Ignition requirements for organic-nitrate propagating reactions

Abstract

As part of the Organic Safety Project at the Hanford Site, theoretical and experimental investigations were performed at Fauske and Associates, Inc. to assess the ignition energy requirements for organic-nitrate propagating reactions. Theoretical considerations suggest that a minimum ignition energy requirement in excess of 1 J is required to produce sustained condensed-phase combustion with a stoichiometric organic-nitrate mixture in the absence of moisture and other diluents. This value is three to four orders of magnitude larger than that required to initiate combustion with flammable gas mixtures. It also is consistent with the finding that organic-nitrate mixtures are generally insensitive to spark, impact, shock, or friction. The necessary large ignition energy also is consistent with the extremely low burn velocities, 10 3 to 10 4 meters per second (m/s), characteristic of condensed-phase organic-nitrate propagating reactions. Experimental evaluations were made of the following ignition sources: hot metal spheres, electrically heated Nichrome wire coils, Watlow heaters, electric matches, and an arc welder. Results indicate that hot metal pieces are the most effective ignition source where the energy approaches the theoretical estimate of the minimum ignition energy requirement. However, the energy requirements increase rapidly with all ignition sources tested as deviations from dry stoichiometricmore » conditions increase including lower fuel concentrations and increasing water concentrations. At the lower combustion limit and in the absence of water, the ignition energy requirement is well above 1000 J. For a stoichiometric organic-nitrate mixture with 10 weight percent (wt%) moisture, using hot metal spheres, the lowest ignition requirement also is measured to be above 1000 J. The use of electrically heated wire coils or Watlow heaters increases the value to above 10,000 J.« less