Copyright ©2025 by the International Astronautical Federation (IAF). All rights reserved.Magnesium/Teflon/Viton (MTV) compositions are extensively used as pyrotechnic igniters in solid rocket motors due to their high energy content and reliability. However, the influence of extreme temperature and pressure conditions on their energy release has not been thoroughly investigated. This study utilizes reactive force field (ReaxFF) molecular dynamics (MD) simulations to assess the performance of a 65:30:05 MTV composition under a range of ignition conditions (2000-4000 K and 1-1000 atm). The objective was to quantify the thermal output and elucidate the decomposition pathways under these varying operational parameters. The simulations revealed a significant inverse correlation between temperature and energy release, with the mean thermal output decreasing by 22.5% from 18856.86 J/g at lower temperatures (2000-2500 K) to 14613.33 J/g at higher temperatures (3500-4000 K). Conversely, pressure variations within the tested range did not have a statistically significant effect on the thermal output. Despite the reduction in energy release at higher temperatures, the composition consistently produced sufficient thermal output to meet the requirements for rocket motor ignition across all simulated scenarios.

© 2025 Academia Brasileira de Ciencias. All rights reserved.The N5⁻ anion, known as pentazolate, represents a groundbreaking advancement in the field of energetic materials, offering promising applications in rocket propulsion, explosive devices, and pyrotechnics. Comprising five nitrogen atoms arranged in a cyclic structure with a negative charge, has captured significant interest due to its unique configuration and high energy potential. In this article, we provide a comprehensive overview of the N5⁻ anion’s potential as an energetic material, alongside the role of RMD simulations in elucidating its behavior. The ReaxFF forcefield was used to simulate the materials pyrolysis. The total energy behavior of different species containing pentazolate, across a range of temperatures (1500 K to 3000 K) revealed distinct trends and characteristics associated with the thermal dynamics and stability of the molecule under varying thermal conditions. Their mechanisms were elucidated, and the kinetic parameters were calculated, indicating that CNN5, with its low activation energy (39.14 kJ/mol), stands out as the most reactive, while PolyN5, with the highest activation energy (52.88 kJ/mol), is the most stable. Overall, the N5- anion represents a promising avenue for the development of high-energy materials.

© 2024, Academia Brasileira de Ciencias. All rights reserved.Currently, it is crucial for the lubricant formulation industry to explore cost-effective and environmentally friendly methodologies for analyzing the tribological properties of engine aviation lubricants under high-temperature and high-pressure operating conditions. This study demonstrates the feasibility of employing molecular dynamic simulations to gain essential insights into the evolution of the tribological properties of lubricants during operation. A three-layer molecular model was devised, comprising nickel aluminide molecules in the top and bottom layers, and polyol ester in the core. The impact of sliding velocities ranging from 20 km/h to 100 km/h was investigated under varying temperature and pressure conditions. Concentration, temperature and velocity profiles, radial distribution function, mean square displacement, and friction coefficient were calculated and analyzed in detail. Notably, the highest friction coefficients – ranging from 2.5 to 0.75-were observed at the lowest temperature and pressure conditions tested. Conversely, other sections of the gas turbine exhibited substantially lower friction coefficients – ranging from 0 to 0.01.Simulations demonstrate that increasing pressure and temperature reduce polymer chain mobility, leading to stronger internal interactions within the lubricant. Consequently, lubricant adsorption onto metal surfaces decreases. Furthermore, the lubricant performs exceptionally well when its molecules encounter higher velocities and temperatures. Based on the results obtained, the research demonstrates that the presented technique provides both quantitative and qualitative tribological information essential for understanding a system molecular behavior, serving as a guiding framework for researchers in the field.

Copyright ©2024 by the International Astronautical Federation (IAF). All rights reserved.Hypergolic fuels are crucial in the space industry, particularly in satellite propulsion systems, where their ability to ignite spontaneously upon contact is extremely valuable. Among the most established hypergolic propellants are hydrazine and nitrogen tetroxide. However, their high toxicity not only drives up the cost of satellite integration but also poses significant environmental risks. To address these challenges, researchers have been focusing on developing new environmentally friendly hypergolic bipropellants using high-concentration hydrogen peroxide as an oxidizer. This study explores the use of different catalysts in the decomposition of 90% hydrogen peroxide, aiming to propose a new green fuel blend based on n-butanol and monoethanolamine (MEA). The catalyst and the optimized fuel composition were selected in terms of the ignition delay time (IDT) with hydrogen peroxide (90%). Finally, a fuel solution consisting of 31.5% n-butanol, 60% MEA, and 8.5% copper nitrate trihydrate with a minimum IDT of 20 ms was achieved, and a characterization of the green fuel blend was made in terms of viscosity, density, flashpoint, and combustion enthalpy. The findings suggest that n-butanol can serve as an additive to enhance MEA, improving the freezing point, IDT, and viscosity of the hypergolic pair with hydrogen peroxide (90%).

