Aluminum Combustion Research Articles

A Review on the Gas‐Phase Modeling Study of Aluminum Combustion in Various Environments

AbstractAluminum combustion is an area of intense research due to its wide‐ranging applications in the aerospace, automotive, energy storage carrier and defense industries. Gas‐phase reaction mechanism plays an important role on the prediction of the combustion intermediates and final products, which can significantly affect the combustion heat releases and combustion organization forms. In recent years, researchers have developed some gas‐phase reaction mechanisms to predict the combustion phenomenon and behavior of aluminum in different environments. This review aims to provide an overview of the current state of the art in gas‐phase modeling study on aluminum combustion with various oxidizers, including oxygen, steam, carbon dioxide and so on. The primary oxidation reactions of aluminum were concluded, and the rate coefficients of these reactions were also reviewed and compared in this work. Besides, the simulations by using the gas‐phase reaction mechanisms were reviewed and the main oxidation reaction pathways of aluminum with various oxidizers were analyzed based on modeling analysis results. Combining phase change reactions and surface reactions, gas‐phase reaction mechanism will become more important for prediction the combustion speed, combustion temperature and combustion mode of aluminum in future.

Numerical study of aluminum combustion with agglomerate size distribution in solid rocket motor

The aluminum agglomerate size distribution plays an important role in influencing the particle distributed combustion in motor, which subsequently affects the performance of solid rocket motor significantly. In this work, a three-phase model to describe distributed combustion of aluminum agglomerates is established based on the Eulerian-Lagrangian method. Then, the agglomerate size, including mono size and distributed size, is studied to reveal its effect on aluminum combustion and motor flow field. The simulated results indicate that the increasing agglomerate mono size observes the obvious decrease of the average temperature inside the motor combustion chamber, implying the low combustion efficiency of large agglomerate size. When considering the agglomerate size distribution, the size distribution mode and the mean size D43 determine the combustion efficiency together. In particular, even the mean size is similar, with different distribution mode, like skewed distribution, bimodal or trimodal distribution, the combustion efficiency and flow field parameters are nonnegligible different. However, when the size distribution mode is the same and the peak range is similar, the mean size D43 becomes the only and predominant factor as the mono size.

Mass Velocity Profiles for Non-Ideal Detonation of Mixtures of Nitromethane and Ammonium Perchlorate Overloaded with Aluminum. Measurements and Calculation

Earlier, by comparing the results of mathematical modeling with experimental data on the non-ideal detonation velocities of triple mixtures of nitromethane and ammonium perchlorate with aluminum excess, the rates of exothermic reactions and the consumption degree of components within the detonation wave reaction zone were determined. A quasi-one-dimensional model of steady detonation was used for calculations, in which all components have a common pressure and move with a common mass velocity, and exothermic conversion is carried out in three stages, which include decomposition of nitromethane and ammonium perchlorate and diffusion combustion of aluminum. To confirm the obtained results and the applicability of the relatively simple theoretical model, calculations of the mass velocity profile during detonation of one of the triple mixtures with 17% nitromethane have been carried out. The calculation results are in agreement with the measured mass velocity profile, concerning the shape of the profile, the amplitude and the rate of decrease of the mass velocity along the detonation reaction zone. A possible explanation of a “leaning” of the beginning portion of the mass velocity profile observed in experiments has been proposed, and an estimate of the rise time of the sensor signal is given, taking into account the calculated curvature of the shock front of the detonation wave.

Effect of aluminum and ammonium perchlorate particle sizes on the condensed combustion products characteristics of aluminized NEPE propellants

Aluminum (Al) is usually added to solid propellants to improve the combustion performance, however the condensed combustion products (CCPs) especially the large agglomerates generated from aluminum combustion can reduce the specific impulse of the engine, and result in two-phase loss, residue accumulation and throat liner ablation. Al and ammonium perchlorate (AP), as important components of NEPE propellants, can affect the formation process of the CCPs of aluminized NEPE propellants. To clarify the effect of Al and AP particle sizes on the properties of the CCPs of aluminized NEPE propellants, a constant-pressure quench vessel was adopted to collect the combustion products of four different formulations of NEPE propellants. It was found that the condensed combustion products are mainly divided into aluminum agglomerates and oxide particles, the diameter of the aluminum agglomerates of these four different formulations of NEPE propellants at 7 MPa was smaller than that in 3 MPa, and the shells of the aluminum agglomerates were smoother and the spherical shape was more perfect. X-ray diffraction analysis of the CCPs of the four NEPE propellants under 3 MPa revealed the presence of both Al and Al2O3. With the increase of the particle size of Al and AP, the oxidation degree of aluminum particles decreases. The particle size of the CCPs of the four different formulations of NEPE propellants under 1 and 3 MPa was analyzed by using a laser particle size analyzer, it is found that the increase of AP particle size is helpful to reduce the size of condensate combustion products. Based on the classical pocket theory, establishing a new agglomeration size prediction model, which can be used to predict the agglomeration size on the burning surface. Compared with the empirical model, the new agglomeration size prediction model is in good agreement with the experimental results.

