Experimental study of detonation limits in CH4-2H2-3O2 mixtures: Effect of different geometric constrictions

Abstract

In this study, the roles of perturbation induced by different shape obstacles on the detonation limits are investigated experimentally with four pressure transducers and soot foil, and the limit pressure of successful transmission is determined. Round, triangular and square orifice obstacles with the blockage ratio (BR) of 0.556, 0.889, 0.923 and 0.96 are considered. The CH4-2H2-3O2 mixtures are tested in a 90 mm diameter circular tube. Only steady detonation regime and fast flame mode are observed, and a sharply speed jump is seen near the limits. In the smooth tube, the value of limit pressure is 3 kPa, and it is enhanced significantly when the orifice plate is guided into the tube. Moreover, the critical pressure is rarely affected by the obstacle geometries at the same blockage ratio (BR). However, more obvious differences in the detonation cellular patterns and the critical values of DH/λ can be found among three obstacle shapes. This indicates that although the critical pressure is nearly independent of orifice shapes, the propagation mechanism may be different among various obstacle geometries. Finally, the values of DH/λ approximately fluctuate around 1 near the limits.