Formation of H‐atoms in the pyrolysis of cyclohexane and 1‐hexene: A shock tube and modeling study

Abstract

Cyclohexane (cC 6 H 12 ) plays an important role in the combustion of practical liquid fuels, as a major component of naphthenic compounds. Therefore, the pyrolysis of cyclohexane was investigated by measuring the formation of H-atoms. The thermal decomposition of 1-hexene (1-C 6 H 12 ) was also studied, because of the assumption that 1-hexene is the sole initial product of cyclohexane decomposition. For cyclohexane, the measurements were performed over a temperature range of 1320-1550 K, at pressures ranging from 1.8 to 2.2 bar; 1-hexene experiments were done at temperatures between 1250 and 1380 K and pressures between 1.5 and 2.5 bar. For each experiment, the time-dependent formation of H-atoms was measured behind reflected shock waves by using the method of atomic resonance absorption spectrometry. For the dissociation of 1-hexene to n-propyl (C 3 H 7 ) and allyl (C 3 H 5 ) radicals, the following Arrhenius expression was derived: k R2 (T ) = 2.3 × 10 16 exp(−36,672 K/T ) s −1 . For cyclohexane, overall rate coefficients (k ov ) were deduced for the global reaction cC 6 H 12 → products + H from the H-atom time profiles; the following temperature dependency was obtained: k ov (T ) = 4.7 × 10 16 exp(−44,481 K/T ) s −1 . For both sets of rate coefficient values, an uncertainty of ±30% is estimated. Especially concerning the isomerization cC 6 H 12 → 1-C 6 H 12 , our experimental results are in excellent agreement with the rate coefficient values given by Tsang (Tsang, W. Int J Chem Kinet 1978Kinet , 10, 1119Kinet -1138. A reaction model was assembled that is able to reproduce the H-atom profiles measured for both sets of experiments. According to this model, H-atoms are mostly stemming from the thermal decomposition of allyl radicals (C 3 H 5 ), which arise from the decomposition of 1-hexene. Furthermore, it will be shown that the recombination of allyl radicals with H-atoms to propene (C 3 H 6 ) also represents a very important subsequent reaction.

Variable high‐pressure and concentration study of cyclohexane pyrolysis at high temperatures

“…Two shock tube studies at around 2 bar were conducted by Peukert et al . The first study investigated the unimolecular decomposition of cyclohexane where it was found that 1‐hexene is the sole initial product of cyclohexane dissociation, and the obtained rate coefficients for the reaction were in agreement with those of Tsang and Kiefer et al .…”

“…Two shock tube studies at around 2 bar were conducted by Peukert et al 11,12 The first study 11 investigated the unimolecular decomposition of cyclohexane where it was found that 1-hexene is the sole initial product of cyclohexane dissociation, and the obtained rate coefficients for the reaction were in agreement with those of Tsang 4 and Kiefer et al 8 The second study by Peukert et al 12 pertained to the reactions involving hydrogen abstraction of cyclohexane. First, experiments with cyclohexane and iodoethane (hydrogen donor) were completed to determine the reaction rate coefficients for the initial hydrogen abstraction from cyclohexane and formation of the cyclohexyl radical, which subsequently isomerizes to hex-5-en-1-yl.…”

An experimental and kinetic modeling study of cyclohexane pyrolysis at low pressure

“…Among cycloalkanes, cyclohexane has received great attention due to its simplicity, and the role as a good starting point to develop cycloalkane models. Many experiments have been carried out to investigate pyrolysis [3][4][5][6], oxidation [7][8][9][10][11][12][13][14][15][16][17] and combustion [18][19][20][21][22][23][24][25] of cyclohexane. In addition to experimental investigations, some theoretical studies have been performed by Handford-Styring and Walker [26], Sirjean et al [27] and Cavallotti et al [28].…”

Determination of rate parameters of cyclohexane and 1-hexene decomposition reactions

“…The numbering of the reactions in this article is in accordance with that of the paper of Peukert et al [4].…”

“…Surrogate fuel mixtures often include cyclohexane and 1-hexene, as representatives of cycloalkanes and alkenes [3]. Recently, Peukert et al [4] investigated experimentally the formation of H-atoms in the pyrolysis of cyclohexane and 1-hexene by applying the shock tube technique combined with the ARAS-technique (atomic resonance absorption spectroscopy). They proposed a detailed chemical kinetic reaction model for reproducing the measured H-atom absorption profiles.…”