Abstract
An extensive experimental study has been performed whose main objective was to characterize the acoustic and fluid-dynamic response of turbochargers to flow pulsations from high speed direct injection diesel engines. Four different turbochargers, with different turbine technologies (FGT, VGT, MFT and AFT) and with centrifugal compressors of different sizes were considered. These turbochargers were excited with pulsating flow in real engine conditions. Wave decomposition was used to obtain incident and reflected pressure perturbations upstream and downstream of the compressors and turbines. This allowed to determine the transmission and reflection coefficients of the turbochargers, and to establish the correlations of these magnitudes with engine and turbocharger operating conditions. A database of experimental results has therefore been created and analyzed in order to develop one-dimensional gas dynamic models capable of calculating pressure wave propagation through compressors and turbines. This work proposes a new methodology for turbocharger characterization under pulsating flow conditions. The paper also describes 1D models for turbochargers that can be easily validated, following the proposed methodology, and implemented in gas-dynamic codes for the prediction of engine performance and noise emission. As an example of the application of this work, the possibility of using the length of the ducts upstream of the compressor to improve the low end torque, and the influence on compressor surge were studied using the proposed models.
Keywords: Turbocharging, unsteady flow, 1D engine modelling, acoustics.