RDX flame structure at atmospheric pressure

Abstract

The chemical structure of an RDX flame at a pressure of 1 atm was studied using probing molecular beam mass spectrometry. The flame was found to contain RDX vapor, and its concentration profile was measured in a narrow zone adjacent to the burning surface. In addition to RDX vapor, ten more species were identified (H 2 , H 2 O, HCN, N 2 , CO, CH 2 O, NO, N 2 O, CO 2 and NO 2 ), and their concentration profiles were measured. Two main chemical-reaction zones were found in the RDX flame. In the first, narrow, zone 0.15 mm wide adjacent to the burning surface, decomposition of RDX vapor and the reaction of NO 2 , N 2 O, and CH 2 O with the formation of HCN and NO occur. In the second, wide, zone 0.85 mm wide, HCN is oxidized by NO to form the final combustion products. The composition of the final combustion products was analyzed from an energetic point of view. The measured composition of the products near the burning surface was used to determine the global reaction of RDX gasification at a pressure of 1 atm. Values of heat release in the condensed-phase calculated by the global gasification reaction and by the equation of heat balance on the burning surface (using data of microthermocouple measurements) were analyzed and compared.

HMX flame structure for combustion in air at a pressure of 1 atm

“…In the first zone at a distance up to ≈0.7 mm from the burning surface, consumption of HMX vapor, NO 2 , and CH 2 O and partial consumption of N 2 O with the formation of H 2 , H 2 O, CO, N 2 , CO 2 , HCN, and NO take place. The zone of full consumption of N 2 O (≈1 mm from the burning surface) is larger than the zone of consumption of HMX vapor (as well as in the RDX flame [30]). In the second zone of the flame at a distance of 0.8-1.5 mm from the burning surface, intense consumption of HCN and NO with the formation of the final combustion products N 2 , CO, and H 2 takes place.…”

“…A more detailed description of this procedure is given in [30]. The stoichiometric coefficient of the ith species is determined as the ratio of the mass flux of the ith species on the burning surface to the flux of HMX.…”

“…The last term in the expression for ΔQ is the sum of positive and negative numbers close in value, and, hence, even small variations in the stoichiometric coefficients can lead to a significant change in ΔQ. In [30], using RDX as an example, it has been shown that agreement between the values of Q determined by different methods can be achieved by modifying the measured composition of the combustion products within the determination error. For RDX, ΔQ ≈ 90 cal/g.…”

“…During HMX combustion at an argon pressure of 1 atm, fluctuations in the peak intensities of the combustion products have not been found. In those studies, only intensity profiles of the mass peak of the main combustion products at m/e = 2, 18,27,28,29,30,42,44,46, and 75 were obtained but species concentrations were not determined. The zone adjacent to the burning surface where mass peak 75 (a characteristic fragmentation peak in the mass spectrum of HMX vapor) was a few tens of micrometers wide.…”

Studying RDX and HMX combustion mechanisms by various experimental techniques

“…The techniques and results of mass-spectrometer studies in the gas phase of combustion waves were described in [23][24][25][26][27][28][29][30][31]. The combustion products were extracted from the gas phase by miniature samplers and were analyzed with a time-of-flight mass spectrometer [23][24][25][26] or with a quadrupole mass spectrometer [27][28][29][30][31].…”