Pressure development due to turbulent flame propagation in large-scale methaneair explosions

Abstract

The results of large-scale methaneair explosion tests performed at Raufoss, Norway (July–September 1980) are described and discussed. These tests were performed in a vented 50-m 3 vessel (a tube 2.5 m in diameter and 10 m long, open at one end) with regularly spaced obstacles in the form of orifice plates providing blockage ratios from 0.16 to 0.84 to the flow in the tube. It is observed that even relatively small repeated obstacles of height 0.1 m (blockage ratio 0.16) have a dramatic influence on the violence of the explosion, generating explosion overpressures larger than 1 bar in the tube. With no obstacles, the maximum overpressure observed in the tube was about 0.1 bar, to be compared with overpressures up to 8.8 bar recorded with repeated obstacles. The results obtained by a systematic variation of obstacle configurations are described and discussed in terms of a generalized venting model which takes into account the folding of the flame due to the presence of obstacles. The results are also compared with safe vent area criteria for central ignition of initially quiescent explosive mixture in near-spherical containers. The present criteria are found to be totally inadequate for large-scale explosions in obstacle environments.