The critical energy of direct initiation and detonation cell size in liquid hydrocarbon fuel/air mixtures

Although the detonation phenomenon in liquid hydrocarbon fuel/air mixtures is a significant issue for chemical processing and development of propulsion materials, very limited amount of critical energy of direct initiation and detonation cell size - which provide a measure of detonability or sensitivity of an explosive mixture - are available in literature. In this study, the critical energies for direct initiation of planar detonations and detonation cell sizes in propylene oxide (PO), petroleum ether, isopropyl nitrate (IPN), n-hexane, n-heptane, n-decane and air mixtures are carried out in a vertical detonation tube with an inner diameter of 200 mm and a length of 6.5 m. In the experiment, direct initiation is achieved via #8 industrial electronic detonator associate with different amount of high explosive (i.e., Hexogen), the initiation energy is estimated accordingly to the amount of the explosive. Characteristic detonation cell sizes of those liquid hydrocarbon fuel/air mixtures are measured and obtained simultaneously. The experimental results show that the relationship between critical energy of direct detonation initiation and equivalence ratio is a 'U' shape behavior. For the alkane fuels, i.e., n-hexane, n-heptane, n-decane, the critical energy rises gradually with the increase of the carbon atom number of the liquid hydrocarbon fuel/air mixtures. By measuring the detonation cell size, it is found detonation cell sizes in the liquid hydrocarbon/air mixtures are very irregular, the behavior between cell size and equivalence is also a 'U' shaped curve. By the comparison of the critical energy and detonation cell size, it is shown PO/air and IPN/air are very sensitive to from a detonation, which followed by n-hexane/air and petroleum ether/air, the detonation sensitivity is relatively weak for n-heptane/air and n-decane/air.