After a decade where inlet turbine variability has dominated variable turbine systems in turbocharging, a simple turbine outlet variability for use with an asymmetrical twin scroll turbine has been presented and investigated in this paper. The mechanical simplicity of the system is able to fulfil the durability requirements for heavy duty diesel engines. By replacing the waste gate function, the characteristic of the variable outlet radial turbine can be considerably improved, offering a wide mass flow variability and high aerodynamic efficiency level. The radial turbine flow field was calculated by means of steady state 3D CFD simulations (Star-CCM+) to predict the mass flow variability as well as the aerodynamic efficiency level and to analyse the influence of loss mechanisms on the variable outlet turbine (VOT). The use of the VOT at high turbine expansion ratios is important to balance out the outlet losses and to improve the turbine efficiency. The efficiency advantage of the VOT leads to a desired operating characteristic, where the turbine efficiency can be kept at a high level across the whole turbine map. At high engine speeds, the required boost pressure is achieved at a lower turbine expansion ratio than that with a waste gate and the engine's fuel consumption can be reduced due to lower negative charge cycle work. Considering the high demands on mass flow variability of radial turbines in gasoline engines, it is favourable to link the turbine inlet with the turbine outlet variability towards to a fully-variable turbine system providing an innovative radial turbine with optimized efficiency for the generation of new and unconventional turbochargers.
Innovative variable turbine concept for heavy duty truck engines
Aufladetechnische Konferenz, 15 ; 79-99
2010
21 Seiten, 14 Bilder, 15 Quellen
Conference paper
English
Innovative variable turbine concept for heavy duty truck engines
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