Low-Temperature Hypergolic Ignition of 1-Octene with Low Ignition Delay Time

Article abstract of DOI:10.1021/acs.jpca.0c08999

The attainment of the efficient ignition of traditional liquid hydrocarbons of scramjet combustors at low flight Mach numbers is a challenging task. In this study, a novel chemical strategy to improve the reliable ignition and efficient combustion of hydrocarbon fuels was proposed. A directional hydroboration reaction was used to convert hydrocarbon fuel into highly active alkylborane, thereby leading to changes in the combustion reaction pathway of hydrocarbon fuel. A directional reaction to achieve the hypergolic ignition of 1-octene was designed and developed by using Gaussian simulation. Borane dimethyl sulfide (BDMS), a high-energy additive, was allowed to react spontaneously with 1-octene to achieve the hypergolic ignition of liquid hydrocarbon fuel at -15 °C. Compared with the ignition delay time of pure 1-octene (565 °C), the ignition delay time of 1-octene/BDMS (9:1.2) decreased by 3850% at 50 °C. Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry confirmed the directional reaction of the hypergolic ignition reaction pathway of 1-octene and BDMS. Moreover, optical measurements showed the development trend of hydroxyl radicals (OH·) in the lower temperature hypergolic ignition and combustion of 1-octene. Finally, this study indicates that the enhancement of the low-temperature ignition performance of 1-octene by hydroboration in the presence of BDMS is feasible and promising for jet propellant design with tremendous future applications.

Full text of DOI:10.1021/acs.jpca.0c08999

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Article
Low-Temperature Hypergolic Ignition of 1‑Octene with Low Ignition
Delay Time
Haoqiang Sheng, Xiaobin Huang,* Zhijia Chen, Zhengchuang Zhao, and Hong Liu
Cite This: J. Phys. Chem. A 2021, 125, 423−434
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ABSTRACT: The attainment of the efficient ignition of traditional liquid hydrocarbons of scramjet combustors at low flight Mach
numbers is a challenging task. In this study, a novel chemical strategy to improve the reliable ignition and efficient combustion of
hydrocarbon fuels was proposed. A directional hydroboration reaction was used to convert hydrocarbon fuel into highly active
alkylborane, thereby leading to changes in the combustion reaction pathway of hydrocarbon fuel. A directional reaction to achieve
the hypergolic ignition of 1-octene was designed and developed by using Gaussian simulation. Borane dimethyl sulfide (BDMS), a
high-energy additive, was allowed to react spontaneously with 1-octene to achieve the hypergolic ignition of liquid hydrocarbon fuel
at −15 °C. Compared with the ignition delay time of pure 1-octene (565 °C), the ignition delay time of 1-octene/BDMS (9:1.2)
decreased by 3850% at 50 °C. Fourier transform infrared spectroscopy and gas chromatography−mass spectrometry confirmed the
directional reaction of the hypergolic ignition reaction pathway of 1-octene and BDMS. Moreover, optical measurements showed the
development trend of hydroxyl radicals (OH·) in the lower temperature hypergolic ignition and combustion of 1-octene. Finally, this
study indicates that the enhancement of the low-temperature ignition performance of 1-octene by hydroboration in the presence of
BDMS is feasible and promising for jet propellant design with tremendous future applications.
is highly desirable for the reliable ignition and efficient
combustion of scramjet combustors at low flight Mach numbers.
Conventionally, methods ensuring that the ignition times of
fuel are less than the residence time are used to solve the starting
problems of scramjet engines. One of the methods is based on
generating a recirculation zone in high-speed flow using
embedded cavities and incident shock waves.4,5 Another method
relies on ignition augmentation, such as the use of plasma
ignitors.6 However, these approaches are disadvantageous in
terms of weight and drag penalty combined with complex
operating systems.7,8 As a result, highly inflammable fuels with a
1. INTRODUCTION
With the continuous development of hypersonic technology,
scramjet engines fueled with hydrocarbon fuels have become the
focus of various technological and military projects world-
wide.1,2 However, the reliable ignition and efficient combustion
of hydrocarbon fuels remain challenging in scramjet combustors
at low flight Mach numbers (Ma 4.0 to 4.5). The total
temperature of the incoming flows ranges between 900 and 1000
K, and the static temperature of supersonic flow in combustors
varies between 500 and 600 K. These values are lower than the
ignition temperatures of the hydrocarbon fuels. Moreover, the
ignition of hydrocarbon fuels with a spark plug is extremely
difficult due to the chemical inertness of hydrocarbon fuels
under extreme conditions. The low total temperature and
supersonic incoming flow shorten the residence time of fuel
when compared with the time required for ignition and
combustion.3 Thus the realization of the low-temperature
combustion of hydrocarbon fuels with a low ignition delay time
Received: October 3, 2020
Revised: December 14, 2020
Published: December 30, 2020
https://dx.doi.org/10.1021/acs.jpca.0c08999
© 2020 American Chemical Society
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Figure 1. Schematic illustration of ignition experimental setup and optical measurement system.
reduced ignition delay time as well as a sufficient burning rate at
low temperatures are required.
the ignition characteristics of hydrocarbon fuels. Alkenes are
prominent components of gasoline, diesel, as well as kerosene.
Although alkenes and alkanes have similarities in the long alkyl
chains, a direct study on the low-temperature ignition
enhancement of such fuels has rarely been carried out.19 In
the process of producing jet fuel and diesel from natural gas
synthetic oil, 1-octene is the extract of high-carbon alkenes. Thus
1-octene offers the advantage of easily available access to raw
materials to achieve the low-temperature ignition of hydro-
carbon fuels by using alkenes. 1-Octene with a CC bond is a
liquid fuel with a low solidifying point and can be conveniently
employed in scramjet engines. The borane complex, a non-self-
igniting material in air, exhibits stability at room temperature,
which increases the operational safety of additives for low-
temperature ignition enhancement hydrocarbon fuels and a
range of hypersonic vehicles. The range of hypersonic vehicles
could also be extended by the addition of a high-energy
additive.20 The hypergolic ignition of hydrocarbon fuel under an
air atmosphere could be carried out by the hydroboration
between the borane complex and the hydrocarbon fuel with
unsaturated bonds. The combustion reaction of alkenes was
changed from oxidation to hydroboration−oxidation. There-
fore, the conversion of hydrocarbon fuels into highly active
substances by chemical reactions at low temperatures might be
feasible to realize the reliable ignition and efficient combustion
of hydrocarbon fuels.
