Laser ignition of explosives: Effects of gas pressure on the threshold ignition energy

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Abstract
This paper describes a method for measuring the effect of initial gas pressure and the type of gas on the threshold ignition energy of several high explosives. The method is based on a 300 W CW CO2-laser. An extensive study of these parameters for PETN and RDX is also presented. These high explosives all show a strong decrease in ignition energy/power with increasing initial gas pressure. The gases tested are air and nitrogen. The studied pressures are in the interval 0.1 to 10 MPa. The ignitability of PETN and RDX was tested at a laser pulse width of 1.2 ms. All tested high explosives had a lower ignition energy/power in air than in nitrogen at low pressures (< 2 MPa), whereas RDX and PETN had a lower ignition energy in nitrogen than in air at high pressures (>4 MPa). For TNT the time to ignition, measured as a function of air pressure, decreased with increasing pressure. These results are interpreted as a multiple phase ignition process. The method was also used for obtaining ignition data for TNT, Comp B-3 and Torpex.