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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Experimental Investigations of Pressure Losses on the Performance of a Micro Gas Turbine System

[+] Author and Article Information
Jan Zanger

Institute of Combustion Technology, German Aerospace Center, Pfaffenwaldring 38-40, Stuttgart 70569, Germanyjan.zanger@dlr.de

Axel Widenhorn, Manfred Aigner

Institute of Combustion Technology, German Aerospace Center, Pfaffenwaldring 38-40, Stuttgart 70569, Germany

J. Eng. Gas Turbines Power 133(8), 082302 (Apr 11, 2011) (9 pages) doi:10.1115/1.4002866 History: Received May 31, 2010; Revised August 03, 2010; Published April 11, 2011; Online April 11, 2011

Pressure losses between the compressor outlet and the turbine inlet are a major issue of overall efficiency and system stability for a solid oxide fuel cell/micro gas turbine (MGT) hybrid power plant system. The goal of this work is the detailed analysis of the effects of additional pressure losses on MGT performance in terms of steady-state and transient conditions. The experiments were performed using the micro gas turbine test rig at the German Aerospace Centre in Stuttgart using a butterfly control valve to apply additional pressure loss. This paper reports electric power and pressure characteristics at steady-state conditions as well as a new surge limit for this Turbec T100 micro gas turbine test rig. Furthermore, the effects of additional pressure loss on the compressor surge margin are quantified and a linear relation between the relative surge margin and additional pressure loss is shown. For transient variation of pressure loss at constant turbine speed, time delays are presented and an instability issue of the commercial gas turbine controller is discussed. Finally, bleed-air blow-off and reduction of the turbine outlet temperature are introduced as methods of increasing the surge margin. It is quantified that both methods have a substantial effect on the compressor surge margin. Furthermore, a comparison between both methods is given in terms of electric power output.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Test rig description and instrumentation

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Figure 2

Flow path section between the compressor outlet and the airside recuperator inlet

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Figure 3

Relative pressure loss between the compressor outlet and the recuperator inlet for 75%, 80%, and 90% turbine speed as a function of recuperator valve opening

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Figure 4

Total compressor outlet pressure and total airside recuperator inlet pressure for 75%, 80%, and 90% turbine speed as a function of additional relative pressure loss Δp0

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Figure 5

Electric power output for 75%, 80%, 87.5%, 90%, and maximum turbine speed as a function of additional relative pressure loss Δp0

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Figure 6

Points of surge and new surge limit on compressor map

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Figure 7

Operating points on compressor map for 75%, 80%, 87.5%, 90%, and maximum turbine speed as a function of pressure loss

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Figure 8

Schematic diagram of the coefficients in the Hesse normal form for the surge limit linear fit

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Figure 9

Relative distance Δdsurge to surge limit for 75%, 80%, 87.5%, and 90% turbine speed as a function of additional relative pressure loss

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Figure 10

Ramp-up of recuperator valve from 52.5% to 100% at different gradients %/s as a function of time

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Figure 11

Comparison of electric power output and the reciprocal pressure loss 1/Δpcr between the compressor outlet and the recuperator inlet as a function of time at valve opening settings from 52.5% to 100% (grad >80%/s at 75% turbine speed)

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Figure 12

Controller instability issue of pressure loss increase at maximum turbine speed (grad 0.2%/s)

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Figure 13

Relative distance Δdsurge to surge limit at 75% Ts as a function of bleed-air mass flow and turbine outlet temperature

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Figure 14

Electric power output at 75% Ts as a function of bleed-air mass flow and turbine outlet temperature

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