The use of catalysts for the catalytic combustion of
hydrocarbon fuels at low temperatures could reduce the
oxidation and combustion energy barrier. Two types of catalysts
are often used for the catalytic oxidation and combustion:
nanometal and nanometal oxide catalysts. For example, Javed et
al. employed aluminum (Al) nanoparticles as a nanometal
catalyst for heptane droplet ignition.9 The addition of 2.5% Al
nanoparticles to heptane resulted in the achievement of ignition
at 400 °C. Farranto et al. used palladium oxide (PdO) supported
on various materials as a nanometal oxide catalyst.10 They
noticed that the oxidation of methane could be initiated at ∼400
°C, leading to the decomposition of PdO to the less active Pd.
Furthermore, Wang et al. tested cobaltosic oxide (Co3O4)
nanocrystals for methane combustion and recorded the 100%
catalytic combustion of methane at 600 °C.11 Bijjula et al.
carried out the catalytic combustion of JP-8 fuel catalyzed with
Pt/γ-Al2O3 in a complex packed bed flow reactor at 196 °C.12
However, the enhancement of hydrocarbon low-temperature
ignition was not outstanding, and the ignition equipment was
also complex. Thus the ignition and combustion of hydrocarbon
fuels at low temperatures using simple and efficient processes is
still a challenging task.
The ignition performance of hydrocarbon fuels may be
improved by adding active additives. For instance, 20% silane
mixed with methane could realize ignition at 370 °C.13 Ryan et
al. showed that 50% trialkylaluminum could improve the low-
temperature ignition characteristics of JP-10.14 The addition of
50% methoxydiethylborane/tetrahydrofuran (MDEB/THF) as
a compound additive could ignite n-decane at low temper-
atures.15 Therefore, the ignition temperature of n-decane
decreased from 644 to 160 °C, showing the best effect on the
ignition performance of hydrocarbons so far. However, although
these additives can improve the low-temperature ignition
performance of hydrocarbon fuels, they are extremely unstable
in air and may be hypergolic at room temperature, making their
transportation, storage, and use inconvenient.
In this study, borane dimethyl sulfide (BDMS) was used as
borane complex to react with 1-octene based on hydroboration
and to achieve the hypergolic ignition of liquid 1-octene. The
low-temperature hypergolic ignition of 1-octene by a directional
reaction process was developed. The proposed directional
reaction was found to be beneficial for not only generating active
product to enhance low-temperature ignition but also changing
the combustion reaction pathway of hydrocarbon fuels to reduce
the energy barrier.
2. EXPERIMENTAL SECTION
2.1. Materials Preparation. 1-Octene (>99% purity, CAS:
111-66-0) was obtained from J&K Scientific and used as the base
hydrocarbon fuel. The BDMS complex (>94% purity, CAS:
13292-87-0) was purchased from Alfa Aesar (China) Chemistry.
The hydrocarbon fuel subjected to hypergolic ignition was
composed of a mixture of pure 1-octene and the BDMS
The hypergolic ignition of rocket fuel is often realized by the
chemical reactions between strong oxidants and strong
reductants.16−18 However, air oxygen is used as an oxidant in
scramjets. This is much weaker than the oxidants employed in
rockets. Therefore, the reduction ability of the reductant
(hydrocarbon fuel) requires further improvements to change
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Figure 2. Schematic illustration of the protection equipment setup. (a) Two-necked flask, (b) magnetic stirrer, (c) double-row tube, and (d) anti-back-
suction bubbler.
complex. In the process, the BDMS complex was employed to
react with 1-octene in air, describing the directional reaction of
the fuel hypergolic ignition at low temperatures with enhanced
outcomes.
1-octene and 1-octene/BDMS at various ratios were also
determined using the high-speed CCD camera. The OH· could
promote the combustion reaction due to the changes in OH·
during combustion at 306.5 nm.28,29 This process was recorded
with a high-speed CCD camera equipped with an ultraviolet
(UV) lens coupled to an image intensifier and a 310 nm optical
filter system (optical measurement system), as shown in Figure
1.
2.4. Synthesis of Trioctylborane and Schematic
Illustration of Nitrogen Protection. Figure 2 shows the
protection equipment setup, which was used for the reaction of
1-octene and BDMS at a certain volume concentration (9:1.2)
under a nitrogen atmosphere. To this end, the two-necked flask
was suctioned to a vacuum with a pump. Nitrogen adjusted with
a double-row tube was then passed through the system. After the
degassing process was performed three times, 1-octene was
added to the two-necked flask. Next, the initiator BDMS was
added drop by drop and stirred magnetically until the
completion of the reaction. The two-necked flask was placed
in a water bath at normal temperature. An anti-back-suction
bubbler was used to observe the nitrogen inflow.
2.5. Fourier Transform Infrared Spectroscopy Experi-
ments. All specimens were characterized by Fourier transform
infrared (FTIR) spectrometry (Nicolet iS10) with a resolution
of 2 cm−1. Solid samples were mixed with KBr and made into
pellets. Liquid samples were coated on KBr pellets (<2 mm in
thickness). A total of 32 scans from 4000 to 400 cm−1 were
collected for each sample, and baseline spectra were automati-
cally corrected by the FTIR spectroscopy. To analyze the
oxidation or combustion processes, FTIR spectra of products
generated by the reaction of 1-octene/BDMS, intermediates
generated by oxidation or combustion, and end products were
all obtained and analyzed.
2.6. Gas Chromatography−Mass Spectroscopy Experi-
ments. Gas chromatography−mass spectroscopy (GC-MS)
analyses of combustion intermediates were performed using an
Agilent 7890B GC fitted with a split−splitless injector and
linked to an Agilent 5977B mass-selective detector. An aliquot
(10 μL) of the sample was first dissolved in ethanol (1 mL), and
1 μL was then injected into the GC in pulsed splitless mode
followed by opening after 1 min. The GC oven temperature was
programmed from 30 to 300 °C at a heating rate of 10 °C/min.
Helium was used as a carrier gas at a flow rate of 1 mL/min, and
the split flow rate after 1 min was 20 mL/min. The peaks
representing individual compounds in the mass chromatograms
were identified by comparing the mass spectra with those from
the NIST05 library (>90% fit taken as acceptable) followed by a
comparison of the relative retention time/elution order with
2.2. Calculations Details. The Gaussian program was
employed for density functional theory (DFT) calculations,21
and the M06-2X/6-31G(d) level was used for geometry
optimization and frequency calculations.22−25 Frequency
calculations were performed to ensure that minima were
found. The single-point calculations were performed at the
M06-2X/6-311+G(d,p) level.26,27 Gibbs free energies were
taken as the sums of single-point energies and thermal
corrections obtained by frequency calculations. All of the
thermodynamical quantities and bond energies were calculated
at 298.15 K. The default integration grid of Gaussian 09 was
employed for all calculations.
