Experimental study on the propagation characteristics of detonation waves in a curved channel with the axial expansion influenced by the dilution ratio

Abstract

In the annular rotating detonation chamber, the reactivity of the mixture influences the propagation characteristic significantly. Meanwhile, the curvature of the channel and the axial expansion also have a great impact on the stable propagation of detonation waves. In order to clarify the impact of the dilution ratio on the stable propagation in a curved channel considering the axial expansion, this study has been conducted utilizing a mixture of ethylene, oxygen, and nitrogen. The influence of the dilution ratio and the equivalence ratio on detonation wave propagation in both confined and semi-confined curved channels has been investigated experimentally. The propagation process was captured using high-speed photography, while the cell width was obtained through the smoked foil method. The CH* chemiluminescence imaging has also been employed to investigate the propagation characteristics. The peak pressures near the outer wall have been measured. The results indicate that introducing the effect of axial expansion significantly increases the deficits of the wave velocity and the peak pressure, particularly for the cases with higher dilution ratios. In addition, the sector analysis method for the region of interest of CH* luminosity signals has been proposed. The signal data provides quantitative insights on the intensity of detonation waves. Under the low dilution ratio, the reaction zone coupled with the reflected shock wave near the outer wall can be observed. As the detonation wave propagates downstream, the CH* signal exhibits periodic oscillations. Meanwhile, five propagation modes have been observed after the stable detonation wave enters the semi-confined curved channel with various dilution ratios. For the stable mode, the critical inner radius should be 9.88 times the average cell width and meanwhile, the minimum detonable mixture height is equivalent to 11.86 times the average cell width. Finally, a new D_n∼κ relation has been established with different dilution ratios.