CBET Award Achievements Notable Accomplishments from CBET Awards 
Flames on Edge! Sandip Ghosal, Northwestern University 

Background: Studying flame phenomena can have significant
multidisciplinary impacts in understanding, predicting, and controlling flames. In
particular, sharp edges can affect how flames react to their environment. What happens
to simple, laminar flames along sharp edges? As a buildingblock approach to future
studies on turbulent diffusion flame phenomena, the Ghosal Group at Northwestern University
specifically studied straininduced local extinction and reignition by observing flames on
simpler surfaces.
The Group studied straininduced local extinction and reignition through laboratory research and by using numerical simulations. Certain flame characteristics are a result of the propagation of the “edge” or boundary between burning and extinction zones. The Ghosal Group sought to obtain a better theoretical understanding of edgeflame phenomena. Results: The Ghosal Group adopted a simple model involving circular flame holes and disks on a laminar counterflow diffusion flame and solved the problem numerically. The Group found a relationship between the strain rate and the radius of the hole. The Group discovered that if the diffusion flame had a strain rate intermediate between the ignition and extinction limits, then a critical hole radius exists (analogous results hold for flame disks) and above which the hole opened up and below which it closed. As the strain rate increases, the critical radius decreases but is finite at all values of the strain rate between the ignition and extinction limits. In the final stage of the collapse, the speed of propagation of points situated on diametrically opposite sides of the collapsing hole increases rapidly due to overlap of their preheat zones. The mechanism is identical to the analogous acceleration of a pair of planar premixed colliding flames for which a similarity solution was derived for unity Lewis numbers. The departure of the Lewis number from unity leads to some interesting unsteady effects. 



Scientific Uniqueness:
The Ghosal Group was able to study laminar flow of flames along an
edge. This work will provide a fundamental basis in flame research and serves as a
buildingblock for future studies. The Group was able to model straininduced local
extinction and reignition numerically as the edges of flames shrink and grow.
Impact on Industry and/or Society: Manifestations of turbulent diffusion flames are everywhere. A few examples are propulsion systems, such as aircraft gas turbine engines and rocket engines; energy generation systems, such as gasturbine generators; automobile engines; and largescale accidental fires, such as forest fires. Consequently, a large research effort is dedicated to the computer modeling of flames in order to enhance our ability to understand, predict and control them. Local ignition, extinction and propagation of fronts within a turbulent flame are the most difficult things to model. Fundamental studies such as the work of the Ghosal Group will lead to improved models for such largescale simulations. Potential Economic Impact: Improved understanding of the combustion process leads to better and more efficient design of devices that rely on combustion. More efficient designs will lower both the operational cost as well as the environmental cost in terms of emission of greenhouse gases and other harmful products of combustion. This work is notable because this Ghosal Group is helping to lay the foundation in flame research through a buildingblock approach by studying how sharp edges of flames shrink or grow. This project addresses the NSF Strategic Goals of: (1) Discovery and (2) Research Infrastructure. The Ghosal Group's contributions to fundamental flame research will lead to better predictive, largescale simulations. This buildingblock approach will have impact on future flame models. 


Program Officer:  Phillip R. Westmoreland  
NSF Award Numbers:  0121051  
Award Title:  Dynamics of Ignition and Extinction Fronts on Diffusion Flame Sheets  
PI Name:  Sandip Ghosal  
Institution Names:  Northwestern University  
Program Element:  1407  

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This Nugget was Updated on 27 June 2008. 