Combustion and heat release characteristics of micron aluminum with extremely large specific surface area obtained by L-malic acid surface corrosion

Aluminum (Al) particles are widely used in propellants, thermite and pyrotechnics. However, commonly used micro Al has drawbacks such as agglomeration, high ignition temperature and slow burning rate, making its energy potential not fully exploited in applications. Therefore, exploring pathways to enhance the combustion of Al particles has become the focus at present. Herein, L-malic acid (LMA) was used to corrode the surface of Al particles to obtain a sample (named LMAl) with an average specific surface area of 11.456 m2/g (corresponding to Al particles with a diameter of 194 nm). The particle size distribution of LMAl did not change significantly compared to pristine Al. The XPS results showed that a small amount of LMA and corrosion products remained on the surface of the LMAl particles. Thermal analysis tests showed that the thermal oxidation rate and efficiency of LMAl was dramatically higher than that of pristine Al. Compared with the pristine Al, the combustion characterization parameters of LMAl such as combustion intensity, ignition delay time, maximum combustion temperature, mass burning rate and combustion efficiency were all improved. This trend was maintained after blending the ammonium perchlorate (AP). The condensed combustion products (CCPs) of Al revealed a large number of agglomerates and unburned Al particles. While many broken particles and tentacle-like structures were found in the CCPs of LMAl. Overall, compared to Al, the combustion of LMAl is significantly enhanced. The thermal reaction and combustion behaviors of the two are quite different. This study provides new insights into improving the ignition and combustion of Al.

Comprehensive modeling of ignition and combustion of multiscale aluminum particles under various pressure conditions

The ignition and combustion of aluminum particles are crucial to achieve optimal energy release in propulsion and power systems within a limited residence time. This study seeks to develop theoretical ignition and combustion models for aluminum particles ranging from 10 nm to 1000 μm under wide pressure ranges of normal to beyond 10 MPa. Firstly, a parametric analysis illustrates that the convective heat transfer and heterogeneous surface reaction are strongly influenced by pressure, which directly affects the ignition process. Accordingly, the ignition delay time can be correlated with pressure through the pb relationship, with b increasing from –1 to –0.1 as the system transitions from the free molecular regime to the continuum regime. Then, the circuit comparison analysis method was used to interpret an empirical formula capable of predicting the ignition delay time of aluminum particles over a wide range of pressures in N2, O2, H2O, and CO2 atmospheres. Secondly, an analysis of experimental data indicates that the exponents of pressure dependence in the combustion time of large micron-sized particles and nanoparticles are –0.15 and –0.65, respectively. Further, the dominant combustion mechanism of multiscale aluminum particles was quantitatively demonstrated through the Damköhler number (Da) concept. Results have shown that aluminum combustion is mainly controlled by diffusion as Da > 10, by chemical kinetics when Da ≤ 0.1, and codetermined by both diffusion and chemical kinetics when 0.1 < Da ≤ 10. Finally, an empirical formula was proposed to predict the combustion time of multiscale aluminum particles under high pressure, which showed good agreement with available experimental data.

Hydration-induced plasma surface modification of aluminum nanoparticles for power generation in oxygen deficient environments

An approach to increase the energy release rate from aluminum (Al) combustion is to modify the alumina (Al2O3) passivation shell surrounding the Al fuel core. One approach uses atmospheric plasma treatment to physically reduce the Al2O3 shell thickness while simultaneously exposing the defected surface to water vapor to promote surface hydration. Combining water-vapor with an atmospheric helium dielectric barrier discharge (DBD) plasma yields a thinner Al2O3 shell with double the surface hydration compared to as-received aluminum nanoparticles (nAl). Non-equilibrium combustion studies on plasma-treated nAl particles demonstrate increased energy release rates owing to the thinned shell and reduced diffusion barrier. Adding hydration further provides more oxidizer species in molecular scale proximity to the core such that the thinned and hydrated shell increased the initial pressurization rate by 50 % compared to as-received nAl. The results introduce a method to modify the native oxide surface and a strategy to control energy release rates from metal particle combustion.

