YoungJoo Lee

Simultaneous temperature and species measurements of the glycidyl azide polymer (GAP) propellant during laser-induced decomposition

Abstract Simultaneous temperature and species measurements were performed to experimentally investigate thermal decomposition of cured Glycidyl Azide Polymer (GAP). Experiments were conducted at atmospheric pressure in argon with heat fluxes of 50, 100, and 200 W/cm 2 delivered by CO 2 laser. A micro-probe/triple quadrupole mass spectrometer system was used to analyze species products, and thermocouples were used to measure temperature. The burning behavior was monitored by a high-magnification video system. The following major species, in descending order of abundance, were detected: N 2 , HCN, CO, CH 2 O, NH 3 , CH 3 CHO, CH 2 CHCHNH, CH 3 CHNH, H 2 O, CH 4 , and C 2 H 4 . The mole fraction of hydrocarbons was about 0.02, while the mole fraction of imines was 0.09. The decomposition of GAP appeared to be dominated by the condensed phase chemistry and few reactions occurred in the gas phase. A significant amount of fine solid powder was observed in the gas phase, which was believed to be imines. It was found that the species and temperature were insensitive to the heat flux level. The mole fractions of the observed species at a heat flux 100 W/cm 2 were almost the same as those at a heat flux of 200 W/cm 2 , and the surface temperature was approximately 1050 K at both heat fluxes.

A study of the gas-phase chemical structure during CO2 laser assisted combustion of HMX

Abstract To study the chemical structure of the HMX flame, species and temperature profiles were measured in the gas phase at heat fluxes of 100 and 300 W/cm2. A microprobe/triple quadrupole mass spectrometer was used to measure quantitative species profiles, and fine wire thermocouples were used to measure temperature profiles. The flame and surface structures were observed using a high-magnification video system. The major species at the surface were H2O, CH2O, HCN, NO2, N2O, N2, CO, and NO at atmospheric pressure with both heat fluxes. There was no CO2 existing at the surface. The mole fraction of triazine was found to be approximately 2.5% at the surface, which has not been reported during combustion of HMX. The species could play an important role in the gas phase chemistry. The species profiles showed two-stage reaction zones. The species profiles also showed that increasing heat flux stretched the secondary reaction zone, but did not stretch the primary reaction zone. No plateau at a typical dark zone temperature was observed for either heat flux. Finally, the temperature profiles in the gas phase and species concentrations obtained at the surface with heat fluxes of 100 and 300 W/cm2 were used as inputs to a 1-D gas-phase flame model. Disagreement between the model and experiments for stable species was observed and investigated in detail.

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

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/cm 2 . 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 H 2 , H 2 O, HCN, H 2 CO, NO, HNCO, N 2 O, and NO 2 at low masses ( m / z ≤ 47). In addition to these species, H 2 CNH 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, C 2 H 2 N 2 , C 2 H 4 N 2 , C 2 H 2 N 2 O, C 3 H 3 N 3 , and C 3 H 3 N 3 O, 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 H 2 CO + N 2 O and HCN + HONO, as well as two subsequent reactions: H 2 CO + N 2 O → H 2 O + CO + N 2 and 2HONO → H 2 O + NO + NO 2 . 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 NO 2 , production of NO and H 2 O, and production and consumption of high-mass species.

Study of the gas-phase chemistry of RDX - Experiments and modeling

The objectives of this work were to identify the species produced during the CO2 laser-induced decomposition of 1,3,5-trinitrohexahydro-s-triazine (RDX) and to obtain species profiles in the gas-phase during laser-assisted combustion for comparison to a one-dimensional model of the flame. In the experiments, a microprobe/mass spectrometer system was used to measure quantitative gas-phase species profiles and a high-magnification video system was used to observe surface behavior and flame structure. Gas-phase species evolved from the surface and also inside a bubble were measured. The species identified at the surface were HCN, NO2, H2O, NO, CO, N2O, N2, and H2; no CO2 was found at the surface. Formaldehyde may have been present, but it could not be unambiguously identified. Species mole fractions measured at 1.0 atm and a heat flux of 400 W/cm were used as input to a one-dimensional model along with a temperature profile obtained from the literature for similar experimental conditions. In order to obtain reasonable agreement between the model and the experiments for stable species, RDX vapor had to be added to the initial species for the model calculations. However, even with this addition, the profiles for OH and NH did not match data available in the literature.

