Chemical structure of a methane counterflow diffusion flame perturbed with the addition of either JP-8 or a jet fuel surrogateIntroductionExperimental setupResults and discussionConclusionsAcknowledgmentsReferencesChemical structure of a methane counterflowdiffusion flame perturbed with the additionof either JP-8 or a jet fuel surrogateLuca Tosatto, Barbara La Mantia1, Hugo Bufferand,Patrick Duchaine2, Alessandro Gomez*Department of Mechanical Engineering, Yale Center for Combustion Studies, Yale University,P.O. Box 208286, New Haven, CT 06520-8286, USAAbstractThe chemical structure of a methane counterflow diffusion flame doped with small amounts of either JP-8 or a jet fuel surrogate was analyzed by gas sampling via quartz microprobes and subsequent GC/MSanalysis. This jet-fuel initial oxidation is consistent with the anticipated chemical kinetic behavior, basedon thermal decomposition of large alkanes to smaller and smaller fragments and the survival of ring-sta-bilized aromatics at higher temperatures. The surrogate captures the general trend but incorrectly mimicsthe behavior of some species such as benzene and ethylene. Furthermore, the comparison in the behavior oflarge alkanes is only qualitative, because of difficulties in separating the components of JP-8 as a result ofisomerism.Ó 2009 Published by Elsevier Inc. on behalf of The Combustion Institute.Keywords: Diffusion flames; Counterflow; Surrogate; Jet fuel; JP-81. IntroductionWith world events imposing enhanced flexibil-ity in the sources of jet fuels, it is becomingincreasingly important to improve scientificknowledge of the combustion properties ofdifferent fuel blends. Jet fuels based upon JP-8,JP-8+100, Jet-A, and Jet A-1 will continue to playa central role from both a logistical and an eco-nomic viewpoint for the next few decades. Thestudy of the combustion processes in real aero-combustor environments is in principle essentialto improve engines efficiency and reduce pollutantformation. However, both the numerical andexperimental studies of these processes arechallenging not only because of the enormouscomputational resources needed and the hostilityof the combustion environment to quantitativediagnostic techniques, but also because real-worldfuels may contain hundreds of chemicalspecies, making their complete chemical kineticcharacterization and modeling a daunting, if nottotally impractical, prospect. Furthermore, the1540-7489/$ - see front matter Ó 2009 Published by Elsevier Inc. on behalf of The Combustion Institute.doi:10.1016/j.proci.2008.06.055*Corresponding author. Fax: +1 203 432 7654.E-mail address: [email protected] (A.Gomez).1Present address: Shell Exploration and ProductionCo., Two Shell Plaza, 777 Walker Street, Houston, TX77002, USA.2Present address: Ecole Central, Paris, France.Available online at www.sciencedirect.comProceedings of the Combustion Institute 32 (2009) 1319–1326www.elsevier.com/locate/prociProceedingsof theCombustionInstitutefuel composition can vary significantly withchanges in the source of the parent crude and inrefinery processing conditions.A practical approach to the simulation of realfuels is to identify surrogate fuel mixtures, havingonly a handful of components, whose combustionbehaviors capture essential features of those of thereal fuels. To date, candidate surrogates have beenidentified for JP-8, for Fischer-Tropsch JP-8, forJet-A and for kerosene, and combustion proper-ties of these surrogates have been compared suc-cessfully with those of the original fuels in somenarrowly defined tests. But, much more compre-hensive testing and surrogate validation is needed.In general, one would need a comprehensive effortaimed at: (a) characterizing the best surrogates;(b) determining their relevant chemical-kineticand transport properties; (c) measuring theirbehaviors over the ranges of pressures and tem-peratures of practical interest; (d) establishingtheir mixing rules for relating mixture propertiesto those of the individual components; and (e)developing reduced-chemistry descriptions thatcan be used in design codes for chemical-propul-sion and energy-conversion systems. A compre-hensive review on the state-of-the-art waspresented in [1]. More recently, a joint contribu-tion from the University of Milan and UC SanDiego studied the autoignition and the extinctionbehavior of a 3-component surrogate [2]. Alsonoteworthy is recent work in a jet stirred reactorin which jet fuel combustion is experimentallystudied at pressures as high as 40 atm and com-pared to the simulation of a kinetic model thatrelies on a three-component surrogate with rea-sonable success [3].Examining the fuel behavior can be performedin a variety of settings, including premixed flames,non-premixed ones, flow or stirred reactors andshock tubes. The latter tend to have better con-trolled conditions for a rigorous characterizationof the fuel chemical kinetic behavior. But the ulti-mate test remains a flame environment, as in prac-tical applications, since it provides the necessarycoupling between chemical kinetics and transport.In this context, the present work, focusing on lam-inar non-premixed flames, is a natural evolutionof a previous contribution from our group [4].Since the challenge is on the chemical kineticfront, whose modeling will require the use of hun-dreds of species and thousands of chemical reac-tions even in a lumped kinetic approach, thefluid mechanics must be kept simple. As a resultcounterflow flames are considered, since they pro-vide the simplest, one-dimensional environmentfor subsequent detailed modeling. Since, espe-cially in the context of aero- and aero-derivativeturbines, non-premixed scenarios are the preferredchoice because of the safety complications associ-ated with the use of the lean premixed alternative,counterflow diffusion flames are considered.One could focus on overall combustion beha-viors, such as ignition, extinction, flame propaga-tion speed. However, detailed probing is necessarybeyond an overall, qualitative characterization toguide the selection of the surrogate compositionand eventually capture also the sooting behaviorof these fuels, which is an issue in most aero-tur-bines, especially at take-off. Sampling in the pres-ence of soot poses additional experimentalchallenges in connection with the occlusion ofthe microprobes that are typically used to mini-mize intrusiveness. As a result, we focused onthe detailed chemical