Combustion Of Composite Solid Propellants Research Articles

Role of Oxides of Iron on the Combustion of Composite Solid Propellants: A Review

The effects of iron oxides (α-Fe2O3, γ-Fe2O3, Fe3O4 in the different size ranges from micron to nano) on the combustion of composite solid propellants, also known as hydroxyl terminated polybutadiene/aluminium/ammonium perchlorate (HTPB/Al/AP) systems, are thoroughly reviewed in this work. The effect of the oxides of iron in (i) condensed phase; (ii) sub-surface and surface; (iii) premix flame (gas phase); and (iv) final flame (gas phase) in deflagration zone are also critically reviewed. The effect of catalyst on the lower pressure limit (LPL), upper pressure limit (UPL) and ignition delay is also studied as a part of the combustion phases. It is understood that unlike during the combustion of pure ammonium perchlorate, the role of iron oxides starts its influence on binder system degradation, binder-ammonium perchlorate reactions at surface and HClO4 decomposition in gas phase. The role of aluminium is to contribute for larger energies in both primary and diffusion flame zone, the heat generated accelerates the surface reactions further. Another interesting topic is nano-oxides of iron, since nanosize contribute for definite increase in burn rate, but the disadvantage of agglomerations both at mixing level and combustion level needs to be addressed. Several strategies are suggested, with the most significant ones being co-precipitation with ammonium perchlorate and the utilization of dispersion agents.

One-step synthesis of ferrocenyl glycidyl ethers as combustion catalysts for the thermal decomposition of ammonium perchlorate

As an oxidant, the pyrolysis behavior of ammonium perchlorate is the key to the combustion of composite solid propellants. Seeking a suitable catalyst to promote AP decomposition has drawn much attention. Ferrocene-based compounds are often used as burning rate catalysts because of their excellent catalytic effect. However, ferrocene-based burning rate catalysts are prone to migration during storage of propellants. In this study, six ferrocenyl glycidyl ethers were designed and synthesized to improve the anti-migration properties, and the related spectra characterization techniques were adopted to confirm their molecular structures. Furthermore, their related properties and mechanisms were also studied. As a result, they showed good redox performance, positive promotion on AP decomposition, excellent combustion and mechanical performance. Meanwhile, they had a higher anti-migration behavior compared with catocene and ferrocene. This study demonstrates that ferrocenyl glycidyl ethers have great potential to be applied as multifunctional burning rate catalysts in composite solid propellants.

Synthesis, Anti‐migration and Catalytic Effect of Ferrocene Azine Derivatives on the Thermal Decomposition of Ammonia Perchlorate

AbstractFerrocene burning rate catalyst (BRC) is a common catalyst to promote the combustion of composite solid propellant because of its high catalytic performance, but this kind of catalyst has the disadvantage of easy migration. Ammonia perchlorate (AP) is the main oxidant of composite solid propellant, and its thermal degradation behavior has an important impact on the combustion of propellant. New mononuclear and polynuclear ferroceneazine BRCs were synthesized, and their structures were characterized by UV‐Vis, NMR, HRMS and IR spectra. The catalytic effects of these ferrocenylazines on the thermal degradation of AP were studied by DSC and TG. The results confirmed that the catalytic performance of azine without bisferrocenylpropane was inferior to that of Catocene (Cat), while the catalytic performance of azine with bisferrocenylpropane was equivalent to that of Cat. Anti‐migration studies showed that both mononuclear ferroceneazines and Cat showed mobility, while polynuclear ferroceneazines did not migrate after long‐term storage. Therefore, polynuclear ferroceneazine is a new kind of high‐efficiency and non‐migration BRC with application prospects.

First-Principles Investigation of Graphene and Fe2O3 Catalytic Activity for Decomposition of Ammonium Perchlorate.