2.3. Ignition Performance Testing and Optical Meas-
urements. The ignition temperatures of pure 1-octene and
pure BDMS were measured by droplet hot-plate impinging
experiments (Figure 1, I). The surface temperature varied from
room temperature to 700 °C and was measured using a K-type
thermocouple located at the center of the lower surface. A
temperature controller was used to maintain a constant surface
temperature with an accuracy of 1 °C during one single run. A
single droplet was generated using a medical syringe pump with
a 150 mm long needle having a gauge number of 16 and
diameter of ∼2.0 mm. The experiment of droplets impinging on
a hot plate was designed to investigate the ignition probability of
pure fuel. At a certain surface temperature, the ignition
probability was used to estimate the ignition performance of
the experiment. The ignition probability is obtained by counting
the ignition 10 times followed by calculation of the ignition
percentage. In this Article, the ignition temperatures of the fuels
were regarded as the hot-plate surface temperature for an
ignition probability of 100%. The volume ratios of hypergolic
ignition hydrocarbon fuels (1-octene/BDMS) were set to 9:0.6,
9:0.9, and 9:1.2 and tested in glass bottles. At volume ratios of
BDMS/1-octene of 9:0.6, 9:0.9, and 9:1.2, the test ignition
temperatures were set to 50, 25, and −15 °C, respectively,
shown in Figure 1, II, III, and IV. BDMS and 1-octene were
tested after heating to 50 °C in a water bath or cooling to −15 °C
using an aluminum cold plate, followed by maintaining the
temperature for 5 min. Photographic observations of the
hypergolic ignition process were captured using a high-speed
charge-coupled device (CCD) camera (Vision, Phantom v6.2e)
with 512 × 512 pixel resolution and a recording rate of 1000
frames/s. The information related to hypergolic ignition was
extracted from the photographs. The ignition delay times of pure
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Figure 3. Gibbs free energy of 1-octene/BDMS reaction and its oxidation.
Figure 4. Bond lengths of the reactants and intermediates.
geochemistry literature data. The identified substances were
then employed to study the reaction paths of the hypergolic
ignition process of 1-octene/BDMS or the oxidation process of
trioctylborane.
3. RESULTS AND DISCUSSION
3.1. Development of Directional Reaction for Hyper-
golic Ignition of 1-Octene. A strategy based on the low-
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temperature hypergolic ignition of hydrocarbon was developed
by using the hydroboration reaction. 1-Octene was converted
into highly active alkylborane by a directional reaction to
participate in the combustion reaction. The Gibbs free energy of
the hydroboration was simulated to analyze the spontaneity of
the reaction by performing Gaussian calculations. Furthermore,
the change in bond lengths of 1-octene/BDMS after hydro-
boration and oxidation was analyzed through the calculations.
To demonstrate the changes in the reaction heat after
hydroboration, the release heat of the reaction of 1-octene/
BDMS was computed.
3.1.1. Calculation of Gibbs Free Energy of 1-Octene in the
Presence of BDMS. In this study, a directional reaction
converting inactive hydrocarbon fuel to active alkyl borane
was employed to allow the spontaneous participation of 1-
octene in the combustion reaction of hydroboration for the first
time. Hydroboration occurs between borane in BDMS and C
C in 1-octene, leading to the 1-octene-directed product
alkylborane as an anti-Markovnikov addition reaction. The B−
H bond in borane and the unsaturated bond in alkene could
form an organic boron compound, achieving the spontaneous
combustion of 1-octene at a low temperature. The spontaneity
of the process can be judged based on the reaction
thermodynamics (Gibbs free energy) at normal temperature.
The Gibbs free energy of the reaction involving pure 1-octene
and 1-octene with BDMS was calculated by using the Gaussian
simulation.30 The Gibbs free-energy difference (ΔG) of 1-
octene/BDMS is presented in Figure 3.
respectively. For trioctylborane, the C−H bond was found to
lengthen from 1.085 Å in pure 1-octene to 1.099 Å. This
indicates that the bond energy of the C−H bond decreases after
hydroboration. The bond length of the C−B bond is 1.579 Å,
significantly larger than that of the CC bond, indicating that
the bond energy of the C−B bond is significantly less than that of
the CC bond (discussed later). When oxygen was around
trioctylborane, the bond lengths of C−C and C−H bonds
increased slightly due to the electrostatic effect of oxygen. After
the oxidation of trioctylborane, the bond lengths of the B−C
bond and the C−H bond in (C8H17)2BOO(C8H17) remained
unchanged, about 1.580 and 1.10 Å, respectively. Furthermore,
the B−C bond of trioctylborane was oxidized to form B−O, O−
O, and O−C bonds, and their bond lengths changed from 1.579
to 1.307, 1.432, and 1.417 Å, respectively. The O−O bond in
(C8H17)2BOO(C8H17) was easy to break and generate radicals.
(See the next section.) When (C8H17)2BOO(C8H17) reacted
with (C8H17)3B to form (C8H17)2BO(C8H17), it was found that
the B−O bond in (C8H17)2BO(C8H17) lengthened by 0.055 Å
compared with that in (C8H17)2BOO(C8H17), and the bond
length of the O−C bond remained unchanged. (C8H17)2BO-
(C8H17) was more stable than (C8H17)2BOO(C8H17), except
for the B−O bond in (C8H17)2BO(C8H17).
Consequently, 1-octene could react with oxygen by the
strategy of a directional reaction at room temperature,
confirmed by the changes in the bond length of 1-octene.
Moreover, the changes in the bond lengths were related to the
stability of intermediates, which was conducive to the analysis of
the oxidation or combustion pathway.
