Research Papers

Optical Measurements of a Lower Calorific Values-Combustor Operated in a Micro Gas Turbine With Various Fuel Compositions

[+] Author and Article Information
Timo Zornek

German Aerospace Center (DLR),
Institute of Combustion Technology,
Pfaffenwaldring 38-40,
Stuttgart 70569, Germany
e-mail: timo.zornek@dlr.de

Thomas Mosbach, Manfred Aigner

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

1Corresponding author.

Manuscript received June 26, 2018; final manuscript received July 10, 2018; published online December 7, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(4), 041032 (Dec 07, 2018) (7 pages) Paper No: GTP-18-1375; doi: 10.1115/1.4040908 History: Received June 26, 2018; Revised July 10, 2018

In a recent joint research project, a new FLOX®-combustion system was developed to couple a fixed-bed gasifier with a micro gas turbine (MGT). Product gases from biomass gasification exhibit low calorific values and varying compositions of mainly H2, CO, CO2, N2, and CH4. Furthermore, combustion characteristics differ significantly compared to the commonly used natural gas. As the FLOX-technology is considered as efficient and fuel-flexible featuring low emissions of hazardous pollutants, the design of the lower calorific value (LCV) combustor is based on it. It contains a two-staged combustor consisting of a jet-stabilized main stage adapted from the FLOX-concept combined with a swirl stabilized pilot stage. The combustor was operated in a Turbec T100 test rig using an optically accessible combustion chamber, which allowed OH*-chemiluminescence and OH-PLIF measurements for various fuel compositions. In particular, the hydrogen content in the synthetically mixed fuel gas was varied from 0% to 30%. The exhaust gas composition was additionally analyzed regarding CO, NOx, and unburned hydrocarbons. The results provide a comprehensive insight into the flame behavior during turbine operation. Efficient combustion and stable operation of the MGT was observed for all fuel compositions, while the hydrogen showed a strong influence. It is remarkable that with hydrogen contents higher than 9%, no OH radicals were detected within the inner recirculation zone, while they were increasingly entrained below hydrogen contents of 9%. Without hydrogen, the inner recirculation zone was completely filled with OH radicals and the highest concentrations were detected there. Therefore, the results indicate a different flame behavior with low and high hydrogen contents. Although the flame shape and position were affected, pollutant emissions remained consistently below 10 ppm based on 15% O2. Only in the case of 0% hydrogen, CO-emissions increased to 43 ppm, which are still meeting the emission limits. Thus, the combustor allows operation with syngases having hydrogen contents from 0% to 30%.

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Fig. 1

Schematic of the test rig [5]

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Fig. 2

Schematic of the combustion chamber [5]

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Fig. 3

Combustor prototype (picture: DLR/frank eppler)

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Fig. 4

Optical combustion chamber

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Fig. 5

Set-up for optical measurements

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Fig. 6

Instantaneous images of the measured OH distribution

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Fig. 7

Analyzed gradients of instantaneous OH-PLIF Images

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Fig. 8

Averaged images of OH*-chemiluminescence (left), OH-PLIF (center), and OH-PLIF gradients (right)

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Fig. 9

Ignition delay of fuel mixtures

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Fig. 10

Pollutant emissions based on 15% O2



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