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

Advanced Combustor Concepts for Low Emissions Supersonic Propulsion

[+] Author and Article Information
Donald J. Hautman

United Technologies Research Center,
East Hartford, CT 06108

Contributed by International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 3, 2012; final manuscript received October 28, 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 051503 (Apr 23, 2013) (12 pages) Paper No: GTP-12-1389; doi: 10.1115/1.4022992 History: Received October 03, 2012; Revised October 28, 2012

Novel lean-burn combustor concepts were designed and evaluated for supersonic aircraft propulsion, with a focus on cruise NOx emissions. Premixing to lean conditions is especially challenging at supersonic cruise because combustor inlet temperatures are high and autoignition times are short. However, combustor pressure is significantly lower than at takeoff, so at cruise this allows heated jet fuel to be vaporized before injection as an aid to mixing. Two concepts—differentiated by swirler aerodynamics, swirler size, and staging method—were evaluated in the work reported here, both using injection of vaporized jet fuel. Computational fluid dynamics (CFD) calculations of mixing and combustion were used to design hardware for each concept. Injectors for each were fabricated using stereolithography (SLA) for cold-flow mixing tests, and using metal fabrication for subsequent combustion tests. Combustion test results show that emissions index for NOx (EINOx) < 5 was achieved for both concepts in single-sector tests at supersonic cruise combustor conditions.

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Fig. 1

Phase diagram for jet fuel, calculated as described by Lee et al. [30] from thermodynamic data for a JP-8 fuel surrogate (defined hydrocarbon mixture) of Violi et al. [28]

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Fig. 2

Measurements of dissolved oxygen in JP-8 and Jet-A fuel as a function of sparging time. Sparging was performed by bubbling N2 through a 0.038 m3 (10 gal) agitated tank of fuel.

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Fig. 3

Chromatograms from GC-MS analysis of Jet-A and JP-8 fuels before and after sparging, showing no measurable change in composition (especially no loss of lighter fractions in the boxed area) after sparging. The top panel shows the before-sparged Jet-A and JP-8 chromatograms, the middle panel shows a comparison of JP-8 fuel before and after sparging (note the blue baseline chromatogram is almost entirely masked by the overlying and nearly identical red sparged chromatogram), and the bottom panel shows a comparison of Jet-A fuel before and after sparging (again, the red line almost entirely overlays the nearly-identical blue line).

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Fig. 4

Schematic of UTRC’s jet fuel heating and vaporization system, which supplied vaporized 672 K (750 °F) Jet-A fuel for the combustion tests reported here

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Fig. 5

Isenthalps for jet fuel, calculated using the JP-8 fuel surrogate of Violi et al. [28], showing temperature variation during constant-enthalpy throttling process such as flash vaporization

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Fig. 6

Swirler-injector concepts developed and tested for low-NOx combustion using vaporized jet fuel. The PICS injector is shown at left (a) and the CRESS injector at right (b).

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Fig. 7

Depiction of counterrotating externally staged swirlers (CRESS) combustor concept configuration. In this depiction a section of an annular combustor is shown, where flow is from left-to-right, the combustor’s inner liner is at the bottom, and the outer liner is at the top.

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Fig. 8

CFD prediction of mixing for PICS injector at supersonic cruise combustor conditions. The color scale indicates fuel-air mixture fraction ξ normalized by the overall mean mixture fraction. Red indicates regions where the normalized ξ is 20% or more above the mean, and blue indicates regions where it is 20% or more below the mean. In this figure bulk flow is from left-to-right (except for the exit plane view), and the swirler centerline is below the bottom of the CFD cross-section shown (below the figure).

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Fig. 9

CFD prediction of mixing for CRESS injector at supersonic cruise combustor conditions. The color scale is the same as in Fig. 8, and shows normalized mixture fraction ξ along a radial swirler cross section and at the swirler exit plane. In this figure bulk flow is from left-to-right (except for the exit plane view at the lower left), and the swirler centerline is indicated by the dashed white line.