The employment of catalysts is an effective way to improve ammonium perchlorate (AP) decomposition performance during the combustion of composite solid propellants. Understanding the micromechanism of catalysts at the atomic level, which is hard to be observed by experiments, can help attain more excellent decomposition properties of AP. In this study, first-principles simulations based on density functional theory were used to explore the effect of the graphene catalyst and iron oxide (Fe2O3) catalyst on AP decomposition. Considering the transfer of a H atom during AP decomposition, the most stable adsorption sites for aforementioned catalysts were found: the top of the C atom of the graphene surface with the adsorption energy of -0.378 eV and the top of the Fe atom of the Fe2O3 surface with the adsorption energy of -1.596 eV. On the basis of adsorption results, our transition state calculations indicate that, in comparison to control groups, graphene and Fe2O3 can reduce the activation energy barrier by ∼19 and ∼37%, respectively, to promote AP decomposition with a transfer process of a H atom on the catalyst surface. Our calculations provide a way for explaining the micromechanism of the catalytic activity of graphene and Fe2O3 nanocomposites in AP decomposition and guide experimental applications of graphene and Fe2O3 for catalytic reactions.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ГОРЕНИЯ СМЕСЕВОГО ТВЕРДОГО ТОПЛИВА, СОДЕРЖАЩЕГО БИДИСПЕРСНЫЙ ПОРОШОК БОРА

A problem of combustion of the composite solid propellants containing various powders of metals and non-metals is relevant in terms of studying the effect of various compositions of powders on the linear rate of propellant combustion. One of the lines of research is to determine the effect of the addition of a boron powder on the burning rate of a composite solid propellant. This work presents the results of numerical simulation of combustion of the composite solid propellant containing bidispersed boron powder. Physical and mathematical formulation of the problem is based on the approaches of the mechanics of two-phase reactive media. To determine the linear burning rate, the Hermance model of combustion of composite solid propellants is used, based on the assumption that the burning rate is determined by mass fluxes of the components outgoing from the propellant surface. The solution is performed numerically using the breakdown of an arbitrary discontinuity algorithm. The dependences of the linear burning rate of the composite solid propellant on the dispersion of the boron particles and gas pressure above the propellant surface are obtained. It is shown that the burning rate of the composite solid propellant with bidispersed boron powder changes in contrast to that of the composite solid propellant with monodispersed powder. This fact proves that the powder dispersion should be taken into account when solving the problems of combustion of the composite solid propellants containing reactive particles.

Ignition and Combustion of Composite Solid Propellants Based on a Double Oxidizer and Boron-Based Additives

The use of boron-based powder materials in solid propellant compositions is an effective method for increasing the energy characteristics in the combustion chamber due to increasing the released energy through the combustion of boron particles. In this study, powders of amorphous boron and aluminum borides, obtained by the method of self-propagating high-temperature synthesis—the SHS method, which were added to the composite solid propellant composition based on a double oxidizer and an energy fuel binder, are studied. The paper presents the characteristics of thermal decomposition, ignition, and combustion for solid propellant samples. The tested samples are ignited using a continuous CO2 laser in the air in the heat flux density range of 90 to 200 W/cm2. The combustion of propellant samples is carried out in a manometric bomb in a nitrogen atmosphere at pressures ranging from 0.5 to 7.0 MPa. It is shown that the use of amorphous boron and aluminum boride powders in the solid propellant composition reduce the ignition delay time and increase the burning rate of the samples compared to the aluminum-based propellant composition, due to the increase in temperature near the surface of the reaction layer of the sample and the specific heat release during the oxidation and burning of boron.

A model for solid propellant burning fluctuations using mesoscale simulations

The combustion of composite solid propellants shows velocity fluctuations which are expected to have marked effects on turbulence or aeroacoustic instabilities. In this work, we propose a specific propellant boundary condition that models such fluctuations using a spectral synthetic turbulence approach. In order to feed this model with reliable input data, we consider mesoscale direct simulations of propellant combustion. This new propellant boundary condition is implemented in a CFD flow solver and applied to a real lab-scale motor. Simulations show that burning fluctuations can trigger aeroacoustic instabilities, in better agreement with experiments.

Binder melt: Quantification using SEM/EDS and its effects on composite solid propellant combustion

The present study reports the development of a novel technique to quantify binder melt on the surface of the propellant. Non-aluminized AP-HTPB propellants of 86% particulate loading are used to illustrate the technique. Elemental maps of unburnt and extinguished propellant surface are obtained using EDS (Energy Dispersive Spectroscopy). Overlap between the elements is identified and the elemental maps are processed to calculate AP and binder area exposed in unburnt and extinguished samples. The AP area exposed is found to be around 72.3% and 63.3% for unburnt and extinguished samples, respectively, indicating a reduction in AP exposed area with extinguished samples. This has been attributed to the binder melt discussed in literature but never quantified. Simulations have been carried out to analyze and understand the effects of this binder melt. A random packing algorithm is used to simulate propellant packs. Also, a methodology to account for binder melt layer is introduced and is used to capture AP exposed areas. Effect of binder melt in propellants with different solid loading and varying particle size is discussed. It is shown that fine AP particles are more prone to being covered by binder melt than the coarse AP particles. A possible explanation to the behavior of plateau burning propellants observed in literature has been provided through this analysis.

