Speciation of the reaction intermediates from n-dodecane oxidation in the low temperature regime

The oxidation of n-dodecane was studied with experiments in a pressurized flow reactor over the low temperature regime (550–830 K) at elevated pressure (0.8106 MPa) and lean equivalence ratio (0.23). n-Dodecane exhibited negative temperature coefficient (NTC) behavior such that fuel reactivity peaked around 700 K and then decreased with increasing temperature. Samples were extracted at a residence time of 120 ms and stable intermediates were analyzed utilizing a gas chromatograph with a flame ionization detector coupled to a mass spectrometer. While a range of species were observed, a significant portion of n-dodecane decomposition was attributed to a select few species. These major carbon contributing intermediates included carbon oxides (CO and CO2), light aldehydes (formaldehyde, acetaldehyde, and propanal), C12 alkylated tetrahydrofurans (2-propyl-5-iso-pentyltetrahydrofuran and two other incompletely identified isomers), lactones (5-methyl-dihydro-2(3H)-furanone and dihydro-2(3H)-furanone), and alkenes (ethene and 3-dodecene). The experimental results were compared to two kinetic models. The models captured the NTC behavior; however, discrepancies in measured formaldehyde, several light unsaturated species, and carbon monoxide indicate areas for model improvement. In the low temperature branching pathway from Livermore, a reaction path was identified (hydrogen abstraction from a secondary carbon followed by molecular oxygen addition and then internal hydrogen shift from the primary carbon) which would, if more active, predict the measured intermediate species. The data from this study provide targets for the continued refinement of kinetic models for n-dodecane.