Aluminum Combustion Research Articles

Effects of Al/O on pressure properties of confined explosion from aluminized explosives

Abstract Pressure histories were tested in a 500-L chamber to identify the pressure load in confined explosion from aluminized explosives. Different aluminized explosives with Al/O, ranging from 0.25 to 1.23, were used. The recorded pressure curves could express the reflection of initial shock wave and the after burning combustion of aluminum. As there is no objective way to gain quasi-static pressure (PQS), method of multipoint averaging was used in smoothing the original pressure curves to gain the PQS. The PQS, rising time of pressure (tQS) which stands for the duration of the initial reflected shock wave, and attenuation coefficient (ω) which stands for the supportive effects of the combustion of aluminum to the PQS are used to characterize the pressure load in the confined explosion from aluminized explosives. The research results showed that the Al/O significantly affected the three characteristic quantities. With the increase of Al/O, the PQS increased at first and decreased later, gaining maximum at Al/O = 0.99; the tQS sustained growth and the ω decreased at first and increased later, gaining minimum at Al/O = 0.99.

Optimization of the Working Cycle for an Underwater Propulsion System Based on Aluminium-Water Combustion

The working cycle of a novel underwater propulsion system based on aluminium combustion with water is researched in order to evaluate the best performance. The system exploits the exothermic reaction between aluminium and water which will produce high temperature, pressure steam and hydrogen mixture that can be used to drive turbine to generate power. Several new system configurations corresponding to different working cycles are investigated, and their performance parameters in terms of net power, energy density and global efficiency are discussed. The results of the system simulation show that using the recirculation steam rather than hydrogen as the carrier gas, the system net power, energy density and efficiency of the system are greatly increased compared, however the system performance is close either using adiabatic compression or isothermal compression. And if an evaporator component is added into system in order to take full use of the solid product heat, the system performance will be improved.

Hydrogen generation for feeding high-temperature fuel cells

Several methods of hydrogen production for feeding high-temperature fuel cells in high-efficiency environmentally friendly small-scale power plants are compared. As the most promising types of energy carriers for such installations, natural gas and aluminum are considered. The possibilities of producing a hydrogen- containing feed gas for high-temperature fuel cells on the basis of technologies we develop for the environmentally friendly burning of low-calorific fuels in volumetric matrix burner devices and for the efficient burning of aluminum in a high-temperature reactor are experimentally explored. It is shown that, in the technology of localized combustion of mixtures in a methane-conversion matrix, the specific yield of feed gas for fuel cells per unit area of the outlet section of the reactor is 3 times higher than that obtained for the combustion of aluminum−water mixtures at atmospheric pressure. The total specific power of the process is also 1.85 times higher. In the technology of distributed reaction, in the bubbling of steam through an aluminum melt, the specific yield of hydrogen per unit area of the reaction surface of the bubbles is an order of magnitude greater than the specific yield of hydrogen in the “cold” reaction of aluminum with a 1 M alkaline solution.

Enhancement of Aluminum Reactivity to Achieve High Burn Rate for an End Burning Rocket Motor

AbstractAluminum is used in solid propellants to increase the specific impulse (Isp). It is desirable to have high propellant loading in any stage as it reduces the structural coefficient and an end burning grain is known to be the one with the highest propellant loading. As aluminum combustion is a slow process, the time available for aluminum combustion in an end burning configuration will be very small at the start of the combustion process. This demands an increase in the reactivity of the aluminum. This study is built on the fact that mechanical activation of aluminum powder with PTFE (poly‐tetra‐flouro‐ethylene) enhances the reactivity of aluminum powder. This study also deals with the use of this activated aluminum powder in conjunction with various other methods to enhance the burn rates of the solid propellant. The temperature sensitivity was also measured. Based on these results, new designs with end burning grains for the third stage of Polar Satellite Launch Vehicle (PSLV) and for the second and third stage of Pegasus launch vehicle have been proposed to increase the payload capacity. With this new design, it is seen that the payload can be increased by 12.7 % and 17.6 % for PSLV and Pegasus, respectively. The novelty of this design is that with no changes to any other hardware of the above two systems the increase in payload can be achieved.