Ignition by laser radiation and combustion of composite solid propellants with bimetal powders

The use of metal powder (usually aluminum) as a fuel in composite solid propellants (CSPs) for propulsion is the most energy efficient method that allows improvement of combustion characteristics of propellants in the combustion chamber and specific impulse. This paper presents the experimental data of the ignition and combustion processes of CSPs containing Alex aluminum nanopowder and mixtures of Alex/Fe and Alex/B nanopowders. It was found that the introduction of Alex/Fe in CSPs leads to 1.3–1.9 times decrease in the ignition time at q = 55–220 W/cm2 and to 1.3–1.4 times increase in the burning rate at p = 2.2–7.5 MPa with respect to that for basic CSP with Alex. When introducing Alex/B in CSP, the ignition times are 1.2–1.4 fold decreased, and the burning rate is practically unchanged. However, the agglomeration is significantly enhanced, which is manifested through the increase in the agglomerate particles content in condensed combustion products by a factor of 1.8–2.2, at 1.6–1.7 fold increase of the agglomerates mean diameter for CSP with Alex/B.

TG–MS study on the kinetics and mechanism of thermal decomposition of copper ethylamine chromate, a new precursor for copper chromite catalyst

Copper chromite is a well-known burn rate modifier for the combustion of composite solid propellants. In this study, basic copper ethylamine chromate (CEC), a new precursor for copper chromite catalyst, was synthesized by precipitation method. The thermal decomposition of the precursor was followed by thermogravimetry–mass spectroscopy (TG–MS) and X-ray diffraction techniques and compared with that of copper ammonium chromate, a conventional precursor for copper chromite catalyst. TG–MS analysis for the decomposition of CEC revealed that the decomposition starts with the liberation of ethylamine. The change in enthalpy for the decomposition reaction of copper ethylamine chromate was higher than that of copper ammonium chromate due to the oxidation of ethyl group. The reducing atmosphere created by the presence of carbon during the decomposition of CEC produced a mixture of Cu, CuCr2O4, CuCrO2 and CuO, while the oxidizing atmosphere of copper ammonium chromate produced a mixture of CuCr2O4 and CuO. Mechanistic study based on Criado and Coats–Redfern methods showed that CEC follows random nucleation (F1) mechanism as the rate-determining step for the thermal decomposition process.

Nanoferrites of Transition Metals and their Catalytic Activity

Recent applications of transition metal nanoferrites as catalyst in thermal decomposition of ammonium perchlorate (AP) and combustion of composite solid propellant (CSP), have been reviewed. Catalytic applications include the use of mainly cobalt, nickel, copper, zinc, manganese, cadmium nanoferrites, as well as their mixed-metal combinations. The nanoferrites are obtained mainly by wet-chemical, sol-gel, solvo-thermal, auto-combustion and co-precipitation methods. Addition of nanoferrites to AP led to shifting of the high temperature decomposition peak toward lower temperatures which shows their catalytic activity. The burning rates of CSPs have also been enhanced by these nanoferrites. Contents of Paper

Calculation of the characteristics of agglomerates during combustion of high-energy composite solid propellants

The problem of calculating the characteristics of the agglomerates formed during combustion of high-energy composite solid propellants is considered. It is shown that the mathematical models developed by the authors can be used for different propellant formulations to evaluate not only the dispersion of agglomerates, but also their quantity, chemical composition, and structure. The rules (algorithm) of using the developed models for a wide range of propellant formulations are determined. Modeling results for a number of propellant formulations based on various components are analyzed.

Catalytic thermal decomposition of ammonium perchlorate and combustion of composite solid propellants over green synthesized CuO nanoparticles

This paper reports on the synthesis of CuO nanoparticles (NPs) by the leaves extract of Calotropis gigantea plant in aqueous medium through green synthesis and their characterizations in terms of morphology, structure, crystallinity and catalytic properties. The synthesized CuO NPs are crystalline in nature having the average sizes in range of 30–40nm. Green synthesized CuO NPs are utilized as effective catalyst in the thermal decomposition of ammonium perchlorate (AP) and combustion of composite solid propellants (CSPs) by measuring the thermo gravimetric analysis–differential scanning calorimetry (TGA–DSC), ignition delay and burning rate. High catalytic activity to AP decomposition and high burning rate for CSPs containing hydroxyl terminates polybutadiene (HTPB) as binder and AP as oxidizer have observed over the surface of green synthesized CuO NPs. Kinetics of thermal decomposition of AP with and without green synthesized CuO NPs was also studied by isoconversional method using isothermal TG data.

