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Shock induced ignitions of oxygen bubbles in cyclohexane under normal conditions

Mitropetros K., Hieronymus H, Steinbach J., Plewinsky B.

Archivum Combustionis

2002

Vol. 22 nr 1-2

55-70

The shock induced explosion behavior of oxygen bubbles in cyclohexane under normal conditions has been investigated. For the investigations a cylindrical autoclave containing a bubble generator was used. High speed optical and pressure measurements were carried out. In the present work the explosion behavior of bubbles was investigated not only in the first pulsations after the icident shock wave passage, as is the general practice in the literature, but also for many pulsations after it. Two types of bubble ignition were observed. One type of explosion is the well known bubble explosion occuring in the first bubble pulsation after the shock wave impact. The other type was previously unknown. It takes place after many bubble pulsations and has a significantly longer ignition delay. The behavior of a single bubble, which showed the second type of ignition is described. Furthermore it is shown by optical measurements that both types of bubble ignition can take place under the same conditions, i.e. during the same experiment.

Characterisation of surface explosions

Hieronymus H, Hofmann M., Bender J., Henschen Ph., Wendler R., Plewinsky B., Steinbach J.

Archivum Combustionis

2001

Vol. 21 nr 2

117-125

This contribution presents the explosion behaviour of liquid solvents such as toluene, cyclohexane, and methanol with smooth surfaces below a gaseous oxidizer composed of oxygen and nitrogen. In these systems, diffusion flames, both types of explosions, i.e. deflagrations and detonations, can occur even when the gas phase, composed of the vapor of the solvent and of the oxidizer, is below the lower explosion limit. Since the presence of the liquid surface plays an important role, explosions in such a system are called surface explosions. For practical reasons it is useful to distinguish between surfaces of a long narrow and a large circular shape. Explosions in these subsystems are called one-dimensional and two-dimensional surface explosions, respectively. Experiments have shown that the most dangerous form of surface explosions, the surface detonations, occur within a specific range of physical and chemical parameters such as the composition of the oxidizer, the iitial pressure, and the geometrical factors of the equipment. Safety characteristics such as "explosion range", "explosion limits", "detonation range", "detonation limits", and "limiting oxygen concentration" are defined and discussed particulary for heterogeneous systems.