Multiscale combustion dynamics, shape oscillations, secondary atomization, and precipitate formation have been elucidated for low vapour pressure nanofuel [n-dodecane seeded with alumina nanoparticles (NPs)] droplets. Dilute nanoparticle loading rates (0.1%–1%) have been considered. Contrary to our previous studies of ethanol-water blend (high vapour pressure fuel), pure dodecane droplets do not exhibit internal boiling after ignition. However, variation in surface tension due to temperature causes shape deformations for pure dodecane droplets. In the case of nanofuels, intense heat release from the enveloping flame leads to the formation of micron-size aggregates (of alumina NPS) which serve as nucleation sites promoting heterogeneous boiling. Three boiling regimes (A, B, and C) have been identified with varying bubble dynamics. We have deciphered key mechanisms responsible for the growth, transport, and rupture of the bubbles. Bubble rupture causes ejections of liquid droplets termed as secondary atomization. Ejection of small bubbles (mode 1) resembles the classical vapour bubble collapse mechanism near a flat free surface. However, large bubbles induce severe shape deformations as well as bulk oscillations. Rupture of large bubbles results in high speed liquid jet formation which undergoes Rayleigh-Plateau tip break-up. Both modes contribute towards direct fuel transfer from the droplet surface to flame envelope bypassing diffusion limitations. Combustion lifetime of nanofuel droplets consequently has two stages: stage I (where bubble dynamics are dominant) and stage II (formation of gelatinous mass due to continuous fuel depletion; NP agglomeration). In the present work, variation of flame dynamics and spatio-temporal heat release (HR) have been analysed using high speed OH* chemiluminescence imaging. Fluctuations in droplet shape and flame heat release are found to be well correlated. Droplet flame is bifurcated in two zones (I and II). Flame response is manifested in two frequency ranges: (i) buoyant flame flickering and (ii) auxiliary frequencies arising from high intensity secondary ejections due to bubble ruptures. Addition of alumina NPs enhances the heat absorption rate and ensures the rapid transfer of fuel parcels (detached daughter droplets) from droplet surface to flame front through secondary ejections. Therefore, average HR shows an increasing trend with particle loading rate (PLR). The perikinetic agglomeration model is used to explain the formation of gelatinous sheath during the last phase of droplet burning. Gelatinous mass formed results in bubble entrapment. SEM images of combustion precipitates show entrapped bubble cavities along with surface and sub-surface blowholes. Morphology of combustion precipitate shows a strong variation with PLRs. We have established the coupling mechanisms among heat release, shape oscillations, and secondary atomizations that underline the combustion behaviour of such low vapour pressure nanofuels.

1.
S. U. S.
Choi
, “
Enhancing thermal conductivity of fluids with nanoparticles
,”
ASME-Publ.-Fed.
231
,
99
106
(
1995
).
2.
ASTM International 4 December
2006
.
3.
J.-H.
Lee
,
K. S.
Hwang
,
S. P.
Jang
,
B. H.
Lee
,
J. H.
Kim
,
S. U.
Choi
, and
C. J.
Choi
, “
Effective viscosities and thermal conductivities of aqueous nanofluids containing low volume concentrations of Al2O3 nanoparticles
,”
Int. J. Heat Mass Transfer
51
,
2651
2656
(
2008
).
4.
R.
Mahtab
,
J. P.
Rogers
, and
C. J.
Murphy
, “
Protein-sized quantum dot luminescence can distinguish between ‘straight,’ ‘bent,’ and ‘kinked’ oligonucleotides
,”
J. Am. Chem. Soc.
117
,
9099
9100
(
1995
).
5.
R.
Shukla
,
V.
Bansal
,
M.
Chaudhary
,
A.
Basu
,
R. R.
Bhonde
, and
M.
Sastry
, “
Biocompatibility of gold nanoparticles and their endocytotic fate inside the cellular compartment: A microscopic overview
,”
Langmuir
21
,
10644
10654
(
2005
).
6.
S.
Jain
,
D. G.
Hirst
, and
J. M.
O’sullivan
, “
Gold nanoparticles as novel agents for cancer therapy
,”
Br. J. Radiol.
85
,
101
(
2012
).
7.
H.
Tyagi
,
P. E.
Phelan
,
R.
Prasher
,
R.
Peck
,
T.
Lee
,
J. R.
Pacheco
, and
P.
Arentzen
, “
Increased hot-plate ignition probability for nanoparticle-laden diesel fuel
,”
Nano Lett.
8
,
1410
1416
(
2008
).
8.
D.
Jackson
,
D.
Davidson
, and
R.
Hanson
, “
Application of an aerosol shock tube for the kinetic studies of n-dodecane/nano-aluminum slurries
,” in
44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference Exhibit
,
2008
.