РАСЧЕТ ХАРАКТЕРИСТИК АГЛОМЕРАТОВ ПРИ ГОРЕНИИ ВЫСОКОЭНЕРГЕТИЧЕСКИХ СМЕСЕВЫХ ТВЕРДЫХ ТОПЛИВ

РАСЧЕТ ХАРАКТЕРИСТИК АГЛОМЕРАТОВ ПРИ ГОРЕНИИ ВЫСОКОЭНЕРГЕТИЧЕСКИХ СМЕСЕВЫХ ТВЕРДЫХ ТОПЛИВ

The effect of encapsulated nanosized catalysts on the combustion of composite solid propellants

In solid rocket propellants, nano-sized catalysts are expected to be more effective than their micron-sized counterparts due to their higher surface area and increased contact with the oxidizer. However, propellant processing becomes more difficult and ultimate mechanical properties can be negatively impacted as catalyst size is reduced. One proposed solution to these issues is to encapsulate a nano-sized catalyst inside the oxidizer. We have previously created composite particles with nano-sized iron oxide catalyst encapsulated in fine ammonium perchlorate (AP). In this paper we explore the effect of the composite particles on the burning rate and flame structure of an AP-based composite propellant. The propellant containing the composite nano-iron oxide/AP particles was compared to a baseline propellant without catalyst, a propellant formulated with micron-sized catalyst, and a propellant with nano-sized catalyst mixed directly. All catalyzed propellants contained the same catalyst mass fraction. High-speed (5kHz) OH planar laser-induced fluorescence (PLIF) and high-speed surface imaging were used to examine differences in flame structure and coarse crystal burning characteristics and determine how the encapsulated catalyst influences the global burning rate. It was found that the burning rate of the propellant with the encapsulated catalyst was 90% higher than that of the baseline propellant, 44% higher than the propellant with micron-scale catalyst, and 15% higher than that of the propellant with nano-sized catalyst added directly. Our results indicate that the high global burning rate of the propellant with the encapsulated catalyst is due to an accelerating effect on the fine AP/binder matrix burning rate, assumed to be caused by the intimate contact between the fine AP and catalyst. At elevated pressures (4.4–7.1atm) flame structure and burning surface morphology change as the catalyst size and location is changed. The coarse crystals are observed to protrude more from the burning surface as the catalyst size decreases. The microscale flame structure is observed to transition from jet-like to lifted arches as the pressure and catalyst size increase.

Stability of composite solid propellant ignition by a local source of limited energy capacity

A numerical simulation of solid-phase ignition of a composite propellant by a single small disk-shaped metal particle heated to a high temperature is performed. In the “heat flux amplitude-ignition delay ” coordinates, an region of stable initiation of combustion of a typical composite solid propellant under local heating by a source of limited energy capacity is selected. The limiting amplitudes of heat fluxes during ignition of the condensed substance under conductive and radiative heating are compared.

Exploring mechanisms for agglomerate reduction in composite solid propellants with polyethylene inclusion modified aluminum

In composite solid propellants, shortening particle residence time at the burning surface and inducing particle microexplosions could decrease aluminum agglomeration, thus reducing two-phase flow losses in a rocket motor. We explore this by using aluminum particles modified with low-density polyethylene (LDPE) inclusion to drive intraparticle outgassing, which could break apart composite particles, yielding smaller and faster burning fragments during composite solid propellant combustion. We find that use of these particles in a propellant results in more prompt particle ignition, and surface residence time is decreased. For composite propellant burning at 6.9MPa, mean coarse agglomerate diameter is decreased from 75.8μm (spherical aluminum) to 29.0μm (Al/LDPE 90/10wt.% particles). Thermal analysis with DSC/TGA shows that 10wt.% LDPE inclusion in aluminum (1.5% of propellant weight) results in enhanced oxidation characteristics that are more similar to nanoaluminum than neat spherical aluminum. Thermochemical equilibrium calculations indicate LDPE inclusion decreases specific impulse by 1.0% from 262.7 to 260.0s, but it is expected that in a motor, LDPE inclusion could produce a net increase in specific impulse due to a substantially reduced agglomerate size. This work shows that reduced agglomeration is possible using gas generating inclusion materials that are only weakly reactive with aluminum.

