Proposal Number: CTS- 0553504 Principal Investigator: Cetegen, Baki M. Institution: University of Connecticut Proposal Title: GOALI: Experimental and Computational Study of Bluff-Body Flame Stabilization with Nonhomogeneous Upstream Mixing
In many practical combustion devices, including aircraft augmentors, flame holding occurs in a high speed turbulent vitiated flow via bluff-bodies placed just downstream of fuel injectors. Significant spatial and temporal variations in mixture composition are expected in the flame stabilization region. There have been numerous experimental studies on fully premixed or nonpremixed flames anchored either by bluff bodies or swirling flow, and separate studies of flame propagation in mixture composition gradients. However, there have been no comprehensive investigations of flame stability in regions with both composition gradients and recirculating hot products, despite their relevance to flame holding in aircraft propulsion systems. The intellectual merits of this project involve a detailed experimental investigation of bluff-body stabilized partially-premixed flames in high velocity flows and a complementary computational effort on flame dynamics and stability. The goal of this work is to improve fundamental understanding of flame propagation in recirculating, partial-premixed flows, to assess model accuracy and to examine reduced order models for predicting flame stabilization. The results of this study are directly applicable to aircraft augmentors, which currently use bluff-body stabilization, but will also be broadly applicable to new combustor designs for hydrogen based syngas fuels, which may require enhanced bluff-body stabilization for fuel flexible operation. Detailed laser diagnostic techniques will be applied to develop an in-depth understanding of local conditions leading to flame blow-off at high velocities, and effects of mixture non-uniformities on the onset of flame blow-off and on flame structure prior to blow-off. The experiments will be performed in a planar two dimensional configuration, and the measurement techniques will include velocity imaging, flame structure imaging through laser-induced fluorescence, and upstream profiling of mixture composition. Thorough documentation and control of boundary conditions will be emphasized for compatibility with numerical simulations. Computational modeling of the geometries studied experimentally will be carried out by our GOALI partner at the United Technologies Research Center (UTRC). Unsteady numerical simulations of bluff-body flame holding will be completed for the same cases studied experimentally. The goal will be to assess the capabilities of these simulations to capture flame propagation in stratified flows and to develop extensions of the numerical approach to partially-premixed flame stabilization. The broader scientific impact of this research will be a better fundamental understanding of flame propagation in partially-premixed flows with recirculation. This has direct impact on the design of industrial devices such as augmentors for aircraft engines, but also expands understanding of basic flame behavior in turbulent flows that could be broadly applicable to improved combustor design for new fuels. The project will facilitate training of two graduate students. By working directly with UTRC, these students will gain experience in this field and they will contribute to the U.S. competitiveness in the area of advanced propulsion system design. This project is co-funded by the Combustion and Plasma Systems Program and the Grant Opportunities for Academic Liaison with Industry (GOALI) Program.
