Potential of Variable-Geometry Method for Compressor Range Extension for Turbocharged Engines

Increasingly stringent requirements on fuel economy and emissions are propelling turbocharging technology to improve the power density of engines. In the future, turbocharged engines with ultrahigh-power density must be equipped with high-pressure compressors. However, the narrow stable operating range of a compressor at a high-pressure ratio is always a restriction. The variable-geometry method, which refers to the combination of a variable-inlet prewhirl and variable diffuser vanes in this paper, will be a preferred choice for the range extension of compressors, and so estimating its potential for range extension is of long-term value. This paper investigated the performance of a centrifugal compressor adopting the variable-geometry method via a steady three-dimensional Reynolds-averaged Navier–Stokes simulation. The combination of variable diffuser vanes, ranging from −10 to 10 deg, and a variable-inlet prewhirl, ranging from −20 to 60 deg, has the potential to improve the stable operating range from 23.5 to 63.0% at a pressure ratio of 4.8. The corresponding increase in the low-end engine torque is estimated to be 53%. The combination shows advantages in terms of operating range and efficiency performance over only adjusting the diffuser vanes or simply changing the inlet prewhirl. The contributions from the variable-inlet prewhirl and variable diffuser vanes to the shifts of the surge line and choke line are discussed as well.