| Traditional turbocharging technology is widely used in marine diesel engines because of its advantages in greatly improving the power,economy and emissions of diesel engines.But due to the mechanical inertia of the turbocharger and the selection of design matching points,diesel engines are prone to problems such as low intake pressure at low loads and excessive supercharging at high loads.Electric-assisted turbocharging technology is an effective technical means to solve the above problems.The motor coupled to the conventional turbocharger can effectively improve low-load power performance and high-load fuel economy.Therefore,this paper takes the marine diesel engine system as the research object to carry out research on the matching performance of the aerodynamic design of the electric-assisted turbocharger and the diesel engine.The influences of key factors of electric-assisted turbocharger on the performance of high-speed diesel engines is studied.The one-dimensional model of diesel engine steady-state performance prediction is established,which is verified by the experimental data.The influence of motor power on the comprehensive thermal efficiency of diesel engines are analyzed in details,the result of which shows that the efficiency of the turbine and compressor is the key factor affecting the overall thermal efficiency of the diesel engine.At the same time,as the motor power increases,the operating point of the turbocharger continues to move to the high efficiency zone,and the surge margin is reduced,which is not conducive to the compressor.For stable and safe operation,a matching design method for electric-assisted turbochargers suitable for this model is initially proposed.The aerodynamic design of the electric-assisted turbocharger turbine is completed.According to the matching design method,the design goal of the radial flow turbine is determined,which can be used to complete aerodynamic design on the basis of the original turbine.The numerical simulation method is used to obtain the flow characteristic curve and efficiency characteristic curve of the turbine,which will be imported to the electric-assisted turbocharged diesel engine model to complete the verification of turbine matching design method.The results show that Reduction of turbine flow range can effectively improve the expansion ratio and isentropic efficiency.The motor recovery power can be increased by 8k W and the thermal efficiency of engine is increased by about 2.0% at 100% load.The optimized design of the compressor is completed.The optimization platform of genetic algorithm,artificial neural network and three-dimensional CFD simulation is used to explore the potential of compressor impeller blade shape in increasing the compressor efficiency.Through the individual optimization of the blade angle distributions,the outlet inclination angle and the trailing edge of the blade,the optimal geometry of each elements has increased the efficiency by 0.8%,1.2%,0.6% and 0.3%,respectively.The inlet and outlet angle at the tip of the blade is more sensitive to the effect of isentropic efficiency.The coupling optimization design improves the maximum efficiency of the compressor and the flow near the blockage by 1.87% and 1.57%.The synergistic mechanism is mainly to weaken the intensity of the shock wave at the blade inlet,and at the same time improve the matching between the impeller and the compressor.The matching performance optimization of the electrically-assisted turbocharged diesel engine system is researched.Based on the matching design method,the operation strategy of the optimized electric-assisted turbocharger is determined,and the simulation calculation is carried out for the electric motor mode and the generator mode,and the comparison and analysis of the traditional turbocharger and the electric-assisted turbocharger before and after the optimization on the diesel engine performance influences.The results show that at low load,the diesel output torque of the optimized electric-assisted turbocharger is greatly increased,and the turbo lag phenomenon is improved;at high load,the diesel overall thermal efficiency can be increased by 0.5%,and the fuel economy can be improved by 6.14%. |
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