Abstract
Turbo charging is a way for car manufacturers to meet the major challenge of fuel economyand reduction of the CO2 emissions. The aim is to replace current engines with a downsized engine in order to improve its fuel consumption. This requires higher specific power and torque especially at very low engine speed. The wide functioning area required for this technique leads to an operation of compressors at low air flow rate and high compression ratio characterised by the occurrence of surge phenomenon. On the engine, it can be intensified by the fuel flow rate pulses consecutive to air flow rate pulses leading to torque oscillations. In fact, surge is an aerodynamic instability that affects both the compressor and its associated network which results in strong pressure and mass flow rate oscillations describing a surge cycle in the compressor map. The surge limit of a centrifugal compressor and its frequency are highly dependant on the geometrical configuration of its associated network. In this paper, the experimental work was focused on the study of the surge behaviour of a centrifugal compressor by means of a turbocharger test bench and the influence of the upstream and downstream circuit (volumes sizes and pipes lengths) and their interaction at the surge limit, the frequency and the unsteady fluctuations amplitude of this phenomenon. A comparative study of our experimental results with the Greitzer model was also done in terms of surge frequency and intensity prediction.
Keywords: Centrifugal compressor;Turbocharger; Surge;Compressor circuit;Greitzer model