Effects of boundary conditions on premixed CH₄+2O₂ detonation characteristics

To find out the exact effects of boundary conditions on premixed CH₄+2O₂ detonation characteristics, detonation experiments were conducted respectively in two cylindrical tubes with inner diameters of 63.5 mm and 50.8 mm and one rectangle tube. The detonation velocity curves were obtained using a signal detection system, and cellar patterns drawn from the smoked-foil records were obtained using a digital image processing program. Quantitative irregularities of CH₄+2O₂ detonation and cell size data under different initial pressures in the three tubes were analyzed and compared. It is found that the average velocities in the three tubes always closely resembled v_cj, showing that the detonation velocity is mainly determined by the initial detonation pressure and mixture type rather than by the boundary conditions. In addition, judging by the detonation velocity curves, the limit pressures of the tubes with inner diameter of 50.8 and 63.5 mm are 5 and 4.05 kPa, respectively. Therefore, the boundary conditions can influence the limit pressure. Quantitative irregularities exert little significant difference under different boundary conditions of the tubes. Besides, as the detonation needs to compensate for the energy loss with the increase of the tube diameter, there is a greater number of spin heads in the tubes.