Effect of scale on the onset of detonations

Critical conditions for onset of detonations are compared at (1) two significantly different scales, (2) for a range of H-2-air mixtures diluted with CO2, H2O, and (3) for two types of geometry - one a long obstructed channel and the other a room with a relatively small aspect ratios. For the range of scales, mixtures, and initial conditions tested, the detonation cell size lambda was shown to be a reliable scaling parameter for characterization of detonation onset conditions. An experimental correlation is suggested for the critical, detonation onset conditions. This correlation is based on a wide variety of available experimental data on DDT in mixtures of hydrogen and hydrocarbon fuels with air and on the use of detonation cell size lambda as a scaling parameter characterizing the mixture.