Copyright © 2024 by the International Astronautical Federation (IAF). All rights reserved.Reactive molecular dynamics simulations were utilized to investigate the reaction between ammonium Perchlorate (AP) and aluminum (Al) particles. Two distinct sets of simulations were conducted, one involving a pure aluminum particle and the other featuring a passivated aluminum particle. The aim was to examine and compare the behavior of the reactive systems under different conditions. The simulations were performed using the ReaxFF force field, allowing for a detailed representation of chemical reactions at the atomic scale. Results revealed significant differences in the reaction dynamics between the two systems. The pure aluminum particle exhibited a more rapid and exothermic reaction with AP, leading to a higher release of energy and potentially enhanced propulsion performance. Conversely, the passivated aluminum particle displayed a slower and less exothermic reaction, attributed to the presence of an oxide layer inhibiting direct contact between aluminum and AP molecules. Additionally, kinetic parameters such as reaction rate constants were calculated for both sets of simulations, providing insights into the reaction kinetics of AP-A1 systems. Furthermore, the initial decomposition mechanism of AP was investigated, shedding light on the early stages of the reaction process. These findings provide valuable insights into the role of aluminum passivation in solid rocket propellant formulations and highlight the potential for optimizing energetic materials through molecular-level simulations. Overall, the comprehensive analysis presented in this study advances our understanding of AP-A1 interactions and offers a foundation for further research aimed at enhancing the performance and safety of energetic materials in propulsion applications.