Effect of flame radiation on aluminium particle combustion time

This work proposes a numerical model to estimate the radiant heat feedback from the flame of a burning aluminium particle. The objective is to evaluate its role on the burning time. It rests on a detailed combustion simulation of a single particle coupled with a simple two-flux approximation for the radiant flux emitted from the oxide smoke. Radiated flux from the flame is found to be around 1 MW/m 2 for atmospheric pressures, going up to more than 5 MW/m 2 for higher pressures (30 bar). Parametric simulations show that aluminium size has a small effect while oxygen-rich atmospheres can double the radiated flux. Overall, the role of flame radiation on aluminium burning rate is calculated to lie roughly between 1 and 25%, depending on conditions. This is the first study that clearly evaluates the role of flame radiation on aluminium combustion ; in most configurations, this effect, however, remains limited.

VOF based model of numerical simulation for single aluminum droplet evaporation and combustion

ABSTRACT This study investigates the combustion of a single aluminum droplet in a high-temperature convective setting, focusing on the interplay between the environment and droplet evaporation combustion. Using the VOF numerical method, a two-dimensional multiphase flow combustion model for micron-sized aluminum droplets is developed. Experimental validation compares predicted droplet diameter with experimental data. The combustion behavior of aluminum droplets in high-temperature convective environments is analyzed, emphasizing gas-phase combustion during stable stages. Parametric variations in flow velocity and oxygen concentration reveal the formation of vortices around the droplet, influencing aluminum vapor accumulation and evaporation rates. Combustion primarily occurs at the droplet’s windward side, with reaction rates decreasing downstream. Increasing gas velocity from 1.5 m/s to 3 m/s thins the aluminum vapor concentration boundary layer, boosting combustion rates by 35%. Elevating oxygen concentration from 20% to 50% brings the flame closer to the droplet, accelerating combustion rates by 2.7 times, suggesting oxygen concentration’s role in reaction acceleration and combustion duration reduction. This research offers insights for simulating aluminum droplets in propellant applications.

VALIDATION OF THE MODEL OF HYBRID DETONATION OF HYDROGEN-AIR MIXTURES WITH ALUMINUM PARTICLES

Verification and validation of the model of the reduced kinetics of hybrid detonation in hydrogen-air mixtures with fine aluminum particles was carried out. The formula of integral heat release is obtained depending on the fuel excess coefficient for poor hydrogenair mixtures. The results are consistent with experimental data on the detonation rate. The constants of the aluminum combustion reactions are determined, which ensure the coordination of the detonation rate in air suspensions of aluminum particles. The processes of gas detonation in hydrogen-air mixtures and hybrid detonation with aluminum particles are numerically modeled. The dependencies of the hybrid detonation rate on the particle concentration are consistent with the known data. The comparison with experiments on cellular gas and hybrid detonation patterns is carried out: the degree of regularity, the size of the cells, the slope of the trajectories of triple points.

Experimental investigation on synergistic slow oxidation and rapid combustion of micron-sized iron and aluminum powders for energy storage application

The investigation into the individual application of iron and aluminum as carbon-free fuel sources has been extensively explored and holds significant promise. However, there remains a gap in understanding synergistic effects achievable through the blending of these two fuels, as well as a need for comparative analyses between the slow oxidation and rapid combustion processes of these fuels to complement each other. This research proposes blending micron aluminum and iron powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The research blending micron iron and aluminum powders to analyze their slow oxidation and rapid combustion features under diverse atmospheric conditions and heating rates, using thermogravimetric methods, kinetic calculations, and in-flow experiments. The findings reveal that the combination of aluminum and iron powders promotes oxidation, resulting in increased weight gain and heat flux rate compared to individual metals. Moreover, the triggering temperature rises from 545 to 652 °C with an increase in aluminum powder content. As heating rates increase, characteristic parameters T1, T2, and Hpeak2, rise for both fuels. However, aluminum powder tends to decrease Ti, while iron powder slightly increases it due to differences in oxide layers. The slow oxidation of aluminum and iron powders conforms to different models, yielding distinct oxidation patterns. The apparent activation energy of aluminum decreases from 258.4 to 238.7 kJ·mol−1 with rising heating rates, while that of iron exhibits a lower increase and remains lower than aluminum providing insights into combustion initiation conditions. Combustion initiation is contingent upon the concentration of metal powder and oxygen, with both aluminum and iron powders combustion being enhanced and subsequently attenuated with increasing excess air ratio. However, due to differing reactivity and surface passivation layers, the excess air ratio required for aluminum powder combustion (1.2–2.4) exceeds that of iron powder (1.3–1.7). The research elucidates the mechanisms underlying the slow oxidation of iron and aluminum fuels, delineates suitable combustion conditions, and furnishes new empirical and theoretical underpinnings for the oxidation characteristics of mixed iron-aluminum fuels, thereby advancing metal-fueled energy storage technologies.

