The effect of initial diameter in spherically symmetric droplet combustion of sooting fuels

1994 ◽  
Vol 446 (1927) ◽  
pp. 255-276 ◽  
Keyword(s):  
Burning Rate ◽  
Rate Constants ◽  
Soot Formation ◽  
Droplet Diameter ◽  
Droplet Surface ◽  
Spherically Symmetric ◽  
Low Gravity ◽  
Initial Droplet ◽  
Initial Diameter ◽  
Burning Rates

The effect of initial droplet diameter on the burning rate of sooting fuels – n-heptane and 1-chloro-octane – was examined experimentally at low gravity. A 1.2s drop tower provided a low gravity environment to minimize buoyancy and achieve spherically symmetric flames for stationary droplets. Free-floating and fibre-supported droplets were burned, and both techniques gave matching results for droplets of similar initial diameter. Burning rate constants for both fuels were measured for a large number of droplets ranging from 0.4 to 1.1 mm in initial diameter. Results showed that burning rate constants decreased monotonically as the initial droplet diameter was increased above 0.6 mm for both fuels. This decrease was considered to be due to the observed increase in soot formation and accumulation in a shell-like structure inside the flame of the larger droplets. The increased collection of soot inside the larger droplet flames reduced the proportional heat release from the flame and may have acted as a barrier to heat transfer from the flame to the droplet. Flame-to-droplet diameter ratio increased monotonically with time, thus suggesting that quasi-steady combustion was not achieved. The flames and soot shells for 1-chloro-octane droplets with their lower burning rates remained closer to the droplet surface than similarly sized n-heptane droplets.

Effects of Initial Diameter on Burning of Nonane Droplets in a Non-Buoyant and Buoyant Ambience: Burning Rate, Soot Formation and Flame Structure

2001 ◽  
Author(s):  
J. H. Bae ◽  
C. T. Avedisian
Keyword(s):  
Burning Rate ◽  
Droplet Size ◽  
Soot Formation ◽  
Droplet Diameter ◽  
Flame Structure ◽  
Large Droplet ◽  
Droplet Combustion ◽  
Small Droplet ◽  
Burning Process ◽  
Initial Droplet

Abstract The results from nonane droplet combustion experiments conducted at 1g and μg are analyzed and compared in the following aspects: the burning rate, soot formation, flame structure. By varying the initial droplet diameter, we observe and discuss the effect of Do on droplet burning. The μg experiments were performed in a drop tower and a drag shield was used to create a low buoyant environment All experiments were fiber-supported and used the same experimental instruments. The droplet size between 0.40 to 0.95mm was examined in the experiments. Results showed that droplet burning is nonlinear in both a buoyant and a non-buoyant environment for the initial droplet diameters examined. Soot formation, which is influenced by Do may strongly affect the droplet burning process in both environments. The large droplet produces more soot and bums slowly whereas the small droplet bums fast because there is less soot.

The evaporation and combustion of levitated arrays of two, three and five droplets at a hot surface

1988 ◽  
Vol 418 (1855) ◽  
pp. 365-382 ◽  
Keyword(s):  
Droplet Diameter ◽  
Flame Height ◽  
Linear Arrays ◽  
Initial Droplet ◽  
Surface Temperatures ◽  
Droplet Array ◽  
Burning Rates ◽  
Hot Surface

The interactions between droplets in several geometrical arrays in Leidenfrost evaporation and combustion on a hot surface were studied. Comparisons between evaporation and burning times of isolated droplets, two- and three-droplet linear arrays, and a five-droplet array (a centre droplet surrounded by four droplets) were made. The liquids studied were water, n -heptane, and n -hexadecane at 0.101 MPa and at surface temperatures above their respective Leidenfrost values. A range of centre distance to initial droplet diameter ratios, L / d 0 , were studied (2 < L / d 0 < ∞). The evaporation or burning rates of droplets in binary arrays were found to be identical to those of isolated droplets ( L / d 0 → ∞). The flames around each droplet, however, merged as the droplets were brought closer together. In three- and five-droplet arrays more significant interactions were observed, with the edge droplets in the arrays burning faster than the centre droplets. The results are explained on the basis of flame-height measurements for the arrays. In pure evaporation, though, the droplets evaporated without regard for their neighbours.