Copyright ©2024 by the International Astronautical Federation (IAF). All rights reserved.Nitramines, like RDX and HMX, are also alternatives to AP as main components in smokeless propellants. They have high specific impulse but are moderately sensitive and have a slightly negative oxygen balance and are therefore unable to contribute positively to the oxygen balance of the propellant. Crystal defects are a constant in applied energetic materials (EMs) and play a crucial role in thermal degradation, combustion and ignition mechanisms, and subsequent aging. Defect engineering is the process of studying how defects affect an EM’s qualities and performances in order to design new EMs that meet the required specifications. An emerging field of study in energetic materials is crystal-defect engineering, which offers previously unheard-of opportunities for regulating physical, chemical, and electrical properties as well as propellants, explosives, and pyrotechnics compositions. There are numerous types of crystal defects, including line defects (dislocation), planar defects (twin, shear band, crack, and surface defect), and volume defects (void). Point defects also include orientational defects and element doping. In this study, ReaxFF molecular dynamics simulations were used to examine the effects of molecule vacancies on the reaction kinetics and thermal decomposition mechanisms of condensed-phase - HMX at different temperatures. The thermal decomposition of HMX is the primary event in the combustion process of solid rocket smokeless propellants, directly affecting the related performance of propellants and even rocket engines. Results showed that three primary initial decomposition mechanisms, namely, NNO2 bond dissociation, HONO elimination, and concerted ring fission, exist at both high and lower temperatures. Molecular vacancies affect how much each of the three pathways contributes to the initial breakdown of HMX, and these effects change with temperature. Molecular vacancies significantly enhance N-N bond cleavage and coordinated ring breaking at high temperatures (3200 K), while impeding the production of HONO bonds. The two main competing reaction pathways are N-N bond dissociation and HONO elimination, with the former being more prevalent during the first breakdown. Additionally, we calculated the first decomposition’s reaction rate constant and activation barriers for various vacancy concentrations. This RMD study showed that molecular vacancies accelerate the decomposition of condensed-phase HMX by increasing the reaction rate constant and reducing activation barriers.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Molecular dynamics simulations have emerged as a powerful tool for studying the passivation of metal surfaces by oxygen, providing insights into the mechanisms underlying this process at the atomic scale. In this study, we have used molecular dynamics simulations to investigate the passivation of an aluminium particle by oxygen, as aluminium is one of the most used metallic additives of solid rocket propellants. Specifically, the interaction between a single aluminium particle and oxygen molecules in a controlled environment. The simulations were performed using ReaxFF forcefield and involved the use of a variety of analytical techniques to analyse the results. The results of the simulations showed that the passivation of the aluminium particle by oxygen occurred through a sequence of reactions. Initially, the oxygen molecules adsorbed onto the surface of the particle, forming oxygen atoms that diffused into the bulk of the metal. This diffusion led to the formation of an oxide layer on the surface of the particle, which effectively passivated the underlying metal. Based on the behaviour observed, the passivation process was highly dependent on the temperature of the system. At low temperatures, the formation of the oxide layer was slower and incomplete, leading to the formation of a highly disordered oxide layer. At higher temperatures, the oxide layer formed much more quickly and was much more ordered, with a crystalline structure. Overall, the study provides valuable insights into the passivation of aluminium particles by oxygen, highlighting the importance of molecular dynamics simulations in the study of materials science. In particular, the results of the study shed light on the mechanisms underlying the passivation process and suggest that temperature plays a critical role in determining the structure and properties of the resulting oxide layer.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Currently Brazil has two rocket launch centers, they are the Hell Barrier Launch Center (CLBI), in the state of Rio Grande do Norte and the Alcântara Launch Center (CLA), in the state of Maranhão. The Alcântara Launch Center is the great Brazilian bet in terms of launches, because it has advantages in several areas: geographical aspect, CLA is located in a region close to the equator, less propellant is spent for positioning in geostationary orbit, there is no change in orbit after launch and there is a gain in momentum; geological aspect, there are no instabilities near the launch center, such as volcanoes; climatic aspect, since there are only occasional rains and no other varieties; aeronautical advantage: it is far from the major centers, so there is no significant air traffic volume of traffic on site, which allows a considerable amount of launches without putting air traffic at risk; demographic advantage: because it is a sparsely populated region, local releases do not put the population at risk. This paper objects to present the advantages of rocket launches in Brazilian launch centers and its potential to be a prominent commercial launch site, demonstrating how Brazil has reformulated its internal policy in search of entering the world aerospace market with the opening of Alcântara Space Center (CEA) to host propels by private companies, national or foreign. In the future, CEA can thus become one of the best locations in the world for commercial exploration or strategic rocket launches, heighten Brazil in the space field to a place compatible with its size.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Molecular dynamics is a computational method used to study the behavior of molecules and atoms over time. By simulating the interactions between individual particles, researchers can improve insights into the physical and chemical properties of materials at the atomic scale. This approach has been applied to a wide range of fields, from drug design to materials science and even rocket propulsion. In this case, for ducted rocket. One area where molecular dynamics has been particularly useful is in the study of boron oxidation. Boron is a lightweight and high-strength material that has potential applications in the aerospace industry. However, boron is also highly reactive with oxygen, which can lead to oxidation and degradation of its mechanical properties. By using molecular dynamics simulations, researchers can study the process of boron oxidation in detail and identify ways to mitigate its negative effects. One potential application of boron in the aerospace industry is in ducted rocket motors. Ducted rockets are a type of propulsion system that use a duct to compress air before mixing it with fuel and igniting it to burn and then generate thrust. This approach has several advantages over traditional rocket motors, including higher efficiency and lower noise levels. However, ducted rockets also require materials that can withstand the high temperatures and pressures generated during operation. Boron-based materials are well-suited for use in ducted rocket motors because of their high strength and heat resistance. However, boron oxidation can also be a concern in this context, as the high temperatures and pressures can accelerate the oxidation process. By using molecular dynamics simulations, researchers can study the interactions between boron and oxygen at the atomic level and identify ways to protect the material from oxidation. In summary, molecular dynamics simulations have a wide range of applications in materials science and engineering. In the context of boron oxidation and ducted rocket motors, this approach can be used to study the behavior of molecules and atoms at the atomic scale and identify ways to protect boron-based materials from oxidation and degradation. With continued research and development, boron-based materials could play an important role in the development of next-generation propulsion systems for aerospace exploration and other applications. Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) was used in this study. LAMMPS is a classical molecular dynamics code with a focus on materials modelling.

Copyright © 2023 by the International Astronautical Federation (IAF). All rights reserved.Electrostatic discharge is recognized as a form of ignition of energetic materials and unanticipated events of this nature get attention due to the magnitude, delay in the development of projects and loss of life. Studies have established the correlation between metallic aluminum present in formulations and the sensitivity of solid propellants to electrostatic discharge (ignition and cracking). To evaluate the influence of the electric field on the formation of cracks in the composite, models were used in the software COMSOL Multiphysics relating the amount of aluminum and the sensitivity to ESD. An experimental design for simplex network mixtures with pseudocomponents was adopted and electrical permittivity was the property observed in hypothetical AP/HTPB/Al mixtures. A model built in the COMSOL simulated external and internal discharges in a rocket motor indicating sensitive points load accumulation - in its structure, represented by the superficial density of load. Furthermore, a model assigned by the Hong group of mechanics and structural materials from Iowa State University was used to evaluate crack formation and its relation to electrical permissiveness. The results associated to the equation obtained from the experimental planning show that the model presented for the study of rupture is in accordance with the literature. The studies carried out presented a new methodology for the study of the influence of electric fields on aluminized solid composites indicating the possibility of ignition via ESD.