Experimental investigation of the combustion products in an aluminised solid propellant

Aluminium is widely used as an important additive to improve ballistic and energy performance in solid propellants, but the unburned aluminium does not contribute to the specific impulse and has both thermal and momentum two-phase flow losses. So understanding of aluminium combustion behaviour during solid propellant burning is significant when improving internal ballistic performance. Recent developments and experimental results reported on such combustion behaviour are presented in this paper. A variety of experimental techniques ranging from quenching and dynamic measurement, to high-speed CCD video recording, were used to study aluminium combustion behaviour and the size distribution of the initial agglomerates. This experimental investigation also provides the size distribution of the condensed phase products. Results suggest that the addition of an organic fluoride compound to solid propellant will generate smaller diameter condensed phase products due to sublimation of AlF3. Lastly, a physico-chemical picture of the agglomeration process was also developed based on the results of high-speed CCD video analysis.

Numerical Simulation of a Vortex Combustor Based on Aluminum and Steam

In this paper we report a new development in the numerical model for aluminum-steam combustion. This model is based on the diffusion flame of the continuum regime and the thermal equilibrium between the particle and the flow field, which can be used to calculate the aluminum particle combustion model for two phase calculation conditions. The model prediction is in agreement with the experimental data. A new type of vortex combustor is proposed to increase the efficiency of the combustion of aluminum and steam, and the mathematical model of the two phase reacting flow in this combustor is established. The turbulence effects are modeled using the Reynolds Stress Model (RSM) with Linear Pressure-Strain approach, and the Eddy-Dissipation model is used to simulate the gas phase combustion. Aluminum particles are injected into the vortex combustor, forming a swirling flow around the chamber, whose trajectories are traced using the Discrete Phase Model (DPM). The simulation results show that the vortex combustor can achieve highly efficient combustion of aluminum and steam. The influencing factors, such as the eccentric distance of the inlet of aluminum particles, particle size and steam inlet diameter, etc., are studied.

Analytical Performance Evaluation of Superdetonative Mode Ram Accelerator; Considering Influence of Aluminum Vapor

In this study, one-dimensional analysis under the assumption of an inviscid flow was conducted for the experiment initiated by the French-German Research Institute of Saint-Louis (ISL) in order to investigate the energy effect of aluminum combustion. Previous theoretical analysis based on the assumptions of isentropic compression and a constant specific heat derived by ISL claimed that the experiment was not affected by the heat of aluminum combustion. However, rigorous analysis in present investigation that considered the average properties behind the shock wave compression and temperature-dependent specific heat showed that the S225 experiment was partially affected by the aluminum combustion. The increase in heat due to aluminum combustion was estimated from the rigorous analysis.

A detailed flame structure and burning velocity analysis of aluminum dust cloud combustion using the Eulerian–Lagrangian method

Aluminum particle dust cloud combustion with oxygen is numerically simulated using an Eulerian–Lagrangian two-phase approach. A single aluminum combustion model containing detailed aluminum combustion phenomena (melting, the heterogeneous surface reaction, alumina shell growth, combustion heat distribution, etc.) is suggested and applied to a three-dimensional, compressible CFD in-house code. High order space discretization and field variable interpolation for particle technics are employed to reduce grid dependency. Flame propagation is simulated in a slip-wall bounded open duct with well distributed aluminum particles in an O2–N2 mixture. The flame structure shows a flame zone that is longer than the pre-heating zone. This is unlike a gas phase flame, and it is due to the long combustion time needed for solid particles. The temperature behaviors of the gas and particle phase are captured reverse as the temperature rises. The dust cloud combustion model is validated by comparing burning velocities with the Bunsen burner experimental data in various oxygen and dust concentrations. Additionally, flame structure analysis is accomplished for better understandings on the behaviors of burning velocity in different conditions.

Agglomerates, smoke oxide particles, and carbon inclusions in condensed combustion products of an aluminized GAP-based propellant

