Fuel droplet vaporization and spray combustion theory

Sirignano, William A.

doi:10.1016/0360-1285(83)90011-4

Cited by 604 publications

(217 citation statements)

References 127 publications

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“…Extensive numerical studies by Sirignano [9] and Aggarwal and Sirignano [10] of spray flames showed that the reaction zone does not consist of an array of flames surrounding separate vaporizing droplets, but exhibits, simultaneously, both diffusion-like and premixedlike characteristics. Vaporisation occurs from droplets both behind, and ahead, of the propagating flame.…”

Section: Introductionmentioning

confidence: 99%

Laminar mass burning and entrainment velocities and flame instabilities of i-octane, ethanol and hydrous ethanol/air aerosols

Bradley

Lawes

Liao

et al. 2014

Combustion and Flame

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The paper reports experiments employing the cloud chamber technique for creating fuel aerosols, in studies of premixed laminar flames. Spherical explosion flames were initiated at different times after the start of expansion of the original gaseous mixture to lower pressure.Flame speeds were measured close to atmospheric pressure, over a range of equivalence ratios of iso-octane, ethanol and hydrous ethanol with air. A methodology was developed for deriving mass burning velocities and entrainment velocities, as well as mass burning fluxes, from the measurements of aerosol number densities, droplet sizes and flame speeds. It was vital to estimate whether droplet evaporation was completed in the flame preheat zone. This was done by calculating the spatial progress of droplet evaporation for the different aerosols from values of the evaporation rate constants of the different fuels.With predominantly the leaner mixtures and smaller droplet diameters, evaporation was close to completion, but the mass burning velocities of the aerosols were somewhat lower than those of the corresponding gaseous phases, because of the lower final temperatures due to the required evaporation enthalpies. However, the mass burning fluxes were higher than those for the purely gaseous flames, due to the higher two-phase reactant densities. At the higher values of the liquid phase equivalence ratio, in overall lean mixtures, the mass burning velocity could exceed that in the purely gaseous phase due to localised enrichment around the droplets.The presence of fuel droplets is shown to enhance the generation of Darrieus-Landau, thermodiffusive instabilities and the associated flame wrinkling. With richer mixtures and larger droplets, it is possible for droplets to enter the reaction zone and further enhance existing gaseous phase instabilities through the creation of yet further flame wrinkling. This leads to the maximum entrained fuel mass flux, in the richest mixture, being significantly higher than that occurring at the maximum burning velocity of a premixed gaseous flame.

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Section: Introductionmentioning

confidence: 99%

Laminar mass burning and entrainment velocities and flame instabilities of i-octane, ethanol and hydrous ethanol/air aerosols

Bradley

Lawes

Liao

et al. 2014

Combustion and Flame

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“…In the current case, the oscillation period is T (Law, 1982;Sirignano, 1983;Lefebvre, 1998;Sirignano, 2010) is also plotted, which is given by…”

Section: Thermocapillary (Marangoni) Effectmentioning

confidence: 99%

“…Therefore, an improved understanding of the temperature distribution inside an emulsion droplet is needed as a key initial condition for accurate modeling of microexplosion/puffing, and will be aimed in this paper. In the literature, the heating process of emulsion droplets has been discussed (Law, 1977;Law et al, 1980;Law, 1982;Sirignano, 1983). However, the knowledge is still not sufficient to determine the initial conditions for microexplosion/puffing of emulsion droplets.…”

mentioning

confidence: 99%

Modeling Temperature Distribution Inside an Emulsion Fuel Droplet Under Convective Heating: A Key to Predicting Microexplosion and Puffing

et al. 2016

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Microexplosion/puffing is rapid disintegration of a water-in-oil emulsion droplet caused by explosive boiling of embedded superheated water sub-droplets. To predict microexplosion/puffing, modeling the temperature distribution inside an emulsion droplet under convective heating is a prerequisite, since the temperature field determines the location of nucleation (vapor bubble initiation from superheated water). In the first part of the present study, convective heating of water-in-oil emulsion droplets under typical combustor conditions is investigated using high-fidelity simulation in order to accurately model inner-droplet temperature distribution. The shear force due to the ambient air flow induces internal circulation inside a droplet. It has been found that for droplets under investigation in the present study, the liquid Peclet number PeL is in a transitional regime of 100

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“…Because of their key role in numerous technological applications, combustion and vaprization of fuel sprays have been the subject of many modelling efforts (see Faeth 1983;Sirignano 1983;Williams 1985;Annamalai & Ryan 1992;Li 1997;Aggarwal 1998;Crowe, Sommerfeld & Tsuji 1998 Knudsen & Pitsch 2010;Luo et al 2011;Shashank 2011;Neophytou, Mastorakos & Cant 2012), including disparate length and time scales associated with the chemistry and with the multiphase nature of the flow, which is highly turbulent in most applications.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of thermal ignition of spray flames in mixing layers

et al. 2013

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Conditions are identified under which analyses of laminar mixing layers can shed light on aspects of turbulent spray combustion. With this in mind, laminar spray-combustion models are formulated for both non-premixed and partially premixed systems. The laminar mixing layer separating a hot-air stream from a monodisperse spray carried by either an inert gas or air is investigated numerically and analytically in an effort to increase understanding of the ignition process leading to stabilization of high-speed spray combustion. The problem is formulated in an Eulerian framework, with the conservation equations written in the boundary-layer approximation and with a one-step Arrhenius model adopted for the chemistry description. The numerical integrations unveil two different types of ignition behaviour depending on the fuel availability in the reaction kernel, which in turn depends on the rates of droplet vaporization and fuel-vapour diffusion. When sufficient fuel is available near the hot boundary, as occurs when the thermochemical properties of heptane are employed for the fuel in the integrations, combustion is established through a precipitous temperature increase at a well-defined thermal-runaway location, a phenomenon that is amenable to a theoretical analysis based on activation-energy asymptotics, presented here, following earlier ideas developed in describing unsteady gaseous ignition in mixing layers. By way of contrast, when the amount of fuel vapour reaching the hot boundary is small, as is observed in the computations employing the thermochemical properties of methanol, the incipient chemical reaction gives rise to a slowly developing lean deflagration that consumes the available fuel as it propagates across the mixing layer towards the spray. The flame structure that develops downstream from the ignition point depends on the fuel considered and also on the spray carrier gas, with fuel sprays carried by air displaying either a lean deflagration bounding a region of distributed reaction or a distinct double-flame structure with a rich premixed flame on the spray side and a diffusion flame on the air side. Results are calculated for the distributions of mixture fraction and scalar dissipation rate across the mixing layer that reveal complexities that serve to identify differences between spray-flamelet and gaseous-flamelet problems.

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Fuel droplet vaporization and spray combustion theory

Cited by 604 publications

References 127 publications

Laminar mass burning and entrainment velocities and flame instabilities of i-octane, ethanol and hydrous ethanol/air aerosols

Laminar mass burning and entrainment velocities and flame instabilities of i-octane, ethanol and hydrous ethanol/air aerosols

Modeling Temperature Distribution Inside an Emulsion Fuel Droplet Under Convective Heating: A Key to Predicting Microexplosion and Puffing

Dynamics of thermal ignition of spray flames in mixing layers

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