Distinguished Paper Selection at 35th International Symposium on Combustion

(top) Photograph of the laboratory-scale wind tunnel used for studying laminar and turbulent boundary layer combustion under forced flow. (bottom) Side-view photograph of an ethanol diffusion flame in a forced flow.

(top) Photograph of the laboratory-scale wind tunnel used for studying laminar and turbulent boundary layer combustion under forced flow. (bottom) Side-view photograph of an ethanol diffusion flame in a forced flow.

Ajay Singh, a Research Assistant in the Department of Fire Protection Engineering and PhD Candidate in Mechanical Engineering and his Adviser, Assistant Professor Michael Gollner recently had their manuscript, “Estimation of local mass burning rates for steady laminar boundary layer diffusion flames” selected as a distinguished paper for the 35th International Symposium on Combustion in the Fire Research Colloquium. The International Symposium on Combustion is the largest conference on Combustion and Fire Phenomena, held bi-annually and hosted by the Combustion Institute. The paper will be made available for free during the month of February on Science Direct here: http://www.sciencedirect.com/science/article/pii/S1540748914000431. 

The article, published in the Proceedings of the Combustion Institute describes a new technique to probe the inner-workings of laminar boundary layer diffusion flames. Modeling the realistic burning behavior of condensed-phase fuels has remained out of reach, in part because of an inability to resolve complex interactions at the interface between gas-phase flames and condensed-phase fuels.  This interaction is even more complex as scales increase, because realistic fires occur under fully turbulent conditions which have yet to be fully replicated or understood at the bench scale, where detailed measurements can be conducted. The current research explores the dynamic relationship between combustible condensed fuel surface and gas-phase flames in both laminar and turbulent boundary layers, representing the small scales in which materials are tested (where much of today’s theoretical knowledge is also isolated) to realistic large-scale turbulent flames present in almost all unwanted fires, hybrid rocket motors and other similar combustion phenomena.

A thorough numerical and experimental investigation of laminar boundary-layer diffusion flames established over the surface of a condensed fuel was explored. By extension of the Reynold’s Analogy, the non-dimensional temperature gradient at the surface of a condensed fuel was related to the local mass-burning rate through a constant of proportionality. This proportionality was tested by using a validated numerical model for a steady flame established over a condensed fuel surface, under free and forced convective conditions. Second, the relationship was tested by conducting experiments in a free-convective environment (vertical wall) using methanol and ethanol as liquid fuels and PMMA as a solid fuel, where a detailed temperature profile was mapped during steady burning using fine-wire thermocouples mounted to a precision two-axis traverse mechanism. The results from the present study suggested that there is indeed a unique correlation between the mass burning rates of liquid/solid fuels and the temperature gradients at the fuel surface. The correlating factor depends upon the Spalding mass transfer number and gas-phase thermo-physical properties and works in the prediction of both integrated as well as local variations of the mass burning rate as a function of non-dimensional temperature gradient. A unique methodology was developed to estimate the local mass burning rates and flame heat fluxes for laminar boundary layer diffusion flames using both liquid and solid fuels. 

Convective and radiative heat feedback from the flames were also measured both in the pyrolysis and plume regions by using temperature gradients near the wall which is presented in a follow-on paper recently accepted by Combustion and flame, to be published shortly. 

The research was sponsored by the Minta Martin Foundation at the University of Maryland. 

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More Details on Ajay’s Research