Acoustically Coupled Combustion of Liquid Fuel Droplets

Karagozian, Ann

doi:10.1115/1.4033792

Cited by 9 publications

(7 citation statements)

References 61 publications

(160 reference statements)

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“…The present work builds upon prior studies of the acoustically coupled droplet combustion of neat fuels (Sevilla-Esparza et al. 2014; Karagozian 2016; Bennewitz et al. 2018) and liquid nanofuel mixtures (Sim et al.…”

Section: Introductionmentioning

confidence: 91%

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Dynamics of acoustically coupled single- and multi-port jet diffusion flames

Vargas,

Kiani,

Hayrapetyan

et al. 2023

J. Fluid Mech.

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The present experimental study investigated the dynamics of single- and multi-port gaseous jet diffusion flames exposed to acoustic excitation via a standing wave situated in a closed waveguide at atmospheric pressure. High-speed imaging of the oscillatory flame was analysed via proper orthogonal decomposition (POD), revealing distinct signatures in both mode shapes and phase portraits for transitions in the acoustically coupled combustion process. For Reynolds numbers between 20 and 100, and for low to moderate forcing amplitudes, the flame exhibited sustained oscillatory combustion (SOC) that was highly coupled to the acoustic forcing. Frequency analysis of the temporal POD modes accurately recovered the forcing frequency and its higher harmonics. At higher forcing amplitudes, a multi-frequency response was observed, resulting from a combination of the forcing frequency and much lower frequency oscillations due to periodic lift-off and reattachment (PLOR) of the flame, preceding a transition to flame blow-off (BO). For both single- and triple-jet flames, transitions from SOC to PLOR to BO were characterized by significant alterations in primary modal energetic content, deflection and eventual smearing in phase portraits, and the development of additional frequencies in modal spectra, although transitional behaviour for the triple jet flames involved additional complexity in the dynamics due to its structure. These features provide the potential for the development of reduced-order models that can characterize and predict acoustically coupled combustion behaviour.

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Section: Introductionmentioning

confidence: 91%

“…In the past, our group at UCLA has explored acoustically coupled combustion of liquid neat fuel and nanofuel droplets (Sevilla-Esparza et al. 2014; Karagozian 2016; Bennewitz et al. 2018; Sim et al.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of acoustically coupled single- and multi-port jet diffusion flames

Vargas,

Kiani,

Hayrapetyan

et al. 2023

J. Fluid Mech.

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“…On the contrary, there was a little observable change in gasification rate when droplet was stationed at velocity node. Further, the droplet diffusion flames were found to be most responsive at low excitation frequencies (~5–330 Hz) 24 , 40 – 44 while they exhibited diminished response at higher forcing frequencies (>400 Hz). This indicates that oscillation mechanisms in combusting droplet exhibit multi-parameter dependence and hence provide an innovative means of manipulation at the droplet scale, which form a sub-grid elements of any gel spray based combustion strategy.…”

Section: Introductionmentioning

confidence: 97%

“…A fundamental understanding of oscillatory droplet combustion is also crucial from an application viewpoint given its relevance to combustion instabilities 40 – 43 in liquid rocket engines. Interestingly, previous studies have shown that the pure fuel (ethanol, methanol) droplet flames are also susceptible to oscillations when subjected to external acoustic excitation either through travelling 24 , 44 or standing pressure waves 40 – 43 . In the latter case, an increase in droplet burn rate by as large as ~15% under normal gravity conditions has been reported when the sound pressure level exceeded ~135 dB and droplet was placed near pressure node.…”

Section: Introductionmentioning

confidence: 99%

Oscillatory bursting of gel fuel droplets in a reacting environment

Miglani

Nandagopalan

John

et al. 2017

Sci Rep

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Understanding the combustion behavior of gel fuel droplets is pivotal for enhancing burn rates, lowering ignition delay and improving the operational performance of next-generation propulsion systems. Vapor jetting in burning gel fuel droplets is a crucial process that enables an effective transport (convectively) of unreacted fuel from the droplet domain to the flame zone and accelerates the gas-phase mixing process. Here, first we show that the combusting ethanol gel droplets (organic gellant laden) exhibit a new oscillatory jetting mode due to aperiodic bursting of the droplet shell. Second, we show how the initial gellant loading rate (GLR) leads to a distinct shell formation which self-tunes temporally to burst the droplet at different frequencies. Particularly, a weak-flexible shell is formed at low GLR that undergoes successive rupture cascades occurring in same region of the droplet. This region weakens due to repeated ruptures and causes droplet bursting at progressively higher frequencies. Contrarily, high GLRs facilitate a strong-rigid shell formation where consecutive cascades occur at scattered locations across the droplet surface. This leads to droplet bursting at random frequencies. This method of modulating jetting frequency would enable an effective control of droplet trajectory and local fuel-oxidizer ratio in any gel-spray based energy formulation.

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“…Droplet combustion experiments have also been conducted on ethanol and their blends with gasoline and diesel [13][14][15][16]. It is well understood that burning the mixtures of alcohol/alkane results in disruptive behavior due to significant volatility differential between the fuel components [17].…”

Section: Introductionmentioning

confidence: 99%

Experimental investigations on nucleation, bubble growth, and micro-explosion characteristics during the combustion of ethanol/Jet A-1 fuel droplets

Rao

Syam

Karmakar

et al. 2017

Experimental Thermal and Fluid Science

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The combustion characteristics of ethanol/Jet A-1 fuel droplets having three different proportions of ethanol (10%, 30%, and 50% by vol.) are investigated in the present study. The large volatility differential between ethanol and Jet A-1 and the nominal immiscibility of the fuels seem to result in combustion characteristics that are rather different from our previous work on butanol/Jet A-1 droplets (miscible blends). Abrupt explosion was facilitated in fuel droplets comprising lower proportions of ethanol (10%), possibly due to insufficient nucleation sites inside the droplet and the partially unmixed fuel mixture. For the fuel droplets containing higher proportions of ethanol (30% and 50%), micro-explosion occurred through homogeneous nucleation, leading to the ejection of secondary droplets and subsequent significant reduction in the overall droplet lifetime. The rate of bubble growth is nearly similar in all the blends of ethanol; however, the evolution of ethanol vapor bubble is significantly faster than that of a vapor bubble in the blends of butanol. The probability of disruptive behavior is considerably higher in ethanol/Jet A-1 blends than that of butanol/Jet A-1 blends. The Sauter mean diameter of the secondary droplets produced from micro-explosion is larger for blends with a higher proportion of ethanol. Both abrupt explosion and micro-explosion create a large-scale distortion of the flame, which surrounds the parent droplet. The secondary droplets generated from abrupt explosion undergo rapid evaporation whereas the secondary droplets from micro-explosion carry their individual flame and evaporate slowly. The growth of vapor bubble was also witnessed in the secondary droplets, which leads to the further breakup of the droplet (puffing/micro-explosion).

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Acoustically Coupled Combustion of Liquid Fuel Droplets

Cited by 9 publications

References 61 publications

Dynamics of acoustically coupled single- and multi-port jet diffusion flames

Dynamics of acoustically coupled single- and multi-port jet diffusion flames

Oscillatory bursting of gel fuel droplets in a reacting environment

Experimental investigations on nucleation, bubble growth, and micro-explosion characteristics during the combustion of ethanol/Jet A-1 fuel droplets

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