Effective Suppression of Surge Instabilities in Turbocharger Compression Systems through a Close-Coupled Compressor Inlet Restriction

The current work demonstrates effective suppression of compression system surge instabilities by installing a variable cross-sectional flow area restriction within the inlet duct of a turbocharger centrifugal compressor operating on a bench-top facility. This restriction couples with the compressor, similar to stages in a multi-stage turbomachine, where the effective pressure ratio is the product of those for the restriction and compressor. During experiments at constant compressor rotational speed, the compressor is stable over the negatively sloped portion of the pressure ratio vs. flow rate characteristics, so the restriction is eliminated within this operating region to preserve compressor performance. At low flow rates, the slope of the compressor alone characteristics reaches a positive value, and the unrestricted compression system enters mild surge. Further reduction of flow rate with the unrestricted compressor inlet results in a sudden transition to deep surge instabilities. Within this low-flow operating range, where surge instabilities occur in the compressor-alone system, the restriction is activated to modify the slope of the combined (restriction plus compressor) characteristics and stabilize the system. An analytical approach is presented to illustrate the impact of compressor inlet restriction on the stability of the combined restriction-compressor system. Over the tested rotational speed range, experimental results demonstrate that a compressor inlet restriction of less than 3 kPa is capable of suppressing surge instabilities and extending the low-flow compressor operating range to approximately one-third of the mass flow rate where deep surge occurred without compressor inlet restriction.