Symposium on Combustion and Flame, and Explosion Phenomena最新文献

The Malard-Le Chatelier picture of the combustionwave is amended by adding a term for radiant heat transfer. On introducing the rate of oxygen diffusion toward individual particles an expression for the burning velocity in dust clouds is obtained, representing its dependence on thermal conductivity, burning and ignition temperatures, radiation characteristics of the dust cloud, dust concentration and particle size.

This serves as working hypothesis in conductingexperiments on the effect of those factors upon stationary dust flames and flames traveling through quiescent dust clouds.

Results obtained with atomized aluminum are:o

1. 1.

   On the lean side of the stoichiometric ratiothe burning velocity increases with increasing concentration.

2. 2.

   The burning velocity increases with decreasingparticle size in the range studied.

3. 3.

   The failure to produce stationary dust flames with burner tubes smaller than 1/2-inch diameter indicates an effect of “radiation quenching” close to the rim in high temperature dust flames.

4. 4.

   A striking increase in the flame velocity ofclosed end ignited dust flames is attributed to turbulence.

The experimental results are in qualitative agreementwith theoretical expectations.

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.

This report describes experimental techniques developed at the Applied Physics Laboratory, The Johns Hopkins University, for investigating the mechanism of flame stabilization in the wakes of bluff bodies. The powder techniques previously used by other investigators for visualization of flow in Bunsen burners have been extended to much higher velocities by the use of new illumination sources. Flow patterns at high velocities about baffles in ducts with and without combustion have been recorded using this technique. High speed motion pictures by schlieren and shadow