Combustion Chemistry of HAN, TEAN, and XM46

Combustion characteristics and related chemical processes were investigated for a HAN-based liquid propellant, XM46, and its ingredients, HAN and TEAN. Experiments were conducted over the pressure range of 0.1 to 1 atmosphere and at the heat fluxes from 50 to 400 W/cm2 in air and inert gas environments. Flame behavior was observed using a high magnification video system. A triple quadruple mass spectrometer (TQMS) and micro-thermocouples were applied for the temporal measurements of gas-phase species and temperature profiles. Species in the XM46 residue left after burning were analyzed using a gas chromatograph/mass spectrometer (GC/MS). No visible flame was observed from XM46 or its ingredients at 1 ATM and 100 W/cm2. However, at 1 ATM and 400 W/cm2, HAN and TEAN showed distinctive flame behaviors, and XM46 exhibited three flames in sequence with the white HAN flame appearing first, followed by the blue and yellow TEAN flames. Gaseous products evolved from HAN and TEAN exhibited a distinctive set of spec...

Thermal Decomposition of 3,3'-Bis-Azidomethyl-Oxetane

Measurements of gaseous species and temperature proe les were performed to study the thermal decomposition of 3,3 9-bis-azidomethyl-oxetane (BAMO). Experiments were conducted at 1 atm of argon with heat e uxes of 100 and 400 W/cm 2 , delivered by a CO 2 laser. Gaseous samples were extracted through the use of a quartz microprobe and analyzed by a triple quadrupole mass spectrometer. Temperature proe les were measured using the microthermocouple technique to investigate gas-phase reaction zones identie ed by the species measurements. Flame structure and surface behavior were observed using a high-magnie cation video system. Major species evolved from the surface were identie ed as N 2, HCN, H2CO, H2O, NH3, CO, and CH4. Minor species include NO, H 2CNH (m/z = 29), CH3CN(41), CH3CHNH(43), C2H3CHO(56), CO(CH)2NH(69), and C2H2. From the species measurements, at both experimental conditions, BAMO was found to undergo simultaneous decomposition of its backbone structure, indicated by the release of high concentrations of H 2CO, H2O, and CO, and of side chains, by the large amounts of N 2, HCN, and some larger molecules. No gas-phase reaction was identie ed, because most of the major species measured exhibited relatively constant concentrations in the gas-phase. The lack of a gas-phase reaction was also evident from the gas-phase temperature proe le that showed a constant value of approximately 1050 K.

A facility for solid-propellant response measurements under pressure-driven conditions

An acoustic driver system was developed to investigate unsteady combustion characteristics of solid propellants under pressure oscillations. Two model airplane engines driven by an electric motor were used to produce nearly sinusoidal pressure variations; a consistent peak-to-peak pressure variation of 10% of the mean pressure was obtained using the engines. A pressure insensitive, sub-miniature load cell was used to measure the thrust response of the solid propellants. The load cell was placed in a ceramic holder to protect it from the high temperature of gaseous products evolved during experiments, and the bottom of the holder was coated with several layers of a damping material to reduce the effect of vibrations produced by the engines. Measurements of the thrust response were successfully made over the frequency range 4-130 Hz near atmospheric pressure in air. A minimum signal-to-noise ratio of 3:1 was obtained using the system, and both amplitude and phase information could be simultaneously extracted from the thrust response data. The reliability of the present acoustic driver system was verified by comparing response data obtained from the present and radiation-driven facilities under radiation-driven conditions. For an AP/HTPB composite propellant under pressure-driven conditions with the present facility, maximum non-dimensional thrust responses at 35 W cm-2 were measured at 12 and 16 Hz, respectively, where the phase passed through approximately zero.