Combustion of Nonane and JP8 Droplets With Additives in Low Convection

2003 ◽  
Author(s):  
J. H. Bae ◽  
C. T. Avedisian
Keyword(s):  
Atmospheric Pressure ◽  
Quantitative Measurement ◽  
Soot Formation ◽  
Droplet Diameter ◽  
Burning Process ◽  
Initial Droplet ◽  
Approximate Order ◽  
Scale Variable ◽  
Glycol Methyl Ether ◽  
Thermal Stability Of

The combustion of nonane and JP8 droplets was studied in an environment to promote spherically symmetric droplet flames. Measurements of the droplet, flame and soot ‘shell’ or ‘cloud’ diameters were made to examine how the burning process and sooting dynamics were influenced by three miscible additives: hexanol, tripropylene glycol methyl ether (TPM), and an additive that had been previously developed to improve thermal stability of JP8, called as ‘+100’. The experimental results presented for nonane were used to compare with JP8 for a comparatively simple fuel. The initial droplet diameters ranged from 0.4mm to 0.7mm to allow quantitative measurement of the influence of droplet diameter on the droplet burning process. Spherical symmetry was promoted by carrying out the experiments in microgravity. The burning conditions were room temperature air at atmospheric pressure. Soot formation was found to be massive for JP8 compared to nonane, with thick dark soot clouds that accumulated significant soot as burning progressed. With hexanol and TPM mixed with JP8, soot formation was noticeably reduced. Soot trends in the approximate order of JP8 &gt; JP8+100 &gt; JP8+100 / TPM (90/10, v/v) &gt; JP8+100 / TPM (80/20) &gt; JP8+100 / hexanol (50/50) &gt; nonane are noted for the fixed initial droplet diameter. Significant droplet heating was found for JP8 compared to nonane, due to the higher liquid thermal diffusivity of nonane compared to JP8 and the lower product of density and specific heat of nonane compared to JP8. A distinct influence of initial droplet diameter on the subsequent evolution of droplet diameter after ignition was found for nonane in that larger droplets burned slower than smaller droplets for the range of initial droplet diameters examined. The evolution of soot shell diameter was independent of additive concentrations for JP8 and still distinct from nonane. A new scale variable is presented which collapses the various ‘standoff’ diameters (soot shell and flame) onto a single curve for a given fuel.

Soot formation during combustion of unsupported methanol/toluene mixture droplets in microgravity

1991 ◽  
Vol 435 (1894) ◽  
pp. 359-369 ◽  
Keyword(s):  
Burning Rate ◽  
Soot Formation ◽  
Liquid Composition ◽  
Microgravity Environment ◽  
Flame Extinction ◽  
Droplet Vaporization ◽  
Toluene Concentration ◽  
Burning Rates ◽  
Pure Methanol ◽  
Made In

An experimental study is reported concerning the influence of liquid composition on soot formation and burning rate of a droplet composed of a binary miscible mixture of liquids. The mixture components represented a highly sooting fuel, toluene, and a non-sooting fuel, methanol. The experimental observations were made in a microgravity environment to create near spherically symmetric burning of the droplets. Mixtures of 5%, 25% and 50% by volume toluene in methanol were burned in room temperature air. Initial droplet diameters ranged from 0.47 mm to 0.60 mm, and the available experimental time was sufficient to record the complete droplet burning history. Toluene concentration in methanol was shown to dramatically influence flame luminosity and soot production. However, neither burning rates nor propensity for flame extinction appeared to be significantly affected by toluene mixture fractions. 5% toluene mixture droplets behaved like pure methanol droplets in terms of burning rate, lack of flame luminosity, and extinction. Increasing the toluene concentration in the droplets to 25% increased flame luminosity, yet no visible soot agglomerates were observed. The 50% mixture droplets, however, burned with highly luminous flames and large amounts of soot agglomerates collecting inside the flame. None the less, all the mixture droplets showed similar burning rates to those of pure methanol and likewise exhibited flame extinction before complete droplet vaporization.