Exploring the combustion mechanism of single micron-sized aluminum particles with a numerical model

In this work, we explore the combustion mechanism of single micron-sized aluminum particles using a numerical model. The Burcat database and Catoire mechanism is considered as the thermodynamic data and the kinetic mechanism for our numerical model of aluminum combustion. Two independent experiments, including particle temperature profiles, ignition delay and burning time, are selected to evaluate the performance of the numerical model. The model shows great agreement for all considered properties. A parametric study is further conducted to identify the effect of involved physical parameters on the combustion process. The diffusion coefficient (D) of oxidizers and the activation energy of surface kinetics (Esurf) and evaporation coefficient (α) of aluminum impact the particle temperature the most. Burning time is most sensitive to the activation energy of surface kinetics (Esurf). The optical measurement in a solid propellant combustion indicates that the contact angle of the oxide cap on Al particle is between 10° and 20°. It is found that the selection of contact angle of the oxide cap significantly impacts the prediction of combustion time and residual of active aluminum. The current work highlights the importance of physical properties on the prediction of Al combustion, suggesting that more detailed evaluation from experiments and theory is encouraged.

Ignition and combustion characteristics of aluminum-based fluorine-containing composite powder

To improve the combustion characteristics of micron-sized aluminum (Al) powder, a composite powder was prepared by doping a small amount (15 wt%) of magnesium fluoride (MgF2), polytetrafluoroethylene (PTFE), and fluorinated graphite (FG) into the aluminum powder through solution dispersion method. The physical phase composition, micro morphology, thermal reactivity, and combustion performance of the composite powders were also characterized. The findings suggest that the promoting effect of the three fluorides on aluminum combustion can be ranked in the following descending order: FG > PTFE > MgF2. The fluorides can to erode the Al2O3 shell layer directly, thus creating cracks and reaction pathways for the Al core enclosed within the shell. Moreover, the gasification of AlF3 within the combustion products can escape from the surface of Al particles and promote the oxidation combustion of the exposed aluminum, which enhances the diffusion reaction on the active aluminum surface.

STUDY OF CATALYTIC BEHAVIOURS OF THE SPINEL STRUCTURE NdxMg1- xAl2O4 COMPOSITION WITH ZSM-5 ZEOLITE IN ETHYLBENZENE DISPROPORTIONATION

Nanosized (10–15 nm) powders of spinel structures NdxMg1–xAl2O4 were obtained by low-temperature combustion of aluminium, magnesium, neodymium nitrate solutions, diethylmalonate, and hydrazine monohydrate with further calcination of nanopowders at 1000 °C, which were used in the preparation of catalytic compositions with ZSM-5 zeolite. The obtained catalytic compositions were characterized by X-ray diffraction, pyridine adsorption, and low-temperature nitrogen adsorption. The acidic properties and porosity of the catalysts were altered by controlling the concentration of nanopowder (1.0–7.0 wt.%) in the catalytic composition. The interaction of the modifier with HZSM-5 zeolite leads to a decrease in specific surface area and pore volume, as well as reduse of strong Bronsted acid sites (B) and an increase in the concentration of medium Lewis acid sites (L), resulting in a change in the B/L ratio from 3.61 to 0.23. The ongoing variations contributed mainly to an enhancement of the para-selectivity of the catalytic composition in the ethylbenzene disproportionation reaction. The catalytic composition of 5% Nd0.1Mg0.9Al2O4 with a pore volume of 0.15 cm3/g and an acid site B/L ratio of 0.27 demonstrates a maximum selectivity to p-diethylbenzene of 75.6% with a conversion of ethylbenzene of 23.7%.

