Increase In Burning Rate Research Articles

Experimental study and theoretical analysis on influencing factors of burning rate of methanol pool fire

A series of experiments were conducted to study the variation law of burning rate of methanol pool fire under natural ventilation and mechanical ventilation. Several factors are considered: size of pan, initial temperature of pan, air flow speed and so on. Also the heat transfer mechanisms of methanol pool fire are analyzed in-depth. The results show that: under natural ventilation, heat transfer from pan to pool by convection plays a significant role on the increase of burning rate. The higher the hydraulic diameter is, the lower the burning rate is. The higher the initial temperature is, the higher the burning rate is under initial development stage and steady burning stage. Under mechanical ventilation, the burning rate of methanol pool decreases followed by increase with the increase of longitudinal air flow speed. The air flow speed at inflection point of burning rate increases gradually with the increase of the characteristic length of pan. The Richardson number for different pans at the infection point of burning rate should be constant, the critical value is about 1 in this research.

Thermal decomposition of ammonium perchlorate over perovskite catalysts: Catalytic decomposition behavior, mechanism and application

Perovskite-based catalysts show a versatile catalytic ability for redox reactions, but are seldom applied for ammonium perchlorate (AP) decomposition. Their catalytic mechanism on AP decomposition still remains unknown. In this study, four different perovskites, namely LaCoO3, La2CuO4, LaMnO3 and LaNiO3, were prepared by co-precipitation method and then applied to catalyze the AP decomposition. LaCoO3 exhibited the best catalytic performance among all the perovskites used, in which the decomposition temperature of AP was lowered to 301.1 °C (114.9 °C lower than pure AP) and the heat release was increased from 768 to 1428 J g−1. A series of characterization on these four perovskites, such as XRD, SEM, NH3-TPD, O2-TPD and XPS, revealed that stronger adsorption abilities of catalysts for NH3 and O2 on the surface led to better catalytic performance, thus explaining their differences in the catalytic performance. Online TG/FT-IR further revealed that perovskite catalysts could significantly inhibit the conversion of N2O to NO, which was benefit to the enhancement of heat release. Finally, the perovskite catalysts were mixed with HTPB-based propellant to test their real application, and the results showed that perovskite containing HTPB-based propellant exhibited an increased burning rate and combustion heat, thus demonstrating their potential application in solid propellant.

Dynamic modeling and simulation of the combustion of aluminized solid propellant with HMX and GAP using moving boundary approach

This research describes the influence of nano-sized aluminum with varying contents (0–20 wt%) on the combustion behaviors of HMX/GAP/Al in aspects such as burning rate, surface temperature, gas phase temperature, mole fraction of species, and specific impulse. A rigorous mathematical model is developed for three phases (solid phase, condensed phase, and gas phase) with detailed kinetics. This model consists of 507 gas phase reactions and 4 condensed phase reactions of HMX/GAP/Al combustion. The model also emphasizes the phase transitions and reactions of aluminum in the gas phase. Based on this model, dynamic simulation is carried out at various propellant compositions and operating pressures by means of the moving boundary approach using gPROMS software package. The simulation results are in close agreement with the experimental data at slight marginal errors for HMX/Al combustion, predicting the combustion behaviors for the HMX/GAP/Al system. Accordingly, the model predicts the gas phase temperature of 3061 K for the 20 wt% Al and the specific impulse of 258.53 s for the 15 wt% Al of HMX/GAP/Al propellant under an operating pressure of 100 atm. The increase in burning rate and specific impulse by increasing the pressure is also indicated. According to this study, the addition of aluminum particles with a content range of 15–20 wt% considerably improves combustion behaviors. By dynamic modeling and simulation, a detailed framework for studying the multi-phase combustion of aluminized solid propellant is introduced.

