Hydrocarbons for the next generation of jet fuel surrogates

Fuel surrogates are a critical component for the detailed combustion modeling of real transportation fuels. Indeed, the numerical study of engine combustion requires the coupling of computational fluid dynamics and chemical kinetic models, and therefore a limited number of chemical species and reactions can be employed due to current numerical capabilities. As a consequence, surrogates are adopted to simulate the behavior of real fuels. In this study, we evaluate various hydrocarbon molecules that can be employed as next generation surrogate components for conventional and alternative jet fuels. Species considered in this study have smaller number of kinetic data as compared to molecules that are currently used in jet fuel surrogates, but they possess greater physical relevance and the potential to achieve closer emulation of properties when used as jet fuel surrogate components. Using a surrogate optimizer model, we analyze various mixtures that can emulate a petroleum-derived jet fuel (Jet-A POSF-4658) and a coal-derived jet fuel (IPK POSF-5642). The results show that n-tetradecane and n-dodecane are suitable normal alkane representatives for jet fuels. Also, the use of three C9 alkylbenzenes (n-propyl-, 1,2,4-trimethyl-, 1,3,5-trimethyl-benzene) leads to surrogate mixtures with an aromatic content and a distillation curve that matches the experimental values of Jet-A much better than mixtures that contain toluene or C10 alkylbenzenes. In addition, the optimization results with three new branched alkanes for the target IPK show that 2,2,4,6,6-pentamethylheptane is a promising surrogate component for representing low ignition quality highly-branched alkanes in jet fuels. This study highlights the need for experimental studies and further kinetic model development for these molecules, which will benefit the surrogate development for the wide variety of jet fuels in the future.