Experimental and numerical investigation on thermochemical erosion and mechanical erosion of carbon-based nozzles in hybrid rocket motors

In order to enhance energy characteristics of propellants in hybrid rocket motors, aluminum particles are added into the solid fuel. However, these particles may lead to nozzle mechanical erosion, which significantly affects the motor performance. This paper intends to study thermochemical and mechanical erosion mechanism of carbon-based nozzles in hybrid rocket motors with aluminum metallized fuel. A firing test is performed, and 95 % hydrogen peroxide and hydroxyl‑terminated polybutadiene based fuel with aluminum particles are utilized. Experimental results show that many metal particles are ejected from the nozzle, and aluminum oxide deposits heavily on the nozzle inner surface. A method of numerical calculation coupled with two-phase flow, combustion of aluminum metallized fuel, thermochemical ablation reactions, and mechanical erosion is established. The errors of combustion chamber pressure and throat erosion rate between numerical calculation and test results are 0.53 % and 7.76 %, respectively. Simulation results indicate that with the increase of aluminum content, nozzle wall pressure gradually increases, while the mass fraction of H2O, CO2, OH, and O declines. The nozzle wall temperature and thermochemical erosion rate raise first and then reduce as aluminum content increases. The mechanical erosion is mainly distributed in the convergent section, and it raises with the increase of aluminum content. When aluminum content is up to 38 %, the maximum mechanical and thermochemical erosion rates are 0.09185 mm/s and 0.0976 mm/s, respectively. This reveals that effects of mechanical erosion on hybrid rocket nozzles should be carefully considered and evaluated under conditions of high aluminum content.

Dual-range emission spectroscopy for temperature measurement of laminar aluminum dust flames

Understanding the temperature fields/profiles in aluminum dust flames is critical to the design of aluminum-based sustainable fuels and the development of aluminum combustion simulation tools. Although emission spectroscopy has been applied in aluminum flames, the signals in most works were integrated along the recording path and over the whole flame and, therefore, the measurements could not provide information of the flame spatial structure. In addition, the details of the diagnostic method were scarcely introduced. This work develops a dual-range emission spectroscopy diagnostic system for 1D measurements of the liquid temperature and the flame temperature of aluminum flames. The important aspects for diagnostics, such as the instrument specifications, signal acquisition strategy, data processing, accuracy and precision, are introduced and quantified in detail. The continuous spectrum from the liquid phase of Al(L) and/or Al2O3(L), rovibrational AlO spectrum from the micro-diffusion flame, and 2D flame luminosity are recorded simultaneously. Based on Planck's law, a linear fitting method is implemented to derive a continuous spectrum temperature. A nonlinear minimization framework based on the stick spectrum is introduced to fit the AlO spectra and derive a AlO temperature. The accuracy and precision are quantified by a comparison of the average temperatures against the equilibrium temperatures and the standard deviations. The effectiveness of this technique for temperature measurements of aluminum dust flames is verified by the agreement of the continuous spectrum temperature and the AlO temperature in the post-flame region. The 1D distribution of the continuous spectrum temperature indicates the boiling of Al and the dissociation/condensation of Al2O3 from upstream to downstream through the flame. The 1D temperature distributions also present a lag of the continuous spectrum temperature compared to the AlO temperature, indicating that the continuous spectrum temperature is dominated by the Al fuel droplets and the Al2O3 caps, instead of the Al2O3 nanometric droplets.

Effect of AP coating or blending on the ignition and combustion of Al particles under a high-pressure water vapour–Ar environment

Overcoming the difficulty of ignition and combustion of aluminium in water vapour is the key to being applied in underwater propellant applications. The effect of coating or blending 20 mass% ammonium perchlorate (namely, AP@Al or AP–Al samples) on the ignition and combustion of Al particles in a 1.0 MPa water vapour–Ar environment was investigated using a constant temperature pressurized combustion chamber and a CO2 laser. The results show that the combustion of Al particles in a water vapour–Ar environment is a non-homogeneous reaction and that agglomeration processes of Al droplets are observed. The ignition and combustion properties of the AP@Al and AP–Al samples under water vapour were greatly improved due to the decomposition of AP for heat/oxygen (particularly, O2 provided a new pathway for AlO(g) generation) supply and the effect of dispersed particles. The maximum pressure change and combustion temperature (Tmax) were increased significantly for the AP@Al and AP–Al samples combustion, while their ignition delay time (ti) and combustion time (tc) decreased remarkably. In addition, the coating form is more effective in the combustion-promoting effect of AP than the blending form. Interestingly, the increase in water vapour concentration is not conducive to the ignition and combustion of samples in this work. It is probably because the reaction system is lean-fuel where the excess water vapour absorbs some of the heat and prevents effective collisions among the radicals. In addition, the chemical equilibrium largely influences the combustion temperature, resulting in a conspicuous effect of changes in water vapour concentration on the Tmax values. The reaction interface largely influences the combustion reaction rate of Al, so changes in particle size have a significant effect on the ti and tc values.

