A Quasi-One-Dimensional Investigation Into the Effect of Combustion Processes on Scramjet Performance

Vanyai, Tristan; Bricalli, Mathew; Brieschenk, Stefan; Boyce, Russell

doi:10.2514/6.2014-2786

Cited by 9 publications

(6 citation statements)

References 9 publications

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“…1.10 show the expected trend that as the inverse contraction ratio is decreased, performance peaks at higher Mach numbers. That is, for higher Mach numbers, the contraction ratio should be increased to maximise performance, in keeping with the findings from [5,9,29].…”

Section: Thermal Compressionmentioning

confidence: 94%

“…As concluded by [5,9,29,30], there is little benefit to operating scramjets above the lowest inlet pressure ratio that produces sufficient combustion within the length of the combustor. This is due to the compromise that must be made between the thermodynamic considerations and practical efficiencies of compression and expansion systems.…”

Section: The Scramjet Cyclementioning

confidence: 99%

“…Engine performance is much higher at low Mach numbers [5,9], primarily due to higher inlet compression efficiencies and lower Rayleigh losses in the combustor. Additionally, higher flow speeds require longer engines, resulting in more combustor drag which is a key contributor to total engine drag [10].…”

Section: Motivationmentioning

confidence: 99%

“…From [5,9,29], a pressure ratio of P r = 60 is quite low, especially for a Mach 10 condition. The constant pressure reaction (Pergament [26]) length at P 2 = 45 kPa is l R > 300 mm, so combustion may be expected to complete towards the end of the combustor.…”

Section: Condition Selectionmentioning

confidence: 99%

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

Vanyai¹

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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.i 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. Numerica...

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Section: Thermal Compressionmentioning

confidence: 94%

Section: The Scramjet Cyclementioning

confidence: 99%

Section: Motivationmentioning

confidence: 99%

Section: Condition Selectionmentioning

confidence: 99%

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

Vanyai¹

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“…The constant-area portion of the combustor reduces the Mach number of the flow to lower levels compared to the constant-pressure heat addition process, which allows the heat to be added at a higher efficiency in the subsequent part of the combustor. An in-depth analysis and discussion on using a constant-area heat addition to improve scramjet performance can be found in [22].…”

Section: Chapter Summarymentioning

confidence: 99%

Numerical study into thermal-compression scramjets

Bricalli¹

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This work presents the first high-fidelity numerical study into thermal compression (TC) scramjets. Unlike conventional scramjet engine designs, TC scramjets are designed with an inlet that delivers purposely induced nonuniform-compression to the combustor. This approach was first proposed by Antonio Ferri in the 1960's, who claimed that TC can be used to improve the performance of fixed-geometry scramjets that must operate over a range of flight Mach numbers. The purpose of this work was to develop new knowledge and insight into TC with the use of high-fidelity computational fluid dynamics.In this study, we investigated how combustion in one region of the combustor ignited the flow in other regions of combustor. The study was performed on a generic nonuniformcompression scramjet flow path that was designed by blending a high-compression two-dimensional profile with a 18 o ramp at the centreline with a low-compression two-dimensional profile with a 8 o ramp at the side wall. The high-compression profile produced sufficient compression for combustion, while the low-compression side produced insufficient compression for combustion. The simple geometry allowed the complex propagation of combustion from the high-compression to the low-compression side to be studied in detail. The free stream flow properties corresponded to a Mach 10 flight condition with a dynamic pressure of 100 kPa.The study was conducted with CFD++ using the Reynolds-averaged Navier-Stokes equations. Turbulence was simulated using the SST turbulence model and combustion with the Jachimowski 13 species 33 reaction mechanism. Two numerical approaches were developed to decouple the fluid dynamic/combustion effects: firstly, combustion was disabled in certain regions with the flow field; and secondly, reacting and inert (nonreacting) fuel was injected into the engine at different fuelling sites.Both premixed and inlet-fuelled injection studies were performed on the generic nonuniformcompression engine. The premixed study provided insight into the combustion behaviour independent of any particular fuel injection method. Three flame propagation processes were identified in the study: three-dimensional flow features, emanating from the high-compression side which produced temperatures in the boundary layer that allowed the flow to ignited in the low-compression side of the engine; radical transport through a shock-induced boundary-layer separation, which enhanced combustion in the low-compression side; and TC from combustion in the high-compression side which coupled with the spanwise shock structure. All three flame propagation processes had a significant influence on igniting the flow in the low-compression side of the engine.The premixed work was extended in the inlet-fuelled injection study to evaluate how the added complexity from the flow structures generated from inlet port-hole injection influenced the flame propagation processes. The additional flow structures caused the three-dimensional shock-induced boundary-layer separation to becom...

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