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Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion

Wang, Xionghui
http://orcid.org/0000-0001-9115-2875
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083

Abstract Details

2017, PhD, University of Cincinnati, Engineering and Applied Science: Aerospace Engineering.
A self-excited instability of liquid-fueled swirling combustion in a laboratory scale combustor is investigated in this study.Liquid fuel is injected through a simplex nozzle and mixed with a swirling air flow generated by an in-house designed, radial-radial, counter-rotating swirler. Air is preheated to 400F (477K). Air flow rate is maintained constant during tests while fuel flow rate is varied to achieve different global equivalence ratios. Pressure perturbations were monitored and recorded by two dynamic pressure transducers (Model PCB 116B) located at 4 and 9.5 inches downstream of a dome plate. Global chemiluminescence filtered by a CH* filter is recorded by a photomultiplier tube (PMT). The data of perturbed pressure and instant chemiluminescence emission are saved simultaneously through a high-response-data-acquisition board. Instant flame image indicating spatial chemiluminescence fluctuations is recorded by a high-speed camera. Acoustic boundaries of the combustion chamber’s inlet and outlet were first characterized. For the no bias flow case, the swirler impedance exhibits classical compact-element characteristics. When bias flow is presented, the swirler impedance greatly depends on flow Mach number. The temperature dependence of the impedance is captured in the wavenumber. The chamber exit impedances were measured and curve-fitted into correlations. Then the flame response to air modulation is studied at four equivalence ratios. A loudspeaker is used to perturb plenum air in a 22.5 inches (0.5715m) long combustion chamber. The flame dynamics are expressed as flame transfer functions which are defined as the ratio of relative global heat release rate oscillations to the relative velocity fluctuations at the base of the flame, and calculated within the range of tested equivalence ratio. The behavior of the flame dynamics indicates that the combustion system is similar to a damped high-order system. At last, the instability map of the studied swirler is established. Pressure and flame chemiluminescence emission oscillations were recorded. Velocity oscillations are computed from pressure perturbations using a two-microphone method. The measurements recovered Rayleigh’s criterion which states that when pressure perturbation and unsteady heat input are in phase, combustion instability tends to occur. During tests, a sudden increase of static pressure was observed while air mass flow rates remained the same when combustion instabilities occurred, indicating the air flow temperature at the exit of the swirler increased. Meanwhile, the intensity of chemiluminescence emissions inside the swirler venturi observed from the top view of the combustion chamber became stronger at the occurrence of combustion instability. A possible theory of burning inside the venturi or burning on the fuel nozzle tip is proposed. The possible relation of burning inside the venturi and the occurrence of combustion instability is investigated. The variation of air mass distribution between the primary swirler and secondary swirler due to burning inside the venturi is checked using a numerical simulation. The increased flow Mach number at the chamber inlet altered the inlet acoustic impedance. The outcomes of burning inside the venturi are in favor of combustion instabilities. The universality of the relationship between burning inside the venturi and combustion instability requires further investigations.
San-Mou Jeng, Ph.D. (Committee Chair)
Jongguen Lee, Ph.D. (Committee Member)
Asif Syed, Ph.D. (Committee Member)
147 p.
Aerospace Materials
Combustion Instability; Swirling Flow; Heat release rate oscillation; Liquid-fueled swirling combustion

Recommended Citations

Citations

  • Wang, X. (2017). Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083

    APA Style (7th edition)

  • Wang, Xionghui. Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion. 2017. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083.

    MLA Style (8th edition)

  • Wang, Xionghui. "Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion." Doctoral dissertation, University of Cincinnati, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083

    Chicago Manual of Style (17th edition)

ucin1516361245616083
499
© 2017, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.