Challenges of Turbocharging a Two-Cylinder Engine
Résumé
Drive train development is facing demands for reduced emissions and growing expectations for driving dynamics coupled with declining fuel consumption. Downsizing in combination with turbocharging is a key technology to ensure increased power density and efficiency, at reduced emission levels. Up to now, quasi-steady behavior of the turbocharger has been assumed in the turbocharger design. However, the inflow conditions for radial turbines are actually quite different for real pulsating engine operations, compared to steady and quasi-steady conditions. The aim of reducing the fuel consumption with fewer cylinders leads to a further change in the boundary conditions for the turbocharger. As a result, the quasi-steady behavior, especially in two cylinder engines, does not seem to be valid and this has to be taken into account during the design process. This paper presents a numerical investigation of a pulse charged turbocharger turbine to gain an understanding of the aerodynamics at different pulse frequencies. A validated CFD-model is used to compute two and four-cylinder pulses. The time dependent boundary conditions for pressure and temperature are generated via 1D simulation. To make both pulse frequencies comparable, the turbine simulations were run with the same specific exhaust cycle enthalpy. The analyses of the results shows a significant deterioration of the turbine operating behavior at low end torque due to the pulsating inflow of a two cylinder pulse compared to a four cylinder pulse. Higher engine speeds reduce the disadvantages. Furthermore it can be shown that the storage effect of the volute and the phase shift in temperature and pressure influences the throughput behavior of the turbine. For that the specific pulsating flow conditions must be considered for an optimization of the turbocharger of a two-cylinder engine.
Domaines
Mécanique [physics]
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