Chemical, thermal and dilution effects of carbon dioxide in oxy-fuel combustion of wood in a fixed bed

Experimental and numerical modeling was performed on eucalyptus wood combustion under oxy-fuel conditions using a fixed bed reactor in order to isolate the role of various carbon dioxide effects on the burning rate. Wood combustion was investigated under four different mixtures of O2 and Ar/CO2/N2: 21 % O2/79 % N2; 21 % O2/22.5 % CO2/56.5 % Ar; 40 % O2/60 % CO2; and 40 % O2/47 % CO2/13 % Ar. The first three mixtures were designed to have the same peak temperatures in order to isolate chemical and dilution effects of CO2. This was achieved by substituting some percentage of CO2 with Ar in O2/CO2 mixture while maintaining a constant concentration of O2. The fourth mixture was meant to isolate the thermal effect of CO2. The results were obtained from both the experimental rig and numerical simulation for a fixed bed configuration. Wood combustion in the fixed bed was modeled using Lagrange-Euler method, where gas-phase was calculated using computational fluid dynamics (CFD), that is Euler phase, while solid-phase was tracked in Lagrange phase using discrete element method (DEM). The results show that ignition time in CO2 environment decreases gradually as O2 concentration is increased. On the other hand, burning rate and flame front speed increase as O2 concentration is increased. It was established that dilution effect is the most influential parameter on the burning rate of wood combustion in an oxy-fuel system.

Comprehensive Study of Ammonium Perchlorate Particle Size/Concentration Effects on Propellant Combustion

The effects of altering ammonium perchlorate (AP) particle size or concentration in composite AP/hydroxyl-terminated polybutadiene (HTPB) solid propellants are well documented. Existing propellant burning rate datasets include these variations, but they have significant holes in their current data span. In the current study, isophorone diisocyanate-cured composite AP/HTPB propellants were manufactured with AP mass concentrations between 70 and 87.5% and unimodal AP sizes between 20 and ; and propellant burning rates were evaluated at pressures of 3.4–21 MPa (500–3000 psia). Decreasing the AP particle size or increasing the AP concentration yielded increases in burning rate, as expected. The AP particle size effect is more drastic than that of the AP concentration. The resulting dataset was coupled with several existing propellant datasets from the literature to develop, for the first time, a simple, empirical correlation that captures these effects. The developed correlation accurately predicts the propellant burning rates for a large span of AP particle sizes and concentrations over a wide range of pressures.

Stability Analysis of the Swirling Majdalani–Fist Mean Flowfield in Solid Rocket Motors

Numerous studies have been performed to show the effects of spinning and swirling flows on increased flight stability characteristics, higher propellant consumption, increased burn rate, greater chamber pressures, and many more. The focus of this work is to understand and quantify the stability characteristics of the “swirling Majdalani–Fist” mean flowfield for solid rocket motors. The study is motivated by the need to quantify the hydrodynamic instability of the flow in cylindrically shaped solid rockets. The aforementioned mean flow profile has been adapted to the current biglobal stability framework. The biglobal stability framework developed here is not limited to a stream function formulation; instead it uses the complete Navier–Stokes equations to the extent of resulting in a linearized eigenproblem, which can be readily solved using a pseudo-spectral method. The governing equations are derived for a two-dimensional spatial wave with sinusoidal temporal dependence. Here a fully two-dimensional biglobal study is carried out using realistic boundary conditions that are consistent with solid rocket chambers. The swirling Majdalani–Fist profile results are compared with results found using the same framework with the well-known Taylor–Culick profile. Finally, future applications and areas of investigation such as headwall injection, multiphasic flow, and compressibility effects are then reviewed.

Micro-properties of Molding Products between Modified Corn Stalk and Pulverized Coal

Taking Shanxi fat coal, Shanxi 4# coke coal and Shenmu low rank pulverized coal as raw materials, three different concentrations of NaOH modified corn stalk were used as binder. The effect of changing NaOH concentrations and coal particle size used in moulding briquette and formed coke on its SEM micrographs, combustion property and FTIR absorption strength were investigated. The micro-properties of corn stalk before and after modification was also discussed. Results showed that the moisture content and ash yield of modified corn stalk increased obviously and the volatile yield showed opposite trend. 2.0% NaOH modified corn stalk showed more voids or porosity which could wrap a large number of coal particles to form strong strength briquette. Addition of modified corn stalk could reduces the briquette burning time and increased burning rate with strong flame and good ignition. From SEM micrograph, briquette had rough surface, and different sizes coal particles and fiber were bound together firmly. Formed coke showed light gray metallic luster, light mass, obvious circular holes and small gaps among particles.The melting colloid and binder could better infiltrate and encapsulate coal particles to form a dense and impermeable entity, which blocked the channels of organic group decomposition during pyrolysis process. Thus, it is forming many holes of different sizes on the surface and inside formed coke. The infrared spectrum of formed coke was simplier than briquette, and the absorption peak number was less and absorption strength was weaker also.