A new fluorocarbon adhesive: Inhibiting agglomeration during combustion of propellant via efficient F–Al2O3 preignition reaction

AbstractInhibiting the agglomeration of molten aluminum particles packed in the binder network is a promising scheme to achieve efficient combustion of solid propellants. In this investigation, the hydroxyl‐terminated structured fluorinated alcohol compound (PFD) was introduced to modify the traditional polyethylene glycol/polytetrahydrofuran block copolymerization (HTPE) binder; that is, a unique fluorinated polyether (FTPE) binder was synthesized by embedding fluorinated organic segments into the HTPE binder via crosslinking curing. The FTPE was applied in aluminum‐based propellants for the first time. Due to the complete release of fluorinated organic active segments in the range of 300°C to 400°C, the burning rate of FTPE‐based propellant increased from 4.07 (0% PFD) to 6.36 mm/s (5% PFD), increased by 56.27% under 1 MPa. The reaction heat of FTPE propellants increased from 5.95 (0% PFD) to 7.18 MJ/kg (5% PFD) under 3.0 MPa, indicating that HTPE binder modified with PFD would be conducive to inhibiting the D90 of condensed combustion products (CCPs) dropped by 81.84% from 75.46 (0% PFD) to 13.71 μm (5% PFD) under 3.0 MPa, in consistent with the significant reduction of aluminum agglomerates observed on the quenched burning surface of the propellants. Those results demonstrated that a novel FTPE binder with PFD can release fluorinated organic active segments, which motivate preignition reaction with the alumina shell in the early stage of aluminum combustion, and then enhance the melting diffusion effect of aluminum to inhibit the agglomeration.

COMBUSTION OF ALUMINUM PARTICLES IN A STREAM OF STEAM

Several models for aluminum combustion have been proposed, thus an overview of the combustion characteristics of aluminum powders is presented, taking into account both early and recent research activities and distinguishing between micron-sized and nano-sized aluminum. A collection of models for the two classes is discussed and compared, considering different environments in terms of oxidizers (H&lt;sub&gt;2&lt;/sub&gt;O, O&lt;sub&gt;2&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;), diluents (N&lt;sub&gt;2&lt;/sub&gt;, Ar), temperature and pressure. In particular, the oxidation and the combustion of aluminum in steam are addressed, highlighting the oxidizing capabilities of various species. Different models are implemented for the complete description of aluminum combustion in the micron range, since smaller particles (1-10 &amp;mu;m) burn differently from bigger ones: both kinetics-based and diffusion-based processes are analyzed, stressing the role of reaction paths as well as diffusive phenomena. A single mechanism (kinetics-based) is identified and modeled for the combustion of nano-sized aluminum, outlining the limits and hypotheses for the application. For both sizes, only homogeneous reactions are considered and a model for the growth of an oxide cap on the surface of the particle is implemented. The results obtained are compared to the available numerical simulations and experimental evidence, aiming at the approximation of the burning time through the D&lt;sup&gt;n&lt;/sup&gt; law. Also, the profile over time of the temperature, the radius of the particle and the concentrations of the different chemical species involved in the reactions are analyzed.

A PHYSICAL MODEL FOR THE PREDICTION OF ALUMINUM OXIDE RESIDUES

This work proposes a new model to estimate the size of oxide residues produced during the combustion of aluminum. Such large oxide residues contribute to the two-phase loss performance in solid rocket motors. The model includes two physical mechanisms: deposition of oxide smoke from the surrounding flame and oxide creation on aluminum surface by heterogeneous reactions. Parametric numerical simulations at the aluminum droplet scale are performed to estimate the rate of deposition and surface production, in order to feed a zero-dimensional model of oxide lobe growth and final oxide residue. Results are in line with available measurements with an oxide residue-to-aluminum size ratio in the range 0.5 &amp;#126; 0.8, depending on conditions. The model suggests that surface reactions are important for low pressures and small particles, while deposition prevails otherwise.