Characterization and Modeling of Turbocharger Dynamic Performance

The range of applications of heavy duty diesel engines is quite diverse. The development of diesel engines has been characterized by a steady increase in power to weight ratios, with the turbocharger being the key component in achieving this increased performance. The turbocharger, consisting of a radial or axial flow turbine and a radial flow compressor, presents perhaps one of the most challenging tasks facing the turbomachinery designer. This is, to a p a t extent, due to the highly unsteady environment in which the turbocharger operates. The time scales of this unsteadiness range fiom those on the order of exhaust valve frequency to those associated with transient operation during acceleration and deceleration.

In order to predict the time-accurate performance of the turbocharger in this environment, a range of dynamic models can be envisioned spanning the range from quasi-steady assumptions to full viscous flow solvers. In between these two extremes are a range of models that attempt to capture the dominant physics of the process while preserving computational efficiency. These include lumped-parameter “cycle” methods as well as discrete control-volume approaches. This paper provides a review of the characteristics of the on-engine turbocharger operating environment, and discusses approaches to improving the modeling of these events.