Multi-point Through-flow Design Approcach Of A Centrifugal Compressor For Internal Combustion Engine Turbocharging

Much greater emphasis of turbocharging technology is being placed on downsizing the internal combustion engine (ICE) to increase fuel economy and reduce CO₂ emissions. But the fundamentally difference between rotating turbomachines and reciprocating piston engines lead to poor engine performance at off-design conditions, which is the main difficulty for engine downsizing. Traditionally, the turbocharger compressor design is independent from the engine system development process and the compressor is not usually designed for the improvement of ICE's performance on all operation conditions.According to the key, a centrifugal compressor multi-point through-flow design approach was developed to improve the ICE's overall performance. The influence of compressor characteristics on turbocharged engine system, sophisticated flow mechanism on different operation conditions and compressor multi-point design optimization was discussed. The thesis work contains contents as follows:The influence of different compressor characteristics on ICE's performance on all operation conditions was investigated. The results show that the compressor off-design characteristics have great effect on engine performance. The location of compressor high efficiency island was the most influential factor for the ICE's performance on low speed and part-load conditions.Through the detail research on a small turbocharger compressor internal flow mechanism, the acting factors which changed the compressor MAP characteristics were investigated. The main compressor geometrical parameters were discussed and it was found that four impeller structures, including inlet tip diameter, inlet tip blade angle, outlet width and outlet backsweep angle, have the greatest influence on compressor overall performance.Based on the inside flow mechanisms of centrifugal compressors, a through-flow model was developed to predict the compressor overall performance with various structure parameters. The model was calibrated and validated with the test data of nine different compressors. Based on the through-flow model, a compressor multi-point through-flow design approach was developed with the objective of ICE's performance for all operation conditions. During the through-flow design process, the direct influence of compressor geometry parameters on ICE's overall performance can be considered.The multi-point through-flow design approach was successfully applied to a 1.8L turbocharged gasoline engine to develop a new turbocharger compressor. The efficiency has been improved obviously on low flow rate conditions of the new designed compressor. Simulation resultes show that the low-end torque of the turbocharged gasoline engine matched with the new compressor has been increased by 21% and part-load fuel consumption has been decreased by 2.4%.