The Gibbs free-energy difference for pure 1-octene during the
production of alkyl radicals was calculated. It is noteworthy that
the alkyl radicals could catch up with the combustion because
the C−H bond in the vinyl group could easily break compared
with other C−H bonds. However, the value of ΔG was
estimated to be 101.3 kcal/mol, which is above 0, and thus no
possible spontaneous generation of alkyl radicals at normal
temperature would occur. Therefore, the realization of the
spontaneous oxidation or combustion of pure 1-octene (ΔG <
0) in air at normal temperature was challenging. Figure 3
demonstrates that the Gibbs free-energy difference of the
reaction between 1-octene and BDMS was estimated to be
−39.6 kcal/mol and thereby below 0 and much less than that of
pure 1-octene during the production of alkyl radicals. Therefore,
this reaction could spontaneously generate trioctylborane by
hydroboration at normal temperature. The production of alkyl
radicals after the oxidation of trioctylborane could follow two
pathways. The Gibbs free-energy differences of both pathways
were estimated to be −28.4 kcal/mol (path I) and −69.8 kcal/
mol (path II), respectively. Both pathways were linked to the
reaction with oxygen. Therefore, the values of ΔG of paths I and
II were less than 0, showing the spontaneous production of alkyl
radicals regarded as the initial stage of combustion of 1-octene.
Compared with the formation of alkyl radicals using pure 1-
octene at normal temperature, 1-octene can spontaneously
produce alkyl radicals by the proposed directional reaction.
Moreover, the combustion reaction path of 1-octene also
changed from oxidation to hydroboration−oxidation in the
presence of BDMS due to the directional reaction.
3.1.3. Total Release Heat of 1-Octene and BDMS. The bond
energies before and after hydroboration and oxidation reactions
were calculated by using Gaussian simulation, and the results are
provided in Tables 1 and 2. The construction strategy of the
Table 1. Bond Energies before and after Hydroboration
product
(hydroboration)
reactant
bond types
CC (1-octene)
B−H (BDMS)
C−B
C−H
δ bond
π bond
63.9
bond energy
(kcal/mol)
103.0
93.8
99.7
96.6
Table 2. Bond Energies before and after Oxidation
product
(oxidation)
reactant
bond types
bond energy (kcal/mol)
B−C
99.7
OO
B−O
120.1
O−O
30.7
O−C
79.0
118.9
directional reaction of 1-octene hypergolic ignition at normal
temperature was based on hydroboration and oxidation. The
bond energies of reactants and products were calculated by using
Gaussian simulations. Furthermore, the release heat of the
reaction could be calculated by using the bond energy as follows
ΔH =
(reactant) −
(product)
∑
∑
E
(I)
E
3.1.2. Changes of Bond Lengths after Hydroboration and
Oxidation. The change of bond lengths of 1-octene/BDMS
after hydroboration and oxidation is shown in Figure 4. The
hydroboration of 1-octene and BDMS generated trioctylborane.
The values of the bond lengths of the CC bond and the B−H
bond in 1-octene and BDMS were 1.330 and 1.209 Å,
That is,
ΔHh = (ECC(π) + EB−H) − (EC−B + EC−H
ΔHo = (EB−C + EOO) − (EB−O + EO−O + EO−C
)
(II)
)
(III)
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Figure 5. (a) Ignition temperature of pure 1-octene and pure BDMS and (b) ignition performance of 1-octene/BDMS at various volume ratios.
ΔHt = ΔHh + ΔHo
BDMS/1-octene decreased. At a volume ratio of 9:0.6, BDMS
was injected into 1-octene after heating to 50 °C in water bath;
then, BDMS reacted violently with 1-octene to spread out the
flame from the bottle. After BDMS injection into 1-octene at a
volume ratio of 9:0.9 and at normal temperature, a violent
reaction was accompanied by the spread of flame.
To investigate the ignition process at high volume ratios of
BDMS and low temperatures, the hypergolic ignition temper-
ature of 1-octene/BDMS was measured on a cold plate. To this
end, 1-octene and BDMS were separately placed on a cold plate
at a temperature of −15 °C for 5 min followed by the injection of
BDMS into 1-octene. 1-Octene/BDMS (9:1.2) realized the
spontaneous combustion of 1-octene at −15 °C. The ignition
temperature of 1-octene reduced from 565 to −15 °C,
equivalent to a decrease of 580 °C compared with pure 1-
octene. This significantly improved the hypergolic ignition
temperature of liquid hydrocarbon fuel.
(IV)
where ΔHt is the total release heat of 1-octene and BDMS. ΔHh
and ΔHo are the reaction heats of hydroboration and trialkyl
borane oxidation, respectively.
The hydroboration reaction heat of BDMS (1 mol) with 1-
octene (3 mol) was estimated to be ΔHh = −115.8 kcal/mol by
the reaction heat calculations. Therefore, a large amount of heat
was released from hydroboration, which was greater than that
due to the decomposition of the C−B or C−H bond but enough
to quickly induce subsequent oxidation reactions and hypergolic
ignition. In other words, the spontaneous combustion of 1-
octene could also be realized by the generated heat from
hydroboration at normal temperature.
The oxidation reaction heat of trialkyl borane (1 mol) with
oxygen (3 mol) was also estimated to be ΔH0 = −33.6 kcal/mol
by using the reaction heat calculations. Moreover, the total
reaction release heat of 1-octene and BDMS (ΔHt) was −149.4
kcal/mol. The reaction heat of the hydroboration was higher
than that of trialkyl borane oxidation. It was indicated that the
reaction heat of hydroboration is the primary factor to realize 1-
octene/BDMS hypergolic ignition.
3.2.2. Ignition Delay Time and Ignition Dynamics of 1-
Octene/BDMS. The ignition delay time values of pure 1-octene
and 1-octene/BDMS at various volume ratios are shown in
Figure 6a,b. The ignition delay time of pure 1-octene reached as
high as 3427 ms at 565 °C (Figure 6a). The ignition delay time
of pure 1-octene decreased with the increase in the temperature
Therefore, according to the thermodynamic analyses and
release heat of hydroboration−oxidation results obtained by
using the Gaussian simulation, the proposed strategy may
achieve 1-octene hypergolic ignition (experimental results of
ignition performance).
3.2. Hypergolic Ignition Performance of 1-Octene by
Directional Reaction. The ignition performances of 1-octene
and BDMS, including the ignition temperature and the ignition
delay time, were further explored at various temperatures by
performing an ignition experiment.
3.2.1. Hypergolic Ignition Temperature of 1-Octene/BDMS.
The ignition temperatures of pure 1-octene, pure BDMS, and 1-
octene/BDMS are displayed in Figure 5a,b. The ignition
probability is obtained by counting the ignition 10 times
followed by the calculation of the ignition percentage. In this
Article, the ignition temperatures of the fuels were regarded as
the hot-plate surface temperature for 100% ignition probability.
