NASA Technical Reports Server (NTRS) 20020027090: Initial Observations on the Burning of an Ethanol Droplet in Microgravity

18 Pages·0.92 MB·English

by  NASA Technical Reports Server (NTRS)

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Initial Observations on the Burning of an
Ethanol Droplet in Microgravity
•qR
Andrei Kazakov, Bradley Urban, Jordan Conley and Frederick L. Dryer
Department of Mechanical and Aerospace Engineering
Princeton University
Princeton, New Jersey 08544-5263
Thisisaprepdntorreprintofapaperintendedforpresentationata
conference.Becausechangesmaybemadebeforeformal
publicationt,hisismadeavailablewiththeunderstandingthatitwill
notbecitedorreproducedwithoutthepermissionoftheauthor.
1999 Fall Technical Meeting of the Eastern States Section of
the Combustion Institute
Raleigh, NC, October 13, 1999
Motivation
droplet studies in microgravity."
•simple geometric configuration - opportunity for
testing/validating theory
•facile method to study the diffusive combustion of
fuel molecular species similar to those in
transportation fuels
•link to multi-droplet (spray) applications
•fire safety criteria in space
ethanol:
•relatively simple and established chemistry
•azeotropic behavior of mixtures with water
•change in sooting tendency with pressure
•important gasoline fuel additive
i O
Fiber Supported Droplet Combustion
FSDC-2
MSL-1/STS-94 (July 1997)
•Drops tethered on silicon-carbide fibers (80, 150 microns),
2 to 5 mm initial diameter.
•Fuels: Methanol, Methanol-Water, Ethanol, n-Heptane, n-
Decane, n-Heptane-Hexadecane.
•Burned in cabin air (1 atm, 22-25 C, 39-46% RH)
•Quiescent (all), convective (n-Heptane, n-Decane), &
multiple drop (n-Heptane, n-Decane) experiments
•Backlighted drop, direct flame video, & dual radiometer
measurements.
Droplet burning history
pure ethanol, do - 3.41 mm
Data reduction
6
E
E
.'-'4
0 .... n .... ! .... i .... L ....
0 5 10 15 20 25
Time (s)
0.7
• ethanol
[] ethanol- reburns
0.6 • ethanol (96%) + water (4%)
E
[] ethanol (96%) + water (4%) - reburns
E
V
0.5
mmm
• i! O[]
[]m
0.4 ohm
¢... [] O• •
[] []
0.3 []
>
<
0.2 [ .... I I ,
2 4 5 6
d (mm)
0
Data reductiola (cont'd)
Ethanol droplet extinction diameter
ooo'
radiative extinction diameter - 4 mm .."'e
w•
5
ojoe •
same diameter ..,'L, •
I ..'"'11
4
(no burning) _-'"'"'"'""" l
ethanol
E ethanol- reburns B•
E ethanol/water • "°° •
3 o•l []
V ethanol/water- reburns ...o
,m
oof
2 ••o
=J•
.o bead
=o°
diameter
o•o"w° •
t"
..o=° _ mt
.,-" Ooo OO •
.;_...,,:.'........................................ _.........._...........
0 ,'" I I I 1 I
0 1 2 3 4 5 6
d (mm)
0
• 0% H20 FSDC-1 //,i
/_/../
• 0% H20 FSDC-2
5 A 10% H20 FSDC-1 /
V 15% H20 FSDC-2
• 20% H20 FSDC-1
4 • 30% H20 FSDC-1 .1_/ _"
Methanol data
-- 0% H20-Model /,I.
......... 10% H20- Model v /'11/:
3
------ 20% H20 - Model •,_./' Q,/..,/
Marchese&Dryer (1999)
--.-- 30% H20- Model / _ :
_.. /./ /'O
2
•/._-/"- _5__"e"o_......._. -''_
i t I I I
0 1 2 3 4 5
Initial Diameter [mm]
Time-Dependent, Spherically Symmetric,
Bi-component Model for Droplet
Combustion
(Based on FEM approach of Cho, et al., 1992) _.---t_--®
Gas Phase:
[ • Multicomponent molecular diffusion
[ _Detailed chemical kinetics
] .Spectral (no--us) thermal radiation
•UV flame emission
=0._(__I_ _ _ _ _1=7-04-(r2P,Y, V, )+(Os
..... mergy_ Lon:
Droplet buriace: -::,:,._:
• Surface regression O(P,_,sr,)
• Evaporation of fuel
• Condensation/Dissolution
of products
• Radiative heat exchange
Net Radiative Heat Flux
Droplet Interior:
O(p,C,.,T,) 1 O{ _ OT,5
Ot =7_-r (r X':_rlJ
-D--:7_t.:D,.,--_=-j
Model: further details
•detailed reaction mechanism of C2HsOH oxidation
(N0rton&Dryer, 1992)
- 33 species
- 142 reversible elementary reactions
•molecular transport parameters
(CHEMKIN database & estimates)
•ethanol/water vapor pressure correlations
(Kurimara et al. 1995)
•improved non-luminous radiation model
Vaporization of suspended ethanol droplets
in dry and humid air (do = 1.6 ram, To = 297 K)
0.015
i 19i8a7lii, iiiiiildry
¢'q
E 0.01
E
v
---.......-.-__ J
¢-
O
0.005
N
O
El.
>
0 I I [ [ I I I
20 60 100 140 180
Time (s)
Preliminary Modeling Results
Ethanol droplet combustion, do= 1 mm, 1 atm, 298 K
(Kb) = 0.59 mm2/s
0.6
0.8 "T,
E
0.6
0.4 E
¢'4
(D
t.-
¢'q
0.4 t-
O
.m
0.2
0.2 I oo
(.9
\
0 0
0 0.4 0.8 1.2 1.6
Time (s)
consistent with experimental data:
-)
•closely follows d2-1aw during most of its burning history[
•very small extinction diameter
Preliminary Modeling Results (cont'd)
1 1
0.8
t-
0.5
¢,,.
O 0.6 .o_
o
.m
ffl
E 0.4 water fractional gasific 0")
I,.. 0
c-
O
_ 0.2 °_
o
U_
0 i i I t -0.5
0.4 0.8 1.2 1.6
Time (s)
0.65
0,,.
0.55
o 0.5
_0.45
0 -_
_- 0.35 0
>
U_
0.25 .... , ........ I , , ,V..... , ....... 0.5
103 10.2 101 10°
Water mass fraction