Match!

Computational Modeling of Unsupported and Fiber-Supported n-Heptane Droplet Combustion in Reduced Gravity: A Study of Fiber Effects

Published on Jan 2, 2015in Combustion Science and Technology1.564
· DOI :10.1080/00102202.2014.971950
Narugopal Ghata1
Estimated H-index: 1
,
Benjamin D. Shaw13
Estimated H-index: 13
Abstract
A detailed numerical investigation of combustion of unsupported and fiber supported n-heptane droplets in reduced gravity is presented. The primary focus is on the effects of support fibers on the droplet burning rates and flame structure. A 21-step n-heptane reaction mechanism consisting of 20 species is employed to model the combustion chemistry. The volume-of-fluid (VOF) method is employed to capture the liquid-gas interface while allowing for time-dependent two-phase multidimensional flows. Computed burning rates and flame stand-off ratios are compared with the experimental results of Jackson. Predicted flame structures are also validated with the experimental results of Mikami. The present computational results agree well with the experimental results. The results indicate that the support fibers can have significant impact on droplet burning rates and flame structure.
  • References (27)
  • Citations (3)
📖 Papers frequently viewed together
18 Citations
2007
10 Citations
2011
4 Authors (F. Wang, ..., Y. Huang)
78% of Scinapse members use related papers. After signing in, all features are FREE.
References27
Newest
#1Tanvir Farouk (USC: University of South Carolina)H-Index: 18
#2Michael C. Hicks (Glenn Research Center)H-Index: 8
Last. Frederick L. Dryer (Princeton University)H-Index: 68
view all 3 authors...
Recently, large diameter, isolated n-heptane droplet experiments under microgravity conditions (aboard the International Space Station) exhibited “Cool Flame” burning behavior, resulting from a heat loss mechanism that extinguishes hot combustion and a transition into a sustained, low temperature second stage combustion. In atmospheric pressure air, a single combustion mode transition to “Cool Flame” burning is followed by diffusive extinction. But with increasing pressure, multiple cycles of ho...
40 CitationsSource
#1Narugopal Ghata (UC Davis: University of California, Davis)H-Index: 3
#2Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
Abstract A detailed numerical investigation of the effects of support fibers on the vaporization of a fiber-supported droplet in reduced gravity is presented. The volume-of-fluid (VOF) method was employed to capture the liquid–gas interface while allowing for time-dependent two-phase multidimensional flows. The calculations allowed for the inclusion of thermocapillary stresses at the liquid–gas interface. The study also investigated the effects of the thickness of fiber, ambient pressure, and am...
12 CitationsSource
#1Daniel L. Dietrich (Glenn Research Center)H-Index: 13
#2Vedha Nayagam (Case Western Reserve University)H-Index: 15
Last. Forman A. Williams (UCSD: University of California, San Diego)H-Index: 54
view all 12 authors...
This paper summarizes the first results from isolated droplet combustion experiments performed on the International Space Station (ISS). The long durations of microgravity provided in the ISS enable the measurement of droplet and flame histories over an unprecedented range of conditions. The first experiments were with heptane and methanol as fuels, initial droplet droplet diameters between 1.5 and 5.0 m m, ambient oxygen mole fractions between 0.1 and 0.4, ambient pressures between 0.7 and 3.0 ...
32 CitationsSource
#1Inkant Awasthi (NU: University of Nebraska–Lincoln)H-Index: 2
#2Daniel N. Pope (UMN: University of Minnesota)H-Index: 9
Last. George Gogos (NU: University of Nebraska–Lincoln)H-Index: 18
view all 3 authors...
Abstract Results are presented from transient numerical simulations of combustion of an isolated heptane (n- C 7 H 16 ) droplet in nearly quiescent ambient air. The focus is on the effects of environment temperature and droplet size on the combustion characteristics. Droplet sizes range from 10 μm to 1 mm, environment temperatures range from 800 K to 1600 K, and pressure is 1 atm. The results show that ignition delay times have a very moderate dependence on droplet diameter. With an increase in ...
14 CitationsSource
#1Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
#2D. F. Wang (UC Davis: University of California, Davis)H-Index: 2
Flame extinction of n-heptane, n-decane, and n-hexadecane droplets freely falling through hot gases from a flat flame burner was investigated. Initial droplet diameters were in the range 270–285 µm. The hot gases from the flat flame burner were injected into straight and contoured flow tubes, providing flow environments that had various degrees of convection. Transport properties were modified through inert gas substitution as an efficient means of adjusting both quasisteady burning rates and ex...
2 CitationsSource
#1Kesong Zhang (SDU: Shandong University)H-Index: 2
#2Zheng Liang (THU: Tsinghua University)H-Index: 1
Last. Zhiming Wang (SDU: Shandong University)H-Index: 2
view all 4 authors...
Based on the low temperature oxidation mechanism of alkane and the assumption that alkyl cracks into ethylenes and methyl directly at high temperature, a reduced mechanism of n-heptane oxidation containing 19 species and 21 reactions is achieved. The calculated ignition delays fit the experimental data reasonably well. Diesel diffusion flame in a constant volume vessel is investigated with CFD simulation using this reduced mechanism, and validated by high speed photography. The calculated result...
