Explosions in closed pipes containing baffles and 90 degree bends

There is a general lack of information on the effects of full-bore obstacles on combustion in the literature, these obstacles are prevalent in many applications and knowledge of their effects on phenomena including burning rate, flame acceleration and DDT is important for the correct placing of explosion safety devices such as flame arresters and venting devices. In this work methane, propane, ethylene and hydrogen-air explosions were investigated in an 18 m long DN150 closed pipe with a 90 degree bend and various baffle obstacles placed at a short distance from the ignition source. After carrying out multiple experiments with the same configuration it was found that a relatively large variance existed in the measured flame speeds and overpressures, this was attributed to a stochastic element in how flames evolved and also how they caused and interacted with turbulence to produce flame acceleration. This led to several experiments being carried out for one configuration in order to obtain a meaningful average. It was shown that a 90 degree bend in a long tube had the ability to enhance flame speeds and overpressures, and shorten the run-up distance to DDT to a varying degree for a number of gases. In terms of the qualitative effects on these parameters they were comparable to baffle type obstacles with a blockage ratios of between 10 and 20%. (C) 2009 Published by Elsevier Ltd.