Laser Initiated Decomposition in Aerosol Fuels: A Method for Probing the Early Stages of Ignition and Detonation

摘要

The DURIP grant has been used to purchase two new infra-red laser systems that have been used to initiate combustion of energetic aerosol particles. One is a CO2 laser capable of delivering up to 1.5 J of pulsed power, while the other is an OPO laser pumped by an existing Nd:YAG laser to provide tunable radiation in the 2.7 to 3.3 micrometers range. These lasers have been used to help unravel the decomposition of base catalyzed nitromethane, CH3NO2. The first four steps in its decomposition have been confirmed by the first positive experimental identification of seven intermediates including CH2NO2(-), R2NH2(+), NO2(-), RNH3(+), and NH4(+). In addition, a controversial reaction step was confirmed by isotopic labeling studies. The mechanism for the base catalyzed nitromethane decomposition is now established. The study of aerosol particles has been advanced by the development of methods to create coated particles and to carry out depth profiling using variable power IR laser heating. The ability to create particles with heterogeneously mixed core and outer layer, coupled with the tunability of the OPO infra-red laser has made it possible to ignite a particle from either the core or from the outside. Finally, a method employing a 'chemical thermometer' has been developed to monitor the temperature of a rapidly combusting particle. The thermometer is the dissociation of glycerol ions, which produces parent and two daughter ions whose intensities depend strongly on the ion vibrational energy.