Supersonic combustion experiments were performed using three different hydrogen fuel-injection configurations in a cavity-based model scramjet combustor with various global fuel–air equivalence ratios. The configurations tested were angled injection at 15° to the flow direction upstream of the cavity, parallel injection from the front step, and upstream injection from the rear ramp. Planar laser-induced fluorescence of the hydroxyl radical and time-resolved pressure measurements were used to investigate the flow characteristics. Angled injection generated a weak bow shock in front of the injector and recirculation zone to maintain the combustion as the equivalence ratio increased. Parallel and upstream injections both showed similar flame structure over the cavity at low equivalence ratio. Upstream injection enhanced the fuel diffusion and enabled ignition with a shorter delay length than with parallel injection. The presence of a flame near the cavity was determined while varying the fuel injection location, the equivalence ratio, and total enthalpy of the air flow. The flame characteristics agreed with the correlation plot for the stable flame limit of non-premixed conditions. The pressure increase in the cavity for reacting flow compared to non-reacting flow was almost identical for all three configurations. More than 300 mm downstream of the duct entrance, averaged pressure ratios at low global equivalence ratio were similar for all three injection configurations.

Supersonic combustion experiments have been performed using three different hydrogen-fuel injection configurations in a cavity-based combustor at three combustor-entrance flow conditions. Angled injection is located upstream of the cavity with 15° angle, parallel injection is positioned on the front step, and upstream injection is on the rear ramp. Planar laser-induced fluorescence of the hydroxyl radical is used to investigate the flow characteristics. Angled injection generates a weak bow shock in front of the injector and recirculation zone to maintain the combustion as the equivalence ratio increases. Parallel and upstream injection tests show similar flame structure over the cavity at low equivalence ratio. Upstream injection enhances the fuel diffusion arid enables ignition with a shorter delay length than with parallel injection. The presence of a flame near the cavity is sensitive to the fuel injection location, the equivalence ratio and total enthalpy of the air flow. The flame characteristics agree with the correlation plot of the stable flame limit of non-premixed conditions.

Planar laser-induced fluorescence of hydroxyl radical and static pressure measurement for supersonic combustion of fuel injection locations were accomplished using angled cavity supersonic combustor with a Mach 3.7 freestream. Hydrogen fuel was injection with sonic speed at 15° angled injection before the cavity, parallel injection on the backward facing step, rearward injection on the rear wall, respectively. Angled injection shows different flame structures according to the equivalence ratio and existence of flame in the cavity as a flameholder, however, parallel and rearward injection schemes generate the flame just above the cavity. Flame penetration of angled fuel injection is higher than parallel and rearward fuel injections. Cavity pressure normalized by stagnation pressure is increased in order of angled, rearward and parallel injection. However for the ratio of combustion to non-combustion, angled injection shows the highest value and parallel and rearward fuel injection are same values regardless of equivalence ratio.

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen fuel) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.

The tomographic reconstruction of supersonic flows faces two challenges. Firstly, techniques used in the past, such as the direct Fourier method (DFM) (Gottlieb and Gustafsson in On the direct Fourier method for computer tomography, 1998; Morton in Tomographic imaging of supersonic flows, 1995) or various backprojection (Kak and Slaney in Principles of computerized tomographic imaging, vol. 33 in Classics in Applied Mathematics, 2001) techniques, have only been able to reconstruct areas of the flow which are upstream of any opaque objects, such as a model. Secondly, shock waves create sharp discontinuities in flow properties, which can be difficult to reconstruct both in position and in magnitude with limited data. This paper will present a reconstruction method, matrix inversion using ray-tracing and least squares conjugate gradient (MI-RLS), which uses geometric ray-tracing and a sparse matrix iterative solver (Paige and Saunders in ACM Trans. Math. Softw. 8(1):43–71, 1982) to overcome both of these challenges. It will be shown, through testing with a phantom object described in tomographic literature, that the results compare favourably to those produced by the DFM technique. Finally, the method will be used to reconstruct three-dimensional density fields from interferometric shock layer images, with good resolution (Faletič in Tomographic reconstruction of shock layer flows, 2005).

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated from the cavity and reflects off the top and bottom wall. For non-reacting flow, fuel makes the shear layer thicker above the cavity therefore, the shock is generated just before the trailing edge. This research has self-ignition in the combustor. For reacting flow, as the equivalence ratio increases, flame starts to generate near the injector or occur in the recirculation zone before the injector. High fuel injection sustains the jet shape in the cross flow and air can mix with fuel along the shear layer. Therefore, two flame layers find above the cavity for high equivalence ratio.

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Different shock tube fill pressures have various inflow conditions. 15˚ inclined hydrogen fuel injection is located before the cavity. Oblique shock is generated from the cavity and reflects off the top and bottom wall. For non-reacting flow, fuel makes the shear layer thicker above the cavity therefore, the shock is generated just before the trailing edge. This research has self-ignition in the combustor. For reacting flow, as the equivalence ratio increases, flame starts to generate near the injector or occur in the recirculation zone before the injector. High fuel injection sustains the jet shape in the cross flow and air can mix with fuel along the shear layer. Therefore, two flame layers find above the cavity for high equivalence ratio.

The application of optical imaging techniques to hypersonic facilities is discussed and examples of experimental measurements are provided. Traditional Schlieren and shadowgraph techniques still remain as inexpensive and easy to use flow visualisation techniques. With the advent of faster cameras, these methods are becoming increasingly important for time-resolved high-speed imaging. Interferometry's quantitative nature is regularly used to obtain density information about hypersonic flows. Recent developments have seen an extension of the types of flows that can be imaged and the measurement of other flow parameters such as ionisation level. Planar laser induced fluorescence has been used to visualise complex flows and to measure such quantities as temperature and velocity. Future directions for optical imaging are discussed.

The supersonic combustion experiments are carried out using T3 free-piston shock tunnel. Hydrogen Fuel is injected in the cavity parallel with air(or nitrogen) flow. The equivalence ratios in this study are 0.132 and 0.447. Experimental measurements use OH-PLIF near the cavity and pressures in the combustor. For parallel fuel injection case, direct fuel add into cavity leads to increase of cavity pressure. And Flame exists just near the bottom wall for low equivalent ratio. There is no flame in the cavity because of no mixing in it. Compared to the inclined fuel injection, ignition delay length is longer for low equivalence ratio in both case. OH distribution is not a single line but a repeatable fluctuation flame structure by turbulence. Pressure distributions have nothing to do with the fuel injection position.