In some cases of spray detonations, blast waves originating from the droplets have been observed. These blast waves eventually catch up with the main front thus providing a means of energy transfer to the front and therefore maintaining a steadily propagating wave. The ignition condition necessary for continued propagation is determined on the basis of the following model. The medium is assumed to be a gaseous oxidizer with monodisperse fuel spray having an average spacing to droplet diameter ratio. At sometime, tig, after the passage of the front, the droplet is ignited and a blast wave is initiated. The energy deposition law for the blast wave is assumed to follow E = Wtβ where E is the heat release from the drop, W = constant, β ≥ 0 and t is the time after the onset of droplet ignition. The blast wave strength at the time of interaction with the front must be of a magnitude sufficient to accelerate the front by an amount equivalent to its deceleration as it moves through the drop spacing. This condition imposes a limit on tig which has been determined. It is found that the ratio of the ignition delay to the droplet breakup time tig tb depends on a heat release parameter which depends on the stoichiometry, the detonation Mach number, the density ratio ρ{variant}t ρ{variant}1 of liquid to gas, the location of the front and β which determines the energy-time profile. For a fuel-oxidizer combination with known tig tb the model implies a detonation radius beyond which a detonation is expected to remain steady. This in turn implies a critical radius and therefore a minimum energy for detonation initiation. The model is applied to a kerosene-air mixture and found to imply that tig tb = 1.3 which is considered a reasonable value. © 1979.