© 2022 Elsevier B.V.This paper presents the results of the Density Functional Theory (DFT) calculations and reactive molecular dynamics (RMD) simulations of the furazanotetrazinedioxide (FTDO) explosive, a novel highly energetic material. The details of the mechanism of the FTDO decomposition have been elucidated for the first time. The calculated activation energy was found to be 30.96 ± 2.25 kJ/mol. The DFT calculation results suggested that FTDO is prone to the fragmentation and decomposition processes. The study results present original mechanisms for the FTDO detonation/decomposition along with the values for the activation energy and frequency factor with high linear determination coefficient.

© 2021 Elsevier LtdThe current work presents the simulation of the pyrolysis and combustion of alternative jet fuels by reactive force field molecular dynamics methods. A comparison has been done between saturated hydrocarbon farnesane and two unsaturated compounds, α-farnesene and β-farnesene, all of them obtained by the fermentation of sugars present in sugarcane juice. The pyrolysis and combustion mechanisms were elucidated for all the three species at a specified temperature. Significant differences have been observed among the compound reactions during the decompositions. Using a first-order approach, the Arrhenius parameters of the global process were obtained with three different temperatures, held constant over time. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene, and β-farnesene were 132.55, 117.28, and 112.88 kJ mol−1, respectively, and for the combustion, the obtained activation energies were 71.63, 37.99, and 37.98 kJ mol−1, respectively. These data are compatible with the results found in the literature for hydrocarbon fuels. A detailed computational study of all three compounds was performed using the B3LYP/6–311 + G(d,p) approach in the gas phase. Analysis of structures, NBO charges, FMOs, MEP plots, and global reactivity parameters unequivocally supports the simulation results obtained using the ReaxFF code, proving noticeably higher potential reactivity of α- and β-farnesenes compared to farnesane, and furthermore higher reactivity of β-farnesene compared to α-farnesene.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Energetic materials have been used over time in civil and military applications. Concomitantly, studies were conducted focusing on the combustion mechanisms of these materials, including their kinetic and thermodynamic behavior during firing. The objective of this work was to systematically study the mechanisms of thermal decomposition of ammonium dinitramide (ADN), and ADN formulated as a solid composite propellant with glycidyl azide polymer (GAP), through reactive molecular dynamics simulations. The main reactions of the mechanisms were elucidated and analyzed, and the Arrhenius parameters were determined for the global processes. Calculated activation energies for the systems were 127.84 and 354.72 kJ/mol for ADN and ADN/GAP, respectively. Comparison to literature data shows up to 14% of deviation, which proves the methodology useful for predictions and kinetic analyzes of combustion/pyrolysis reactions of energetic materials.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In propulsion systems, to ensure a suitable thrust, the selection of the pair fuel/oxidizer is of utmost importance. Combination of propellant influences the characteristics of the chemical reaction process, the fuel vaporization speed, the ignition temperature, the volatility of hot gases. After the propellant, a suitable injector design is important, which allows better use of the propellant mixture, and thus achieve better engine performance and less combustion instability. This study evaluated the radial injector data, compared with those for other types of injectors, orifice-plate and swirl. Combustion behaviour was analysed by reactive molecular dynamics simulations. It was analysed how each contributes to the engine’s performance, by using solid fuel-based paraffin and oxygen gas in the gas phase (GOx), constituting a hybrid propellant. For orifice plate and swirl injectors, the specific impulse values were higher at higher test pressures. However, for the radial injector, the Isp was increased to the test pressure up to 25 bar. All injectors yielded good operation and met the goal of injecting oxidizer flow efficiently. The RMD simulation was able to show the behaviour of paraffin during decomposition and combustion, as well as explain the pressure effects on the system by the gaseous molecules generation.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In this work are presented pyrolysis and combustion simulations of alternative jet fuels using reactive molecular dynamics methods. Three fuels obtained from renewable resources are compared: farnesane, α-farnesene and β-farnesene. The pyrolysis and combustion simulations were done in different temperatures. Significant differences have been observed among the compound reactions during the decompositions. The Arrhenius parameters of the global process were obtained for all species, considering a first-order approach. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene and β-farnesene were 132.55, 117.28 and 112.88 kJ mol-1, respectively.

