Auto-ignition control using an additive with adaptable chemical structure. Part I: Development of a kinetic model for 1,3-cyclohexadiene and 1,3,5-hexatriene combustion

Abstract

Abstract 1,3-cyclohexadiene (1,3-CHD) can be transformed into cis-1,3,5-hexatriene (1,3,5-HT) upon light irradiation, which makes it a potential additive able to change the reactivity of a conventional fuel. This paper presents the development of a detailed chemical kinetic model for the low-temperature (500–1200\u202fK) combustion of 1,3-cyclohexadiene and 1,3,5-hexatriene. Theoretical calculations were performed to compute the thermochemistry of a large number of intermediates involved in the reaction mechanism, and for several kinetic parameters. In particular, the pericyclic reactions of 1,3-cyclohexadiene, linking it to cis-1,3,5-hexatriene, were studied theoretically. It was shown that 1,3,5-HT is inherently a secondary molecule of the 1,3-CHD mechanism and a comprehensive set of its oxidation reactions were included. Simulation of literature data (ignition delays and products speciation) measured in rapid compression machines for 1,3-CHD were performed using the newly developed kinetic model. A good agreement with experiments was found, and kinetic analyses highlighted the decomposition mechanism of 1,3-CHD and the most sensitive reactions affecting the auto-ignition delay times. Simulations of cis-1,3,5-HT auto-ignition in an RCM were also performed and compared to the ignition behaviour of 1,3-CHD. The simulation results showed that 1,3,5-HT combustion involves an induction period characterized by the predominant formation of 1,3-CHD, whose decomposition starts the radical chain mechanism.