Forebody Combustion Experiments on an Unducted Scramjet

Samantha Coras (2011). Forebody Combustion Experiments on an Unducted Scramjet MPhil Thesis, School of Mechanical and Mining Engineering, The University of Queensland.

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Author Samantha Coras
Thesis Title Forebody Combustion Experiments on an Unducted Scramjet
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
Publication date 2011-11
Thesis type MPhil Thesis
Supervisor Allan Paull
David Mee
Total pages 141
Total colour pages 12
Total black and white pages 129
Language eng
Subjects 09 Engineering
Abstract/Summary High density fluid within the combustion chamber of a traditional scramjet generates substantial viscous drag, arguably posing one of the greatest impediments to the attainment of sustained hypersonic flight. This crippling effect could be allayed, therefore, by reducing the quantity of the combustion surfaces, such that burning is allowed to occur without any physical containment. Although unconfined burning has been successfully applied in transonic and supersonic flows to reduce drag and enhance lift, its application to hypersonic flight has been largely unexplored. The potential of implementing external burning for propulsion is herein investigated experimentally. This process contrasts to that used in ducted scramjets because fuel is intentionally burnt on the compressive forebody. The experimental results conclude that thrust production using unconfined supersonic combustion differs fundamentally from the confined burning achieved routinely in ducted scramjet engines. It is found that the unducted scramjet generates thrust primarily via a reduction in Mach number due to burning on the forebody, prior to expanding the flow onto a thrust surface. Any pressure increase produced on the forebody due to unconfined burning is a second order effect. In contrast, a traditional ducted scramjet generates thrust primarily by increasing the pressure in the combustion chamber prior to expanding the higher pressure flow onto a thrust surface; the decrease in Mach number within the combustion chamber due to the burning process is generally a second order effect. A simple double-wedge configuration, comprised of a forebody surface and a thrust surface, was used to demonstrate the principles of thrust production via external combustion. In practice, a more isentropic compression would be used, albeit with a total deflection angle approximating the single wedge angle used here. The wedge compression angle is necessary to achieve the flow temperatures required for auto-ignition. The experiments were conducted in a shock tunnel using hydrogen fuel and a Mach 7.6 freestream. Pressure and heat flux signals were recorded along the compression and expansion surfaces and were combined with holographic interferometry to investigate the mode, extent and efficacy of the unconfined burning. A thrust surface pressure three times higher with heat addition than without was consistently generated across the test matrix. Modes of heat release on the forebody, other than constant pressure, were also observed. These included both the extremes of delayed, gradual combustion and sudden, rapid heat release. The experimental results are compared with quasi one-dimensional, analytical predictions. The results indicate that external combustion on a forebody, or other compression surface, could be applied to hypersonic flows to generate thrust, lift or a change in pitching moment.
Keyword external combustion, inlet injection, shock tunnel, scramjet, hypersonic, hydrogen
Additional Notes 34, 49, 57-59, 64, 71, 75, 81, 83, 85, 88 *nb above page numbers refer to the numbering of the PDF document, not the number printed on the bottom of the page

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Created: Fri, 18 Nov 2011, 11:07:18 EST by Miss Samantha Coras on behalf of Library - Information Access Service