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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Investigation of the Effect of Incomplete Droplet Prevaporization on NOx Emissions in LDI Combustion Systems

[+] Author and Article Information
Christian H. Beck

Institut für Thermische Strömungsmaschinen, Universität Karlsruhe (TH), 76128 Karlsruhe, Germanychristian.beck@its.uka.de

Rainer Koch, Hans-Jörg Bauer

Institut für Thermische Strömungsmaschinen, Universität Karlsruhe (TH), 76128 Karlsruhe, Germany

J. Eng. Gas Turbines Power 130(5), 051504 (Jun 13, 2008) (8 pages) doi:10.1115/1.2906185 History: Received November 09, 2007; Revised November 12, 2007; Published June 13, 2008

The influence of incomplete liquid fuel prevaporization on the emissions of nitric oxides in a swirl stabilized model gas turbine combustor is investigated experimentally and numerically. The design of the model combustor enables the variation of the degree of prevaporization. This is achieved by using two liquid fuel injectors. One injector is located far upstream of the combustor and generates a fully prevaporized and premixed air fuel mixture. The second injector is located at the combustor inlet. Consequently, the liquid fuel mass flow split between the two injectors determines the fraction of nonprevaporized fuel present in the reaction zone. The NONO2 measurements were performed with a chemoluminescence analyzer. In accordance to the findings of other researchers, the present experimental study revealed that the influence of prevaporization on nitric oxide emissions is of significance for practical applications. The experimental studies were accompanied by numerical studies of partially prevaporized lean combustion in an abstracted configuration. The purpose of this numerical study is to gain a detailed understanding of the influence of droplet slip on droplet flame position and peak temperature. The droplet slip velocity was found to have a significant impact on the peak temperature of the droplet flame and, therefore, NO formation rates within the droplet flame. The combustion system used for the experimental investigation was characterized regarding droplet slip velocities with an extended laser Doppler anemometry technique. The comparison between numerical and experimental results shows that the droplet slip velocities in the macroscopic reaction zone are within the transition range from an envelope to a wake flame. It is concluded that small-scale mixing effects play a significant role in the formation of nitric oxides in spray combustion systems with incomplete prevaporization.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the rig; detail of the burner and combustion chamber

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Figure 2

Radial distribution of liquid fuel equivalence ratio for three atomizer air pressure levels, ϕ=0.55, α=0.5

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Figure 3

CDF of liquid fuel equivalence ratio for three atomizer air pressure levels, ϕ=0.55, α=0.5

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Figure 4

Influence of liquid fuel mass fraction on overall NO emissions

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Figure 5

Abstracted flame structure of partially prevaporized combustion

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Figure 6

Dimensionless NO formation rate of single droplet flames

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Figure 7

Effect of slip velocity on temperature and CH mass fraction

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Figure 8

Chemiluminescence intensity, time averaged and deconvoluted, band pass filtered for CH* emission around 431nm; ϕ=0.5, α=0.5

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Figure 9

Axial gas phase velocity and droplet slip velocity magnitude, ϕ=0.5, α=0.5, thick black line: cax=0m∕s

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