Oscillatory fuel droplet vaporization - Driving mechanism for combustion instability

Duvvur, A.; Chiang, Chen‐Yu; Sirignano, William A.

doi:10.2514/3.24036

Cited by 67 publications

(33 citation statements)

References 8 publications

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“…This heat and mass transfer process drives droplet heating and vaporization. Furthermore, the pressure-coupled response of the droplet vaporization is commanded by the coupling between the acoustic and thermal processes occurring in an immediate vicinity of the gas film [7]. We assume that the ambient gas heat and mass transfer may be viewed as quasi-steady.…”

Section: Description Of the Problem And Modelmentioning

confidence: 99%

“…The emphases are placed on whether droplet vaporization can respond to oscillatory environments, including a vary range of frequencies and amplitudes of pressure oscillation. For example, Sirignano et al [7][8][9] model some pioneering studies in these research fields, their results show that if vaporization is the heat release rate-control process, the gain or response function associated with the oscillatory vaporization rate component in phase with the pressure is shown to be sufficiently large to sustain instability. Yang et al [10][11][12] studied the response of droplet vaporization to ambient pressure oscillation at supercritical condition; their results indicate that a rapid enlargement of the vaporization occurs when the droplet surface reaches its critical point, mainly due to the strong variations of latent heat of vaporization and thermo-physical properties at the critical state.…”

Section: Introductionmentioning

confidence: 95%

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Dynamic response of vaporizing droplet to pressure oscillation

2016

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inertia of the droplet also plays a considerable role in determining the phase lag. List of symbols A PSurface area of the droplet (m 2 ) B M Spalding mass transfer number B T Spalding heat transfer number C D Drag coefficient C P,F Specific heat of droplet vapor evaluated at the reference conditions in the gas film (J/kg K) C P,g Gas specific heat evaluated at the reference conditions (J/kg K) C P,l Droplet specific heat (J/kg K) D i,m Binary diffusion coefficient evaluated at the reference conditions (m 2 /s)Frequency of fluctuation (Hz) F M Diffusion film thickness correction factor F T Thermal film thickness correction factorGas conductivity valuated at the reference conditions in the gas film (W/m K) k l Droplet conductivity (W/m K) LeLewis numbeṙ mMass vaporization rate (kg/s) m P Droplet mass (kg) M w,i Molecular weight of droplet vapor (kg/kmol) M w,j Molecular weight of ambient gas (kg/kmol) Nu Actual Nusselt number Nu * Modified Nusselt number Nu 0 Nusselt number for the non-vaporizing droplet Abstract Combustion instability is a major challenge in the development of the liquid propellant engines, and droplet vaporization is viewed as a potential mechanism for driving instabilities. Based on the previous work, an unsteady droplet heating and vaporization model was developed. The model and numerical method are validated by experimental data available in literature, and then the oscillatory vaporization of n-Heptane droplet exposed to unsteady harmonic nitrogen atmosphere was numerically investigated over a wide range of amplitudes and frequencies. Also, temperature variations inside the droplet were demonstrated under oscillation environments. It was found that the thermal wave is attenuated with significantly reduced wave intensities as it penetrates deep into droplet from the ambient gas. Droplet surface temperature exhibits smaller fluctuation than that of the ambient gas, and it exhibits a time lag with regard to the pressure variation. Furthermore, the mechanism leading to phase lag of vaporization rate with respect to pressure oscillation was unraveled. Results show that this phase lag varies during the droplet lifetime and it is strongly influenced by oscillation frequency, indicating droplet vaporization is only capable of driving combustion instability in some certain frequency domains. Instead, the amplitude of the oscillation does not have very significant effects. It is noteworthy that thermal

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Section: Description Of the Problem And Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Dynamic response of vaporizing droplet to pressure oscillation

2016

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“…The candidate mechanisms for this challenging phenomena result from the interaction between the combustion chamber acoustics and one or more processes which are related to liquid injection, primary atomization, secondary atomization, chemical kinetics, evaporation and liquid heating and mixing [15,54,26]. Particularly, in the past, the vaporization process, as one of the key factors driving combustion instability, has been investigated by large number researchers [47,49,12]. Compared with the other processes associated with combustion chamber, vaporization, in general, is the slowest, and hence may be the rate-controlling process, as pointed out by Sirignano et al [54].…”

Section: Introductionmentioning

confidence: 99%

Chaotic modelling and control of combustion instabilities due to vaporization

Lei

Turan

2010

International Journal of Heat and Mass Transfer

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“…These design parameters and operating conditions are generally controlled by other system performance requirements that cannot be readily modified in an effort to stabilize the combustor. Since the combustion time is generally dominated by the droplet vaporization time and in unstable combustors is of the order of the acoustic time [11,12], it is possible that "slow" active control of the fuel spray droplet properties may change the combustion time and, thus, reduce the driving of the instability by the combustion process, resulting in system stabilization.…”

Section: Introductionmentioning

confidence: 99%