Compressor Surge Precursors for a Turbocharger Coupled to a Pressure Vessel

Abstract

Dynamic compressors operating region is mainly constrained by fluid-dynamic instabilities occurring at low mass flow rate conditions, such as surge and rotating stall. This work presents a vibro-acoustic experimental investigation on a centrifugal compressor of an automotive turbocharger aimed to identify and confirm some surge precursor values in correspondence of its inception conditions. The experimental campaign was carried out on a turbocharger equipped by a vaneless diffuser compressor exploited for the pressurization of an innovative solid oxide fuel cell (SOFC) emulator. The investigated turbocharger is coupled with a pressure vessel for a former emulation activity on a pressurized SOFC. In such kind of plants, the joint effect of large volume size downstream the compressor makes more complex the dynamic behavior of the whole system during transients, thus significantly increasing surge onset risk. The main goal is to define a suitable quantitative indicator to detect in advance surge inception by relying only on system vibro-acoustic response. Several transient from a compressor stable condition to surge instability onset were performed by progressively closing specific valves in the air line. When moving close to surge , vibro-acoustic signals were acquired at a high sampling rate to investigate blade passage phenomena which might interact with rotating stall inception. Meanwhile, pressures, temperatures and mass flow rates measured at a lower sampling rate to correlate compressor vibro-acoustic and performance behavior. Cyclostationary analysis was performed on vibro-acoustic acquired signals to provide innovative diagnostic and predictive solutions (precursors) for early surge detection.

Early surge detection on a turbocharger used to pressurize a SOFC plant emulator

“…The centrifugal compressor investigated is the same considered in this work used to pressurize the same SOFC emulator plant. Indeed, the reported activity is a further development of a previous experimental investigation into early surge detection performed by the authors on the same SOFC emulator plant [15].…”

“…Vibro-acoustic measurements were performed by relying on a Siemens Scadas portable data acquisition system, which allows sampling of frequencies up to 204.8 kHz for each channel, simultaneously. Vibrational signals were collected by exploiting mono-axial accelerometers placed both at the compressor inlet and at its outlet plus a micro-accelerometer (with resonant frequency > 95 kHz and measurement uncertainty of ±3 dB, from 5 Hz to 65 kHz) located on the compressor housing in axial direction with reference to its volute [15]. Said microaccelerometer can enlarge vibration observation field up to higher frequencies, in such a way that Blade Pass Frequency (BPF) range can be investigated.…”

“…In [15] cyclostationary analysis was applied to system vibro-acoustic responses in order to deepen knowledge of fluid-dynamic instability phenomena occurring at low mass flow rates. Such a signal processing technique proved its reliability in rotating stall cell detection and early surge identification.…”

Operation extension in gas turbine-based advanced cycles with a surge prevention tool

“…A complete description of the system, that is not discussed here for the sake of brevity, is reported in [40]. Moreover, the exhaustive description of the experimental campaign is presented in [41]. Regarding the turbocharger compressors instability, the authors also suggest reading of Marelli's works [42].…”

Early surge detection in a mGT plant coupled with large volumes

“…Indeed, a variation in structural response signal spectral pattern can be clearly identified: the energy of some frequency components significantly increases with respect to system structural behavior previously observed in stable conditions, far from the surge line. In particular, the sub-synchronous range is investigated since it is the more likely frequency interval where rotating stall cells energy can be detected when approaching surge [25][26]. In particular, two spectral contents can be identified at roughly 294Hz and 361 Hz which increase their energy in incipient surge conditions.…”