Experimental Investigation of a 3D Thermal Compression Scramjet Using Advanced Optical Techniques

Vanyai, Tristan (2018). Experimental Investigation of a 3D Thermal Compression Scramjet Using Advanced Optical Techniques PhD Thesis, School of Mechanical and Mining Engineering, The University of Queensland. doi:10.14264/uql.2018.247

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Author Vanyai, Tristan
Thesis Title Experimental Investigation of a 3D Thermal Compression Scramjet Using Advanced Optical Techniques
School, Centre or Institute School of Mechanical and Mining Engineering
Institution The University of Queensland
DOI 10.14264/uql.2018.247
Publication date 2018-02-23
Thesis type PhD Thesis
Supervisor Tim McIntyre
Stefan Brieschenk
Richard Morgan
Language eng
Subjects 0205 Optical Physics
090107 Hypersonic Propulsion and Hypersonic Aerodynamics
Formatted abstract
Scramjet engines are limited in performance due to engine starting problems at low hypersonic speeds. For an accelerating hypersonic vehicle, intake contraction ratios are typically fixed to the low speed starting requirements. This reduces engine performance at higher Mach numbers, where higher contraction ratios are required to efficiently combust flow within a practically-sized combustor.

The use of a combustion process called “Thermal Compression” was suggested in the 1960s that could improve the performance of low intake contraction scramjet engines. In such an engine, the flow field is non-uniform within the combustor, with regions of locally high pressure and temperature even at low net intake contraction ratio. The flow properties in these regions are suitable for combustion of air-fuel mixtures, inducing autoignition. As heat is released, increased temperature and pressure are transmitted to the surrounding flow through pressure waves. Conditions in the surrounding flow become suitable for combustion, and this process continues until combustion completes throughout the entire flow field.

This work presents results from experimental and numerical analysis of a three-dimensional, thermal compression scramjet engine at two high Mach number flight conditions. Experiments were conducted in the T4 Shock Tunnel at The University of Queensland. The tunnel test gas simulated flow that had been processed by an engine forebody at either 8.0 or 8.8 angle of attack, in an equivalent flight condition of Mach 10, 50 kPa dynamic pressure.

An engine test model was developed to examine the effect of thermal compression on combustion-induced pressure rise at these inflow conditions. Non-uniform combustor flow was generated using a three-dimensional intake with a ramp angle that varied in the spanwise direction. This produced a low compression side and a high compression side throughout the scramjet engine. Fuel injection plenums were split such that different gases could be injected in either the low compression or high compression side. Combustion was induced by injecting hydrogen fuel, or suppressed by injecting helium.

Pressure measurements were taken along the streamwise length of the engine, in three spanwise locations. Optical techniques, including emission and laser-induced fluorescence (LIF) methods, were used to visualise the distribution of OH radicals throughout the combustor. These experimental results were then compared to fully-combusting, RANS CFD simulations.

The influence of thermal compression was determined by comparing combustion-induced pressure rise in the fully-fuelled case to the sum of both cases where combustion was suppressed on each side of the engine. It was found that for the forebody angle of 8.8◦ case, thermal compression increased pressure rise by 14.4 ± 6.0 % and 6.7 ± 6.2 % for fuel-air equivalence ratios of φ = 0.8 and φ = 1.0 respectively. Emission from OH radicals, which is qualitatively indicative of combustion, also increased by 19 – 54 % in the rear of the combustor. Numerical simulations of the φ = 0.8 condition also showed a pressure increase of 15.9 % and a 27 % increase in combustion efficiency due to thermal compression.

These are the first detailed, experimental results that show that thermal compression can significantly improve combustion in a scramjet engine. The present results indicate that thermal compression can be applied with a practical engine design to improve performance in low contraction ratios scramjet engines.
Keyword scramjet
air-breathing propulsion
thermal compression
supersonic combustion
optical diagnostics
laser-induced fluorescence

Document type: Thesis
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Created: Thu, 08 Feb 2018, 10:23:56 EST by Tristan Vanyai on behalf of University of Queensland Graduate School