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TECHNICAL PAPERS

The Effects of Air Preheat and Number of Orifices on Flow and Emissions in an RQL Mixing Section

[+] Author and Article Information
James D. Holdeman1

National Aeronautics and Space Administration, Glenn Research Center, Cleveland, OH 44135jjdholdeman@aol.com

Clarence T. Chang

National Aeronautics and Space Administration, Glenn Research Center, Cleveland, OH 44135

1

Corresponding author.

J. Fluids Eng 129(11), 1460-1467 (May 02, 2007) (8 pages) doi:10.1115/1.2786531 History: Received September 07, 2006; Revised May 02, 2007

This study was motivated by a goal to understand the mixing and emissions in the rich-burn/quick-mix/lean-burn combustor scheme that has been proposed to minimize the formation of oxides of nitrogen (NOx) in gas turbine combustors. The study reported in this paper was a reacting jet-in-crossflow experiment at atmospheric pressure in a cylindrical duct. The jets were injected from the perimeter of the duct through round-hole orifices into a fuel-rich mainstream flow. The number of orifices investigated in this study gave over- to optimum to underpenetrating jets at a jet-to-mainstream momentum-flux ratio of 57. The size of individual orifices was decreased as their number increased to maintain a constant total area. The jet-to-mainstream mass-flow ratio was held constant at 2.5. The experiments focused on the effects of the number of orifices and inlet air preheat and were conducted in a facility that provided the capability for independent variation of jet and main inlet air preheat temperature. The number of orifices was found to have a significant effect on mixing and the distributions of species, but very little effect on overall NOx emissions, suggesting that an aerodynamically optimum mixer may not minimize NOx emissions. Air preheat was found to have very little effect on mixing and the distributions of major species, but preheat did increase NOx emissions significantly. Although the air jets injected in the quick-mix section of a RQL combustor may comprise over 70% of the total air flow, the overall NOx emission levels were found to be more sensitive to mainstream air preheat than to jet stream air preheat.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 7

(a) CO distribution plots at x∕R=1 and J=57 for modules with different number of round holes with both the main and jet air preheated. Average=2.91±1.98% (b) CO2 distribution plots at x∕R=1 and J=57 for modules with different number of round holes with both the main and jet air preheated. Average=6.39±1.15%. (c) O2 distribution plots at x∕R=1 and J=57 for modules with different number of round holes with both the main and jet air preheated. Average=7.96±3.13%.

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Figure 8

Comparison of local NOx data at x∕R=1 and J=57 for the 12 round-hole module with different air streams preheated

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Figure 9

NOx distribution plots at x∕R=1 and J=57 for the 12 round-hole module with different air streams preheated. Average=16.91±2.13ppm.

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Figure 10

Effect of air preheat on area-weighted NOx data at x∕R=1 and 57 for the 12 round-hole module with different air streams preheated

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Figure 11

(a) CO distribution plots at x∕R=1 and J=57 for the 12 round-hole module with different air streams preheated. Average=2.63±2.37%. (b) CO2 distribution plots at x∕R=1 and J=57 for the 12 round-hole module with different air streams preheated. Average=7.24±2.73%. (c) O2 distribution plots at x∕R=1 and J=57 for the 12 round-hole module with different air streams preheated. Average=7.46±3.33%.

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Figure 6

Area-weighted planar average NOx emissions at x∕R=1 and J=57 for modules with different number of round holes with both the main and jet air preheated

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Figure 1

Schematic of experimental rich product generator with quartz RQL module

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Figure 2

Measurement locations: (a) data plane locations; (b) data point locations

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Figure 4

Comparison of local NOx data at x∕R=1 and J=57 for modules with different numbers of round holes with both the main and jet air preheated

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Figure 5

NOx distribution plots at x∕R=1 and J=57 for modules with different number of round holes with both the main and jet air preheated. Average=24.15±2.83ppm.

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