(271d) Thermal Decomposition Mechanism and Kinetic Modeling Study of JP-10 At Low Pressure

Thermal decomposition
mechanism and kinetic modeling study of JP-10 at low pressure

Heng
Li¹,
Guozhu Liu^{1, **}, Rongpei Jiang¹, Guozhu
Li¹, Qingfa
Wang¹, Jijun
Zou¹, Lidong
Zhang², Li Wang¹ and Xiangwen
Zhang¹

¹Key Laboratory
for Green Chemical Technology of Ministry of Education, School of Chemical
Engineering and Technology, Tianjin University, Tianjin 300072, PR China

²National
Synchrotron Radiation Laboratory, University of Science and Technology of
China, Hefei, Anhui 230029, PR China

Abstract

JP-10,
a
kind of polycyclic hydrocarbon, named as exo-tetrahydrodicyclopentadiene
or tricyclo[5.2.1.0^2,6]decane, is usually used as aviation fuel for
its excellent properties of high energy density, high thermal stability and low
freezing point. This single-component fuel is also utilized as the coolant of the
thermal management system of supersonic aircraft for its favorable endothermic
capacity during pyrolysis. The design and optimization of the cooling system depend
on the comprehensive understanding of reaction network of JP-10 pyrolysis. Therefore,
a detail kinetic model is required to elaborate the decomposition chemistry of JP-10
at various stages during the whole pyrolysis process.

In
this work, a detail kinetic model was developed to simulation JP-10 pyrolysis
at low pressure. Before simulation, a set of credible experimental data had
been obtained by a pyrolysis experiment at low pressure using tunable
synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS),
which had identified approximately 30 species including products, intermediates,
radicals or even some isomers involved in reactions. So the key reactions
procedure associated with special radicals could be verified by the online
measurement, which also laid the basis of analysis of JP-10 pyrolysis mechanism.
Subsequently, the JP-10 decomposition channels were discussed and calculated by
quantum chemical theory. Approximately 19 unimolecular initial decomposition
channels were calculated at CBS-QB3 level. Compared with the experimental
results, some channels with lower energy barriers were selected as the primary
mechanism and the structures of corresponding products were optimized. These
primary reaction channels may dominate JP-10 initial decomposition and produce
some crucial intermediates associated with some
observed species. Moreover, the initial reaction rate constant was further
estimated by employing the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The
following reaction network was analyzed by the radical chain reaction mechanism.

With
the overall analysis of reaction network, a detail kinetic model was developed
to simulate the JP-10 pyrolysis, which is mainly base on our research on the initial
mechanisms of JP-10 pyrolysis in this work and some other mechanisms for minor
species derived from JetSurF version 2.0¹, toluene
pyrolysis model developed by Zhang et al.² and cyclohexane
pyrolysis mechanism proposed by Wang et al.³. The
simulation values of mole fraction for primary products are in good agreement
with the experimental runs. The rate of production (ROP) analysis showed
the contribution of the major generation or consumption pathways of principle
species at different temperatures and illustrated the C₁₀H₁₆=4-methyl-2,3,3a,4,5,7a-hexahydro-1H-indene and C₁₀H₁₆=C₁₀H₁₅+H
strongly influence the formation of some minor molecules from the following
reactions at low pressure. Meanwhile, trace amounts of PAH observed in the
middle and late period could also agree well with this modeling results associated
with some important second reactions mechanism from this model.

Furthermore,
a special species 4-methyloctahydro-1H-indene (m/z=138) forming
at the initial stage of JP-10 pyrolysis showed well consistency with the
simulation results. The corresponding decomposition and saturation mechanism(JP-10¨DBR2¨D4-methyloctahydro-1H-indene)
was verified in the initial stage, which indirectly confirmed that the BR2 may
be a key intermediate dominating the diradical pathways in the JP-10 initial
pyrolysis through the unstable diradical is not easy to observe in the experiment.
Thus, some
diradicals may be statured through seizing H atoms from reactant molecular in early
decomposition period and the forming radicals continue to decompose to some species
with minor mass-to-charge ratio, which accelerates decomposition reactions in
the initial stage of JP-10 pyrolysis.

References

1.            Wang
H, Dames E, Sirjean B, et al. A high-temperature chemical kinetic model of
n-alkane (up to n-dodecane), cyclohexane, and methyl-, ethyl-, n-propyl and
n-butyl-cyclohexane oxidation at high temperatures. JetSurF version 2.0, September
19, 2010; <http://melchior.usc.edu/JetSurF/JetSurF2.0>.

2.            Zhang
L, Cai J, Zhang T, Qi F. Kinetic modeling study of toluene pyrolysis at low
pressure. Combust. Flame. 2010;157(9):1686-1697.

3.            Wang
Z, Cheng Z, Yuan W, et al. An experimental and kinetic modeling study of
cyclohexane pyrolysis at low pressure. Combust. Flame. 2012;159(7):2243-2253.