The ignition temperatures of pure 1-octene and pure BDMS
were measured by droplet hot-plate impinging at 565 and 100
°C, respectively (Figure 5a). These materials required external
heating to achieve ignition. Figure 5b illustrates high-speed
camera pictures of 1-octene/BDMS combustion at various
volume ratios (9:0.6, 9:0.9, and 9:1.2). The pictures of 1-octene/
BDMS combustion showed a minimum ignition temperature
with a 100% ignition probability. With the increase in the
volume ratio of BDMS, the hypergolic ignition temperature of
Figure 6. Ignition delay time of (a) pure 1-octene and (b) 1-octene/
BDMS at various volume ratios.
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Figure 7. Dynamic behaviors and combustion process of pure 1-octene and 1-octene/BDMS.
Figure 8. (a) FTIR spectra of pure BDMS and pure 1-octene as well as the reactions products of BDMS and 1-octene and (b) diagram showing the
reaction mechanism.
of the hot-plate surface. At temperatures above 595 °C, the
decreasing trend of the ignition delay time of pure 1-octene
obviously slowed down. However, the ignition delay time of
pure 1-octene was still above 1000 ms at 625 °C.
which the droplet of pure 1-octene could be ignited with a 100%
ignition probability. A droplet of pure 1-octene formed a
spherical shape on the hot-plate concave surface and then
evaporated. Pure 1-octene droplets were ignited on the hot-plate
surface after evaporation. The ignition delay time of a pure 1-
octene droplet was t0 + 3427 ms at 565 °C, which was
determined based on the chemical property and vaporization.
For 1-octene/BDMS, the ignition delay times were all lower
than those of pure 1-octene. With the increase in the
temperature of 1-octene/BDMS from 25 to 50 °C, the
development of the flame was changed from the bottom-up to
the top-down. This was attributed to the fact that the hypergolic
ignition reaction between 1-octene and BDMS was more intense
at a higher temperature, leading to the reduction in the ignition
delay time to 89 ms from 304 ms. Thus the hypergolic ignition
strategy and temperature adjustment could significantly reduce
the ignition delay time and enhance the ignition performance of
1-octene.
Figure 6b shows that the hypergolic ignition delay time of 1-
octene/BDMS obviously decreases with the increase in
temperature. The ignition delay time of 1-octene/BDMS
(9:1.2) was estimated to be 382 ms at −15 °C. With the
increase in temperature to 50 °C, the ignition delay time of 1-
octene/BDMS (9:0.6) declined to 139 ms. At a certain
temperature, the ignition delay time of 1-octene/BDMS
decreased with the content of BDMS. At 50 °C, the ignition
delay time of 1-octene/BDMS (9:1.2) was 89 ms. Compared
with the ignition delay time of pure 1-octene (565 °C), the
ignition delay time decreased by 3850%. At a certain
temperature, the ignition delay time does not significantly
decrease with the increase in the content of BDMS (Figure S1 in
the Supporting Information).
Tamura et al. reported the typical modes of evaporation,
vaporization, and combustion of a liquid drop touching a hot
surface.31 The hypergolic ignition fuels were mixed in the bottle;
then, the fuel was ignited after reaction and vaporization.
Figure 7 shows the dynamic behaviors and ignition of pure 1-
octene and a 9:1.2 volume fraction of 1-octene/BDMS fuel
droplets at 565 and 25 °C (50 °C), respectively. The surface
temperature of 565 °C was the lowest surface temperature at
3.3. Hypergolic Ignition Mechanism of 1-Octene/
BDMS. On the basis of the hydroboration and oxidation of 1-
octene discussed in previous sections, the causes leading to low-
temperature hypergolic ignition were analyzed based on the
hydroboration reaction, oxidation, and combustion processes.
The low-temperature hypergolic ignition reaction pathway was
proposed according to FTIR spectroscopy, GC-MS, and optical
measurements after further confirmation.
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3.3.1. Hydroboration of 1-Octene and BDMS. The reaction
of 1-octene with BDMS under air resulted in the release of
substantial reaction heat and induced immediate ignition.
However, the analysis of 1-octene/BDMS oxidation in air was
difficult to carry out, and thus the reaction products of 1-octene
and BDMS (9:1.2) were obtained by hydroboration under a
nitrogen atmosphere. This would allow analysis of the oxidation
products in air and exploration of the hypergolic ignition path of
1-octene/BDMS. The FTIR spectra of BDMS, 1-octene, and the
reaction products are provided in Figure 8.
characteristic peaks of B−O (1370 and 730 cm−1) and C−O
(1095 cm−1) are shown in Figure 9b, indicating the oxidation of
trioctylborane.32 Therefore, trioctylborane was oxidized after
the hydroboration of BDMS and 1-octene under air. Figure 9b,c
illustrates that no obvious difference was observed between the
oxidation intermediate products after 480 min and those of the
liquid phase during combustion, except for the characteristic
peak of −OH. Comparative analysis of Figure 9c,d revealed that
the characteristic peak of C−O at 1095 cm−1 vanished,
indicating the occurrence of the reaction of oxidized
trioctylborane to generate the end product of B2O3 after
combustion. The peaks at 1460 and 798 cm−1 shown in Figure
9d are attributed to the characteristic peaks of the asymmetric
triangular stretching vibration and the bending vibration of
B2O3, respectively. The characteristic peak of B−O showed a
blue shift from 1370 and 730 cm−1 to 1460 and 798 cm−1 due to
differences in the chemical structures of the intermediate
product and the end product B2O3. Moreover, the B−O bond of
B2O3 was more stable than those of the intermediate products.
On the contrary, a stretching vibration characteristic peak of
−OH appeared at 3220 cm−1, indicating the absorption of some
water vapor by B2O3.
After ignition, 1-octene and BDMS reacted together to form
combustion intermediates, which led to the formation of boron
oxide. No significant differences between the combustion
intermediates of BDMS/1-octene and the oxidation intermedi-
ate product of trioctylborane were noticed in FTIR spectra.
3.3.3. Hypergolic Ignition Reaction Pathway of 1-Octene/
BDMS. To gain a better understanding of the low-temperature
hypergolic ignition process, the oxidation/combustion mecha-
nism of 1-octene/BDMS was researched. Notably, the oxidation
mechanism of alkylborane was only seldom studied through its
combustion in air.33 DMS was used to stabilize BH3 and did not
react with 1-octene during hydroboration. Therefore, the
oxidation or combustion pathway was considered for only the
BH3 reaction to simplify the oxidation or combustion analyses.
The oxidation reaction of trialkylborane or hydrocarbons is
based on the free-radical chain reaction.34−37 Combined with
thermodynamic simulations, the oxidation pathway of trialkyl-
borane could be summarized as follows.