Computer modelling of nano-aluminium agglomeration during the combustion of composite solid propellants

Previously reported computer modelling of agglomeration of micrometre-sized aluminium particles during the combustion of composite solid propellants fails when applied to nano-aluminium particles because of the enormous number of the latter particles. A modified algorithm for three-dimensional casting and burning of composite propellants containing nano-aluminium particles on the computer is developed in the present work. In this, a regular grid is constructed overlaying the computer cast of coarse and fine ammonium perchlorate (AP) particles in the propellant, and the nano-aluminium particles are placed at randomly selected grid points outside of previously placed AP particles. Moreover, this is done one grid layer at a time in the burning direction to save computer memory. Further, since the burning surface is regressed at known burning rates over a larger step size than the above grid spacing, all the nano-aluminium particles located at grid points within one step of surface regression are lumped together and represented by an equivalent micrometre-sized particle. The agglomeration algorithm previously reported is then applied to this representative computer propellant cast. Results are compared with previously reported experimental data for two propellants with different coarse AP particles, one of them at three pressures. The predicted agglomerate size distribution agrees well with the experimental data.

Activated charcoal: as burn rate modifier and its mechanism of action in non-metalized composite solid propellants

Modification of composite solid propellant burning rates becomes a requirement based on the necessities of a mission. Literature discusses about various burn rate modifiers which can modify the burning rates effectively. This paper attempts to understand the behavior and mechanism of (dry) activated charcoal (a recently reported burn rate modifier) in composite solid propellant combustion. Extensive experimental studies are performed to achieve this objective. Effects of activated charcoal are studied on the individual components (fuel and oxidizer) of a composite solid propellant. Its behavior when present at various locations in a sandwich propellant and the quenched surface structures these sandwich propellants is also studied. These studies are further extended to composite propellants as well. From these studies, it is concluded that activated charcoal acts on the primary diffusion flame and enhances the binder melt flow over the surface. The unique features observed with activated charcoal (enhancement in burning the rates is observed only at low pressures and burn rate pressure index reduced) are justified with the proposed mechanism and site of its action. Understanding the mechanism of activated charcoal provided an opportunity to tailor a propellant composition, with activated charcoal coated on ammonium perchlorate, which exhibited very high burning rates (17.34 mm/s at 70 bar) and a near plateau burning (n ~0.08) in the pressure range of 20–70 bar. Also, this paper proposes a mechanism, as to what causes a propellant to have a relatively larger binder melt flow and consequently lower n has been answered.

Studies on the role of iron oxide and copper chromite in solid propellant combustion

Iron oxide and copper chromite are the known burn rate enhancers used in a composite solid propellant. Lot of research has been carried out to understand the mechanism or location of action of the burn rate modifiers so as to better tailor the burning rate of a composite propellant. The literature is still very confusing in affirming the mechanism. Here, a systematic study has been carried out, by undertaking experiments at varying levels of combinations of the individual components (ammonium perchlorate, which is oxidizer and hydroxyl terminated poly butadiene, which is both fuel and binder) of composite solid propellant. Firstly, thermal gravimetric analysis, differential scanning calorimetry and burning rate measurements on the individual components are carried out to study the effect of iron oxide and copper chromite on the components themselves. It has been noticed that though both iron oxide and copper chromite are effective on ammonium perchlorate, iron oxide is slightly more effective than copper chromite. Also, copper chromite enhanced the binder melt flow, while iron oxide reduced it. These are followed-up by experiments on sandwich propellants, which give greater insight and enables better understanding of the behavior of iron oxide and copper chromite in composite propellants, as these are simple two-dimensional analogue of the composite solid propellants. Finally, experiments are carried out on the composite solid propellants to obtain a holistic understanding of the behavior/location of action of iron oxide and copper chromite in them. These studies are used to explain certain unexplained but observed phenomena, at the same time elucidating the location of action of these burn rate modifiers in composite solid propellant combustion. Based on these observations, it has been proposed that both iron oxide and copper chromite are primarily acting on the condensed phase. These studies are further complimented with experiments to analyze the thermal conductivity measurements of various propellant samples. This is pursued to understand the reason for the differences in burn rate pressure index for the composite propellants with iron oxide and with copper chromite. It has been understood from these studies that the thermal conductivity of a composite propellant is a key parameter, which affects the burn rate pressure index. Literature has never addressed it from this perspective.