Venting of deflagrations: Hydrocarbon-air and hydrogen-air systems

A set of 34 experiments on vented hydrocarbon-air and hydrogen-air deflagrations in unobstructed enclosures of volume up to 4000 m³ was processed with use of the advanced lumped parameter approach. Reasonable compliance between calculated pressure-time curves and experimental pressure traces is demonstrated for different explosion conditions, including high, moderate, low and extremely low reduced overpressures in enclosures of different shape (L_max:L_min up to 6:1) with different type and position of the ignition source relative to the vent, for near-stoichiometric air mixtures of acetone, methane, natural gas and propane, as well as for lean and stoichiometric hydrogen-air mixtures. New data were obtained on flame stretch for vented deflagrations. The fundamental Le Chatelier-Brown principle analog for vented deflagrations has been considered in detail and its universality has been confirmed. The importance of this principle for explosion safety engineering has been emphasized and proved by examples. A correlation for prediction of the deflagration-outflow interaction number, χ/μ, on enclosure scale, Bradley number and vent release pressure is suggested for unobstructed enclosures and a wide range of explosion conditions. Fractal theory has been employed to verify the universality of the dependence revealed of the deflagration-outflow interaction number on enclosure scale. In spite of differences between the thermodynamic and kinetic parameters of hydrocarbon-air and hydrogen-air systems, they both obey the same general regularities for vented deflagrations, including the Le Chatelier-Brown principle analog and the correlation for deflagration-outflow interaction number.