Engine turbocharger performance prediction: One-dimensional modeling of a twin entry turbine

As the automotive industry develops technology strategies to meet increasingly stringent vehicle emission regulations, turbocharging has become the primary enabler for engine downsizing, a building block for improving fuel consumption and reduced CO2 emissions. Engine manufacturers routinely use one-dimensional engine cycle simulation for performance and emissions prediction, and accurate engine-turbocharger matching is a key aspect. Turbocharger turbines are subject to the highly unsteady, pulsating flow inherent to reciprocating engines, however standard 1D turbine models rely on steady state test measurements. Simplification of turbine geometry is unavoidable, especially in 1D performance studies, yet this must not be taken so far that it prohibits acceptable prediction accuracy. This paper presents the geometrical effects of 1D numerical models of a twin entry turbocharger turbine under full admission pulsating flow conditions. Several turbine volute models of increasing complexity were developed and the corresponding performance predicted using a 1D compressible flow solver. The predicted mass flow rate is strongly dependent on local total state flow parameters, and higher secondary mass flow rate fluctuation was noticed as model complexity increased. Finally, a two-inlet constant cross-section model with junction tongue gave the best compromise of flow prediction accuracy and geometrical complexity.