Simultaneous Temperature and Species Measurements During Self-Oscillating Burning of HMX

The near-surface species and surface temperature were simultaneously measured during self-oscillatory burning of octahydro-l,3 ,5,7-tetranitro-l,3,5,7-tetrazocine (HMX). A CO2 laser was used to heat the propellant surface at atmospheric pressure in argon. A microprobe/tri ple quadrupole mass spectrometer system was used to measure species profiles, and fine-wire thermocouples were used to measure surface temperature. Oscillations of species, temperature, and burning rate were observed with an average surface temperature of —633 K and frequency of 4 ± 0.2 Hz. The mole fraction of NO2, HCN, and triazine oscillated in phase with temperature, whereas the mole fractions of N 2O, CH2O, and the species at mass 28 were 180 deg out of phase with temperature. NO2 and CH2O were the most abundant species followed by HCN, N2O, H2O, the species at mass 28, and other species. The production of NO 2 and HCN was favored with an increase in temperature and burning rate, whereas the production of N 2O and CH2O became more important with a decrease in temperature and burning rate. This was qualitatively in line with the accepted global reaction branches in the condensed phase of HMX. From these data, variations of the mole fractions of NO 2, N2O, CH2O, and HCN could be directly related to surface temperature. Analysis of the data indicates that the observed oscillatory burning might be related to multiple-step reactions in the condensed phase.

A triple quadrupole mass spectrometer system for studies of gas-phase combustion chemistry of energetic materials

A triple quadrupole mass spectrometer (TQMS) system utilizing the collision-induced dissociation process has been constructed for studies of gas-phase combustion chemistry of energetic materials under various conditions of pressure and incident laser heat flux. A unique feature of the TQMS system is its capability to differentiate species at the same mass-to-charge value and to identify chemical structures of the gaseous species evolved from the energetic materials, through the recognition of the fragmentation characteristics of chemical functional groups in species. Two different settings for high and low collision energy modes were developed for the daughter mode of operation. A calibration method at the two settings in the daughter mode was also developed for the quantification of the measured species. The TQMS system developed also includes integrated vacuum system, quartz microprobes for gas species sampling, customized software for data acquisition and data reduction. Typical results are presented to illustrate the methods used to differentiate the measured species and to identify their chemical structures.

Thermal decomposition of RDX/BAMO pseudo-propellants

Abstract Measurements of gaseous species and temperature profiles for RDX/BAMO pseudo-propellants were performed to study their decomposition and the chemical and physical effects of their binder ingredient, 3,3′-bis-azidomethyl-oxetane (BAMO), on the base ingredient, 1,3,5-trimethylene trinitramine (RDX). The propellants were made from a physical mixture of RDX and BAMO in weight ratio of 80:20. Experiments were conducted at atmospheric pressure in argon with heat fluxes of 100 and 400 W/cm 2 delivered by a CO 2 laser. Gaseous samples 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 surface and gas-phase reaction zones identified by the species measurement. Results of species and temperature measurements showed chemical and physical interactions between the two ingredients. From the species measurements, products of each ingredient, RDX and BAMO, were found to exist simultaneously throughout the gas phase; however, primary reaction chemistry in the gas phase was dominated by RDX. Three different categories of gaseous products were identified in the species measurements: species common to both BAMO and RDX; from RDX or BAMO only; and those which can not be attributed to RDX or BAMO alone. Surface temperatures were ∼640 and ∼670 K at 100 and 400 W/cm 2 , respectively, while that of RDX was ∼610 K for both heat fluxes. The temperature profiles showed the existence of an isothermal region in the gas phase, with the temperature of ∼1200 K at 100 W/cm 2 and ∼1500 K at 400 W/cm 2 . The effect of BAMO in RDX/BAMO was clearly evident in the change of surface mole fractions and profiles of major species, expansion of reaction zones, and the constant temperature profile in the gas phase. .