Triisobutylaluminum additive for liquid hydrocarbon burn enhancement

Metallizing hydrocarbons has received renewed attention as a potential means to increase energy density and burn rate. Particle agglomeration however, is a significant concern, impeding both performance as well as practical implementation due to system fouling. Achieving a metallized hydrocarbon without nanoparticles in suspension would avoid particle agglomeration problems. Previous proof-of-concept work with highly reactive organometallic Al-based clusters stabilized by ligands and dissolved in a hydrocarbon showed such a scheme is not only possible, but the decreased size of the cluster molecules relative to nanoparticles substantially increases reactivity and at least an order of magnitude less active aluminum. To increase understanding of how such burning rate effects manifest with dissolved aluminum, a higher valency alkyl aluminum historically used as a hypergol, triisobutylaluminum (IBu3Al), is dissolved in toluene and isolated droplet combustion is characterized showing up to 60% burning rate increase with 810 mM IBu3Al relative to that of pure toluene attributed specifically to the aluminum content of the additive molecule. Flame emission spectroscopy observing AlO emission supports the vital role of gas eruption and droplet disruption to transport additives into the flame.

Combustion characteristics of char from pyrolysis of Zhundong sub-bituminous coal under O2/steam atmosphere: Effects of mineral matter

In the oxy-coal combustion steam system (OCCSS), the demineralized coal is consumed by reacting with O2 and steam. The stability and efficiency of demineralized coal combustion at high steam concentrations could be a critical issue to the development of mature OCCSS technology. In this study, Zhundong coal and its acid-washed sample were used for conducting experiments. Pyrolysis chars were firstly prepared from the raw coal and the demineralized coal in a high-temperature drop tube furnace at 1200 °C. The effects of the reaction atmosphere (O2/steam and O2/N2) and temperature (1100–1400 °C) on the combustion characteristics of the two char samples were then investigated. The results show that compared to the char from pyrolysis of raw coal, the char from demineralized coal contained abundant macropores with low specific surface area. For the pyrolysis char from demineralized coal at 1200 °C, the steam-char gasification reaction rate was significantly lower than that of O2-char reaction. The presence of high concentration of steam could alter the heat/mass transfer on the char surface, thus indirectly reducing the rate of O2-char reactions. The combustion of char without minerals in an O2/steam atmosphere accelerated significantly with increasing temperature, while the increase in combustion rate with increasing reaction temperature for char containing minerals was very limited. The steam-char gasification reaction of demineralized char at 1300 °C has promoted the carbon conversion of char. The demineralized char combustion reaction required a relatively high oxygen concentration (i.e. above 40%) to show high burning rate.

Effects of enhanced tumble ratios on the in-cylinder performance of a gasoline direct injection optical engine

Improving engine efficiency and reducing pollutant emissions are the everlasting pursuit for engine researchers. While increasing tumble ratio of the engine intake airflow was shown to benefit the engine performance, rarely any systematic study has been carried out on the effect of tumble flow on engine in-cylinder performance and its mechanism. To fill in this gap, we designed tumble deflectors with desired tumble ratio using computer-aided design and computational fluid dynamics in this work. Afterwards, tumble deflectors with a tumble ratio of 1.5 and 2.2 were 3D printed. Finally firing tests of the optical engine installed with different tumble deflectors were performed. A high-speed color camera and pressure transducer were used to record crank angle-resolved flame natural luminosity and cylinder pressure. Results show that higher tumble ratio leads to faster blue flame development and less yellow flame generation, which indicates an increase in flame burning rate and a decrease of the soot formation. This is closely related to the enhanced turbulence kinetic energy before ignition as was shown in the computational fluid dynamics simulation. Besides, the engine effective pressure is increased by higher tumble ratio, but the cycle to cycle variation of flame characteristics first decreases then increases with tumble ratio.

