Conceptual Design of a Variable Geometry, Axial Flow Turbocharger Turbine

Paper #:
  • 2017-24-0163

  • 2017-09-04
The automotive industry is under increasing pressure to reduce emissions in order to comply with regulations emanating from the Kyoto Protocol, a universally acknowledged treaty aiming at reducing exhaust gas emissions. In order to achieve the required future emission reduction targets, further developments on gasoline engines are required. One of the principal technologies being implemented to achieve this goal is engine downsizing. Engine downsizing by definition requires some form of boosting and turbocharging is widely adopted as it is a cost effective method to achieve the downsizing an engine whilst reducing exhaust gas emissions, reducing fuel consumption and practically maintaining prior performance targets. For these reasons, turbocharging is becoming an increasingly popular technology with automotive engine manufacturers. Despite the wide spread of this technology, there are still drawbacks present in current turbocharging systems. The main problem is overcoming the issue of turbo-lag, which is the poor initial response of the turbocharger to the driver commands due to its inertia. The conventional turbine plus compressor layout in a turbocharger is characterized by a rotational inertia resulting in poor response compared to naturally-aspirated engine due to finite amount of time taken by the exhaust pressure build-up to be converted to boost-developing rotational speed at the desired level. In this work, an innovative solution to the turbo-lag phenomenon will be analyzed: a vane-less variable geometry, axial flow turbine. The proposed turbine configuration will improve the transient response of the system due to the fact that the axial turbine has an intrinsically lower inertia than the radial turbine for designs that handle similar flows. The entire design process is presented in this paper and particular attention has been given to the fluid dynamic aspect of the machine design. Several CFD investigations have been carried out in order to understand the behavior of the new turbine and the implementation of a 1D model of the target engine has allowed the validation of the new design on-engine.
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