In solid propellants, aluminum is widely used to improve the performance, however the condensed combustion products especially the large agglomerates generated from aluminum combustion significantly affect the combustion and internal flow inside the solid rocket motor. To clarify the properties of the condensed combustion products of aluminized propellants, a constant-pressure quench vessel was adopted to collect the combustion products. The morphology and chemical compositions of the collected products, were then studied by using scanning electron microscopy coupled with energy dispersive (SEM-EDS) method. Various structures have been observed in the condensed combustion products. Apart from the typical agglomerates or smoke oxide particles observed before, new structures including the smoke oxide clusters, irregular agglomerates and carbon-inclusions are discovered and investigated. Smoke oxide particles have the highest amount in the products. The highly dispersed oxide particle is spherical with very smooth surface and is on the order of 1–2µm, but due to the high temperature and long residence time, these small particles will aggregate into smoke oxide clusters which are much larger than the initial particles. Three types of spherical agglomerates have been found. As the ambient gas temperature is much higher than the boiling point of Al2O3, the condensation layer inside which the aluminum drop is burning would evaporate quickly, which result in the fact that few “hollow agglomerates” has been found compared to “cap agglomerates” and “solid agglomerates”. Irregular agglomerates usually larger than spherical agglomerates. The formation of irregular agglomerates likely happens by three stages: deformation of spherical aluminum drops; combination of particles with various shape; finally production of irregular agglomerates. EDS results show the ratio of O to Al on the surface of agglomerates is lower in comparison to smoke oxide particles. C and O account for most element compositions for all the carbon inclusions. The rough, spherical, strip shape and flake shape carbon-inclusions are believed to be derived from the degradation products of the binder or oxidizer, while the fiber silk is possibly the combustion product of fiber inside the heat insulation layer of the propellants. Images of products at different pressures reveal high pressure reduces the degree of agglomeration. The chemical compositions, size range and content of all the observed structures are given in this paper. Results of our study are expected to provide better insight in the working process of solid rocket motor.

Hydrogen generation by means of the combustion of aluminum powder/sodium borohydride in steam

Hydrogen generation by means of the combustion of aluminum powder with sodium borohydride (NaBH4) addition in steam was studied by a pipe furnace at different temperatures. The ignition temperature and the maximum combustion temperature were obtained by an S-type thermocouple. Ignition delay times and combustion efficiencies were measured. The results show that aluminum powder is not ignited at 450 °C, but aluminum powder with NaBH4 addition is ignited under the same condition. The addition of NaBH4 significantly decreases the ignition delay time of aluminum powder. Moreover, the ignition delay times of aluminum powder without or with NaBH4 addition can decrease with increasing the temperature. Combustion products were analyzed by scanning electron microscopy, X-ray diffraction and a portable hydrogen analyzer. The results indicate that NaBH4 displays a key influence on hydrogen generation. Especially, for aluminum powder with 7 wt% NaBH4 addition, the obtained maximum volume concentration of hydrogen is about 21,000 ppm at 650 °C.

Comments on: “Combustion of nano-sized aluminum particles in steam: Numerical modeling”, by V.B. Storozhev and A.N. Yermakov

This comment points out the large discrepancy between the predictions of the recently published model by Storozhev and Yermakov (Storozhev and Yermakov, Combust. Flame 162 (2015) 4129–4137) and the large body of accumulated literature on aluminum combustion. Their model predicts burning times between 40-63 ms for a cloud of nanometric aluminum particles (20 or 50 nm) burning in steam at initial temperatures around 2300 K. These predictions are roughly two orders of magnitude larger than the measured combustion times of micron and submicron aluminum particles from various experiments, which are on the order or hundreds of microseconds to milliseconds. Experimentally measured flame speeds of aluminum flames in the products of hydrocarbon flames, and the burn rates of metal-water propellants, also point to much faster burning rates of aluminum particles in steam than predicted by this model. As such, the predictions of the model by Storozhev and Yermakov cannot be reconciled with the available experimental evidence.

Enhancing ignition and combustion of micron-sized aluminum by adding porous silicon

Micron-sized aluminum (Al), due to its large volumetric energy density, is an important fuel additive for broad propulsion and energetic applications. However, micron-sized Al particles are difficult to ignite and react slowly, leading to problems such as incomplete combustion and product agglomeration. Many pioneering strategies have been investigated to overcome the above challenges, ranging from reducing Al particles to nanoscale, coating them with metallic or polymeric materials, to blending Al with other materials to form composites. On the other hand, porous Si has emerged as a promising energetic material with a volumetric energy density comparable to Al, high reactivity at low temperature, and ultrafast flame propagation speeds. To date, the potential of using porous Si as an additive to enhance ignition and combustion of micron-sized Al has not been explored. Herein, we experimentally investigated the effect of porous Si addition on the ignition and combustion characteristics of micron-sized Al with CuO nanoparticles. We consistently observed that the addition of porous Si facilitates both ignition and combustion of Al/CuO mixtures over a wide range of experimental conditions, ranging from slow heating rate conditions in differential scanning calorimetry, fast heating rate conditions in Xe flash ignition, flame propagation in microchannels, to constant-volume pressure vessel experiments. The enhancement effects are attributed to the easy ignition and fast burning properties of porous Si, which elevate the ambient temperature and/or pressure, and hence enhance the ignition, reaction rate, and combustion efficiency of micron-sized Al particles. This work demonstrates that adding porous Si is another viable strategy toward enhancing the ignition and combustion properties of micron-sized Al particles.