© 2020 IOP Publishing Ltd. All rights reserved.Predicting explosion parameters is an important step when planning for blast tests or the design of blast resistant buildings and of explosive materials and formulations. This paper presents reactive molecular dynamics simulations of furazanotetrazinedioxide (FTDO) explosive, a new and highly energetic material, calculated with the software LAMMPS with ReaxFF force field. The decomposition steps and chemical mechanism of the material decomposition was elucidated and the Arrhenius parameters of the global decomposition reaction was calculated based on a first order approach with six different isothermal simulations sets. Results present an original mechanism for the detonation/decomposition and an activation energy and frequency factor with high linear determination coefficient. These results are the first ones published for this material and present a good comparison for future experiments.

© 2020 Elsevier LtdLaminar burning velocity is considered as being one of the fundamental properties of a premixed flame and reliable data are constantly required for practical applications. Although it is possible to find an extensive amount of experimental laminar burning velocity data for fuels containing one or two components, data for fuels with three or more components are scarce. The goal of this study is to help fill this gap by providing experimental laminar burning velocity data for a fuel mixture with five components (H2:CO:CO2:CH4:N2). The fuel composition utilized is proposed as surrogates of the fuel provided by a downdraft gasifier, the most common and the most efficient type of gasifier. Experimental measurements were carried out for different fuel-to-air equivalence ratios (0.88 < ϕ < 1.74) at atmospheric conditions, 954 mbar and 298 K. The method utilized was the conical-flame surface using OH PLIF images (Planar-Laser-Induced Fluorescence imaging of OH). The area method provides a good approximation of the unstretched laminar burning velocity. Experimental data were compared with the simulated results obtained from a CHEMKIN chemical kinetics software. The highest experimental laminar flame speed of a downdraft syngas air mixture was 0.3491 m s−1 and occurred when ϕ ∼1.3.

© 2020 Sociedade Brasileira de Quimica. All rights reserved.The molecular dynamics simulations were used to study the epoxy ring-opening in the determination of kinetic parameters, with a temperature range from 1500 to 2500 K in a 20 x 20 x 20 Å unit cell containing 15 molecules of C2H4O (ethylene oxide) and 35 molecules of CH6N2 (methanediamine). The activation energy values for epoxy and diamine was 66 and 92 kJ mol-1, respectively. The simulation showed epoxy ring breakage in some of the molecules, but mainly the release of ammonia by diamine. It was observed that the activation energy involved in diamine consumption for ammonia formation is higher than for the epoxy ring opening. The results of the epoxy ring-opening study show that the polymerization occurs slowly, which leads to high computational simulation values.

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The design of solid rocket motors is considered relatively dominated technology in the various areas of knowledge. Even so, there are variables that still need to be better explored. Therefore, the topic presented in this work is related to problems found in designs of HTPB-AP-AL based solid rocket motors that are related to the formation of Plateau in the performance curves (pressure and thrust). This phenomenon has been studied by many researchers, in the way that studies mention different causes. Among the main causes studied, research reports that this phenomenon is related to Ammonium Perchlorate and its granulometric distribution and size, the thermal decomposition kinetics of Ammonium Perchlorate, the distribution and morphology of aluminum and also to the curing agents used in the propellant formulations. The main objective of this work is to present a model built with propellant formulations, considering these variables above mentioned in order to address a good practice to avoid this phenomenon. This work presents burning rates as a function of pressure of several propellant formulations based on ammonium perchlorate (AP) and hydroxyl-terminated polybutadiene cured by isophorone diisocyanate (IPDI) and aluminum (Al), in order to evaluate values of the pressure exponent of the burning rate in distinct pressure ranges, termed as plateau burning rate trends.

© 2019, The Brazilian Society of Mechanical Sciences and Engineering.Propellants based on HTPB/AP (hydroxyl-terminated polybutadiene/ammonium perchlorate) are the most commonly used in most of the rocket engines used by the Brazilian Armed Forces. This work aimed at the possibility of extending its useful life (currently in 10 years) by performing chemical kinetic analysis of the energetic material via differential scanning calorimetry (DSC) and also performing computer simulation of aging process using the software Large-scale Atomic/Molecular Massively Parallel Simulator. The simulations presented the experimental behavior of the aging process, showing the bending and cross-link of the binder with the volume contraction and the energetic stabilization. Thermal analysis via DSC was performed in triplicate and in 3 heating ratios (5 °C, 10 °C and 15 °C) of rocket motor with 11-year shelf-life, using the Arrhenius equation to obtain its activation energy, using Ozawa and Kissinger kinetic methods, allowing comparison with manufacturing period data (standard motor). The obtained activation energies were 126.67 kJ/mol (Ozawa) and 122.85 kJ/mol (Kissinger), much higher than that of the aged propellants (~ 78 kJ/mol, based on literature data), showing that the propellant has not yet aged significantly. In addition, the kinetic parameters of internal pressure of the combustion chamber in 8 rocket engines with 11 years of shelf-life were also acquired, for comparison purposes with the engine start-up data.

