Incipient Surge Detection in Automotive Turbocharger Compressors

Nowadays, turbocharging is a technique widely used to improve fuel consumption and exhaust emissions in automotive engines. Centrifugal compressors are typically adopted, even if an efficient engine integration is often restricted by surge phenomena. The focus of the present work is to describe an experimental analysis developed with the aim at characterizing and identifying compressor behavior in incipient surge conditions. The acoustic and vibrational operative response of two automotive centrifugal compressors has been experimentally analyzed on the test facility operating at the University of Genoa. Each compressor is characterized by a classical architecture and one of them is equipped with a “ported shroud”, which enlarges stable zone. Compressors characteristic curves have been measured under steady flow conditions for different levels of corrected rotational speed from the choking region to the surge line. Moreover, transient operations have been taken into account where, starting from a stable condition, surge phenomenon was generated progressively closing a valve positioned downstream the compressor or increasing rotational speed keeping fixed the circuit characteristics. Accelerometer and microphone signals have been acquired and analyzed both in the sub-synchronous contents and in higher frequencies range related to blade passage phenomenon. In addition, instantaneous compressor outlet pressure, turbocharger rotational speed and temperature (captured close to the rotor) have been recorded. Different signal processing techniques in time and frequency domain have been considered to analyze components and to separate the whole signal into individual source contributions to identify the system status. The obtained results provide an interesting diagnostic and predictive solution to detect compressor instabilities at low mass flow rate operating conditions.