Upper Flammability Limits of Hydrogen and Light Hydrocarbons in Air at Subatmospheric Pressures

Abstract

The upper flammability limits (UFL) of hydrogen–air, methane–air, ethane–air, n-butane–air, and ethylene–air were determined experimentally at room temperature (20 °C) and initial pressure of 1.0, 0.7, 0.5, 0.3, 0.1, and 0.05 atm. Experiments were conducted in a closed cylindrical stainless steel vessel (i.d. 10.22 cm, length 100 cm) with upward flame propagation. The UFL of hydrogen was observed to be inversely proportional to the initial pressure in the range from 1.0 to 0.3 atm and proportional to the initial pressure from 0.3 to 0.05 atm. In contrast, the UFLs of the lower alkanes and ethylene decreased with the initial pressure. The average flame propagation velocities at UFL concentrations of hydrogen, methane, ethane, n-butane, and ethylene in air at reduced pressures were also examined. It was found that the flame propagation velocity of hydrogen was larger than those of the hydrocarbons, increased when the initial pressure decreased from 1.0 to 0.3 atm, and then decreased with further decrease of...