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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

## Abstract

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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## Figures

Figure 1

Schematic of experimental rich product generator with quartz RQL module

Figure 2

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

Figure 3

Probe design

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

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.

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

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%.

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

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.

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

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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