The full-scale fire testing of aircraft power plants has suggested that laboratory closed-vessel spontaneous ignition tests give results which are pessimistic for many practical applications. The results of a number of test programs involving specific configurations of hot and cool surfaces have indicated that, for a particular fluid, it might be possible to establish a thermal correlation which would enable the risk of ignition to be calculated at the design stage.
Tests have been carried out on two rigs, both incorporating a hot bottom plate surface onto which the test fluid was sprayed, the side walls and top plate being somewhat cooler. The first rig was a static rig in which top and bottom plate temperatures and the gap between them was varied. The effects of mixture strength, atomization, and wall materials were studied for kerosine, and the ignition temperatures for various fluids have been determined for a limited number of configurations.
The second rig consisted of a small wind tunnel in which the effect of air velocities up to 10 ft/sec and altitudes up to 20,000 ft were investigated. It is shown that air velocities up to 3 ft/sec have a large effect on spontaneous ignition temperatures.
A correlation based on gas temperature and distance from the nearest wall shows good agreement for the static and wind tunnel rigs and for closed-vessel tests of other investigations. An outline of the future program of work is given.