4286 r2009 American Chemical Society pubs.acs.org/EF Energy Fuels 2009, 23, 4286–4294 : DOI:10.1021/ef900324e Published on Web 08/19/2009 Evolution of Soot Particle Size Distribution Function in Burner-Stabilized Stagnation n-Dodecane-Oxygen-Argon Flames Aamir D. Abid, Joaquin Camacho, David A. Sheen, and Hai Wang* Department of Aerospace and Mechanical Engineering, University of Southern California, Los Angeles, California 90089, USA Received April 10, 2009. Revised Manuscript Received June 26, 2009 We investigate the evolution of particle size distribution of incipient soot formed in laminar premixed n- dodecane-oxygen-argon flames. The flames are established on a porous flat flame burner with equivalence ratio equal to 2 and a maximum flame temperature of 1800 and 1870 K. Detailed size distributions are obtained by the burner-stabilized stagnation (BSS) flame sampling approach using a scanning mobility particle sizer. The flame temperature profiles are determined for each separation distance between the burner surface and stagnation surface/probe orifice. It is shown that the flames can be modeled closely using an opposed jet flame code without having to estimate the effect of probe perturbation. The measured and simulated temperature profiles show good agreement. The evolution of the soot size distributions for n-dodecane flames are similar to those observed in ethylene flames. The size distributions are characteristically bimodal, indicating strong, persistent nucleation over a large range of residence times in the flame. Under similar conditions, the nucleation mode in the n-dodecane flames is stronger than that in comparable ethylene flames. Introduction Basic understanding of the reaction kinetic process of jet- fuel combustion is a critical element toward optimal design of aviation gas-turbine engines. Soot formation is an integral part of this kinetic process. Because jet fuels contain a large number of compounds, and the composition may vary from batch to batch, a direct kinetic description of their combustion behaviors, including soot formation, is not feasible. A viable approach is to use a fuel surrogate, containing five to six pure compounds, to mimic jet-fuel behaviors. 1 Typical jet-fuel surrogate mixtures contain mainly straight- chained, branched, and cyclic aliphatic hydrocarbons of which n-dodecane is an important n-alkane surrogate com- ponent. 2 In recent years, efforts have been directed at devel- oping combustion reaction models for the surrogate fuel components. 3-7 At present, these models have been advanced to explain global combustion behaviors, such as ignition delay times, 8 laminar flame speed, 5,9,10 and detailed time or spatial evolution of species concentrations resulting from fuel pyrol- ysis and oxidation in laboratory reactors. 7,11 We expect that these models will have to be extended to include soot chemistry, but reliable data for soot formation in n-dodecane flames do not exist. Studies have shown that for a wide range of high-tempera- ture combustion conditions, the oxidation kinetics of n-dode- cane is governed, at least in part, by fuel cracking to smaller components (H 2 , CH 4 ,C 2 H 4 ,C 3 H 6 , etc.) followed by oxida- tion of cracked fragments. 5,12-14 Likewise, soot nucleation and growth in n-dodecane flames is expected to start from the reactions of cracked products. It is generally understood that the volume fraction of soot formed in laminar premixed flames is not particularly sensitive to fuel structure, since the fuel must undergo cracking before reaching the main flame zone; and soot forms behind the flame. 15-19 In other words, reactions and especially the process of soot formation have little to no memory of the parent fuel structure in premixed flames. It is unclear, however, whether the detailed particle size distribution function (PSDF) is also insensitive to the fuel *To whom correspondence should be addressed. E-mail: haiw@ usc.edu. 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