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.

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.

scholarly journals Evaporation and Ignition of a Fuel Droplet on a Hot Surface : Part 3, Effects of Initial Droplet Diameter

1979 ◽  
Vol 22 (171) ◽  
pp. 1266-1273 ◽  
Author(s):  
Masahiko MIZOMOTO ◽  
Akio MORITA ◽  
Shigeru IKAI
Keyword(s):  
Droplet Diameter ◽  
Fuel Droplet ◽  
Surface Part ◽  
Initial Droplet ◽  
Hot Surface

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.

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.

Combustion Characteristics of Isolated Free-Falling Droplets of Jet A Blended With Ethanol and Butanol

2018 ◽  
Author(s):  
Álvaro Muelas ◽  
Pilar Remacha ◽  
Javier Ballester
Keyword(s):  
Gas Turbines ◽  
Alternative Fuels ◽  
Droplet Diameter ◽  
Combustion Process ◽  
Combustion Characteristics ◽  
Shell Size ◽  
Pure Ethanol ◽  
Promising Alternative ◽  
Burning Rates ◽  
Alcohol Mixtures

Recent studies on experimental gas turbines suggest that the addition of ethanol or butanol to Jet A are viable alternatives for reducing CO and NOx emissions while maintaining similar performance to that of pure Jet A. In light of this potential, experimental data regarding the burning characteristics of Jet A/ethanol and Jet A/butanol blends are required in order to better understand their combustion process. Following a previous study on Jet A/butanol droplet combustion, the scope has been extended in order to also include ethanol and a Jet A/ethanol mixture as well as to perform a more detailed characterization. In this work the combustion characteristics of Jet A, butanol, ethanol and their mixtures (20% vol. alcohol in kerosene) are presented for different test conditions. The evaluated combustion characteristics include droplet, flame and soot shell size evolutions, burning rates and image-based soot estimations. The influence of oxygen availability is also ascertained. The evolution of droplet diameter and burning rates for Jet A and its blends with both alcohols are very similar, whereas pure ethanol and butanol display more distinct behaviors. Soot indices are found to be quite different, with a clear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. These results support the feasibility of kerosene-alcohol mixtures as promising alternative fuels with similar combustion characteristics, but with much lower sooting propensity than pure kerosene.

scholarly journals A Novel Fabrication Technique for Developing Metal Nanodroplet Arrays

2006 ◽  
Vol 940 ◽  
Author(s):  
Christopher Edgar ◽  
Chad Johns ◽  
M. Saif Islam
Keyword(s):  
Elevated Temperature ◽  
Large Scale ◽  
Droplet Diameter ◽  
Experimental Results ◽  
Fabrication Technique ◽  
Rayleigh Instability ◽  
Linear Arrays ◽  
Nanoscale Particles

ABSTRACTMetal patterned lines on a substrate have been annealed and broken down into isolated linear arrays of alloyed metal nanoscale droplets. These droplets are selectively fabricated across large-scale areas by controlling the location metal is present on a substrate. The metal instability and formation into nanoscale particles forms similar to studies in Rayleigh Instability of metal at an elevated temperature. Experimental results discussed here show a change in droplet diameter and formation by controlling the metal width.

Droplet Burning and Evaporation Times for Distillate and Residual Fuel Oils

1980 ◽  
Author(s):  
P. C. T. de Boer
Keyword(s):  
Gas Turbine ◽  
Constant Velocity ◽  
Droplet Diameter ◽  
Diffusion Constant ◽  
Gas Mixture ◽  
Residual Oil ◽  
Gas Turbine Combustor ◽  
Initial Droplet ◽  
Fuel Oils ◽  
Industrial Gas Turbine

Estimates are given of the burning and evaporation times of No. 2 distillate and No. 6 residual oil droplets, under conditions typical of industrial gas turbine combustors. Account is taken of the temperature dependence of the specific heat, the diffusion constant, and the thermal conductivity of the gas mixture surrounding the droplet. Detailed calculations are presented of the factor by which the droplet lifetime is reduced as a result of convection, for the case that the droplet is released in a gas moving at constant velocity. This factor is on the order of four for the conditions of interest. Using estimates of initial droplet diameter based on data reported by Jasuja, it is found that the ratio of characteristic droplet burning time to characteristic droplet residence time in a typical industrial gas turbine combustor is much smaller than 1 for distillate oil, but may be on the order of 1 for residual oil.

Minimization of the Number of Cooling Holes in Internally Cooled Turbine Blades

1991 ◽  
Author(s):  
George S. Dulikravich ◽  
Branko Kosovic
Keyword(s):  
Optimization Algorithm ◽  
Turbine Blades ◽  
Heat Fluxes ◽  
Convergence Criteria ◽  
Surface Temperatures ◽  
Function Formulation ◽  
Internally Cooled ◽  
Hot Surface ◽  
Automatic Switching

This work represents an extension of the earlier research on inverse determination of proper locations and sizes of a given number of coolant flow passages (holes) subject to specified surface temperatures and heat fluxes. The methodology is extended to allow designer to guess the required number of holes and the minimal allowable diameter of a hole. A constrained optimization algorithm is then used to minimize the total number of cooling holes, while satisfying user-specified hot surface temperatures and heat fluxes. Premature termination of the optimization process due to the existence of local minimas has been satisfactorily resolved by automatic switching of the objective function formulation whenever the local minima is detected. The convergence criteria of the iterative process, which can be specified by the user, was found to have a strong influence on the accuracy of the entire inverse design optimization algorithm.

Evaluation of a Hot-Surface Ignition System for a Direct-Injection of Natural Gas Engine

2018 ◽  
Author(s):  
Gordon McTaggart-Cowan ◽  
Jian Huang ◽  
Marco Turcios ◽  
Ashish Singh ◽  
Sandeep Munshi
Keyword(s):  
Natural Gas ◽  
Ignition Time ◽  
Direct Injection ◽  
Experimental Tests ◽  
Reacting Flow ◽  
Initial Development ◽  
Hot Surface Ignition ◽  
Surface Temperatures ◽  
Constant Volume Combustion Chamber ◽  
Hot Surface

Non-premixed combustion of directly-injected natural gas offers diesel-like performance and efficiency with lower fuel costs and reduced greenhouse gas emissions. To ignite the fuel, a separate ignition source is needed. This work reports on the initial development of a new hot-surface based ignitor, where a small quantity of natural gas is injected and ignited by a hot element. This generates a robust pilot flame to ignite the main gas injection. A series of experimental tests were conducted to evaluate the sensitivity of the pilot flame formation process to hot surface temperature and geometry and to gas pilot injection geometry. Tests were conducted in a constant-volume combustion chamber at up to 6 bar with hot surface temperatures up to 1750 K. Reacting-flow computational fluid dynamics (CFD) evaluation is used to help interpret the results and to extrapolate to engine-relevant pressures. The results show that hot surface temperatures around 1500 K can minimize the pilot ignition time. An injector geometry where the pilot gas jets are angled such that they impinge on the hot surface but retain sufficient momentum to convect mass into the main chamber helps to ensure rapid and stable ignition. The CFD results indicate that, at engine pressures, a stable gas pilot flame could be established within 1–2 ms using the proposed injector geometry. These results will be used to underpin further development activities on this concept.

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