9.
C.
Allen
,
G.
Mittal
,
C.-J.
Sung
,
E.
Toulson
, and
T.
Lee
, “
An aerosol rapid compression machine for studying energetic-nanoparticle-enhanced combustion of liquid fuels
,”
Proc. Combust. Inst.
33
,
3367
3374
(
2011
).
10.
B.
Rotavera
,
A.
Kumar
,
S.
Seal
, and
E. L.
Petersen
, “
Effect of ceria nanoparticles on soot inception and growth in toluene–oxygen–argon mixtures
,”
Proc. Combust. Inst.
32
,
811
819
(
2009
).
11.
Y.
Gan
and
L.
Qiao
, “
Combustion characteristics of fuel droplets with addition of nano and micron-sized aluminum particles
,”
Combust. Flame
158
,
354
368
(
2011
).
12.
Y.
Gan
,
Y. S.
Lim
, and
L.
Qiao
, “
Combustion of nanofluid fuels with the addition of boron and iron particles at dilute and dense concentrations
,”
Combust. Flame
159
,
1732
1740
(
2012
).
13.
I.
Javed
,
S. W.
Baek
, and
K.
Waheed
, “
Evaporation characteristics of heptane droplets with the addition of aluminum nanoparticles at elevated temperatures
,”
Combust. Flame
160
,
170
183
(
2013
).
14.
I.
Javed
,
S. W.
Baek
, and
K.
Waheed
, “
Autoignition and combustion characteristics of heptane droplets with the addition of aluminium nanoparticles at elevated temperatures
,”
Combust. Flame
162
,
191
206
(
2015
).
15.
A.
Miglani
,
S.
Basu
, and
R.
Kumar
, “
Insight into instabilities in burning droplets
,”
Phys. Fluids
26
,
032101
(
2014
).
16.
A.
Miglani
,
S.
Basu
, and
R.
Kumar
, “
Suppression of instabilities in burning droplets using preferential acoustic perturbations
,”
Combust. Flame
161
,
3181
3190
(
2014
).
17.
A.
Miglani
and
S.
Basu
, “
Coupled mechanisms of precipitation and atomization in burning nanofluid fuel droplets
,”
Sci. Rep.
5
,
15008
(
2015
).
18.
A.
Miglani
and
S.
Basu
, “
Effect of particle concentration on shape deformation and secondary atomization characteristics of a burning nanotitania dispersion droplet
,”
J. Heat Transfer
137
,
102001
(
2015
).
19.
T.
Edwards
,
M.
Colket
,
N.
Cernansky
,
F.
Dryer
,
F.
Egolfopoulos
,
D.
Friend
,
E.
Law
,
D.
Lenhert
,
P.
Lindstedt
,
H.
Pitsch
 et al, “
Development of an experimental database and kinetic models for surrogate jet fuels
,” in
45th AIAA Aerospace Science Meeting and Exhibit
(
The American Institute of Aeronautics and Astronautics
,
2015
), p.
770
.
20.
S. S.
Vasu
,
D. F.
Davidson
,
Z.
Hong
,
V.
Vasudevan
, and
R. K.
Hanson
, “
n-Dodecane oxidation at high-pressures: Measurements of ignition delay times and OH concentration time-histories
,”
Proc. Combust. Inst.
32
,
173
180
(
2009
).
21.
S. S.
Vasu
,
D. F.
Davidson
, and
R. K.
Hanson
, “
Jet fuel ignition delay times: Shock tube experiments over wide conditions and surrogate model predictions
,”
Combust. Flame
152
,
125
143
(
2008
).
22.
E. W.
Lemmon
,
M. O.
McLinden
, and
D. G.
Friend
, “
Thermophysical properties of fluid systems
,” in
NIST Chemistry WebBook
(
NIST
,
1998
).
23.
See https://pubchem.ncbi.nlm.nih.gov/compound/9989226 for “National Center for Biotechnology Information,” PubChem Compound Database, CID=9989226 (accessed on March
2017
).
24.
See RSC Chemical Methods Ontology (CMO) for information about ultrasonication (accessed on March,
2017
).
25.
K. S.
Suslick
and
G. J.
Price
, “
Applications of ultrasound to materials chemistry
,”
Annu. Rev. Mater. Sci.
29
,
295
326
(
1999
).
26.
C. K.
Law
,
Combustion Physics
(
Cambridge University Press
,
2010
).
27.
N.
Otsu
, “
A threshold selection method from gray-level histograms
,”
Automatica
11
,
23
27
(
1975
).
28.
K.
Kannaiyan
and
R.
Sadr
, “
The effects of alumina nanoparticles as fuel additives on the spray characteristics of gas-to-liquid jet fuels
,”
Exp. Therm. Fluid Sci.