Experimental investigation on the combustion characteristics of aluminum in air

With the aim of revealing the detailed process of aluminum combustion in air, this paper reports an experimental study on the combustion of aluminum droplets. In this work, the aluminum wires were exposed and heated by a CO2 laser to produce aluminum droplets, and then these droplets were ignited and burnt in air. The changing processes of aluminum wires, droplets and flames were directly recorded by a high-speed camera, which was equipped with a high magnification zoom lens. Meanwhile, the spectrum distribution of the flame was also registered by an optical spectrometer. Besides, burning residuals were collected and analyzed by the methods of Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometer (EDS). Experimental results show that, during combustion, the aluminum droplet is covered by a spherical vapor-phase flame, and the diameter of this flame is about 1.4 times of the droplet diameter, statistically. In the later stages of combustion, the molten aluminum and condensed oxide products can react to generate gaseous Al and Al2O spontaneously. Little holes are found on the surface of residuals, which are the transport channels of gaseous products, namely the gaseous Al and Al2O. The combustion residuals are consisted by lots of aluminum oxide particles with diameters less than 1μm.

On the role of heterogeneous reactions in aluminum combustion

This work addresses the role of heterogeneous reactions occurring during aluminum combustion. Direct numerical simulations are conducted on a single aluminum burning particle accounting for both detailed gas-phase and surface kinetic mechanism. A surface kinetic solver has been developed to take into account surface and gas/surface interactions. The model is validated against experimental measurements and appears to be predictive. Calculations are performed through different pressure regimes (1 and 10 bar), atmospheres (O2, CO2, CO and H2O) and droplet sizes (from 1 to 400 µm). Flames structures (temperature and AlO profile) computed by the model are consistent with experimental measurements and observations. The reaction zones for CO and H2O atmospheres are computed to be very close to the surface which is an evidence of a combustion mostly driven by chemical surface phenomena. In some cases surface reactions promote self-sustained combustion for smaller size particles at low pressure regimes. Calculated burning times are also consistent with experimental measurements. In O2/Ar, surface chemistry is more important when particles are small (under 20 µm) which guides the combustion to a more kinetically-limited regime than a diffusion-limited regime. The importance of surface reactivity is different regarding the particle size and the atmosphere of interest. Calculations of alumina residue size reveals that surface reactions could explain alumina residue formation. The model predicts a strong oxidizer effect on alumina residue size. According to the model, CO2 environment lead to large residue size while H2O environment lead to small residue size. This work definitely stresses the potential role of heterogeneous reactions in aluminum combustion.

Effect of temperature and O2 pressure on the gaseous species produced during combustion of aluminum

Effect of temperature and O2 pressure on the gaseous species produced during the combustion of aluminum is studied using first principles calculations and considering the thermodynamics of the gas phase equilibrium composed of Al, O2, AlO, Al2O, AlO2, Al2O2 and Al2O3. AlO partial pressure dominates all the range of O2 pressures/temperatures. AlO2 is the second most abundant species at low to intermediate temperatures (1200⿿1727°C) and Al2O at higher temperatures (⿼3300°C). Al2O and Al2O2 are stable when ionized into mass spectrometer. Al2O3, AlO2 and, to a lesser extent AlO, will decompose, hindering their quantitative observation using this technique.

