Multiscalar Measurements in Supersonic Flames

Texas A&M Engineering Experiment Station, College Station TX

Investigators

Abstract

0933633 Karpetis This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). When Chuck Yeager broke the sound barrier with the first supersonic flight in 1947, the crucial technologies of the day that enabled such an endeavor were associated with aerodynamic design and strength of materials. During the last few decades a more insidious sound barrier, associated with the combustion process necessary for propulsion, has imposed practical limits on aircraft speeds. Specifically, flow through the engine may become fast enough to compete with the chemistry that must take place for complete combustion, resulting in suppression and, ultimately, extinction of even the fastest flame. The research work in this award advocates a combined experimental and theoretical approach to the study of high-speed flames for aerospace propulsion. Its objective is to contribute to the fundamental understanding of supersonic combustion and ultimately to enable the technology that must be in place before new, commercial hypersonic aircraft can take flight in the coming decades. The main issue that will be addressed is the interaction between fluid dynamics and chemistry in turbulent compressible flames operating at extreme conditions. The central hypothesis of the present work is the importance of high Mach number and the associated pressure variation it induces onto flame suppression and extinction. Line-imaging spectroscopy of the rotational and vibrational Raman scattering will allow for complete measurements of local thermochemistry; the technique is capable of measuring pressure, temperature, and all major species along the line of the laser in a single-shot fashion within supersonic flames. The line-imaging experiments will also yield valuable information of two derived quantities: conserved scalar and scalar dissipation rate. The first is invaluable in the examination of flame structure, while the second serves as the best available measurement of the local characteristic timescale of the flow field. Both derived quantities will be used in this study to examine the flame suppression and eventual extinction in high Mach-number flames. Spatial and scalar supersonic flame structures will be examined in ¡¥canonical¡¦ configurations designed to maximize the flow-chemistry interaction effects. Fundamental understanding of the interaction between fluid mechanics and chemistry under supersonic conditions is the key expected outcome, and the experimental results from this work should prove valuable for model development as well as computational comparisons. The study of flow-chemistry interaction in turbulent flames that exhibit pressure variation has large significance to a wide range of aerospace propulsion applications, from jet engine combustors and afterburners, to pulse-detonation engines and rocket exhausts. In addition, graduate and undergraduate students will learn by participating in cutting-edge research involving laser diagnostics and supersonic flames. Students working with the group will also benefit from summer visits to Sandia National Laboratories and participation in conferences and workshops. The PI will also develop practical experimental educational modules on issues in optics and physics for use in grades 9-12. The modules deal with fundamental issues in optics and physics, and are closely related to the research aspects of the proposed work. Members of under-represented groups will be engaged by the outreach as well as the research program>