EXPLOSION PROCESSES AND DDT OF VARIOUS FLAMMABLE GAS/AIR MIXTURES IN LONG CLOSED PIPES CONTAINING OBSTACLES

In this work results of experimental investigations towards explosions processes in long pipe systems are presented. The experiments were carried out in pipes with diameters of 0.159 m as well as 0.200 m, and overall lengths of up to 23 m. Three flammable gases mixed in air were used, including propane, ethene, and ethyne. All mixtures were set up to a similar maximum experimental safe gap (MESG) of about 0.94 mm - 0.97 mm (explosion group IIA). It was observed that the maximum pressures as well as the flame speeds differed significantly. The more the mole fraction of the investigated gases in air had to be reduced to achieve a similar MESG (compared to propane/air in stoichiometric composition), the less severe was the explosion. Turbulence inducing elements enhance the heat and mass transfer in reactive flows. Therefore, the influence of various baffles (blockage ratios of 36%, 51%, 64%, 77%, and 91%) installed into the pipe system on the explosion characteristics was investigated for a stoichiometric propane/air mixture and an industrial mixture consisting of hydrogen, carbon monoxide, carbon dioxide, nitrogen, and air. As a result of the use of baffles, deflagration to detonation transitions (DDT) occurred in the pipe system. Absolute pressures of more than 100 bar joined by supersonic flame speeds of >2000 m/s were determined by piezoelectric sensors and photodiodes.