An Experimental Investigation of a Thermal Compression Scramjet with OH Imaging

An Experimental Investigation of a Thermal Compression Scramjet with OH Imaging

Scramjet engines must be designed to operate over a range of Mach numbers. In order to maintain robust starting characteristics at low freestream Mach numbers, the inlet contraction ratio must be minimized, reducing performance at high Mach numbers. The technique of thermal compression can be used to maintain robust combustion at low mean pressure and temperature, improving the performance of low inlet contraction ratio engines over a range of Mach numbers. This paper examines a scramjet engine with a three-dimensional inlet that induces spanwise gradients of pressure and temperature, producing high inlet compression on one side and low inlet compression on the other. The effect of combustion in each half on pressure throughout the entire flowfield is examined by suppressing combustion on either half of the combustor through injecting either a combusting fuel, hydrogen, or a non-combusting replacement, helium. Two optical techniques are used to examine how the concentration of the OH radical varies throughout the combustor. Images of OH* Chemiluminescence and OH Planar Laser-Induced Fluorescence (PLIF) map the concentration and production of OH radicals indicating chemical activity throughout the combustion process. The thermal compression effect is isolated, and is shown to increase combustion-induced pressure rise in a scramjet engine.

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