Laser ignition

The editor has encountered numerous studies of laser ignition, usually of explosives. These demonstrate that the ignition is normally a thermal effect, caused by heating solid particles, not photochemical, and thus the MIE is not lower than other methods. This may not obtain if the light be of a frequency (visible or uv) sufficient to excite the early steps of the explosion reaction, as, for example, photodissociation of halogens to the atomic radicals which are the start of their explosive reactions with fuels. 

Fig. 5.5 Molecular structures of three prominent laser ignitable explosives CP, BNCP and HTMP.

S. R. Ahmad, M. Cartwright, Laser Ignition of Energetic Materials, Wiley, Weinheim, 2015. 

Timings (f) between the laser ignition (narrow) and the gating pulse for the PIN switch (shaded) to pulse the microwave (MW). In Exp. 1, the MW-width was typiccdly 50 ns. In Exps. 2 and 3, the MW-width was fixed to 20 ps. (Reproduced from Ref. [19] by permission from Springer Verlag KG)... 

L. Strakouskiy, A. Cohen, R. Fifer. R. Beyer, and B. Forch, Laser Ignition of Propellants and Explosives. ARL-TR-1699, Army Research Laboratory. Aberdeen Proving Ground, MD, 1998. 

In the past nine years, two review articles have been published about laser ignition and initiation [40,41]. hi this section, facts are presented that are connected with studies of initiation reactivity of explosives. 

Merson, J.A., Salas, F.J., Harlan, J.G. The development of laser ignited deflagration-to-detonation transition (DDT) detonators and pyrotechnic actuators. In Proceedings of 19th International Pyrotechnics Seminar, pp. 191-206, Christchurch, NEW ZEALAND, Feb 21-25, 1994... 

The ignition of Magnesium/Teflon/Viton (MTV) by radiative or conductive heat transfer has been investigated in order to understand processes in both bulkhead and laser igniters (Table 7.1). Lombard appears to be the first to have tested radiative ignition of MTV. He used a solar furnace that allowed a maximum irradiance, H = 100 W cm [2]. Mg/PTFE (polytetrafiuoroethylene) samples of unknown stoichiometry were tested at = 20 W cm. The ignition temperature was determined from radiometric measurements and was found to be quite low, 217 °C. This corresponds to 29 s irradiation at the reported irradiance level and translates into a heating rate of 6 K s. ... 

Ostmark, H. (1987) Laser ignition of explosives ignition energy dependence of particle size. 3e Congres International de Pyrotechnie du Groupe de Travail de Pyrotechnie Spatiale et 12e International Pyrotechnics Seminar, Juan-Les-Pins France, June 8-12, p. 241. 

Combustion characteristics and CO2 laser ignition behaviour of boron/magnesium/PTFE pyrotechnics. 14th International Pyrotechnics Seminar, Jersey Channel Islands, September 18-22. p. 691. 

Fig. 4.18 Minimum ignition energy for H2 + air mixtures for laser ignition (the solid curve) and at spark ignition (the dashed curve). Atmospheric pressure and room temperature...

Fig. 4.19 Change in minimum ignition energy Emin of H2 + air mixtures diluted by CO2. Laser ignition at atmospheric pressure and room temperature...

In hydrogenous diluted mixtures, in particular, in (H2 + CO2) mixtures, the laser ignition energy measured data also correspond to a U-shaped relation. It follows from Fig. 4.19 that the minimum ignition energy increases and the area of the measured data narrows when the mixture is diluted by CO2. 

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