On low-gravity droplet combustion

1988 ◽  
Vol 420 (1858) ◽  
pp. 183-200 ◽  
Keyword(s):  
Experimental Method ◽  
Unique Feature ◽  
Free Fall ◽  
Spherically Symmetric ◽  
Droplet Combustion ◽  
Fuel Droplet ◽  
Low Gravity ◽  
Piezoelectric Generator ◽  
Burning Rates ◽  
Good Agreement

An experimental method is described for studying the combustion of a stationary unsupported fuel droplet in a stagnant ambience under very low gravity. A unique feature of the method is that of being able to observe the droplet burning history over the entire period from ignition to extinction or complete burning. The procedure consisted of propelling a droplet from a piezoelectric generator in a near vertical trajectory and then releasing the chamber within which the droplet was introduced, as well as associated instrumentation, into free fall when the droplet reached the apex of its trajectory. Results with the technique are described for toluene and heptane droplets. A phenomenon believed to be indicative of extinction was observed for an unsupported heptane droplet, whereas the evidence for extinction of toluene was less clear. Measured burning rates were in good agreement with both early theories that have assumed spherically symmetric combustion, and with prior limited experiments on heptane droplets obtained under low gravity that, however, were capable of recording a more limited fraction of the total burning history.

scholarly journals Combustion of Submillimeter Heptane/Methanol and Heptane/Ethanol Droplets in Reduced Gravity

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
I. Aharon ◽  
V. K. Tam ◽  
B. D. Shaw
Keyword(s):  
Mass Fraction ◽  
Droplet Diameter ◽  
Reduced Gravity ◽  
Initial Droplet ◽  
Burning Rates ◽  
Measurement Uncertainties

Reduced-gravity experiments were performed on combustion of droplets composed of n-heptane mixed with methanol or ethanol. The initial alcohol mass fraction in a droplet was 0% (pure heptane) or 5%. The experiments were performed at 0.1 MPa and 25°C with air or with ambients of oxygen and helium with oxygen mole fractions of 0.3 or 0.4. Initial droplet diameters were in the range 0.67 mm to 0.92 mm. After considering measurement uncertainties, burning rates decreased appreciably as the initial droplet diameter increased for combustion in air but not for combustion in the oxygen/helium environments. It was also found that addition of either methanol or ethanol did not influence burning rates appreciably and that burning rates were larger for the oxygen/helium environments than for air if initial droplet diameter dependences were accounted for.

Interactive influences of convective flow and initial droplet diameter on isolated droplet burning rate

2004 ◽  
Vol 47 (8-9) ◽  
pp. 2029-2035 ◽  
Author(s):  
Guangwen Xu ◽  
Masiki Ikegami ◽  
Senji Honma ◽  
Kouji Ikeda ◽  
Daniel L. Dietrich ◽  
...  
Keyword(s):  
Burning Rate ◽  
Convective Flow ◽  
Droplet Diameter ◽  
Initial Droplet

Droplet combustion near a cold surface

1990 ◽  
Vol 429 (1877) ◽  
pp. 481-503 ◽  
Keyword(s):  
Burning Rate ◽  
Soot Formation ◽  
Liquid Droplet ◽  
Ambient Pressure ◽  
Vertical Surface ◽  
Liquid Composition ◽  
Liquid Volume ◽  
Low Gravity ◽  
Cold Surface ◽  
Theoretical Analyses