9 CitationsSource
#1D. Shringi (UC Davis: University of California, Davis)H-Index: 3
#2Harry A. Dwyer (UC Davis: University of California, Davis)H-Index: 25
Last. Benjamin D. Shaw (UC Davis: University of California, Davis)H-Index: 13
view all 3 authors...
Abstract Numerical calculations are carried out to study flows around liquid droplets held in place by cylindrical fibers. Two configurations were considered: (1) a droplet supported at the middle of a fiber that extends into the gas phase on both sides of the droplet and (2) a droplet suspended at the end of a fiber. Calculations are done for droplet Reynolds numbers based on droplet diameters of 0–100. The flow around a supported droplet loses its axisymmetry even for very thin support fibers....
3 CitationsSource
#1Vedha NayagamH-Index: 15
#2Daniel L. Dietrich (Glenn Research Center)H-Index: 13
Last. Forman A. Williams (UCSD: University of California, San Diego)H-Index: 54
view all 5 authors...
Abstract Experimental observations of anomalous combustion of n-heptane droplets burning in microgravity are reported. Following ignition, a relatively large n-heptane droplet first undergoes radiative extinction, that is, the visible flame ceases to exist because of radiant energy loss. But the droplet continues to experience vigorous vaporization for an extended period according to a quasi-steady droplet-burning law, ending in a secondary extinction at a finite droplet diameter, after which a ...
73 CitationsSource
#1Tanvir Farouk (Princeton University)H-Index: 18
#2Frederick L. Dryer (Princeton University)H-Index: 68
Abstract Tethered methanol droplet combustion in carbon dioxide enriched environment is simulated using a transient one-dimensional spherosymmetric droplet combustion model that includes the effects of tethering. A priori numerical predictions are compared against recent experimental data. The numerical predictions compare favorably with the experimental results and show significant effects of tethering on the experimental observations. The presence of a relatively large quartz fiber tether incr...
22 CitationsSource
#1A G Luis Forero (UPB: Pontifical Bolivarian University)H-Index: 5
#2A J Jorge Velásquez (UPB: Pontifical Bolivarian University)H-Index: 5
A methodology to determine the A, B, C, and D constants from the Wagner equation is presented. The constants for 274 pure substances were determined by minimization in the sum of the squares of the relative deviation in liquid vapour pressure. For 69 chemical compounds, vapour pressures exist over the range from 1 kPa to the critical pressure and an average absolute deviation in vapour pressure of 0.039% was calculated. Using Antoine equation coefficients and initial guesses for a correlation in...
21 CitationsSource
Cited By3
Newest
DropletSMOKE++ is a multiphase CFD framework based on OpenFOAM, originally developed and validated for suspended droplets evaporation in a gravity field and convective conditions. In this work the solver is further extended to account for gas-phase combustion introducing: (i) an operator-splitting methodology to efficiently solve the gas-phase chemistry with large kinetic mechanisms, (ii) a model for the flame radiation and (iii) a double vaporization model to account for possible boiling. This ...
#1A.E. Saufi (Leonardo)H-Index: 1
#2Alessio Frassoldati (Leonardo)H-Index: 35
Last. Alberto Cuoci (Leonardo)H-Index: 30
view all 4 authors...
Abstract This paper aims at presenting the DropletSMOKE++ solver, a comprehensive multidimensional computational framework for the evaporation of fuel droplets, under the influence of a gravity field and an external fluid flow. The Volume Of Fluid (VOF) methodology is adopted to dynamically track the interface, coupled with the solution of energy and species equations. The evaporation rate is directly evaluated based on the vapor concentration gradient at the phase boundary, with no need of semi...
2 CitationsSource
#1C. L. Vang (UC Davis: University of California, Davis)
#2B. D. Shaw (UC Davis: University of California, Davis)
Combustion experiments on heptane–hexadecane mixture droplets were conducted onboard the International Space Station. The ambient consisted of oxygen mixed with either helium or nitrogen at 1 atm. Initial droplet diameters were in the 1.7–4.8 mm range with initial heptane mass fractions of 0.95 or 0.80. Because of limitations on resources, only fiber-supported experiments were possible. Vaporization of the more volatile fuel component (heptane) was favored during the droplet combustion process, ...
Source
#1C. L. Vang (UC: University of California)H-Index: 1
#2Benjamin D. Shaw (UC: University of California)H-Index: 13
Results from International Space Station experiments on combustion of n-propanol/glycerol droplets are reported. The initial n-propanol mass fraction was 0.95 and droplets had initial diameters in the 2 – 5 mm range. Some droplets were fiber supported while others were free floating, and the environment was either an oxygen/nitrogen mixture at 1 atm or an oxygen/helium mixture at pressures of 1 and 3 atm. The droplets burned in a multi-stage manner where n-propanol was preferentially evaporated ...
2 CitationsSource