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Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion

Pinchak, Matthew D.
http://orcid.org/0000-0003-4936-1053
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522319737952261

Abstract Details

2018, PhD, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
The operation of gas turbine engines in increasingly harsh environments while constrained by stringent emissions regulations requires multiple advances in combustion technology. This dissertation addresses two different ways to enhance the stability and control of the combustion process under such conditions: the reacting jet in vitiated cross-flow (Part I) and ozone-assisted combustion (Part II). The first chapter of original research (Chapter 4) examines several fundamental aspects of the reacting jet in cross-flow (RJICF). A circular nozzle and high aspect ratio slotted nozzle of identical area were investigated for jet to cross-flow momentum flux ratios ranging from J = 5 to 65 for jet equivalence ratios of up to φj = 5.0. Particle image velocimetry was utilized to study the flow-field and OH* chemiluminescence was used to capture features of the flame behavior. The nozzle geometry was determined to have a significant effect on RJICF flame stability, with substantially expanded blow-out limits for the high aspect ratio slotted nozzle. Enhanced operability of the slotted nozzle is attributed to the substantially larger and stronger recirculation zone on the leeward side of the jet when compared to the circular nozzle. This area is characterized by a more disperse region of elevated vorticity levels, resulting in the entrainment of more hot combustion products with a longer residence time in the recirculation zone, which in turn provides a stronger and more stable ignition source to the oncoming, unburned reactants. The RJICF is a highly dynamic phenomenon, and its unsteady characteristics are discussed in Chapter 5. It is shown that both the non-reacting and reacting flow-fields are characterized by a peak oscillation frequency present in both the streamwise and transverse velocity components. The wake Strouhal numbers (Stw) of the isothermal slotted jet match values of Stw ≈ 0.13 reported in previous studies, whereas under combusting conditions Stw increases from 0.152 to 0.173 as J is increased from 10 to 35. Proper-orthogonal decomposition (POD) was performed on the data to extract the primary coherent structures present in the flow-field. It was shown that the strongest modes correspond to structures associated with the fluctuating wake vortices. Chapter 6 investigates the effects of cross-flow fueling on the RJICF. It is demonstrated that as the cross-flow equivalence ratio, φ∞, is increased, less fuel is required in the jet fluid to stabilize a flame. For φ∞ = 0.7, no fuel is required in the jet and a flame can be stabilized by a pure air jet. Part II is an investigation comprised of detailed experiments and numerical simulations on the effects of the addition of ozone on the combustion process for gaseous ethylene (C2H4) and liquid n-heptane (C7H16) and toluene (C7H8) mixtures. The experimental results show increases in the laminar flame speed when 7.8% of the O2 in the air is converted to 11,000 ppm O3. Simulations showed that most of the O3 is consumed through two dominant pathways: decomposition through collision with N2 and the direct reaction with H. Significantly, it was demonstrated that flow conditions influence the amount of flame speed enhancement for a constant amount of O3 addition. It was found that as the stretch rate is increased, the H that is produced at higher temperatures later in the flame does not have to diffuse as far upstream to react with O3. Increased flux through this pathway results in elevated levels of heat release earlier in the flame and, depending on the fuel, diverts H from detrimental pathways, resulting in increased flame propagation rates.
Ephraim Gutmark, Ph.D. (Committee Chair)
Shaaban Abdallah, Ph.D. (Committee Member)
Prashant Khare, Ph.D. (Committee Member)
Timothy Ombrello, Ph.D. (Committee Member)
242 p.
Aerospace Materials
Reacting jet in cross flow; Plasma-assisted combustion; Ozone-Assisted Combustion; Particle image velocimetry; Fluidic flame stabilization

Recommended Citations

Citations

  • Pinchak, M. D. (2018). Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522319737952261

    APA Style (7th edition)

  • Pinchak, Matthew. Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion. 2018. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522319737952261.

    MLA Style (8th edition)

  • Pinchak, Matthew. "Enhanced Flame Stability and Control: The Reacting Jet in Vitiated Cross-Flow and Ozone-Assisted Combustion." Doctoral dissertation, University of Cincinnati, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522319737952261

    Chicago Manual of Style (17th edition)

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