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Fig. 10

Histogram showing distribution of normalized fuel transit time, from fuel injection orifice to swirler exit plane, as calculated by CFD for the PICS injector

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Fig. 11

Histogram showing distribution of normalized fuel transit times, from fuel injection orifice to swirler exit plane, as calculated by CFD for the CRESS injector

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Fig. 12

Photograph of cold-flow mixing experiment, with SLA PICS injector installed. This photograph shows an aft-looking-forward (ALF) view (flow direction is out of the page).

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Fig. 13

Cold-flow mixing measurements from early PICS injector. These measurements were obtained along a radial traverse at the injector exit and show excellent repeatability.

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Fig. 14

Contour-plot comparison of measured and predicted equivalence ratio for early PICS injector, for the ambient mixing test conditions. Here dark blue indicates ξ/ξmean = 0 (pure air) and red indicates ξ/ξmean = 2.5 (a fuel-air mixture 2.5 times richer than average).

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Fig. 15

Measured mixture fraction at exit plane of the final PICS injector design. The left-hand panel shows measurements obtained along radial traverses in the annulus of the injector’s primary swirler exit, and the right-hand panel shows a contour plot of the entire exit plane. In the contour plot, dark blue indicates ξ/ξmean = 0 and red indicates ξ/ξmean = 1.25.

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Fig. 16

Mixing at ambient cold-flow rig conditions (left-hand panel) versus supersonic cruise conditions (right-hand panel), as predicted by both RANS and LES turbulence models

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Fig. 17

Measured mixture fraction at exit plane of the small CRESS injector design. The left-hand panel shows measurements obtained as a function of radial distance from the swirler centerline, and the right-hand panel shows a contour plot of the right-half exit plane. In the contour plot, dark blue indicates ξ/ξmean = 0 and red indicates ξ/ξmean = 1.2.

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Fig. 18

Solid-model view of high-pressure combustion test stand used for the combustion tests reported here. For these tests, the replaceable test section was water cooled. A five-sample emissions probe was inserted from the aft end and has the ability to rotate or translate axially during combustion tests.

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Fig. 19

Photograph of single PICS injector installed in 10.2 cm (4 in.) square water-cooled combustor rig, from aft-looking-forward (ALF) view

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Fig. 20

Photograph of two large CRESS injectors installed in UTRC’s 7.6 cm × 12.7 cm (3 in. × 5 in.) water-cooled combustor (with the nearer sidewall removed for the photograph). The gas-sampling emissions probe is also visible in this photograph.

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Fig. 21

Emissions from the single-injector PICS combustor at supersonic cruise combustor conditions, showing EINOx <5 and combustion efficiency >99.99% (based on CO and UHC emissions). For these high-power tests, vaporized Jet-A fuel (at 672 K (750 °F)) was delivered to the PICS injector’s main-stage, and unheated liquid Jet-A was delivered to the pilot-stage. Emissions are plotted against FAR as measured at the emissions probe, normalized by the FAR at sea-level takeoff (SLTO) for this engine cycle. FAR/FARSLTO = 1.10 at supersonic cruise.

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Fig. 22

Emissions data for PICS injector operating at idle conditions on the pilot-stage only, using unheated liquid Jet-A fuel. Data represent operation at idle combustor inlet conditions and are plotted versus the metered FAR, normalized by FARSLTO for this engine cycle. The target idle condition is near FAR/FARSLTO = 0.57.

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Fig. 23

Emissions from the two-injector CRESS combustor, showing EINOx ∼ 5 and combustion efficiency >99.98% at supersonic cruise combustor conditions. For these high-power tests, vaporized Jet-A fuel (at 672 K (750 °F)) was delivered to both CRESS injectors. Emissions are plotted against FAR as measured at the emissions probe, normalized by the FAR at sea-level-takeoff (SLTO) for this engine cycle. FAR/FARSLTO = 1.10 at supersonic cruise.




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