The experimental apparatus is illustrated in Fig. 7.1. The spherical vessel is 600 mm in diameter and 110 L in volume. Moreover, there is a duct connected to the vessel, which is 250 mm in length. The two cylindrical pipes are 2000 mm in length and 60 mm in internal diameter are connected by flanges, then connect the pipe to the duct. Finally, the end of the pipe is sealed with a blind flange, and a closed pipe-connected spherical vessel is formed. A spark-plug 1 and a charge/exhaust valve 2 are installed on the spherical vessel. The pressure transmitters are flushed to the surface of the spherical vessel, both sides of the porous material and the end of pipes; the positions of the pressure transmitters are denoted as 4, 5, 6 and 7.