© 2020, Eduem - Editora da Universidade Estadual de Maringa. All rights reserved.Predicting explosion parameters is an important step when planning for blast tests or the design of blast resistant buildings. This paper presents a comparison of recorded pressure that was reflected on the surface of reinforced concrete slabs with and without EPS (Expanded Polystyrene) foam retrofit measured from a detonation of 2.7 kg of non-confined plastic explosive. Two 50 MPa reinforced concrete slabs measuring 1.0×1.0×0.08 m, simply supported on two sides were tested. The explosive was suspended at a distance of 2.0 m from the upper surface of the slabs; one of the slabs had 5.0 cm thick foam on the top side. Eight piezoelectric pressure sensors were positioned at a distance of 2.0 m from the explosive. Results showed that the foam retrofit reduced the reflected pressure by approximately 57% when compared to the slab without EPS foam retrofit.

© 2019 Sociedade Brasileira de Quimica. All rights reserved.The present work presents combustion simulations of hydroxyl-terminated liquid polybutadiene loaded with ammonium perchlorate and aluminum, using Chemkin software and the “Plug Flow” type reactor. These materials are widely used in solid composite propellant formulations. Through this study, the effect of parameters of axial velocity, equivalence ratio, pressure and temperature during the firing of the propellant were discussed. The objective of this work was to discuss how to define the best parameter value based on the obtained results, and thus generate optimized formulations.

© 2019 Sociedade Brasileira de Quimica. All rights reserved.This work aims to determine the kinetic parameters of the thermal decomposition of a lubricating grease based on perfluoropolyether (PFPE) and the computational simulation of this decomposition. The determination of kinetic parameters of thermal decomposition was done by thermal analysis using thermogravimetry (TG) at different heating rates (β) of 10, 15 and 20 °C min-1. With the TG curves obtained, the kinetic parameters were determined by the kinetics methods of Goldfarb et al. and Duvvuri et al., Flynn-Wall-Ozawa and Kissinger. The activation energy of the thermal decomposition of the PFPE grease in the kinect models ranged from 63.54 to 112.3 kJ mol-1. The results of the thermogravimetry indicated that the PFPE grease is thermally stable up to 300 °C. A simulation of the thermal decomposition of the PFPE oil base was carried out by molecular dynamics simulation, using LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator) in a temperature range of 0 to 3500 K during 50 ps. The value of the activation energy in the simulation was 92 kJ mol-1. The results show that PFPE oil base and PFPE lubricant grease can be used in high-temperature applications.

© 2019, The Brazilian Society of Mechanical Sciences and Engineering. This paper presents a study about injectors, where the radial injector was evaluated. This type of injector was chosen because only a small amount of information on it was found. Thus, the radial injector will be compared with other two types of injectors, the orifice plate and the swirl, in terms of parameters, such as discharge coefficient (C d ), regression rate r, and specific impulse (I sp ). In respect of the regression rate, the values appeared increasingly with the test pressure and, consequently, with the injection pressure. Thus, each injector model responded in the same way as for the regression rate behavior; however, the same behavior was not observed in relation to the specific impulse.

© 2018 Sociedade Brasileira de Quimica. All rights reserved.The combustion process of triethylaluminum is investigated by means of reactive molecular dynamics simulations using the ReaxFF force field. The behavior of the system in five different temperatures ranging from 2000-4000 K was evaluated. As a pyrophoric material, TEA reacts also with water, generating gaseous hydrogen, whose content increases with the system temperature. Rapid water formation and O2 depletion were observed and, using Arrhenius equation, the preexponential factor and activation energy were found to be 9.67E+09 s-1 and 1.242 kJ mol-1, respectively. The results obtained are in accordance to the expected for pyrophoric materials and the simulation in question can help elucidating and analyzing the complex reaction mechanism of TEA combustion.