Mechanism of flame acceleration and detonation transition from the interaction of a supersonic turbulent flame with an obstruction: Experiments in low pressure propane–oxygen mixtures

The present paper seeks to determine the mechanism of flame acceleration and transition to detonation when a turbulent flame preceded by a shock interacts with a single obstruction in its path, taken as a cylindrical obstacle or a wall in the present study. The problem is addressed experimentally in a mixture of propane–oxygen at sub-atmospheric conditions. The turbulent flame was generated by passing a detonation wave through a perforated plate, yielding flames with turbulent burning velocities 10 to 20 larger than the laminar values and incident shock Mach numbers ranging between 2 and 2.5. Time resolved schlieren videos recorded at approximately 100 kHz and numerical reconstruction of the flow field permitted to determine the mechanism of flame acceleration and transition to detonation. It was found to be the enhancement of the turbulent burning rate of the flame through its interaction with the shock reflection on the obstacle. The amplification of the burning rate was found to drive the flame burning velocity close to the speed of sound with respect to the fresh gases, resulting in the amplification of a shock in front of the flame. The acceleration through this regime resulted in the strengthening of this shock. Detonation was observed in regions of non-planarity of this internal shock, inherited by the irregular shape of the turbulent flame itself. Auto-ignition at early times of this process was found to be negligibly slow compared with the flow evolution time scale in the problem investigated, suggesting that the relevant time scale is primarily associated with the increase in turbulent burning rate by the interaction with reflected shocks.

Burning Characteristics of the HMX/CL‐20/AP/Polyvinyltetrazole Binder/Al Solid Propellants Loaded with Nanometals

AbstractThe paper investigated the effect of metal nanopowders additive on the combustion properties of HMX/CL‐20/AP/polyvinyltetrazole binder/Al propellants. Using thermal analysis, the authors described the effect of aluminum, boron, zinc, nickel, copper, and molybdenum and identified the combustion in a pressure range from 4 to 10 MPa with a pressure step of 1 MPa. No significant correlation between the oxidation properties of the n‐Me powders and the combustion properties of propellants was discovered. An addition of nanopowders caused an increase in the propellant burning rate by approximately 30 % for n‐Al, n‐B, n‐Ni, and n‐Mo independent from the pressure values. An addition of n‐Cu resulted in a burning rate increase by a factor of 4.9 due to coppers’ probable catalytic activity during interaction with nitroesters and cyclic nitramines in a solid phase. n‐Zn additive increased the propellant burning rate by factors 2.3 and 3.6 at 4 and 10 MPa, respectively, due to catalytic activity of zinc in a gaseous phase.

Combustion wave of metalized extruded double-base propellants

Aluminum metal fuel, with combustion heat of 32,000 J/g, is of interest as high energy density material. Aluminum is able to react not only with free oxygen but also with inert combustion gaseous products. This study reports on the impact of ultrafine aluminum particles on combustion characteristics of double-base propellant. Metalized double-base propellant formulations were developed by solventless extrusion process. Combustion characteristics were evaluated using small-scale ballistic evaluation test motor. There was an increase in average operating pressure, burning rate, and characteristic exhaust velocity C∗ with aluminum content. Even though there was no oxidizer available for aluminum oxidation; aluminum alone offered 7.6% increase in average operating pressure, 24.6% increase in burning rate, 7.8% increase in C∗. The main outcome of this study is that this superior performance was achieved at 4 wt% solid loading level. Aluminum particles could alter the combustion wave by increasing the combustion flame temperature, average operating pressure inside the combustion chamber, thermal conductivity of DB propellant. All these combustion criteria could decrease the thickness of the dark zone, allowing the luminous flame to be more adjacent to the burning surface; therefore the reaction could proceed faster. Even though the developed metalized DB formulations were found to be more energetic with an increase in calorific value by 4.6%; they demonstrated good thermal behavior to reference formulation using DSC. These findings confirmed that aluminum is an outstanding energetic ingredient for solid rocket propulsion. It has unique ability to react with inert gases generating substantial heat output.

