Design And Matching Study Of Turbocharger Variable Geometric Axial Flow Turbine For Low Speed Diesel Engine

Marine high-power,low-speed diesel engines have high power and require large air flow,while radial turbines cannot meet the requirements of large flow,so axial flow turbines are needed.The variable geometric axial flow turbine can change the turbine flow and efficiency by changing the opening of the nozzle,thus changing the performance of the diesel engine when the turbocharger and the diesel engine run together.This paper obtained the flow characteristics and efficiency characteristic of turbine by numerical simulation.The turbine characteristics were simulated with the low-speed diesel engine for steady-state one-dimensional simulation,and the matching performance of the turbine,compressor and diesel engine was analyzed.Based on the fixed-geometry turbine,the adjustable nozzle was designed,and the performance and matching calculation of the variable geometry turbine were studied.First,based on the NREC impeller design software,the one-dimensional design of the axial flow turbine was carried out according to the exhaust parameters of a low-speed diesel engine under a certain load.The main parameters of the turbine blade profile and cascade as well as the inlet and outlet velocity triangle of the rotor blade at the design point were obtained,and the one-dimensional design of the turbine was transformed into a threedimensional model.By numerical simulation of the three-dimensional model,the calculation range of variable condition was determined according to the exhaust turbine parameters of the target diesel engine,the flow characteristics and efficiency characteristics of the turbine were calculated,and the change law of the flow field in the turbine under variable condition was analyzed.Secondly,a turbine simulation model is established in GT-power based on the turbine characteristics obtained from turbine numerical simulation.Keep the turbine efficiency characteristics unchanged,adjust the turbine flow scaling coefficient in GT-power,improve and reduce turbine flow capacity,and obtain three kinds of turbine simulation models: large turbine,medium turbine(designed turbine)and small turbine.The compressor simulation model is derived from the data of the original compressor.According to the different flow capacity of the turbine,the compressor flow scaling coefficient is adjusted proportionally and matched with the turbine,three turbocharger models of large turbocharger,mediumturbocharger and small turbocharger were obtained,and the steady-state co-simulation with low speed diesel engine was carried out.The results show that the designed turbine is well matched with the compressor and diesel engine.If the turbine flow capacity is reduced,the fuel economy and dynamic performance of the diesel engine will be improved,but the detonation pressure and exhaust temperature rise.Finally,based on the fixed-geometry turbine,the variable-geometry axial flow turbine is designed.By changing the nozzle opening,the flow characteristics and efficiency characteristics of the variable-geometry turbine are obtained,and the influence of the nozzle opening change on the turbine flow field is analyzed.According to the variable geometry turbine numerical simulation to get the variable geometry turbine characteristics of variable geometry turbine simulation model is established,according to different nozzle opening the change of the turbine flow,scaling coefficient of flow in compressor working can be adjusted in proportion with turbine matching,get the nozzle under different opening of turbocharger simulation model,based on GT-Power associated with low-speed diesel engine for steady state simulation platform,the variation law of turbocharger and diesel engine performance under different nozzle opening is studied,and the control strategy of variable geometry turbine is put forward.The results show that the fuel economy and performance of diesel engine can be improved only when the nozzle opening is reduced below a certain value.The decrease of nozzle opening will cause the cylinder implosion pressure to exceed the limit value at 100% load.When the low-speed engine runs according to the propulsion characteristics,the nozzle opening can be reduced during partial load to improve the economic and dynamic performance.When approaching the full load,the nozzle opening should be increased to limit the cylinder implosion pressure,so that the diesel engine can run safely.