The Woodruff School

SUMMARY

Understanding the mechanisms and physics of flame stabilization and blowoff of premixed flames, is critical towards the design of high velocity combustion devices. Due to the high bulk flow velocities typical of practical combustors, the flame anchors in the shear layers where the local flow velocities are much lower. However, within the shear layer, the flame is subject to a wide range of unsteady phenomenon, due to the highly turbulent nature of the flow, which can alter the local burning characteristics of the flame. Local fluid strain rates can alter the flame burning area through flame stretch acting to either enhance or degrade the flame. Operation of these combustors is limited by an upper limit in bulk flow velocity for which stable combustion is attainable. This bulk flow velocity limit is presumably due to the associated maximum fluid strain rates that the flame is able to withstand.
This work will focus on developing a deeper understanding of the mechanisms of flame stabilization and extinction for shear layer stabilized, premixed flames. These studies will focus on the in-plane physics at the attachment point of a swirl stabilized flame. Through high resolution, simultaneous PIV & CH-PLIF measurements, the instantaneous flow field and flame position will be captured enabling for 2D flame stretch at the attachment point to be characterized. In addition, these measurements will capture the unsteady behavior of the attachment point exposing instances where the flame is attached, locally detached, or completely absent from the field of view. These flame stretch measurements will be compared against the calculated extinction stretch rate from the reduced order laminar opposed jet model. This model is widely used to study the effect of fluid strain rates on flames. Based on the experimental behavior observed, the opposed jet model will be adapted to include additional physics, such as the effect of exhaust gas recirculation, in order to capture the mean flame stretch behavior observed experimentally.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Christopher Foley

TIME:	Wednesday, August 28, 2013, 9:30 a.m.

PLACE:	Bunger Henry, 311

TITLE:	Attachment Point Characteristics and Modeling of Shear Layer Stabilized Flames in an Annular, Swirling Flowfield

COMMITTEE:	Dr. Tim Lieuwen, Chair (Aerospace/Mechanical Engineering) Dr. Jerry Seitzman (Aerospace Engineering) Dr. Ben T. Zinn (Aerespace/Mechanical Engineering) Dr. Andrei Fedorov (Mechanical Engineering) Dr. Michael Renfro (Mechanical Engineering, University of Connecticut)

SUMMARY Understanding the mechanisms and physics of flame stabilization and blowoff of premixed flames, is critical towards the design of high velocity combustion devices. Due to the high bulk flow velocities typical of practical combustors, the flame anchors in the shear layers where the local flow velocities are much lower. However, within the shear layer, the flame is subject to a wide range of unsteady phenomenon, due to the highly turbulent nature of the flow, which can alter the local burning characteristics of the flame. Local fluid strain rates can alter the flame burning area through flame stretch acting to either enhance or degrade the flame. Operation of these combustors is limited by an upper limit in bulk flow velocity for which stable combustion is attainable. This bulk flow velocity limit is presumably due to the associated maximum fluid strain rates that the flame is able to withstand. This work will focus on developing a deeper understanding of the mechanisms of flame stabilization and extinction for shear layer stabilized, premixed flames. These studies will focus on the in-plane physics at the attachment point of a swirl stabilized flame. Through high resolution, simultaneous PIV & CH-PLIF measurements, the instantaneous flow field and flame position will be captured enabling for 2D flame stretch at the attachment point to be characterized. In addition, these measurements will capture the unsteady behavior of the attachment point exposing instances where the flame is attached, locally detached, or completely absent from the field of view. These flame stretch measurements will be compared against the calculated extinction stretch rate from the reduced order laminar opposed jet model. This model is widely used to study the effect of fluid strain rates on flames. Based on the experimental behavior observed, the opposed jet model will be adapted to include additional physics, such as the effect of exhaust gas recirculation, in order to capture the mean flame stretch behavior observed experimentally.