DETERMINATION OF TEMPERATURE PROFILES OF SELF-DEFLAGRATING RDX BY UV VISIBLE ABSORPTION-SPECTROSCOPY AND FINE-WIRE THERMOCOUPLES/

Temperature profiles of self-deflagrating RDX in a nitrogen environmen tal pressures up to 0.79 MPa were determined using UV/Visible absorpti on spectroscopy and fine-wire thermocouples (TCs). The burning surface of RDX was covered by a very dynamic two-phase foam zone, and the thi ckness of the foam lone decreases very rapidly with an increase of pre ssure. The temperatures within the foam zone were readily identified i n the thermocouple traces, especially at low pressures. Depending upon the pressure, the temperature was found to be around 500-520 K at the bottom surface of the foam zone, and around 590-690 K at the top surf ace of the foam zone. These temperatures are higher than the RDX melti ng temperature (477K at one atmosphere). A relationship between RDX bu rning surface temperature and pressure was developed for pressures bet ween 1 and 90 atm using data from this study and Zenin's TC data. The final flame temperature of RDX increases with an increase of pressure: 2,950 K at 0.17 MPa, 3,002 K at 0.45 MPa, and 3,204 K at 0.79 MPa, wh ich agree well with chemical equilibrium calculations. The flame heigh t, determined from temperature traces, decreases very rapidly with an increase of pressure. Profiles of OH concentrations were also deduced; however, because of the severe non-one-dimensionality of the flame st ructure, the deduced OH concentrations in the final-flame region were smaller than equilibrium calculations. A ''flow-replenishing'' process was deduced from the recorded video images of RDX burning. Due to thi s process, a planar-regression mode can still occur even when the burn ing surface is subject to a non-uniform heat flux over its cross secti on.