Development of a chemical surrogate for JP-8 aviation fuel using a pressurized flow reactor
Authors:   , Agosta Alessandro , Miller David Leslie , Cernansky Nicholas Peter 
Published: July 2021

The next generation of military vehicles will demand higher performance propulsion systems that deliver increased power, fuel efficiency, and lower observable emissions. There is strong evidence that low and intermediate temperature hydrocarbon fuel chemistry controls the important preignition processes through heat release and formation of reactive species. The elucidation of the rate controlling chemical mechanisms during these phases of operations remains an important goal of combustion chemistry as it applies to engine and vehicle systems. This study is an effort to expand the actual knowledge of the chemistry controlling the ignition of single and multi-component mixtures of full boiling range distillate hydrocarbon fuels (diesel and jet fuels) as well as to develop a surrogate for the complex military aviation fuel JP-8. The oxidation and ignition characteristics of pure alkanes (n-dodecane and isocetane), napthenes (methylcyclohexane and decalin), and aromatics (a-methylnapthalene and hexylbenzene) and of their mixtures have been experimentally studied using the Drexel Pressurized Flow Reactor and our CO reactivity mapping technique. A negative temperature coefficient (NTC) region has been clearly identified for both the alkanes and naphthenic compounds through several controlled cool down (CCD) bench scale tests. The analysis of the interactions controlling the ignition of binary, ternary and larger mixtures of the compounds listed above has been applied to the synthesis of a multi-component surrogate for the worldwide utilized aviation fuel JP-8. The surrogate has been tailored to closely match the hydrocarbon distribution in JP-8: a mixture containing 26% n-dodecane, 36% isocetane, 18% a-methylnapthalene,14% methylcyclohexane, and 6% decalin, was shown to accurately reproduce the chemical behavior of JP-8 over different experimental conditions. Due to its compositional reproducibility and tractability, the JP-8 surrogate is suitable for both well-controlled fundamental modeling and experimental studies in lieu of the otherwise complex and chemically undefined parent fuel. A cooperative effort is ongoing with the group of Prof. E. Ranzi at Politecnico di Milano, Italy, to extend their hierarchically constructed semi-detailed kinetic model already available for the oxidation of alkanes and simple aromatic molecules, in order to model the oxidation of the JP-8 surrogate (and thus of the parent fuel) in the low and intermediate temperature regions. The experiments have been carried out over a range of reaction conditions that are representative of actual engine conditions prior to and during the ignition process. Therefore, results from this study provide useful kinetic and mechanistic information to formulate hypotheses on autoignition mechanisms, to determine the relative effect of the various classes of components within multi-component mixtures, and to provide combustion models that can be used in the design and evaluation of combustors and engine systems.