© 2018 Sociedade Brasileira de Quimica. All rights reserved.Prediction of chemical explosions parameters is an important step for blast tests for civil and military applications. Applying computational chemistry and experimental results, this paper presents the decay rate of pressure in air from the epicenter of 2.70 kg of PBX-Plastic bonded explosive detonation to the distance of 2.0 meters. Pressure in the epicenter was calculated using reactive molecular dynamics simulations and the incident pressure at 1.3; 1.6 and 2.0 meters were measured with piezoelectric pressure sensors. The explosive for the full-scale test were non-confined in a cylindrical shape. Results of simulation and recorded values were consolidated and the rate of pressure decay was verified by statistic regression. Good agreement was verified between computational and experimental pressures data. This research can help designers to prepare protection devices in test areas, storages of explosives or important buildings for military proposes.

This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 °C for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 °C. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.

Aluminum that is incorporated in an energetic material such as a propellant plays a significant role in the combustion process by means of stabilization with regard to the burning and generation of additional energy. The use of simulation softwares to model the combustion mechanism and kinetic parameters of the elementary reactions that compose the oxidation were used as the pressure variation of the combustion chamber of a rocket motor conditions. The behavior of the molar fraction of the chemical species during the combustion and its posterior stabilization were observed. The systems submitted to higher pressures tend to stabilize more rapidly, according to the greater chemical speed of the elementary reactions.

The burning simulation of hydrogen was carried on in the reactor model Aurora, present in the software Chemkin, with three different experimental data sets and one calculated set, by quantum chemistry methods (MP2). The analysis of the calculated parameters for each reaction was made and compared to the experimental ones through burning simulations. A detailed study of the mechanism was realized, while setting specific time inputs, showing the concentrations of chemical species and the rates of production/consumption of reactants, intermediates and products. The ignition step of the combustion was simulated, when varying the time from 0 to 3 nanoseconds. All the mechanisms showed different results in this step. More refinement is needed in the theoretical data in order to successfully simulate the ignition phase. This methodology allows the insertion of new reactions in several mechanisms and also the calculation of parameters for reactions which cannot be determined experimentally. © 2012 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

The aggregation behavior of the non-ionic surfactant Renex-100 in aqueous solutions and mesophases was evaluated by SAXS in a wide range of concentrations, between 20 and 30°C. Complementary, water interactions were defined by DSC curves around 0°C. SAXS showed that the system undergoes the following phase transitions, from diluted to concentrated aqueous solutions: 1) isotropic solution of Renex aggregates; 2) hexagonal mesophase; 3) lamellar mesophase; and 4) isotropic solution. DSC analysis indicated the presence of interfacial water above 70wt%, which agreed with the segregation of free water to form the structural mesophases observed by SAXS bellow this concentration.

The combustion simulation of ammonium perchlorate was carried out with the software Chemkin, in two steps: the burning behavior of pure ammonium perchlorate and the one of formulated ammonium perchlorate with hydroxyl terminated polybutadiene binder. In both cases, the room pressure varied in order to verify its influence in the system. The burning environment conditions were diverse. During the combustion process, the data obtained from the kinetic chemistry simulation software were compiled. The flame structure can be described by the molar fraction of the burning products and the temperature evolution from the surface of the material.

The addition of nanosized metal particles in propulsion systems such as solid and liquid propellants, hybrid propellant and ramjet motors has recently became a major focus of research. Significant increases in the burning velocity and in the specific impulse are some of the advantages of using nano-scale energetic materials in many different types of propulsion systems. Aluminum has been largely employed as a metallic additive in energetic materials, also in a recently new propulsion system (aluminum/ice propulsion, "Alice"), and some studies show that the advantages of using nanosized aluminum instead of microsized aluminum are facilitating the ignition of the systems and allowing better incorporation of the components in the formulations and improving its homogeneity. Some of the combustion processes that require high pressures and even higher temperatures can occur in moderate conditions due to the increase of the surface area of the reactants, in this case, the metallic additive.

In missile propulsion technology it is conventional to employ solid rocket boosters. These boosters are loaded with solid propellants, which are energetic compositions where raw materials are comprised of solid particulates, such as fuel, and oxidizer particles, in which are dispersed and immobilized throughout a binder (polymeric) matrix. The processability of these compositions is not simple because it is difficult to incorporate a high percentage of solids in polymeric matrix. Its has been problematic to formulate a safe composition so as to prevent an accidental ignition of solid propellant or other device that uses energetic materials. Accidents and incidents with solid rocket motor, during production, handling and storage, without apparent causes, led to studies by independent groups [1,2,3,4]. These studies generated important conclusions on the realm of solid rocket motor safety; furthermore, subsequent investigations suggest that spontaneous motor ignition can be attributed to electrostatic discharge. The solid composite propellant grain can be considered in a microscale heterogeneous system in which conductive and nonconductive particles and different types of binders had direct influence in the grain electrical characteristics. Nonconductive particles have a geometrical effect to influence the spacing of the conductive particles [5]. The aim of this paper is to present the methodologies and the respective results of electrical and electrostatic discharge tests. These results allow us to choose a less ESD sensitive formulation of solid propellant increasing the reliability in manufacturing, handling and storage of solid rocket motor. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