Culturability of Bacillus spores on aerosol collection filters exposed to airborne combustion products of Al, Mg, and B·Ti

Destruction of bioweapon facilities due to explosion or fire could aerosolize highly pathogenic microorganisms. The post-event air quality assessment is conducted through air sampling. A bioaerosol sample (often collected on a filter for further culture-based analysis) also contains combustion products, which may influence the microbial culturability and, thus, impact the outcome. We have examined the interaction between spores deposited on collection filters using two simulants of Bacillus anthracis [B. thuringiensis (Bt) and B. atrophaeus (referred to as BG)] and incoming combustion products of Al as well as Mg and B·Ti (common ingredient of metalized explosives). Spores extracted from Teflon, polycarbonate, mixed cellulose ester (MCE), and gelatin filters (most common filter media for bioaerosol sampling), which were exposed to combustion products during a short-term sampling, were analyzed by cultivation. Surprisingly, we observed that aluminum combustion products enhanced the culturability of Bt (but not BG) spores on Teflon filters increasing the culturable count by more than an order of magnitude. Testing polycarbonate and MCE filter materials also revealed a moderate increase of culturability although gelatin did not. No effect was observed with either of the two species interacting on either filter media with products originated by combustion of Mg and B·Ti. Sample contamination, spore agglomeration, effect of a filter material on the spore survival, changes in the spore wall ultrastructure and germination, as well as other factors were explored to interpret the findings. The study raises a question about the reliability of certain filter materials for collecting airborne bio-threat agents in combustion environments.

Burning Rate Calculation for a Frozen Nanosized Aluminum Suspension

The paper presents a mathematical model for combustion of a frozen nanosized aluminum suspension (ALICE), taking into account the combustion of aluminum in water vapor, the motion of combustion products, and the velocity lag of particles compared to gas. The model was formulated based on Belyaev’s approach to modeling the combustion of volatile fuels [1]. The burning rate calculated is in agreement with the experimental data on the ALICE burning rate and its variation with pressure.

Regression rate behaviors of HTPB-based propellant combinations for hybrid rocket motor

The purpose of this paper is to characterize the regression rate behavior of hybrid rocket motor propellant combinations, using hydrogen peroxide (HP), gaseous oxygen (GOX), nitrous oxide (N2O) as the oxidizer and hydroxyl-terminated poly-butadiene (HTPB) as the based fuel. In order to complete this research by experiment and simulation, a hybrid rocket motor test system and a numerical simulation model are established. Series of hybrid rocket motor firing tests are conducted burning different propellant combinations, and several of those are used as references for numerical simulations. The numerical simulation model is developed by combining the Navies–Stokes equations with the turbulence model, one-step global reaction model, and solid–gas coupling model. The distribution of regression rate along the axis is determined by applying simulation mode to predict the combustion process and heat transfer inside the hybrid rocket motor. The time-space averaged regression rate has a good agreement between the numerical value and experimental data. The results indicate that the N2O/HTPB and GOX/HTPB propellant combinations have a higher regression rate, since the enhancement effect of latter is significant due to its higher flame temperature. Furthermore, the containing of aluminum (Al) and/or ammonium perchlorate(AP) in the grain does enhance the regression rate, mainly due to the more energy released inside the chamber and heat feedback to the grain surface by the aluminum combustion.

Analysis of Aluminum Dust Cloud Combustion Using Flame Emission Spectroscopy.

In this study, aluminum flame analysis was researched in order to develop a measurement method for high-energy-density metal aluminum dust cloud combustion, and the flame temperature and UV-VIS-IR emission spectra were precisely measured using a spectrometer. Because the micron-sized aluminum flame temperature was higher than 2400 K, Flame temperature was measured by a non-contact optical technique, namely, a modified two-color method using 520 and 640 nm light, as well as by a polychromatic fitting method. These methods were applied experimentally after accurate calibration. The flame temperature was identified to be higher than 2400 K using both methods. By analyzing the emission spectra, we could identify AlO radicals, which occur dominantly in aluminum combustion. This study paves the way for realization of a measurement technique for aluminum dust cloud combustion flames, and it will be applied in the aluminum combustors that are in development for military purposes.

Combustion and detonation of mechanoactivated aluminum–potassium perchlorate mixtures

The properties of mechanoactivated energetic composites based on aluminum and potassium perchlorate with high rates of self-sustaining chemical reactions under conditions of combustion and detonation are examined. The results of experiments on studying the combustion, deflagration-to-detonation transition, and sensitivity to friction of these composites are reported. The activation duration and aluminum content in the mixture are varied. The experiments on the deflagration-to-detonation transition of mechanoactivated composites are supplemented by the results of numerical simulations. The calculations and experiments on the dynamics of development of a blast wave and on the steady detonation velocity are found to be in qualitative agreement. It is shown that the velocity of the observed process is significantly (by about 40%) lower than the normal detonation velocity obtained from thermodynamic calculations.