High temperature experimental and computational studies of the pyrolysis and oxidation of endothermic fuels

Methylcyclohexane (MCH) and decahydronaphthalene (Decalin) are both proposed endothermic jet fuels and significant constituents of current commercial automotive and aviation fuel blends. In order to understand the combustion characteristics of these cyclic aliphatics in both aircraft and automobile engine environments, pyrolysis and oxidation experiments of both fuels were performed over the temperature range 1015--1200 K (and for the oxidation studies, over the equivalence ratio range 0.44--1.29) in the Princeton Atmospheric Pressure Turbulent Flow Reactor.; The pre-exponential and activation energy terms associated with the overall pyrolysis of MCH and Decalin in the flow reactor were determined to be: 3.73 x 1013 sec-1 and 63.3 kcal/mol for MCH and 3.18 x 1011 sec-1 and 52.3 kcal/mol for Decalin, respectively. These flow reactor studies also revealed ethene, 1,3-butadiene, methane, and propene to be the dominant products formed during MCH pyrolysis as well as the major intermediates of the MCH oxidation studies. In contrast, the dominant species formed during Decalin pyrolysis were not only these four compounds, but also cyclopentadiene, benzene, and toluene. Furthermore, the Decalin oxidation studies not only revealed the formation of these seven compounds, but also revealed the formation of substantial amounts of phenol and benzaldehyde. However, the formation of these two species appears to be due to the concurrent oxidation of benzene and toluene, respectively, and not to any fundamental change in the primary Decalin radical homolysis reaction schemes.; Neither fuel generated substantial amounts of its aromatic analog (MCH/toluene; Decalin/naphthalene) under either pyrolytic or oxidative conditions. Also not observed in these subcritical experiments were products associated with so-called "caging" reactions that prevail in the high concentration environments of supercritical pyrolysis studies associated with both these compounds. Indeed, both MCH and Decalin exhibit atmospheric vapor phase oxidation characteristics that are essentially those of other aliphatic hydrocarbons.; The above experimental Decalin results served as a basis for a computational kinetic model of the Decalin pyrolysis system that was constructed in this study. This model was strongly analogous to another computational kinetic mechanism constructed in this study---that of the cyclohexane pyrolysis system. Both models involve an initiation process centered on biradical species produced through C-C ring bond homolysis reactions. Once this initiation scheme generates a sufficiently sized radical pool, hydrogen abstraction reactions between the radicals and the fuel molecules then generate the primary fuel radicals that dominate the system kinetics. Upon further study of cyclic radical isomerization rates, the methodology presented here can be implemented to construct a full Decalin pyrolysis model. Though presently incomplete because of this lack of knowledge of cyclic radical isomerization rates, the final Decalin pyrolysis model presented captures the fuel decay characteristics over the temperature range of this study and illustrates the major reaction paths responsible for the formation of the seven products listed above.