This work describes the development of an acrylic laminated transparent compound that can be applied in aeronautics and astronautics transparencies. The case here studied, is a laminated double curved transparency (bubble form), used in an observation side window of a military aircraft. Side windows needs specific resistance and characteristics, like the windshields; it allows the perfect visualization and image capitation. Laminated transparencies composed by different materials, joint better qualities than monolithic, due this way achieves great mechanic and chemical resistance, high transparency, no spall and easy maintenance or recovering. Much information about materials and process was jointed, with the intention to build the reinforced transparence, and to make valid this information, by the analysis of the final results, in both of points of view: mechanic resistance and optical quality. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

The process of fuel injection in combustion chambers is of vital importance, under several aspects, for the ideal operation of each motor. The responsible element for the introduction of liquid and gaseous propellants in the combustion chamber of rockets and for the transformation of liquid masses in sprays is the injector, that converts the potential energy of the propelants in kinetic energy, for the pressure fall in its interior, forming a jet or liquid sheet that dissolves in drops. Swirl type pressurized injectors, mono or bipropelants, are object of constant studies to understand its operation in rocket-motor with liquid propelant, because they produce conical liquid sheets and present a serie of differences in relation to the axial type in terms of improvement of the combustion process as a whole. The fast formation of a high number of drops, of convenient diameters, distributed in an extensive area, favors the vaporization mechanisms due to the high surface of all, that quickly vaporize and enter in combustion. Its production is a challenge for the techniques of conventional fabrication, because of the complexity, dimensions, work conditions and its fixation in the injection head. Injectors production from preexistent designs and the assembly of a structure which allowed the tests of the same, was the object of this work, that generated pieces in brass which allowed cold tests with the fluids kerosene and cut oil to confirm the formation of the hollow conical spray and hot tests with melted paraffin to confirm the formation of spherical drops of several sizes, which were measured in a profile projector, and analyzed by the process of test sieving, revealing the existence of drops within the range of those already found in literature. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

During service, gas turbine blades and vanes are exposed to thermal stresses and to oxidation and hot corrosion from the hot combustion gas. Therefore, the coating process is a good alternative to protect the turbine. In the present work is studied the benefits of the application of two coating layers to enhance the corrosion and oxidation resistance of niquel base blades and vanes. The specimens were first cleaned and then the coatings were applied through a pre-programmed furnace. Photomicrographies of the specimens were taken, showing the steps of the coatings and the results of the oxidation tests. There was no evidence of damage and the oxidation characteristics of the two coatings were similar to one. The proposal to use multilayer VPA coatings increases the average of the coating deposited and as a result the life of the substrates. © 2009 by the American Institute of Aeronautics and Astronautics, Inc.

In this work, the combustion process of ammonium dinitramide, ADN, has been modeled in two different situations: decomposition in open environment, with abundant air and decomposition in a rocket motor internal, environmental conditions. The profiles of the two processes were achieved, based on molar fractions of the species that compose the products of ADN combustion. The velocity of formation, and quantity of species in the open environment was bigger than the ones in the rocket motor environment, showing the effect of the different atmosphere in the reactions kinetics.

The thermal decomposition of aged and non-aged samples of ammonium perchlorate(AP)/hydroxyl-terminated-polybutadiene(HTPB), the AP/HTPB solid propellant, were studied at different heating rates in dynamic nitrogen atmosphere. The exothermic reaction kinetics was studied by differential scanning calorimetry (DSC) in non-isothermal conditions. The Arrhenius parameters were estimated according to the Ozawa method. The calculated activation energies were 134.5 kJ/mol (non-aged) and 79.0 kJ mol-1 (aged), the pre-exponential factors, A, were 2.04 1010 min -1 for the non-aged samples and 1.29.106 min-1 for the aged samples and the reaction orders for the global composite decomposition were estimated in 0.7 and 0.6 (non-aged and aged samples decomposition, respectively) by the kinetic Shimadzu software based in the Ozawa method. The Kissinger method for obtaining the activation energy value was also used for a comparison purpose. These results are here discussed. © 2008 by the American Institute of Aeronautics and Astronautics, Inc.