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

Fuel Injection Scheme for a Compact Afterburner Without Flameholders

[+] Author and Article Information
Shai Birmaher, Philipp W. Zeller, Petter Wirfalt, Yedidia Neumeier, Ben T. Zinn

School of Aerospace Engineering, Georgia Institute of Technology, Atlanta, GA 30332

J. Eng. Gas Turbines Power 130(3), 031502 (Mar 28, 2008) (12 pages) doi:10.1115/1.2836478 History: Received April 26, 2007; Revised October 01, 2007; Published March 28, 2008

State-of-the-art afterburners employ spray bars and flameholders to burn the fuel. Such afterburner designs significantly increase the length (and thus weight), pressure losses, and observability of the engine. This paper presents a feasibility study of a compact “prime and trigger” afterburner that eliminates the flameholders and, thus, eliminates the above-mentioned problems. In this concept, afterburner fuel is injected just upstream or in between the turbine stages. As the fuel travels through the turbine stages, it evaporates and mixes with the bulk flow without any significant heat release from combustion, a process referred to as “priming.” Downstream of the turbine stages, combustion is initiated either through autoignition or by using a low power plasma radical generator to “trigger” the combustion process. The prime and trigger injection and ignition scheme has been investigated using an experimental setup that simulates the operating conditions in a typical gas turbine engine. In this study, a trigger was not used and combustion of the fuel was initiated by autoignition. In a parallel effort, a physics-based theoretical model of the priming stage was developed in order to predict the location of fuel autoignition. The theoretical predictions and the experimental measurements of temperature and CH* chemiluminescence confirm the feasibility of the proposed prime and trigger concept by demonstrating the controlled autoignition of the afterburner fuel.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the developed facility

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Figure 2

Top view of sections downstream of the primary combustor. Ports are labeled according to section and downstream order. The section labels are plenum, PL; converging section, CV; diverging section, D; and afterburner section, AB. “CL” is the port on the left side of the converging section.

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Figure 3

Coaxial airblast atomizer for Jet A injection. Jet A flows from the inner tube and air flows through the annulus. The i.d. and o.d. of fuel tube are 0.08in. and 0.125in., respectively. At the discharge, the i.d. of the air tube is 0.18in.

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Figure 4

Vector diagram and schematic showing the relation between the velocity vectors across a turbine stage and across the turbine simulator

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Figure 5

Flow analysis results for Case A: (a) total pressure (open) and static pressure (closed) and (b) total temperature (open), static temperature (closed), and wall temperature (dash)

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Figure 6

Predicted bulk velocity (solid) and predicted droplet velocity (dashed) for Case A. Injection location is 1.41m.

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Figure 7

Case A priming process indicators: reaction percent line, normalized droplet diameter, ignition integral lines for each element. Fuel injection location is 1.41m.

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Figure 8

Reaction percent lines for Case A with varying injection locations

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Figure 9

Injection/ignition map for Case A. The pairs of vertical and horizontal lines delineate the location of the TS. Four regions of injection locations are identified that characterize different ignition behaviors.

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Figure 10

Droplet evaporation time for Case A operating conditions with varying injection locations. Vertical lines delineate location of the TS.

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Figure 11

Thermocouple and pressure transducer data for Case 1

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Figure 12

Case 1 normalized temperature increase (circles) and theoretical reaction percent (solid line). Dashed vertical lines delineate the TS.

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Figure 13

Injection/ignition map for Case 1. Thick vertical line extends from the fuel injection location at 1.46m.

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Figure 14

Thermocouple and pressure transducer measurements for Case 2

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Figure 15

Case 2 normalized temperature increase (circles), reaction percent line for injection at 1.3m (bold, solid line), and reaction percent line for injection at 1.38m (bold, dashed line). Dashed vertical lines delineate the TS.

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Figure 16

Injection/ignition map for Case 2. Thick vertical lines extend from injection locations at 1.3m (solid) and 1.38m (dashed).

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Figure 17

Chemiluminescence images, intensity plots, and predicted injection/ignition maps for (a) Case 3, (b) Case 4, and (c) Case 5

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