A detailed chemical model for the combustion of n-heptane in a low pressure reactor

A detailed chemical model, describing the combustion of n-heptane in a low-pressure batch reactor, has been developed. The proposed detailed chemical mechanism consists of 315 species and 758 reactions and is implemented using the Chemkin-II computer software package. The model is tested against the experimental work of a previous worker. Varying degrees of success are observed when the results obtained from numerical simulations are compared to the experimental data. Phenomenological features such as the variation of induction time to a cool flame with initial temperature or initial pressure compare satisfactorily; however, comparison between numerically simulated concentrations of chemical species and experimental ones show that an underprediction, in numerically simulated concentrations, is observed. Results from the numerical simulations indicate that the induction time to a cool flame is greatly influenced by the rate parameters assigned to the chain-branching reaction of the ketoheptylhydroperoxide species: O=QOOH → O=QO. + .OH Furthermore, of the possible chain-branching agents included in the chemical model, the relatively large concentrations of the two species 2-ketoheptyl-4-hydroperoxide and 4-ketoheptyl-2-hydroperoxide calculated from numerical simulations leads to the suggestion that these species are the chain-branching agents responsible for autoigntion. Support is given to this claim from sensitivity analysis performed in the study. The influence of heat loss on the numerical simulations has also been investigated in the study. Results show that numerically simulated cool flame multiplicity varies with the magnitude of the calculated heat loss rate. The heat loss models incorporated into the numerical calculations are necessarily simplified in order to avoid a drastic decline in computer processing performance due to the large chemical mechanism employed. However, such a simplification is questionable when attempting to model physical and/or chemical processes within a batch reactor