An Experimental Investigation of a Thermal Compression Scramjet with OH Imaging

Abstract

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 threedimensional 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. Nomenclaturemomentum flux ratio = forebody shock angle LC = low compression = ratio of specific heats M = Mach number = forebody turning angle N = rotational quantum number = standard deviation P = pressure = fuel-air equivalence ratio q = dynamic pressure Re = Reynolds number 2 Subscripts e = nozzle exit T = total i = shot index ∞ = freestream s = stagnation

Thermal Protection System and Thermal Management for Combined-Cycle Engine: Review and Prospects

“…Figure 28 shows part of the numerical simulation process. Vanyai et al [106] did an experiment on thermal compression scramjet based on OH imaging [107], and found that such three-dimensional air inlet of supersonic ramjet can generate pressure and temperature gradients of the fluid. The combustion of any part of the combustor was suppressed by injecting combustion fuel, hydrogen, or non-combusting helium to check how the combustion of these parts affected the pressure and temperature of the entire flow field, the concentration and production of OH radicals was depicted by OH chemiluminescence and planar laser induction fluorescence (PLIF) images see ( Figure 29) [108] so as to detect the chemical activity throughout the entire combustion process.…”

“…Schematic diagrams of OH Chemiluminescence (left) and OH Planar Laser-Induced Fluorescence (right) of the combustion chamber of scramjets[106].…”

Investigation of supersonic turbulent combustion in a Mach 10 scramjet engine

“…The high-compression side ignites the fuel and promotes combustion, which increases the pressure and releases heat. This pressure increase compresses the low-compression side, promoting combustion there [23,122].…”

“…To evaluate the effect of increased injected mass flow rate, a case with φ = 0.13 was simulated with extra helium being injected with the fuel. Helium was chosen due to its similar molecular weight to hydrogen, and its previous use in experimental campaigns in impulse facilities at The University of Queensland as a replacement for fuel [122]. The total mass flow rate for fuel plus helium, and thus momentum ratio, was the same as that for fuel in the φ = 0.22 case.…”

“…There are two concomitant effects here, as discussed in this paper: thermal compression due to heat release from combustion and the extra compression caused by the injection of fluid into the intake air (hence fluidic compression). Thermal compression has been shown to increase combustion in a scramjet with a non-uniform inlet [122]. Regarding fluidic compression, there are the combined effects of increased jet to free-stream momentum ratio, caused by the increase in injectant, which leads to increased penetration and affects the downstream flow [16,45], and also an increase in bulk mass flow.…”