Historical survey on enhanced mixing in scramjet engines

Computational Simulation of Scramjet Combustors - A Comparison between Quasi-One Dimensional and 2-D Numerical Simulations

“…These regions of reversed flow act as the radical production and flame-holding regions [21]. The normal injection of fuel, due to the bow shock formation causes significant loss in total pressure, leading to reduced scramjet cycle efficiency [55]. A perspective view of the normally injected fuel interaction with the mainstream is shown in Figure 32 [56].…”

“…Wall injection, on the other hand causes significant total pressure losses, therefore, interest was turned to parallel or nearly parallel injection schemes as they result in lower total pressure loss [55]. The parallel injection schemes have lower combustion efficiency due to poor mixing at supersonic speeds, but as per Dimotakis [61], the mixing efficiency can be enhanced using parallel injection scheme if it were accompanied with generation of axial vorticity [55]. These axial streamwise vortices produce turbulent fluctuations perpendicular to the flow, thus breaking down large 2-D flow structures into small turbulent vortices which enhance diffusion and mixing [62].…”

Performance Measurements of Direct Air Injection in a Cavity-Based Flameholder for a Supersonic Combustor

“…Parallel wall injection also has lower total pressure losses than those associated with strut injection, which will be mentioned later. Seiner et al (1999) demonstrated that parallel injection provides for minimal pressure losses, as the core flow is not obstructed. One concern with wall injection comes from its difficulty in establishing combustion.…”

“…Adding swirl to the injectant has been reported by Seiner et al (1999) to increase the spread of the fuel plume laterally across the combustor section and has been shown to increase the amount of mixing within the shear layer. Gruber et al (2000) showed that elliptical fuel injection ports can improve lateral spreading qualities of the fuel plume, while reducing the transverse spread of the same.…”

“…The presence of the ramp in a supersonic flow field creates both shock and expansion waves. Seiner et al (1999) theorized that these waves cause the density and pressure gradients to be non-parallel to each other, resulting in vorticity induced by baroclinic torque. The induced vorticity leads to an often observed lobe structure of the fuel plume, as shown by Rogers et al (1998).…”