Lawrence Livermore National Laboratory

A detailed chemical kinetic mechanism has been developed and used to study the oxidation of cyclohexane in a rapid compression machine (RCM) and a jet-stirred reactor (JSR). The series of experiments investigated to validate the model incorporated a pressure range of 1 to 12.5 atm, temperature range of 650 K-1150 K, and equivalence ratios of 0.5 to 1.5. The RCM experiments used simulated air mixtures with the diluent composition containing varying amounts of Ar/N2/CO2. In the JSR experiments, the diluent was 99% N2. Please see references below for additional details, including comparisons between experiments and model. Rules for reaction rate constants were developed for the low-temperature combustion of cyclohexane and were based on those previously developed for the low-temperature oxidation of methylcyclohexane with particular reference to the use of cyclic reaction rate rules (see Pitz et al., Proc Combust. Inst., 2007). These rules establish a methodology for addressing cyclic systems and can be used for in chemical kinetic mechanisms for other cycloalkanes.

The direct elimination of cyclohexene and HO2 from RO2 is included in the treatment using a modified rate constant of Cavallotti et al. (Proc. Combust. Inst. 31, 201, 2007). In addition, we developed a heat loss model for the Lille RCM, an improvement on other studies on cyclohexane. The heat loss model is available by request from the author. Intermediate species data from the RCM study were used to help complement and refine the low- and intermediate-temperature portions of the reaction mechanism, leading to good predictions of intermediate product formation in most cases. The model predicts the formation of benzene from the parent fuel via the sequential dehydrogenation pathway. Possible alternative H-atom isomerizations leading to different products from the parent O2QOOH radical were included in the low-temperature chemical kinetic mechanism and we observed that these pathways play a significant role.

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Silke, E. J., W. J. Pitz, and C. K. Westbrook, "Detailed Chemical Kinetic Modeling of Cyclohexane Oxidation," J. Phys. Chem. A 111 (19)(2007) 3761-3775, DOI: 10.1021/jp067592d (2007).