Silicone bridged iron metallocene butadiene composite solid propellant binder: aspects of thermal decomposition kinetics, pyrolysis and propellant burning rate

ABSTRACTPropellant binders are essential components of composite solid propellants (CSP’s) used in launch vehicles and missiles. Binders act as a fuel and contribute directly to the combustion in conjunction with oxidizer particles and metallic fuel apart from imparting structural integrity to the solid propellant grain .The performance of CSP’s are directly related to the burn rate of the propellant. The burn rates of the ammonium perchlorate (AP) propellants are generally moderated using various types of transition metal oxide (TMO) catalysts. However, TMO’s are associated with inherently large dispersions in propellant burn rates and compromise on energetics. One of the most suitable methods for achieving lower dispersion in burn rate is using binders wherein a burn rate catalyst is grafted to the polymer matrix. In the present paper, the thermal decomposition of ferrocene bound hydroxyl terminated polybutadiene (FC-Si-HTPB) grafted to butadiene backbone via hydrosilylation was investigated The thermal degradation mechanism, stability and its effectiveness as burn rate catalyst are the most important aspects for use in CSP’s. The mechanism of decomposition of the neat resin and in combination with AP has been elucidated using pyrolysis gas chromatography–mass spectrometric technique (GC-MS). FC-Si-HTPB exhibits single stage decomposition in the temperature range of 263–491°C. The decomposition of FC-Si-HTPB with AP oxidizer follows a two stage mechanism in the 195–490°C.The char residue was characterized using FTIR, Raman spectroscopy and FE-SEM analysis, which enables to vindicate the mechanism of reaction. The activation energy for the decomposition of HTPB is 283.6 kJ/mol, FC-Si-HTPB is 251.5 kJ/mol and for Fc-Si-HTPB-AP system is 67.1 kJ/mol. The major pyrolysis products of neat FC-Si-HTPB are ferrocenyl derivatives, silylated ferrocenyl derivatives and precursors emanating from polybutadiene backbone. The propellants based on the new binder exhibited an increase in burn rate with iron content and higher fine content. A comparison of propellant burn rate with conventional micron sized ferric oxide exhibited an improvement of 34%.Based on the thermal analysis studies, the thermal endurance of the system was computed to be FC-HTPB> HTPB> FC-HTPB-AP.

Numerical simulation and validation of flame acceleration and DDT in hydrogen air mixtures

Combustion of hydrogen can take place in different modes such as laminar flames, slow and fast deflagrations and detonations. As these modes have widely varying propagation mechanisms, modeling the transition from one to the other presents a challenging task. This involves implementation of different sub-models and methods for turbulence-chemistry interaction, flame acceleration and shock propagation. In the present work, a unified numerical framework based on OpenFOAM has been evolved to simulate such phenomena with a specific emphasis on the Deflagration to Detonation Transition (DDT) in hydrogen-air mixtures. The approach is primarily based on the transport equation for the reaction progress variable. Different sub-models have been implemented to capture turbulence chemistry interaction and heat release due to autoignition. The choice of sub-models has been decided based on its applicability to lean hydrogen mixtures at high pressures and is relevant in the context of the present study. Simulations have been carried out in a two dimensional rectangular channel based on the GraVent experimental facility. Numerical results obtained from the simulations have been validated with the experimental data. Specific focus has been placed on identifying the flame propagation mechanisms in smooth and obstructed channels with stratified initial distribution. In a smooth channel with stratified distribution, it is observed that the flame surface area increases along the propagation direction, thereby enhancing the energy release rate and is identified to be the key parameter leading to strong flame acceleration. When obstacles are introduced, the increase in burning rate due to turbulence induced by the obstacles is partly negated by the hindrance to the unburned gases feeding the flame. The net effect of these competing factors leads to higher flame acceleration and propagation mechanism is identified to be in the fast deflagration regime. Further analysis shows that several pressure pulses and shock complexes are formed in the obstacle section. The ensuing decoupled shock-flame interaction augments the flame speed until the flame coalesces with a strong shock ahead of it and propagates as a single unit. At this point, a sharp increase in propagation speed is observed thus completing the DDT process. Subsequent propagation takes place at a uniform speed into the unburned mixture.