Figure 8a demonstrates that the peak at 2410 cm−1 for pure
BDMS corresponds to the B−H stretching vibration of −BH3 in
BDMS, and those at 1640 and 3080 cm−1 for 1-octene are
associated with the stretching vibration of CC and C−H,
respectively. After hydroboration of 1-octene and BDMS, the
characteristic peaks at 1640 and 3080 cm−1 corresponding to the
CC and C−H bonds of 1-octene vanished, and a new peak
of the B−C bond appeared at 1350 cm−1. This indicated that the
double bond in 1-octene reacted with BH3 of BDMS to yield the
borohydride product trioctylborane (Figure 8b). The character-
istic peak of B−H obviously weakened but did not vanish at
1640 cm−1 because BDMS only slightly contributed to the
hydroboration reaction, leading to the formation of products
with small amounts of remaining BDMS. Therefore, the reaction
of 1-octene and BDMS generated trioctylborane after hydro-
boration. In addition, these results have been confirmed by the
11B NMR (nuclear magnetic resonance) experiment in the
Supporting Information Section 2.
3.3.2. Intermediates and End Product of Oxidation and
Combustion of 1-Octene/BDMS. The FTIR spectra of
trioctylborane and the intermediate products of trioctylborane
oxidation at normal temperature for 480 min, the intermediate
products of the liquid phase during the combustion of 1-octene
and BDMS at normal temperature, and the end products of
combustion are all shown in Figure 9.
Figure 9a,b exhibits the existence of an obvious −OH
characteristic peak at 3620 cm−1, showing a slight excess of BH3
reacting with oxygen to form boric acid under air. The
R3B + O2 → R2BOOR
(1)
then
R2BOOR → R2BO· + ·OR
(2)
or
R2BOOR + R3B → R2BOR + R· + R2BO·
(3)
The reaction pathway of R2BO· generated by the oxidation of
trialkylborane would evolve as follows
3R2BO· → R3B3O3 + 3R·
(4)
The intermediate products of oxidation and combustion
processes were analyzed by a GC-MS experiment. The GC-MS
spectra of the oxidation intermediates of trioctylboranes are
displayed in Figure 10a. On the basis of the detected substances
(marked in red) and trioctylborane, the reactions of
trioctylborane oxidation at normal temperature are summarized
in Figure 10b. On the basis of the oxidation reaction pathway of
alkyl borane reported in the literature study, the presence of R·
(C8H17·) and RO· (C8H17O·) in R(2) and R(3) could be
determined according to Figure 10a,b. Moreover, a large
number of alkyl radicals tend to form 2,6-dimethyheptane and
Figure 9. FTIR spectra of (a) trioctylborane, (b) intermediate products
of trioctylborane oxidation at normal temperature for 480 min, (c)
intermediate products of the liquid phase during combustion of 1-
octene and BDMS at normal temperature, and (d) end products of
combustion.
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Figure 10. (a) GC spectra of oxidation intermediates and their chemical structures detected by MS and (b) reaction formulas of detected substances in
the oxidation process.
Figure 11. (a) GC spectra of hypergolic ignition intermediates and their chemical structures detected by MS and (b) reaction formulas of generated
substances in hypergolic ignition process.
Figure 12. Scheme of the 1-octene hypergolic ignition reaction pathway in the presence of BDMS.
n-hexadecane. The GC-MS spectra of 1-octene/BDMS hyper-
golic ignition intermediates are shown in Figure 11a. The
reaction formula might be deduced by detecting the formed
substances (marked in red), as shown in Figure 11b. According
to the oxidation of alkylborane and the GC-MS spectra of 1-
octene/BDMS hypergolic ignition intermediates, the reaction
process of trioctylborane could be determined in the hypergolic
ignition process. A large number of alkanes was also generated in
the combustion process. It indicated that the product of alkyl
borane after hydroboration was oxidized to produce a large
number of free radicals, which participated in the subsequent
combustion reaction. The combustion reaction is violent;
therefore, MS did not detect the presence of −C8H17 in the
branched chain caused by cracking or chain-branching during
combustion (Figure 11b, R(4) and R(5)).
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Figure 13. Development trend of OH· during the combustion process: (a−d) OH· accumulation stage after ignition, (e−h) OH· acceleration
generation stage, and (i−l) OH· before flame out.
The comparative analysis of oxidation intermediates of
trioctylborane and the hypergolic ignition intermediates of 1-
octene/BDMS in GC-MS revealed the absence of R3B3O3
(R(4)) in oxidation intermediates of trioctylborane at normal
temperature. It also showed the difference between the
hypergolic ignition of BDMS/1-octene and the oxidation of
trioctylborane. 1-Octene reacted with BH3 (BDMS) to form
trioctylborane, releasing substantial heat during hydroboration.
Therefore, the oxidation reaction occurred to generate
(C8H17)3BOO. Two scenarios could be envisaged for
(C8H17)3BOO: (i) the direct decomposition of (C8H17)3BOO
and (ii) the reaction with trioctylborane to generate an alkyl
radical. Finally, the reaction of the alkyl radical with O2 produced
OH·. The formation of OH· promoted the combustion reaction.
The substances containing boron atoms continued to oxidize
and decomposed into B2O3. Previous research dealing with
alkylborane oxidation combined with GC-MS data, Gaussian
simulations, and FTIR results led to a better understanding of
the hypergolic ignition reaction pathway of BDMS/1-octene.
The detailed reaction pathway for the 1-octene hypergolic
ignition of BDMS is shown in Figure 12.
3.3.4. Hydroxyl Radicals during Hypergolic Ignition and
Combustion Processes. Combustion is a chain reaction
initiated by a highly active hydroxyl and other free radicals.
Higher concentrations of free radicals could promote low-
temperature combustion. Moreover, the production of OH·
(hydroxyl radicals) in the early stage was the most significant
factor that determined whether hydrocarbons could be ignited.
The development trend of OH· during combustion monitored
by optical measurements is summarized in Figure 13.
OH· to accelerate the combustion reaction. In the last stage, a
reduction in OH· occurred, generating the flame due to the rapid
consumption of combustible materials after the acceleration
stage. Therefore, the directional reaction method not only
achieved the hydroboration of 1-octene but also generated a
substantial amount of OH· to promote the combustion reaction
and realize the hypergolic ignition of liquid hydrocarbon fuel at
−15 °C.
