Effects of obstacles and deposited coal dust on characteristics of premixed methane–air explosions in a long closed pipe

An experimental system including pressure transducer, electric spark ignition device, data acquisition and control unit was set up to investigate methane–air explosions in a horizontal pipe closed at both ends with or without the presence of obstacles and deposited coal dust. The experimental results show that explosion characteristics depended on the methane content, on the layout of obstacles, and on the deposited coal dust. Pressure fluctuation with a frequency of 150 Hz appeared in its crest when the methane content was close to the stoichiometric ratio (9.5% methane percentage by volume). The pressure rise rate increased locally when a single obstacle was mounted in the pipe, but it had little effect on the pressure peak. Repeated obstacles mounted in the pipe caused the pressure to rise sharply, and the mean maximum explosion overpressure increased with the increase of the obstacle’s number. The amplitude of pressure fluctuation was reduced when deposited coal dust was paved in the bottom of the pipe. However, when repeated obstacles were arranged inside, the maximum overpressures were higher with coal dust deposited than pure gas explosions.

► CH4–air explosions with deposited coal dust were investigated experimentally.
► Explosion overpressures were recorded and analyzed during explosions.
► An obstacle set far away the ignition point will lead to two peaks of pressure.
► Pressure fluctuation was damped by deposited coal dust.
► Maximum overpressure varied with obstacle quantities and deposited coal dust.