Pressure dependence of the auto-ignition temperature of methane/air mixtures

The results of experiments conducted to determine the auto-ignition tempera ture (AIT) and the cool flame temperature (CFT) of methane/air mixtures at elevated pressures (200-4700 kPa) and for concentrations from 30 up to 83 v ol.% are reported. The experiments were performed in a closed spherical ves sel with a volume of 8 dm(3). It is shown that methane/air mixtures can rea ct spontaneously for methane concentrations far outside the flammability li mits. Cool flames are observed for methane concentrations higher than 40 vo l.%. The AIT and CFT are strongly pressure-dependent and decrease with incr easing pressures. A Semenov correlation is developed for the CFT as a funct ion of the pressure. The upper explosion limit (UEL) of methane/air mixture s at elevated pressure and temperature is linked with the CFT. It is shown that for certain conditions of pressure and temperature, the flammability r ange increases considerably even for a small temperature rise. (C) 1999 Els evier Science B.V. All rights reserved.