The combustion of a liquid droplet adjacent to a cold surface was studied experimentally. To isolate the effect of the proximity of the droplet to the surface, the ambient pressure (0.101 MPa), liquid composition ( n -heptane), initial liquid volume (7 x 10 -4 ml), surface material (quartz) and ambient temperature (20 ± 2°C) were held constant. A range of distances L from the surface were studied (1 mm < L < ∞). Both horizontal and vertical surface orientations were examined. A more limited set of experiments were carried out in a low gravity (i. e. low buoyancy) environment to provide a basis of comparison with relevant theoretical analyses. The flame shape, soot formation, fuel condensation, and droplet burning rate were all found to be strongly affected by the proximity of the droplet to the surface. For sufficiently large L the flame was observed to be closed around the droplet throughout burning. As L decreased, the flame was truncated. The droplet burning rate decreased as the droplet was brought progressively closer to the surface (in qualitative agreement with a relevant closed form potential flow solution to the analogous problem of a droplet burning adjacent to an adiabatic surface) and the burning rate of a droplet adjacent to a vertical surface was larger than for a horizontal surface. Surface orientation effects were observed to be absent for burning at low gravity. The extent of sooting as revealed by the flame colour was decreased, and fuel vapours condensed in a lens-like shape on the surface, as L was sufficiently reduced.

scholarly journals Airborne Particulate Matter from Sparkling Fireworks

2017 ◽  
Vol 6 (1) ◽  
pp. 19
Author(s):  
Haruki Shimazu
Keyword(s):  
Particulate Matter ◽  
Burning Rate ◽  
Airborne Particulate Matter ◽  
Emission Characteristics ◽  
Particulate Matters ◽  
Burning Time ◽  
Airborne Particulate ◽  
Suspended Particulate ◽  
Burning Rates ◽  
The Mean

The present study examines the emission levels of particulate matters (PM) from sparkling fireworks and to know the emission characteristics of PM. Particulate matter <2.5 microns (PM2.5) and suspended particulate matter (SPM) were determined while burning six brands of sparkling fireworks. The average PM concentrations before burning were levels of 10 μg/m3, but the average concentrations after burning were 741 μg/m3 for PM2.5 and 810 μg/m3 for SPM. The mean ratio of the concentrations of PM2.5 and SPM after burning in all of the sparkling fireworks was 0.890. The emissions per firework ranged from 6.5 mg to 151 mg for PM2.5, and from 7.1 mg to 160 mg for SPM. The means of the emissions per combustible amount of the firework ranged from 0.017 to 0.066 mg/mg for PM2.5, and from 0.018 to 0.071 mg/mg for SPM. The influences of the burning time, burning rate and combustible amount of the fireworks on the PM emissions were investigated. As a result, PM2.5 and SPM emissions tend to increase with the burning rates. This suggests that the burning rate of firework have an influence on the PM emissions.

scholarly journals Droplet Characteristics of Rotating Packed Bed in H2S Absorption: A Computational Fluid Dynamics Analysis

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 724
Author(s):  
Wang ◽  
Wu ◽  
Yang ◽  
Wang ◽  
Liu ◽  
...  
Keyword(s):  
Residence Time ◽  
Droplet Diameter ◽  
Packed Bed ◽  
Droplet Velocity ◽  
Radial Position ◽  
Selective Absorption ◽  
Rotating Speed ◽  
Initial Droplet ◽  
Rotating Packed Bed ◽  
Computational Fluid Dynamics Analysis

Rotating packed bed (RPB) has been demonstrated as a significant and emerging technology to be applied in natural gas desulfurization. However, droplet characteristics and principle in H2S selective absorption with N-methyldiethanolamine (MDEA) solution have seldom been fully investigated by experimental method. Therefore, a 3D Eulerian–Lagrangian approach has been established to investigate the droplet characteristics. The discrete phase model (DPM) is implemented to track the behavior of droplets, meanwhile the collision model and breakup model are employed to describe the coalescence and breakup of droplets. The simulation results indicate that rotating speed and radial position have a dominant impact on droplet velocity, average residence time and average diameter rather than initial droplet velocity. A short residence time of 0.039–0.085 s is credited in this study for faster mass transfer and reaction rate in RPB. The average droplet diameter decreases when the initial droplet velocity and rotating speed enhances. Restriction of minimum droplet diameter for it to be broken and an appropriate rotating speed have also been elaborated. Additional correlations on droplet velocity and diameter have been obtained mainly considering the rotating speed and radial position in RPB. This proposed formula leads to a much better understanding of droplet characteristics in RPB.

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