The effects of SiO2 and TiO2 on the two-phase burning behavior of aqueous HAN propellant

Silica and titania nanoparticles were included at mass loadings of 1% and 3% in aqueous HAN propellants to evaluate their effects on liquid- and gas-phase decomposition and combustion. Both the liquid-phase and overall burning rates of propellant formulations were indirectly measured in a constant-volume strand burner filled with Argon from pressures of 3–22 MPa using a novel, pressure-based method developed by the authors in recent work. This approach provides overall burn times for propellants such as aqueous HAN which continue to burn beyond the disappearance of the liquid, making it superior to methods based solely on visual observation which only monitor the liquid surface regression. The presence of silica nanoparticles increased the liquid-phase burning rate in the low- and medium-pressure regimes (<10 MPa) and increased the overall burning rate at all pressures evaluated. The maximum amount of burning rate enhancement was realized at the lowest evaluated pressure (3 MPa) which corresponded to 80% and 670% increases in the liquid-phase and overall burning rates, respectively, for a silica loading of 1%, and 160% and 830% increases in the liquid-phase and overall burning rates, respectively, for a silica loading of 3%. The presence of titania did not measurably affect the liquid-phase burning rate, but it did increase the overall burning rate in the low-pressure regime (<5.7 MPa). This low-pressure overall burning rate enhancement was not amplified by further titania loading from 1% to 3% and was maximized at the lowest evaluated pressure (3 MPa) which corresponded to a 500% increase in the overall burning rate. The observed enhancements of the propellant's liquid-phase and overall burning rates were attributed to the presence of catalytic processes which diminish at higher pressures. This work represents the first time nanoparticle additives have been utilized to tailor the combustion of liquid HAN-based monopropellants.

Catalytic Action of Submicrometer Spherical Ta/Ph‐Fe on Combustion of AP/HTPB Propellant

AbstractThis paper describes the preparation of two combustion catalysts Tannin‐Fe (Ta−Fe) and Phloroglucinol‐Fe (Ph−Fe) by spray drying. The particle size and morphology of the particles are observed by scanning electron microscopy (SEM). The results of SEM image show that the particles are regular spherical and very good dispersion. The diameter of most spherical particles is about 1 μm. The effects of Ta−Fe and Ph−Fe on the thermal decomposition of RDX and AP were tested by differential scanning calorimeter (DSC). DSC dates show that Ta−Fe and Ph−Fe can advance the high temperature exothermic peak of AP 18.0 °C and 16.1 °C, respectively. The burning rates illustrates that both Ta−Fe and Ph−Fe can significantly increase the combustion rate of HTPB propellants. The formulation with 2 mass% Ta−Fe shows an average 21.31 % increase in burning rate and has a low value of the exponent n=0.48. The formulation with 2 mass%Ph−Fe has a burning rate 20 to 60 % larger than that of the initial AP/HTPB/Al formulation, and has a lowest exponent n=0.45.

Combustion of the foamed emulsion containing biochar microparticles

Foamed emulsion containing biochar particles can serve as a perspective type of fuel for contemporary power engineering. Such a combustible system represents a multiphase system consisting of oxygen bubbles dispersed in the oil-in-water emulsion which in turn contains biochar microparticles. The paper considers the issues related with combustion of foamed emulsion containing biochar particles. In the process of experimental study we determined the dependencies of flame speed in the foamed emulsion on the concentration of biochar microparticles for different types of aliphatic hydrocarbons (hexane, heptane, isooctane and nonane). It is found that the use of biochar microparticles could lead to rather significant increase in total burning rate of the foamed emulsion. Thus, for example, the addition of biochar particles into the isooctane-based foam leads to the four-times increase in total burning rate. Herewith, the dependence of total burning rate of the foam on the biochar particles concentration is non-monotonic, so the maximum burning rate is achieved at some moderate biochar particles concentration. With the help of laser-lighted photography of multiphase flow the experimental data is obtained for the diameter of water droplets forming in the process of foamed emulsion decay during its combustion. It is obtained that biochar particles favor finer dispersing of liquid phase of the foam since they represent by themselves heterogeneous centers of vapor bubbles nucleation. In turn the diameter of water droplets defines the heat losses from the flame front and therefore the flame speed. On the basis of simple phenomenological representations we obtained the estimate for flame speed in the foamed emulsion containing biochar microparticles. Obtained relations makes it possible to substantiate the non-monotonic manner the total burning rate depends on the biochar microparticles content in the emulsion.