4. CONCLUSIONS
The hypergolic ignition of hydrocarbon fuels was successfully
realized at low temperature by designing and performing a
directional hydroboration reaction for the first time. The
construction strategy, ignition performance, oxidation or
combustion process, and hypergolic ignition pathway were all
studied.
The Gaussian simulation results showed that the hydro-
boration reaction of 1-octene and BDMS could be realized
spontaneously to release 149.4 kcal/mol of heat. 1-Octene and
BDMS achieved hypergolic ignition at −15 °C with a volume
concentration of 9:1.2. Compared with the ignition delay time of
pure 1-octene (565 °C), the ignition delay time of 1-octene/
BDMS (9:1.2) reduced by 3850% at 50 °C. The FTIR
spectroscopy and GC-MS experiments revealed the successful
hypergolic ignition pathway of 1-octene and BDMS, beneficial
for the combustion of supporting free-radical OH·, as confirmed
by optical measurements. These findings provide further
guidance for the reliable ignition and efficient combustion of
hydrocarbon fuels in scramjet combustors.
Figure 13 demonstrates that the development trend of OH·
can be divided into the following three stages: the OH·
accumulation stage after ignition (panels a−d), the OH·
acceleration generation stage (panels e−h), and OH· before
flame out (i−l). In the first stage, active OH· radicals were
generated by the oxidation of trioctylborane after hydroboration
between 1-octene and BDMS. This led to the accumulation of
OH·, allowing the ignition and promotion of combustion when
compared with pure 1-octene because alkyl or alkoxy radicals
could easily be produced by the proposed strategy. In the second
stage, the combustion reaction entered the accelerating stage,
and the flame sprayed out of the bottle, causing large amounts of
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jpca.0c08999.
Ignition delay time of 1-octene with a high concentration
of BDMS at 25 and 50 °C, and confirmation the
hydroboration reaction of 1-octene with BDMS and the
reaction product via 11B NMR experiments (PDF)
Movie S1. BDMS/1-octene hypergolic ignition at 25 °C
(MP4)
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Encapsulated Cobalt Nanocapsules Creates Highly Active Cobalt
Oxide Catalysts for Hydrocarbon Combustion. Nat. Commun. 2015, 6,
7181.
(12) Bijjula, K.; Vlachos, D. G. Catalytic Ignition and Autothermal
Combustion of JP-8 and Its Surrogates over a Pt/γ-Al2O3 Catalyst. Proc.
Combust. Inst. 2011, 33, 1801−1807.
(13) Northam, G. B.; McLain, A. G.; Pellett, G. L.; Diskin, G. Effect of
Silane Concentration on the Supersonic Combustion of a Silane/
Methane Mixture. AIAA/ASME/SAE/ASEE 22nd Joint Propulsion
Conference 1986, 1386−1396.
(14) Ryan, T. W., III; Schwab, S. T.; Harlowe, W. Aluminum Alkyl
Derivatives-Ignition and Combustion Enhancers for Supersonic
Combustors. J. Propul. Power 1995, 11, 124−129.
(15) Li, X.; Huang, X.; Liu, H. A Composite-Fuel Additive Design
Method for n-Decane Low-Temperature Enhancement. Combust.
Flame 2018, 188, 262−272.
(16) Li, S. Q.; Gao, H. X.; Shreeve, J. M. Borohydride Ionic Liquids
and Borane/Ionic-Liquid Solutions as Hypergolic Fuels with Superior
Low Ignition-Delay Times. Angew. Chem., Int. Ed. 2014, 53, 2969−
2972.
Movie S2. BDMS/1-octene hypergolic ignition at −15 °C
(MP4)
Movie S3. OH radicals in hypergolic ignition process at
−15 °C (MP4)
AUTHOR INFORMATION
Corresponding Author
Xiaobin Huang − Shanghai Jiao Tong University School of
Aeronautics and Astronautics, Shanghai 200240, China;
orcid.org/0000-0002-6564-016X; Email: xbhuang@
sjtu.edu.cn
■
Authors
Haoqiang Sheng − Shanghai Jiao Tong University School of
Aeronautics and Astronautics, Shanghai 200240, China
Zhijia Chen − Shanghai Jiao Tong University School of
Aeronautics and Astronautics, Shanghai 200240, China
Zhengchuang Zhao − Shanghai Jiao Tong University School of
Aeronautics and Astronautics, Shanghai 200240, China
Hong Liu − Shanghai Jiao Tong University School of
Aeronautics and Astronautics, Shanghai 200240, China
(17) Thomas, A.; Chambreau, S. D.; Vaghjiani, G. L. Ignition Delay
Reduction with Sodium Addition to Imidazolium-Based Dicyanamide
Ionic Liquid. J. Phys. Chem. A 2019, 123, 10−14.
(18) Zhang, Q. H.; Shreeve, J. M. Energetic Ionic Liquids as
Explosives and Propellant Fuels: A New Journey of Ionic Liquid
Chemistry. Chem. Rev. 2014, 114, 10527−10574.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jpca.0c08999
(19) Hellier, P.; Ladommatos, N.; Allan, R.; Rogerson, J. Combustion
and Emissions Characteristics of Toluene/n-Heptane and 1-Octene/n-
Octane Binary Mixtures in a Direct Injection Compression Ignition
Engine. Combust. Flame 2013, 160, 2141−2158.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science
Foundation of China (no. 91941301).
(20) Pfeil, M. A.; Son, S. F.; Anderson, W. E. Influence of Ammonia
Borane on the Stability of a Liquid Rocket Combustor. J. Propul. Power
2014, 30, 290−298.
■
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E. et al.
Gaussian 16, revision C.01; Gaussian, Inc.: Wallingford, CT, 2016.
(22) Morera-Boado, C.; Martinez Gonzalez, M.; Miranda-Quintana,
R. A.; Suarez, M.; Martinez-Alvarez, R.; Martin, N.; Garcia de la Vega, J.
M. Theoretical Study on the Mechanism of the Thermal Retro-
Cycloaddition of Isoxazolinofullerenes. J. Phys. Chem. A 2016, 120,
8830−8842.
(23) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals
for Main Group Thermochemistry, Thermochemical Kinetics, Non-
covalent Interactions, Excited States, and Transition Elements: Two
New Functionals and Systematic Testing of Four M06-Class Func-
tionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120, 215−
241.
(24) Hehre, W. J.; Ditchfield, R.; Pople, J. A. Self-consistent Molecular
Orbital Methods. XII. Further Extensions of Gaussian-Type Basis Sets
for Use in Molecular Orbital Studies of Organic Molecules. J. Chem.
