In this thirteenth installment of a 14-part series of monthly articles, The Combustion Institute recognizes the 2017 Distinguished Papers selected from among the scientific papers presented during the 36th International Symposium on Combustion. Congratulations to J. Contreras, J.-L. Consalvi, and A. Fuentes for winning the DPA in the Fire Research colloquium.

The authoritative paper, Oxygen index effect on the structure of a laminar boundary layer diffusion flame in a reduced gravity environment, explores the effects of the oxygen index (OI) on the structure of Laminar Boundary Layer Diffusion Flames (LBLDF) under microgravity conditions. Research focused on the influence of the oxygen index, the oxidizer flow velocity, and the fuel injection velocity on the flame geometry, characterized by the stand-off distance, flame length and the soot production.

Development of present research was encouraged by the opportunity to study the radiative extinction and the effect of the oxygen index (OI) on the structure of a flame representative of a fire scenario. LBLDFs under microgravity conditions offer the possibility to study the effect mentioned above. The availability of experimental data and the feasibility to test an advanced numerical tool used previously for coflow diffusion flames could provide insights about the competition processes between soot formation and soot oxidation, and the resulting flame radiation that could become important at the trailing edge of the flame in the absence of buoyancy, where quenching can occur.

The data available could provide valuable information to study radiative flame quenching. In these flames, the fuel is not fully consumed at the flame tip. That situation was confirmed through a scaling analysis that demonstrated that the behavior predicted by theory based on complete combustion was not followed by experimental data. Also, the scientific team thought to provide physical information about the behavior of the stand-off distance, that represents the position of flame, for use in material flammability procedures.

The increase in oxygen has conflicting influences in the kinetics of the soot formation/oxidations mechanism. The net effect of oxygen enrichment is therefore determined by the relative importance of these two effects. A research goal was to study this behavior in LBLDFs. Research demonstrated that, for a given soot formation residence time, the peak of SVF first increases when the OI is enhanced from 21% to 35% and then decreases when the OI is further enhanced to reach 50%.

The immediate impact of the paper provides experimental data to test numerical models for diffusion flames under microgravity conditions. The non-monotonic behavior of SVF with OI in the findings creates opportunities to discover new insights about this trend and to improve soot production prediction tools. In the long-term, the non-monotonic behavior of characteristic time of soot formation with the OI should motivate subsequent numerical studies to provide new information that could improve tools for the study of oxygen-enriched combustion. Also, the physical explanation of radiative quenching and the behavior of the stand-off distance over the burner could help to characterize the very first moment of a fire over a flat plate to influence flammability procedures.

The direct beneficiaries of the findings in the paper are researchers in the fire research community, especially among those working in soot production, radiative extinction and those working in microgravity fire safety.

Research data was obtained in parabolic flight campaigns on board the Novespace A300-Zero G in Bordeaux, France. The analysis of the experimental data was completed at the Institut Universitaire de Systemes Thermiques Industriels (IUSTI) at the Aix-Marseille Université, France. Research efforts for the paper started in 2015 and the paper was finalized at Universidad Técnica Federico Santa María, Chile prior to the 36th International Symposium on Combustion in Seoul, Korea.

About 1,300 papers were submitted to the 36th Symposium in 14 combustion science colloquia. Those papers were categorized by teams of colloquium coordinators and co-chairs, and then distributed to approximately 1,000 scientific reviewers. One paper in each discipline was awarded the recognition of Distinguished Paper.

The 14 Distinguished Papers undergo committee review for consideration to receive the Silver Combustion Medal that will be awarded during the 37th Symposium in Dublin, Ireland. A paper selected for this honor exemplifies quality, achievement, and significance to advance a field of combustion science. Distinguished papers are selected biennially from among the scientific papers presented during the International Symposium on Combustion and accepted for publication in the Proceedings of The Combustion Institute.

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