Aluminized composite propellant combustion modeling with Heterogeneous Quasi-One dimensional (HeQu1-D) approach

The Heterogeneous Quasi One-dimensional (HeQu1-D) model for AP/HTPB composite propellant combustion is extended to aluminized propellants. Following the serial burning approach of HeQu1-D, a statistical particle path through an aluminized propellant is taken to consist of aluminized binder-matrix coated AP particles of various sizes. Extending the idea of homogenization of fine-AP particles, aluminum particles are assumed to be homogenized with the binder-matrix. Large Al particles (nominal size ≥ 15 µm) in the binder-matrix are assumed to get ejected into the gas phase and hence do not contribute to heat feedback to the burning surface. With these modifications, the model is shown to accurately predict the burn rate variation with pressure and initial temperature of propellants using Al of nominal sizes in the range of 15–50 µm (termed conventional aluminum, CAl). The experimentally observed reduction in propellant burn rate with substitution of AP by CAl is shown to be due to the increase in fuel richness and energy sink effect of melting of Al. Catalytic effects due to addition of burn rate modifiers (Fe2O3 in space shuttle booster propellant, for instance) are also accounted for by modifications to gas phase rate parameters. Increase in burn rate up to 25% with Al particles of a few µm (3–6 µm) in comparison with non-aluminized propellant is explained by recognizing that there will be non-negligible fraction of sub-micron Al due to the associated particle size distribution. This leads to heat release by sub-micron Al combustion close to the surface and an enhancement in the heat feedback, by a combination of convective and radiative mechanisms. Dramatic increase in burn rate with sub-micron Al (a factor of 4–5 as compared to CAl) is captured by invoking radiation from fine-Al/Al2O3 particles to propellant surface. Agglomeration of sub-micron Al particles is invoked to explain the saturation of burn rate enhancement with reduction in Al particle size and the effectiveness of sub-micron Al substitution in smaller fractions (bi-modal Al). Predictions for over fifteen different propellants with varying fractions of fine and coarse aluminum from earlier literature have been presented. Comparisons of the predictions from the model with experimental results from different sources is shown to be excellent-to-good for most cases. The hitherto unknown radiation dominated ablation (r˙>50mm/s) of coarse AP particles and the effect of Al particle size on propellant temperature sensitivity are brought out. The MATLAB® code based on the model offers opportunity for design of AP-HTPB composite propellants with combination of fine and coarse aluminum with confidence.

Rare‐Earth Complexes with the 5,5′‐Bitetrazolate Ligand – Synthesis, Structure, Luminescence Properties, and Combustion Catalysis

A complete series of complexes of the lanthanides and yttrium (except radioactive Pm) with the 5,5′‐bitetrazolate (BT2–) ligand were synthesized from sodium 5,5′‐bitetrazolate and available rare‐earth (RE) salts. Eight new complexes were structurally characterized by single‐crystal XRD. The [M(BT)(H2O)7]2[BT]·6H2O [M = Pr (1), Gd (2)] complexes are isomorphous and consist of [M(BT)(H2O)7]+ ions in which only one BT2– ligand acts as a chelate for each metal center. The complexes [M(H2O)8]2[BT]3·4H2O [M = Y (3), Dy (4), Ho (5), Tm (6), Yb (7), Lu (8)] are saltlike compounds that do not exhibit any significant metal–nitrogen contacts. Luminescence was very informative for the determination of the number of inner‐sphere coordinated water molecules in the solid samples. Despite its low luminescence intensity owing to its high hydrate composition, the deuterated europium complex exhibited an internal quantum yield of 44 %. The catalytic activities of the 5,5′‐bitetrazolate salts for the decomposition and combustion reactions of energetic materials were tested. Although no effect was found for nitramine (HMX) explosive, the impact of the salts on the thermolysis of ammonium perchlorate (AP) was established. The addition of 5 % [Dy(H2O)8]2[BT]3·4H2O decreases the temperature at the maximum reaction rate by 100 °C. The catalytic effect during combustion is apparently masked by the inhibitory influence of water; however, for [Pr(BT)(H2O)7]2[BT]·6H2O, a 20 % increase in the AP burning rate was observed.