Numerical simulation of two-dimensional detonation propagation in partially pre-vaporized n-heptane sprays

In this paper, two dimensional detonation propagation in partially prevaporized n-heptane sprays is studied by using Eulerian/Lagrangian methods. The effects of droplet preevaporation on the detonation propagation are investigated. The general features and detailed structures of two-phase detonations are well captured with the present numerical methods. The results show that the detonation propagation speed and detonation structures are significantly affected by the preevaporated gas equivalence ratio. The numerical soot foils are used to characterize the influence of preevaporated gas equivalence ratio on the detonation propagation. Regular detonation cellular structures are observed for large preevaporated gas equivalence ratios, but when decreasing the preevaporated gas equivalence ratio, the detonation cellular structures become much more unstable and the average cell width also increases. It is also found that the preevaporated gas equivalence ratio has little effects on the volume averaged heat release when the detonation propagates stably. Moreover, the results also suggest that the detonation can propagate in the two-phase heptane and air mixture without preevaporation, but the detonation would be first quenched and then re-ignited when the preevaporated gas equivalence ratio is small or equal to zero

Investigation of the mixing characteristics in a transverse hydrogen injection combustor with an inlet compression ramp

A shock-enhanced mixing in a transverse hydrogen injection combustor with an inlet compression ramp is carried out by using Large-eddy simulation (LES). Effects of a shock train induced by the inlet compression ramp on the mixing process have been investigated at three jet to cross-flow momentum flux ratios, J. The counter-rotating vortex pairs (CVP), promoting the mixing process of the fuel jet plume and mainstream air, is significantly affected by the reflected shock. The vorticity analysis is constructed to further understand the turbulent mixing mechanism. The shock-induced baroclinic torque is found to play an important role on the generation of the vorticity in the near field of the fuel jet, and the place where the reflected shock interacts with the jet plume. In addition, the probability density function (PDF) of mixture fraction is also investigated

Characteristics and mixing enhancement of a self-throttling system in a supersonic flow with transverse injections

A three-dimensional self-throttling system is proposed in a scramjet combustor with transverse fuel jet, and investigated by Reynolds-averaged Navier-Stokes (RANS) simulations with the k-ω SST turbulence model. Numerical validation has been carried out against experiment and LES results. The effects of the jet-to-cross-flow momentum flux ratio and the throttling angle on mixing performance, fuel jet penetration depth and total pressure losses are all addressed. Through the proposed throttling system, the higher pressure upstream of the transverse fuel injection can drive part of the low momentum mainstream air into the downstream lower pressure region. The flow structures and the interactions between the shock waves and boundary layer are significantly changed to improve the mixing performance. The enhancement of mixing efficiency in the self-throttling system is closely related to the magnitude of the jet to crossflow momentum flux ratio, and a smaller throttling angle is found to further improve the mixing. On the other hand, the self-throttling system has a good performance in reducing the total pressure losses

Investigation of an optimal pulsed jet mixing and combustion in supersonic crossflow

The enhanced mixing and combustion mechanism of pulsed sonic jet with optimal frequency in supersonic crossflow with a 10° ramp has been investigated using Large Eddy Simulation (LES). The results show that the energetic structures from the barrel shock and shear vortex are further enlarged at the phase of 1/4T0 periodically due to the swing forward and backward effect of the bow shock. There coexists clockwise and counter-clockwise rotating shear layer vortex structures in the pulsed jet, while only counter-clockwise rotating shear layer vortex structure is found in the steady case. The mixing process and the flame distribution are significantly affected by these structures of different scales. The reflected shock waves in the transverse jet in supersonic crossflow have strong coupling effects with the heat release rate. The pulsed jet is also found to improve the non-premixed dominant heat release rate, but not the premixed one. The mechanism of enhanced mixing and combustion efficiency relevant to the optimal frequency of 50 kHz is studied with Power Spectral Density (PSD) and wavelet analysis, and it is interesting to notice that the optimal pulsed jet frequency has strong coupling effects with the bow shock swing back and forward frequency, the jet shear layer and barrel shock frequencies (i.e., 50 kHz). However, for the non-pulsed steady case, the bow shock characteristic frequency is found to be 40 kHz, which suggests the optimal pulsed jet frequency can be 40 kHz. In order to further validate it, Unsteady Reynolds Averaged Navier Stokes (URANS) simulations have been performed with the pulsed jet frequency of 40 kHz. It is optimising to see that the mixing and combustion efficiency are further improved