Phys. 1972, 56, 2257−2261.
(25) Hariharan, P. C.; Pople, J. A. The Influence of Polarization
Functions on Molecular Orbital Hydrogenation Energies. Theor. Chim.
Acta 1973, 28, 213−222.
(26) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. V. R.
Efficient Diffuse Function-Augmented Basis Sets for Anion Calcu-
lations. III. The 3-21+G Basis Set for First-Row Elements, Li-F. J.
Comput. Chem. 1983, 4, 294−301.
(27) He, X.; Zeng, Q.; Zhou, Y.; Zeng, Q. X.; Wei, X. F.; Zhang, C. Y. A
DFT Study Toward the Reaction Mechanisms of TNT with Hydroxyl
Radicals for Advanced Oxidation Processes. J. Phys. Chem. A 2016, 120,
3747−3753.
(28) da Silva, G. Oxidation of Carboxylic Acids Regenerates Hydroxyl
Radicals in the Unpolluted and Nighttime Troposphere. J. Phys. Chem.
A 2010, 114, 6861−6969.
REFERENCES
■
(1) Urzay, J. Supersonic Combustion in Air-Breathing Propulsion
Systems for Hypersonic Flight. Annu. Rev. Fluid Mech. 2018, 50, 593−
627.
(2) Vanyai, T.; Bricalli, M.; Brieschenk, S.; Boyce, P. R. Scramjet
Performance for Ideal Combustion Processes. Aerosp. Sci. Technol.
2018, 75, 215−226.
(3) Yang, K.; Pan, Y.; Wang, Z. G.; Wang, N.; Li, X. P. Experimental
Investigation of the Ignition Characteristics of Vaporized RP-3
Kerosene in Supersonic Flow. Acta Astronaut. 2020, 174, 1−10.
(4) Ben-Yakar, A.; Hanson, R. K. Cavity Flame-Holder for Ignition
and Flame Stabilization in Scramjets: An Overview. J. Propul. Power
2001, 17, 869−877.
(5) Mai, T.; Sakimitsu, Y.; Nakamura, H.; Ogami, Y.; Kudo, T.;
Kobayashi, H. Effect of the Incident Shock Wave Interacting with
Transversal Jet Flow on the Mixing and Combustion. Proc. Combust.
Inst. 2011, 33, 2335−2342.
(6) Li, Y. H.; Chen, C. T.; Fang, H. K. Effects of a Microwave-Induced
Corona Discharge Plasma on Premixed Methane-Air Flames. Energy
2019, 188, 116007.
(7) Grady, N. R.; Pitz, R. W.; Carter, C. D.; Hsu, K. Y. Raman
Scattering Measurements of Mixing and Finite-Rate Chemistry in a
Supersonic Reacting Flow over a Piloted. Combust. Flame 2016, 165,
310−320.
(8) Li, X.; Qin, S.; Huang, X.; Liu, H. Multi-Component Effect and
Reaction Kinetics for Low-Temperature Ignition of Kerosene with
Composite Enhancer. Combust. Flame 2019, 199, 401−410.
(9) Javed, I.; Baek, S. W.; Waheed, K. Evaporation Characteristics of
Heptane Droplets with the Addition of Aluminum Nanoparticles at
Elevated Temperatures. Combust. Flame 2013, 160, 170−183.
(10) Farrauto, R. J. Low-Temperature Oxidation of Methane. Science
2012, 337, 659−660.
(29) Khaled, F.; Giri, B. R.; Liu, D. P.; Assaf, E.; Fittschen, C.; Farooq,
A. Insights into the Reactions of Hydroxyl Radical with Diolefins from
Atmospheric to Combustion Environments. J. Phys. Chem. A 2019, 123,
2261−2271.
(11) Wang, H.; Chen, C.; Zhang, Y.; Peng, L.; Ma, S.; Yang, T.; Guo,
H.; Zhang, Z.; Su, D. S.; Zhang, J. In Situ Oxidation of Carbon-
433
https://dx.doi.org/10.1021/acs.jpca.0c08999
J. Phys. Chem. A 2021, 125, 423−434

The Journal of Physical Chemistry A
pubs.acs.org/JPCA
Article
(30) Li, J.; Zhang, Z.; Wu, L.; Zhang, W.; Chen, P.; Lin, Z.; Liu, G.
Site-Specific Allylic C-H Bond Functionalization with a Copper-Bound
N-Centred Radical. Nature 2019, 574, 516−521.
(31) Tamura, Z.; Tanasawa, Y. Evaporation and Combustion of A
Drop Contacting with a Hot Surface. Symp. (Int.) Combust., [Proc.]
1958, 7, 509−522.
(32) Curran, D. P.; Mcfadden, T. R. Understanding Initiation with
Triethylboron and Oxygen: The Difffferences Between Low-Oxygen
and High-Oxygen Regimes. J. Am. Chem. Soc. 2016, 138, 7741−7752.
(33) Davies, A. G.; Ingold, K. U.; Roberts, B. P.; Tudor, R. Homolytic
Organometallic Reactions. Part II. The Kinetics and Rate Constants for
the Autoxidation of Organoboron Compounds in Solution. J. Chem.
Soc. B 1971, 60, 698−712.
(34) Schneider, A.; Mantzaras, J.; Jansohn, P. Experimental and
Numerical Investigation of the Catalytic Partial Oxidation of CH4/
O(2) Mixtures Diluted with H2O and CO2 in A Short Contact Time
Reactor. Chem. Eng. Sci. 2006, 61, 4634−4649.
(35) Zeng, Z.; Altarawneh, M.; Oluwoye, I.; Glarborg, P.;
Dlugogorski, B. Z. Inhibition and Promotion of Pyrolysis by Hydrogen
Sulfide (H2S) and Sulfanyl Radical (SH). J. Phys. Chem. A 2016, 120,
8941−8948.
(36) Brown, H. C.; Midland, M. M. Initiation Rates for Autoxidation
of Trialkylboranes. Effect of A Steric Factor on the Initiation rate. J.
Chem. Soc. D 1971, 699−700.
(37) Sonnenschein, M. F.; Webb, S. P.; Kastl, P. E.; Arriola, D. J.;
Wendt, B. L.; Harrington, D. R.; Rondan, N. G. Mechanism of
Trialkylborane Promoted Adhesion to Low Surface Energy Plastics.
Macromolecules 2004, 37, 7974−7978.
434
https://dx.doi.org/10.1021/acs.jpca.0c08999
J. Phys. Chem. A 2021, 125, 423−434