The Ignition of gas mixtures by impulsive pressures

Abstract

A study has been made of the igniting power of the pressure effects set up when a body of compressed air is suddenly released into an inflammable gas mixture by the rupture of an intervening diaphragm. A general description of the pressure effects has been given, their characteristic properties being linked with the bursting pressure of the diaphragm. The most important result is that ignition ofstrong methane-oxygen and ethylene-oxygen mixtures is directly caused by the pressure effects from diaphragms bursting at very low pressures. The diaphragms may be made of copper, cellophane or paper. The ignition process has been studied photographically and there is no measurable lag when ignition takes place under these conditions. Flame develops in the front of the main disturbance, leading in general to detonation. Ignition of weak mixtures is obtained at some-what higher pressures, but flame does not always become established, though the cause of this failure may lie in the experimental method. A 9.5 per cent methane-air mixture is weakly ignited but without the flame ever becoming established; the corresponding methane-oxygen mixture is ignited much more vigorously and flame spreads further from the diaphragm, but not throughout the column of mixture in the explosion chamber. Closing the end of the explosion chamber leads to the explosion of some mixtures not ignited directly by the pressure effects; the ignition is now mainly caused by simple adiabatic compression. The experimental work is unfinished and many points require further investigation before the process of ignition is fully understood. That ignition can be caused by shock waves of quite low intensity has, however, been clearly established. The author is grateful to the Ministry of Fuel and Power (London) for permission to publish this account of work carried out at their Buxton Research Station.