87
,
93
103
(
2017
).
29.
A.
Faghri
and
Y.
Zhang
,
Transport Phenomena in Multiphase Systems
(
Academic Press
,
2006
).
30.
M.
Elimelech
,
J.
Gregory
, and
X.
Jia
,
Particle Deposition and Aggregation: Measurement, Modelling and Simulation
(
Butterworth-Heinemann
,
2013
).
31.
B.
Pathak
,
P.
Deepu
,
S.
Basu
, and
R.
Kumar
, “
Modeling of agglomeration inside a droplet with nanosuspensions in an acoustic field
,”
Int. J. Heat Mass Transfer
59
,
161
166
(
2013
).
32.
D. M.
Newitt
,
N.
Dombrowski
, and
F.
Knelmann
, “
The mechanism of drop formation from gas or vapour bubbles
,”
Trans. Inst. Chem. Eng.
32
,
244
(
1954
).
33.
N. M.
Aybers
and
A. K.
Dagsöz
, “
The mechanism of drop formation from gas or vapour bubbles
,”
Heat Mass Transfer
1
,
80
86
(
1968
).
34.
A.
Pearson
,
E.
Cox
,
J. R.
Blake
, and
S. R.
Otto
, “
Bubble interactions near a free surface
,”
Eng. Anal. Boundary Elem.
28
,
295
313
(
2004
).
35.
J. M.
Boulton-Stone
and
J. R.
Blake
, “
Gas bubbles bursting at a free surface
,”
J. Fluid Mech.
254
,
437
466
(
1993
).
36.
J. R.
Blake
and
D. C.
Gibson
, “
Growth and collapse of a vapour cavity near a free surface
,”
J. Fluid Mech.
111
,
123
140
(
1981
).
37.
F. M.
White
,
Fluid Mechanics
5th ed. (
McGraw-Hill Book Co.
,
Boston
,
2003
).
38.
W. A.
Sirignano
,
Fluid Dynamics and Transport of Droplets and Sprays
(
Cambridge University Press
,
Cambridge
,
2000
).
39.
B.
Pathak
and
S.
Basu
, “
Phenomenology of break-up modes in contact free externally heated nanoparticle laden fuel droplets
,”
Phys. Fluids
28
,
123302
(
2016
).
40.
S.
Tanvir
and
L.
Qiao
, “
Effect of addition of energetic nanoparticles on droplet-burning rate of liquid fuels
,”
J. Propul. Power
31
,
408
415
(
2014
).
41.
M.
Rahaman
and
M. N.
Rahaman
,
Ceramic Processing
(
CRC Press
,
2006
).
42.
J.
Oh
,
P.
Heo
, and
Y.
Yoon
, “
Acoustic excitation effect on NOx reduction and flame stability in a lifted non-premixed turbulent hydrogen jet with coaxial air
,”
Int. J. Hydrogen Energy
34
,
7851
7861
(
2009
).
43.
M.
Lauer
,
M.
Zellhuber
,
T.
Sattelmayer
, and
C. J.
Aul
, “
Determination of the heat release distribution in turbulent flames by a model based correction of OH* chemiluminescence
,”
J. Eng. Gas Turbines Power
133
,
121501
(
2011
).
44.
B. O.
Ayoola
,
R.
Balachandran
,
J. H.
Frank
,
E.
Mastorakos
, and
C. F.
Kaminski
, “
Spatially resolved heat release rate measurements in turbulent premixed flames
,”
Combust. Flame
144
,
1
16
(
2006
).
45.
R.
Santhosh
and
S.
Basu
, “
Transitions and blowoff of unconfined non-premixed swirling flame
,”
Combust. Flame
164
,
35
52
(
2016
).
46.
V.
Nori
and
J.
Seitzman
, “
Chemiluminescence measurements and modeling in syngas, methane and jet-A fueled combustors
,” in
45th AIAA Aerospace Science Meeting and Exhibit
(
The American Institute of Aeronautics and Astronautics
,
2007
), p.
466
.
47.
L.-D.
Chen
,
J. P.
Seaba
,
W. M.
Roquemore
, and
L. P.
Goss
, “
Buoyant diffusion flames
,”
Symp. (Int.) Combust.
22
,
677
684
(
1989
).
48.
I.
Kimura
, “
Stability of laminar-jet flames
,”
Symp. (Int.) Combust.
10
,
1295
1300
(
1965
).
49.
T.-Y.
Toong
,
R. F.
Salant
,
J. M.
Stopford
, and
G. Y.
Anderson
, “
Mechanisms of combustion instability
,”
Symp. (Int.) Combust.
10
,
1301
1313
(
1965
).
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