Isomerization of cis-1,2-dimethylcyclohexane in single-pulse shock tube experiments

Cyclic hydrocarbons are major constituents of jet fuels and reference compounds in jet fuel surrogates. The kinetic and thermal stability and reaction mechanisms of fuel molecules are essential input parameters in the models and simulations used in the design of novel fuels, renewable energy technologies, and devices. A detailed study and analysis of the pyrolytic chemistry of cis-1,2-dimethylcyclohexane has been performed in single-pulse shock tube experiments. The investigations are carried out over the temperature range of 1100 to 1200 K at about 2.5 atm pressure. The isomeric products are trans-1,2-dimethylcyclohexane, 1-octene, and (cis + trans)-2-octene. The three octene isomers can be attributed to internal disproportionation processes. Assuming a diradical mechanism and that cis-1,2-dimethylcyclohexane is formed in equal amount with respect to its trans isomer, the total rate expression for isomerization is kC-C = 10(15.5±0.8) exp(-38,644 ± 2061 K/T) s(-1). The rate constants are over an order of magnitude smaller than the equivalent noncyclic hydrocarbon system. The presence of the isomeric octenes suggests that internal disproportionation is an important component of the isomerization process.