Numerical and experimental study on temperature and heat transfer characteristics in centrifugal compressor diffuser

Abstract

Lubrication oil aerosol deposit and coking in the compressor diffuser is a typical issue for the high power density internal combustion engine (ICE) using the closed crankcase ventilation (CCV) system. The aerosol coking significantly negatively influences the compressor's performance, leading to a penalty on ICE performance. The severity of the coking effect is highly dependent on temperature. In order to predict occurrence of coking and to clarify how to avoid aerosol coking in the compressor, the temperature distribution and heat transfer characteristics are investigated in this study. An experimental investigation on the diffuser temperature distribution at shroud side was carried out first. Numerical simulations that consider the heat transfer between the solid domain and the fluid domain are conducted, aiming at analyzing the temperature distribution of inner surface. The detailed simulation model of small high-pressure-ratio compressor for predicting coking risk is established. Furthermore, the simulation model is validated by the experimental results. The results indicate that the shroud side of the diffuser sees the highest temperature level in the diffuser. Under typical operation conditions, the temperature at the diffuser wall exceeds the threshold coking temperature of lubrication oil aerosol, this location most likely to have severe coking issues. Thus, the location of the shroud plate is the primary region that needs to be cooled down to mitigate the coking issue. Meanwhile, the intensity of heat transfer between the fluid and solid domain in the diffuser region degrades significantly along the flow direction and sees an 80% drop from diffuser inlet to outlet, indicating the requirements for further enhancement of heat transfer in diffuser shroud side along streamwise.