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.

 

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  *Financial support from the National Natural Science Fund of China (U1232134) is gratefully acknowledged.

^**Corresponding authors: (Tel: 022-27892340, Email: gliu@tju.edu.cn)