A study of the chemical and physical processes governing CO2 laser- induced pyrolysis and combustion of RDX

Youngjoo Lee, Ching Jen Tang, Thomas A. Litzinger

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Abstract

The flame structure of 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) propellants under laser-assisted combustion was studied to better understand related chemical and physical processes in the gas phase. Experiments were conducted from 0.1 to 3 ATM in pressure with heat fluxes of 50 to 600 W/cm2. Gaseous products were extracted through the use of quartz microprobes and analyzed by a triple quadrupole mass spectrometer (TQMS). Temperature profiles were measured using micro-thermocouple techniques to investigate reaction zones in RDX flames. Flame behavior was observed using a high- magnification video system. Major species in RDX flames were identified as H2, H2O, HCN, H2CO, NO, HNCO, N2O, and NO2 at low masses (m/z ≤ 47). In addition to these species, H2CNH with m/z = 29 was found to exist in the near-surface reaction zone as an important minor species. Higher molecular weight species were found at m/z values of 47, 54, 56, 70, 81, and 97; with the daughter mode operation of TQMS, they were identified as HONO, C2H2N2, C2H4N2, C2H2N2O, C3H3N3, and C3H3N3O, respectively. Increasing heat flux and decreasing pressure stretched out the reaction zones and were useful for investigating reactions near the deflagrating surface. However, the conditions appeared to have no effect on major reaction pathways. Two- stage chemical reaction pathways in the gas phase were explicitly identified from the major species profiles at all experimental conditions. Also, the reactions of minor high-mass species occurred in the primary reaction zone. The decomposition of RDX at the surface showed evidence of the two competing branch reactions into H2CO + N2O and HCN + HONO, as well as two subsequent reactions: H2CO + N2O → H2O + CO + N2 and 2HONO → H2O + NO + NO2. With the consideration of the previous four reactions, the branching ratio for the two decomposition pathways of RDX was estimated to be about 2:1. For all experimental conditions, temperature profiles had a near-surface region where temperature increased very slowly; the extent of this zone increased as the near-surface reaction zones expanded. After this region, the temperature profiles increased to final flame temperatures without any dark zone temperature plateau. Based on comparisons of species and temperature profiles, this near-surface region is believed to be related to the consumption of NO2, production of NO and H2O, and production and consumption of high-mass species.

Original languageEnglish (US)
Pages (from-to)600-628
Number of pages29
JournalCombustion and Flame
Volume117
Issue number3
DOIs
StatePublished - May 1999

All Science Journal Classification (ASJC) codes

  • Chemistry(all)
  • Chemical Engineering(all)
  • Fuel Technology
  • Energy Engineering and Power Technology
  • Physics and Astronomy(all)

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