Effects of Bond Location on the Ignition and Reaction Pathways of trans-Hexene Isomers

Chemical structure and bond location are well-known to impact combustion reactivity. The current work presents new experimental autoignition and speciation data on the three trans-hexene isomers (1-hexene, trans-2-hexene, and trans-3-hexene), which describe the effects of the location of the carbon-carbon double bond. Experiments were conducted with the University of Michigan rapid compression facility to determine ignition delay times from pressure time histories. Stoichiometric (ϕ = 1.0) mixtures at dilution levels of buffer gas:O2 = 7.5 (mole basis) were investigated at an average pressure of 11 atm and temperatures from 837 to 1086 K. Fast gas sampling and gas chromatography were also used to quantitatively measure 13 stable intermediate species formed during the ignition delay period of each isomer at a temperature of ∼900 K. The measured ignition delay times and species measurements were in good agreement with previous experimental studies at overlapping conditions. The results were modeled using a gasoline surrogate reaction mechanism from Lawrence Livermore National Laboratory, which contains a submechanism for the trans-hexene isomers. The model predictions captured the overall autoignition characteristics of the hexene isomers well (within a factor of 2), as well as the time histories of several of the intermediate species (e.g., propene). However, there were discrepancies between the model predictions and the experimental data for some species, particularly for the 3-hexene isomer.