Study On Influence Of EGR On Performance Of Centrifugal Compressor

In purpose of investigating the influences of low pressure EGR on the performances of centrifugal compressor, numerical simulations are carried out on the J90 turbocharger compressor. Research contents are as follows:First, the intersection position and connecting type between the EGR pipe and compressor inlet pipe are considered as two major factors of EGR pipe geometric features.Their influences on the compressor performances are thus investigated. Results indicate that the low pressure EGR has negative influences on the compressor performances and leads to efficiency drop. Decrease of the distance between intersection and impeller leading edge, as well as the decrease of the divergence angle between EGR pipe and compressor inlet flow, are helpful for minimizing the decrease of compressor performances.Second,the reason for performance change of the compressor is investigated through numerical simulation of internal flow field characteristics.The flow of compressor is simplified as the flow in the circular tube and the flow loss within the compressor is divided into the friction loss and the local loss. Impact on centrifugal impeller inlet and the tip leakage flow under different EGR structure are analyzed.The result shows that inlet total pressure distortion caused by EGR increases the relative flow angle and the blade loading,and consequently improves the driving power of tip leakage flow,which leads to the breakdown of tip leakage vortex prior to the case without EGR.Finally, the influences of the EGR flow conditions on the compressor performances are investigated.The normalized performances as well as the of centrifugal compressor under different conditions of exhaust pipe inlet parameters is analyzed,as well as the characteristics of the compressor.Results indicate that the increase of EGR temperature leads to the efficiency drop and the debases the operating range of the compressor.Increase of the percentage of EGR result to efficiency drop,and remain unchanged when EGR reach20%.