Group Combustion of Liquid Droplets

Chiu, H. H.; Liu, T. M.

doi:10.1080/00102207708946823

Cited by 259 publications

(73 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Experimental studies have been conducted to characterize the flame propagation mechanism in the presence of fuel spray, [6][7][8] in which different combustion modes were identified depending on the spray density. For a systematic investigation of the flame-spray interaction, flame spread along an array of droplets has been extensively investigated.…”

Section: Introductionmentioning

confidence: 99%

A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources

Sim

Chung

2015

Physics of Fluids

View full text Add to dashboard Cite

A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources Droplet evaporation by a localized heat source under microgravity conditions was numerically investigated in an attempt to understand the mechanism of the fuel vapor jet ejection, which was observed experimentally during the flame spread through a droplet array. An Eulerian-Lagrangian method was implemented with a temperaturedependent surface tension model and a local phase change model in order to effectively capture the interfacial dynamics between liquid droplet and surrounding air. It was found that the surface tension gradient caused by the temperature variation within the droplet creates a thermo-capillary effect, known as the Marangoni effect, creating an internal flow circulation and outer shear flow which drives the fuel vapor into a tail jet. A parametric study demonstrated that the Marangoni effect is indeed significant at realistic droplet combustion conditions, resulting in a higher evaporation constant. A modified Marangoni number was derived in order to represent the surface force characteristics. The results at different pressure conditions indicated that the nonmonotonic response of the evaporation rate to pressure may also be attributed to the Marangoni effect. C 2015 AIP Publishing LLC. KAUST Repository[http://dx

show abstract

Section: Introductionmentioning

confidence: 99%

A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources

Sim

Chung

2015

Physics of Fluids

View full text Add to dashboard Cite

show abstract

“…droplets crossing the stagnation plane, would clearly be beneficial in clarifying sprayignition characteristics in turbulent mixing layers for St = 0(1). The present work, however, is not relevant for St = 0(1) or larger, under which conditions individualdroplet combustion or droplet-cloud combustion may occur, the latter been favoured by large mass-loading ratios (Chiu & Liu 1977;Labowsky & Rosner 1978;Correa & Sichel 1982). For St < 1, the droplets behave as flow tracers and become entrained in the largescale turbulent eddies, where they come into contact with the high-temperature air, thereby promoting vaporization and ignition of the fuel spray in the resulting mixing layers.…”

Section: Droplet Dispersion and Ignition In Turbulent Mixing Layersmentioning

confidence: 93%

Dynamics of thermal ignition of spray flames in mixing layers

et al. 2013

View full text Add to dashboard Cite

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.

show abstract

“…Thus, as noted by Sichel & Palaniswamy (1984), the parameter e is exactly equal to the inverse of the square of the Thiele modulus V employed by Labowsky & Rosner (1978). Also, under the condition of small droplet Reynolds number used in deriving (2.3), e becomes equal to the reciprocal of the group combustion number G introduced by Chiu and co-workers (Chiu & Liu 1977;Chiu et al 1978) times the Lewis number. In many practical applications, the parameter e takes on small values, causing vaporization to occur in a sheath or vaporization front that separates the spray, in saturated equilibrium, from the surrounding droplet-free hot gas, with the flame standing outside the spray in combustion configurations.…”

Section: Pjmentioning

confidence: 99%

Sheath vaporization of a monodisperse fuel-spray jet

Arrieta

Sánchez

Liñán³

et al. 2011

J. Fluid Mech.

View full text Add to dashboard Cite

The group vaporization of a monodisperse fuel-spray jet discharging into a hot coflowing gaseous stream is investigated for steady flow by numerical and asymptotic methods with a two-continua formulation used for the description of the gas and liquid phases. The jet is assumed to be slender and laminar, as occurs when the Reynolds number is moderately large, so that the boundary-layer form of the conservation equations can be employed in the analysis. Two dimensionless parameters are found to control the flow structure, namely the spray dilution parameter 1, defined as the mass of liquid fuel per unit mass of gas in the spray stream, and the group vaporization parameter e, defined as the ratio of the characteristic time of spray evolution due to droplet vaporization to the characteristic diffusion time across the jet. It is observed that, for the small values of e often encountered in applications, vaporization occurs only in a thin layer separating the spray from the outer droplet-free stream. This regime of sheath vaporization, which is controlled by heat conduction, is amenable to a simplified asymptotic description, independent of e, in which the location of the vaporization layer is determined numerically as a free boundary in a parabolic problem involving matching of the separate solutions in the external streams, with appropriate jump conditions obtained from analysis of the quasi-steady vaporization front. Separate consideration of dilute and dense sprays, corresponding, respectively, to the asymptotic limits 1<€ 1 and A > 1, enables simplified descriptions to be obtained for the different flow variables, including explicit analytic expressions for the spray penetration distance.

show abstract

Group Combustion of Liquid Droplets

Cited by 259 publications

References 4 publications

A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources

A computational study of droplet evaporation with fuel vapor jet ejection induced by localized heat sources

Dynamics of thermal ignition of spray flames in mixing layers

Sheath vaporization of a monodisperse fuel-spray jet

Contact Info

Product

Resources

About