioration of total power and fuel consumption under high altitudes.In response to the problem of power decline and fuel consumption deterioration for series turbocompound engine at high altitudes,the effects of turbocharger turbine and power turbine with different flow capacities on the variable altitude performance of engine were studied.The results show that using the fixed geometry turbocompound system cannot effectively solve the problem of high altitudes.Further research was conducted on the effects of variable geometry turbocharger turbine,variable geometry power turbine,and exhaust bypass power turbine on the variable altitudes performance of series turbocompound engine.The variable geometry power turbine has the best performance.Compared with turbocharged engine,the series turbocompound engine with variable geometry power turbine achieves 1.2%increase in total power and 2.99%BSFC reduction when operated at 4km and 1900 rpm.Compared with the original series turbocompound engine,it achieves 20.1%increase in total power and 2.1%BSFC reductionFinally,in response to the problem of increasing turbine flow loss of the electric turbine composite system under pulsing flow,the influence mechanism of design parameters,including the A/R ratio of the volute,the outlet radius of the volute,cross-sectional shape and turning angle of the volute inlet pipe,on flow loss was studied.The results show that increasing the outlet radius of the volute can supplement the airflow to the rotor channel near the volute tongue,which reduces the flow non-uniformity at the volute tongue position under the pulse peak.The outlet radius of the volute is determined by R₁/R ₂.Increasing R₁/R₂from 1.062 to 1.154 can improve average efficiency of the turbine by 4%.In addition,the A/R ratio of the volute has a significant impact on the turbine performance,while the cross-sectional shape and turning angle of the volute inlet pipe have a relatively small impact on the turbine performance.更多还原