Research On Dual Flexible Turbochaeging System Of Vihecle Diesel Engine

In order to solve the conventional turbocharged diesel engine’s shortcomings including insufficient boost pressure at low speed condition,surplus exhaust energy at high speed condition and turbo lag,the study proposes a dual flexible turbocharged(DFT)system in which the turbine and compressor are decoupled.The influence of DFT system applied in the vehicle diesel engine on steady-state performance and transient response performance is researched by numerical simulation.Firstly,based on the theory of diesel engine’s numerical simulation,a vehicle diesel engine’s baseline steady-state model is built by GT-Power,and the model is verified.Based on the fundamental steady-state model,the steady-state model of DFT diesel engine is built.Secondly,the influence of turbine power generation system on engine’s steady-state performance and turbine matching’s influence law are researched.A high-efficient turbine is designed by one-dimensional design method,and its performance is analysed.The results shows that,in high speed condition the DFT engine’s overall efficiency is improved a lot compared to baseline engine.The higher the engine’s speed,the greater overall efficiency’s improvement.By controlling turbine’s speed,turbine’s efficiency can be best in all conditions,and maximum lift amount of turbine’s efficiency is 1.2%.After turbine’s preliminary design,overall efficiency of DFT engine can be improved by 5.2% compared to the baseline engine in 2200r/min.Thirdly,the influence of electric compressor system on engine system’s steady-state performance is researched,including the potential of electric compressor system for enhancing the engine’s low-speed torque,the impact on engine’s overall efficiency and compressor matching’s influence law.A high-efficient compressor is designed by one-dimensional aerodynamic design method,and finally the fuel economy of the engine system is analyzed.The results shows that,the engine’s torque in low speed condition can be enhanced effectively by increasing the electric compressor,and the potential area is formed by the envelope of the maximum combustion pressure boundary and the excess air factor boundary.The engine’s torque in low speed conditions by be improved up to 24% compared to the baseline engine while engine’s overall efficiency is also improved.The overall BSFC of DFT engine in 2200r/min and full load condition is reduced 6.56%compared to baseline engine,in the driving cycle ESC condition reduced by5.68%,and in WHDC condition reduced by 3.17%.Finally,the influence of DFT system on the engine system’s transient performance is researched.The diesel engine’s transient model is bulit,and comparative study of the transient performance between baseline engine and DFT engine in different transient conditions is completed.The influence of key parameters of the electric compressor system on transient response performance is researched.The result shows that,in sudden loading and low speed condition,the DFT engine’s transient response time can be reduced nearly 70%,while has no significant effect for improving the transient response in high speed condition.In constant torque and sudden acceleration,the DFT engine’s transient response time can be reduced nearly52%.When the motor’s maximum power is higher,or the moment of inertia of the electric compressor system is smaller or mechanical efficiency is higher,the transient response time is shorter.