Research Papers

The Variable Outlet Turbine Concept for Turbochargers

[+] Author and Article Information
Elias Chebli

Turbocharger Aero-Thermodynamics,
Development Heavy Duty Engines,
Daimler AG,
Stuttgart 70546, Germany
e-mail: elias.chebli@daimler.com

Michael Casey

Institute of Thermal Turbomachinery,
University Stuttgart
Stuttgart 70546, Germany

Ricardo Martinez-Botas

Imperial College London,
Department of Mechanical Engineering,
London SW7 2AZ, UK

Siegfried Sumser

Group Research & Advanced Engineering Powertrain,
Daimler AG,
Stuttgart 70546, Germany

Markus Müller

Turbocharger Development,
Development Heavy Duty Engines,
Daimler AG,
Stuttgart 70546, Germany

Stefan Künzel

Performance Development,
Development Heavy Duty Engines,
Daimler AG,
Stuttgart 70546, Germany

Johannes Leweux

Turbocharging Development,
Development Heavy Duty Engines,
Daimler AG,
Stuttgart 70546, Germany

Andreas Gorbach, Wolfram Schmidt

Engine Development,
Department Heavy Duty,
Daimler AG,
Stuttgart 70546, Germany

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) Division of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received July 1, 2014; final manuscript received July 26, 2014; published online August 26, 2014. Editor: Ronald Bunker.

J. Turbomach 136(12), 121001 (Aug 26, 2014) (14 pages) Paper No: TURBO-14-1105; doi: 10.1115/1.4028231 History: Received July 01, 2014; Revised July 26, 2014

A variable geometry concept for advanced turbocharger (TC) systems is presented. The variability of the device is based on outlet area changes as opposed to the more common systems that are based on inlet turbine geometry changes. In addition to the conventional variable turbine geometry (VTG), the new variable turbine type is termed variable outlet turbine (VOT). The flow variability is achieved by variation of the flow cross section at the turbine outlet using an axial displacement of a sliding sleeve over the exducer and provides a simple solution for flow variability. In order to predict the aerodynamic performance and to analyze the loss mechanisms of this new turbine, the flow field of the VOT is calculated by means of steady state 3D-CFD (computational fluid dynamics) simulations. The VOT design is optimized by finding a good balance between clearance and outlet losses. Furthermore, experimental results of the VOT are presented and compared to a turbine equipped with a waste gate (WG) that demonstrates an efficiency advantage of 5%. Additionally, engine performance measurements were carried out to investigate the influence of the VOT on fuel consumption and to asses the functionality of the new pneumatic actuating system. The VOT engine tests show also performance advantage in comparison to a WG turbine especially toward high engine loads. It is found that the use of the VOT at this condition shows a turbine efficiency advantage of 6% related to a reduction in engine fuel consumption of 1.4%. The behavior at part load is neutral and the peak turbine efficiency of the VOT is comparable with a fix turbine geometry.

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Fig. 1

Typical mass flow characteristic of a VNT for various IGV's settings

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Fig. 2

h-s diagram and velocity triangles illustrating the impact of a VTG on ΓT

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Fig. 3

Influence of the degree of reaction on the efficiency of a VNT for various inlet guide vane settings and constant pressure ratio

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Fig. 4

Description of the asymmetrical radial turbine stations

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Fig. 5

The distribution of Mach number shows the location where choke occurs in radial turbines operated at high pressure ratios

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Fig. 6

Schematic concept of the VOT indicating the two extreme operating modes

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Fig. 7

Beneficial operation characteristic of VOT compared to fixed turbine geometry and to a turbine with WG

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Fig. 8

Influence of the VOT on loss distribution of a radial turbine [15]

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Fig. 9

Sectional drawing of the VOT demonstrating a potential actuating mechanism for the axial sliding sleeve

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Fig. 10

The predicted characteristic maps of the VOT

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Fig. 11

Predicted isentropic velocity ratio map of the VOT: (a) degree of reaction characteristic and (b) efficiency characteristic

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Fig. 12

Predicted maps of the VOT flow angles

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Fig. 13

Detailed analysis of the flow path through the VOT

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Fig. 14

Velocity vectors for different sliding sleeve positions at ΠT,ts = 3.5,nr = 105 rpm

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Fig. 15

Blade loading distribution of the VOT for different slider positions at 50% blade span

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Fig. 16

Detailed analysis of the flow physics at the impeller exit of the VOT for different sliding sleeve positions

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Fig. 17

Prototype of the VOT with explosion view showing the integrated actuating mechanism

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Fig. 18

The experimental characteristic map of the VOT compared to a WG turbine

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Fig. 19

Comparison of predicted power map with experimental results

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Fig. 20

VOT installation on the heavy duty engine performance test facility

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Fig. 21

Turbine efficiency and fuel consumption comparison of VOT and WG at rated engine speed and power

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Fig. 22

Mass flow parameter and fuel consumption comparison of VOT and WG performance map at engine full load



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