| In order to meet the high dynamics and high economic indicators of the internal combustion engine,the matching turbocharger is required to have a wide applicable flow range,and at the same time achieve a higher-pressure ratio and efficiency.The use of compressor intake bypass recirculation structural(i.e.CIR structural)is one of the most effective technologies to reduce the NOx emissions of diesel engines,has become an important technical measure for modern diesel engines to meet Euro six-emission regulations,and is currently the most effective technical measure to broaden the compressor flow range.Therefore,it has been widely used.This paper combined with the two-zone model of compressor impeller,established a gas-thermal coupling mathematical model of compressor with CIR structural.Taking the structural parameters of the CIR structural of a certain type of centrifugal compressor as the research object,through the design of different schemes of the CIR structure parameters and the simulation analysis,the influence of different recirculation slots width,position,angle change and structural form on the performance of the compressor is studied,and the accuracy of the simulation results is further verified by setting different experimental schemes,and the total efficiency experiment is carried out,combined with the BP neural network and NSGA-II algorithm for multi-objective optimization,and the following conclusions are obtained: After the compressor with the CIR structural,the waste heat loss increases and the efficiency decreases,but the pressure ratio and the density of the pressurized air are improved.The width of the circulation slots increases,the bypass flow rate also increases,and the flow range of the compressor is appropriately broadened,but the pressure ratio will be reduced,and the range of the high-efficiency decreases with the increase of the width of the circulation slots.The closer the recirculation slots position is to the compressor inlet,the wider the compressor flow range,and the higher the total efficiency of the turbocharger.In the high efficiency zone,the 20° and24° slot scheme impeller outlet have borne the highest loading,the pressurized gas density is the largest,the loading peak is the highest,and the work ability is the strongest.The high-speed area of the compressor with the chute intake structure is greater in the surge margin and the narrower range of the high efficiency zone.Compressors with intake ring structures have a smaller surge margin and the smaller range of high-efficient than compressors without intake ring structures.After the multi-objective optimization,the compressor performance is better than the optimal result obtained by the single parameter change,and the compressor performance curve is not significantly affected at low speed,and the performance is improved at medium and high speed.Under the rated speed,compared with the optimal scheme of the previous one-parameter change of width,position and angle,the percentage change of the flow range is 15.86%,12.99% and9.54%,respectively.Moreover,the optimization scheme has the highest-pressure ratio,the efficiency is the highest under small flow,the lowest under large flow,and the high efficiency area is closer to the small flow direction than other schemes.The influence of the geometry and structure of the CIR structural on the performance of the compressor provides an important theoretical basis for the optimal design of the compressor.This paper contains 129 figures,9 tables and 139 references. |
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