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

Investigation of Air Injection and Cavity Size Within a Circumferential Combustor to Increase G-Load and Residence Time

[+] Author and Article Information
Andrew E. Cottle

Department of Aeronautics and Astronautics,
Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH 45433

Marc D. Polanka

Department of Aeronautics and Astronautics,
Air Force Institute of Technology,
Wright-Patterson Air Force Base, OH, 45433

Larry P. Goss

Innovative Scientific Solutions, Inc.,
7610 McEwen Road,
Dayton, OH 45459

Corey Z. Goss

Innovative Scientific Solutions, Inc.,
7610 McEwen Road,
Dayton, OH 45459

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 26, 2017; final manuscript received July 4, 2017; published online September 19, 2017. Editor: David Wisler. This work is in part a work of the U.S. Government. ASME disclaims all interest in the U.S. Government's contributions.

J. Eng. Gas Turbines Power 140(1), 011501 (Sep 19, 2017) (12 pages) Paper No: GTP-17-1182; doi: 10.1115/1.4037578 History: Received May 26, 2017; Revised July 04, 2017

A gas turbine combustion process subjected to high levels of centrifugal acceleration has demonstrated the potential for increased flame speeds and shorter residence times. Ultracompact combustors (UCC) invoke the high-g phenomenon by introducing air and fuel into a circumferential cavity which is recessed radially outboard with respect to the primary axial core flow. Upstream air is directed tangentially into the combustion cavity to induce bulk circumferential swirl. Swirl velocities in the cavity produce a centrifugal load on the flow that is typically expressed in terms of gravitational acceleration or g-loading. The Air Force Institute of Technology (AFIT) has developed an experimental facility in which g-loads up to 2000 times the earth’s gravitational field (“2000 g’s”) have been demonstrated. In this study, the flow within the combustion cavity is examined to determine factors and conditions which invoke responses in cavity g-loads. The AFIT experiment was modified to enable optical access into the primary combustion cavity. The techniques of particle image velocimetry (PIV) and particle streak emission velocimetry (PSEV) provided high-fidelity measurements of the velocity fields within the cavity. The experimental data were compared to a set of computational fluid dynamics (CFD) solutions. Improved cavity air and fuel injection schemes were evaluated over a range of air flows and equivalence ratios. Increased combustion stability was attained by providing a uniform distribution of cavity air drivers. Lean cavity equivalence ratios at a high total airflow resulted in higher g-loads and more complete combustion, thereby showing promise for utilization of the UCC as a main combustor.

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Fig. 1

AFRL UCC stability map [5]

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Fig. 2

AFIT discrete-source hardware illustration (top) highlighting the guide vane detail and air/fuel injection ring (bottom) [14]

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Fig. 3

AFIT common-source test hardware illustration cutaway (left) and full view (right)

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Fig. 4

AFIT common-source hardware components (top) and interior detail (bottom)

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Fig. 5

Experimental test setup from the approximate camera location; quartz window, exhaust cowling, and exhaust duct are removed

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Fig. 6

Sample PESV image processing progression

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Fig. 7

Computational domain (top) and axial reference positions (bottom)

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Fig. 8

Top row: PIV results showing velocity magnitude (m/s) for conditions 1 (left), 2, and 3. Bottom row: CFD results with approximate matching region highlighted (identical contour levels).

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Fig. 9

PESV results of bulk velocity magnitude (m/s) for constant ϕcav=0.94 (top row) at low, mid, and high flow; and constant total inlet flow rate of 0.15 kg/s (bottom row) at ϕcav={0.75, 0.97, 1.26}

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Fig. 10

Cavity injection scheme comparison; front view of temperature contours (K) (top), and fuel injection stream traces colored by temperature (bottom) of the old (left) and new (right) experimental configuration

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Fig. 11

Single-point fuel injection stream traces colored by temperature (K); midlean (top-left), med-rich (top-right), high-lean (bottom-left), and high-rich (bottom-right)

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Fig. 12

Local equivalence ratio contours in the combustion cavity (position C2) for the high-flow case at lean (left) and rich overall cavity equivalence ratios

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Fig. 13

Cut planes at position D1 of temperature (top) and local equivalence ratio (bottom) for lean (left) and rich (right) flows

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Fig. 14

Radial profiles of circumferentially averaged temperatures in the combustion cavity

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Fig. 15

Radial profiles of circumferentially averaged g-loads in the combustion cavity

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Fig. 16

Velocity vectors (aft view) colored by tangential velocity for, from top to bottom, cases med-lean, med-rich, high-lean, and high-rich

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Fig. 17

Velocity vectors (aft view) colored by temperature (K) for the high-lean case at fore (top), mid, and aft cavity axial positions




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