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Institute for Commercialization

Variable Geometry Turbocharger (VGT)

Reference Number: K 08-04

Inventors: Chapman, Kirby; Honnegar, Ueli

Owner: Kansas State University Research Foundation


Invention Summary

The operating range of a turbocharger compressor is limited by the surge and choke flow conditions that define its range at low and high flow-rates, respectively. In general, conventional vaned diffusers lead to an improvement in efficiency and pressure ratio when compared to a diffuser without vanes, but suffer from a reduced operating range. This occurs because a conventional full length vaned diffuser creates a throat that acts as a blockage and thereby reduces the flow range. In addition, incidence effects at low flow rates can have an adverse effect on the surge condition. It has therefore been found that deficiencies in the operating range can be eliminated by the adoption of variable geometry diffusers.

With this in mind, numerical studies were conducted to experimentally investigate the performance of a centrifugal compressor turbocharger as provided by different diffuser vane setting angles. Simulation results showed that the diffuser vane setting angle influenced the compressor operating range and its efficiency. A higher pressure ratio and a wider high efficiency island were achieved when the vanes were moved 10° closer to the impeller in comparison to the baseline vane settings. To verify the computational results, a Cooper ET-18 turbocharger was redesigned to allow the diffuser vanes to rotate in real time while operating the turbocharger throughout its operating and speed range.

This invention provides the means to adjust the turbocharger compressor diffuser vanes in real time to achieve optimal compressor efficiency, regardless of engine operating and ambient conditions. The VGT can be used to prevent compressor surge, maintain optimal compressor efficiency, and fine-tune the turbocharger operating point.


  • Maintain peak compressor efficiency independent of turbocharger speed and ambient conditions

  • Expand engine operating range

  • Simple design, with few moving parts


Large bore, multi-cylinder legacy engines in the following fields

  • Pipeline

  • Rail

  • Marine

  • Back-up Generation