Browsing by Author "Altman, Igor"

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Comprehending Metal Particle Combustion: a Path Forward
(2022) Altman, Igor; Pantoya, Michelle L. (TTU)
The paper discusses the physics required for accurate modeling of metal particle combustion and includes aspects previously neglected. Specifically, three physical phenomena are emphasized: 1) internal boiling on the condensed oxide-metal interface; 2) condense-luminescent loss during nano-oxide formation; and, 3) suppressed heat transfer on the metal particle surface due to a low energy accommodation coefficient (EAC) are essential. The last two phenomena were explored in previous work. Internal particle interface boiling detailed in the current work enables the semi-heterogeneous combustion of Al particles, an important process needing attention for accurate modeling. The interface boiling mechanism allowing for the semi-heterogeneous combustion explains a number of experimental puzzles related to metal particle combustion. In particular, the semi-heterogeneous combustion justifies the coexistence of two burning regimes of Al particles (slow and fast) recently observed. Based on reported findings, revising current numerical models for metal particle combustion to include these three physical phenomena is necessary. Implications toward enhancement of energetic performance for metal-containing formulations are also discussed.
Condense-luminescence and global characterization of metal particle suspension combustion
(2022) Tran, Quan (TTU); Pantoya, Michelle L. (TTU); Altman, Igor
Thermal processing of aluminum (Al) particles such as annealing followed by rapid quenching had been previously shown to affect single metal particle burning rates. This study extends single particle combustion to a global material-based energy exchange model. Experiments were designed to investigate the global energy exchange resulting from Al powder suspensions processed to induce different (fast and slow) burning regimes. Thermally processed and untreated Al particles were reacted as suspended powder in a closed bomb calorimeter. The calorimeter monitored the transient temperature changes resulting from energy release upon powder combustion. The product residue was analyzed for species concentration using X-ray diffraction. Results link the phase fractions of the aluminum oxide combustion products with global radiant fluxes in the calorimeter system. Metastable alumina associated with nano-oxide formation is in substantially higher concentration for thermally processed powder reactions and also produces greater energy transfer rates. The increased energy transfer rates correspond to higher radiant energy emission which may result from condensation energy associated with nano-oxide particle formation. This study qualifies condense-luminescence as a means for increasing the energy release rates of aluminum particles. By strategically altering metal fuels to control formation of nano-oxide particles upon combustion, appreciable increases in the radiant energy flux can transform energy release rates.
Demonstrating the significance of radiant energy exchange during metal dust combustion
(2023) Jones, Harrison; Dube, Pascal; Tran, Quan (TTU); Pantoya, Michelle L. (TTU); Altman, Igor
Metal combustion is a process accompanied by strong light emission. Correspondingly, radiative loss can significantly affect the overall energy balance, and needs to be considered in the global numerical models describing metal dust combustion. In this work, we experimentally estimated the fraction of radiative loss during aluminum (Al) dust combustion by studying the heat release in a modified constant volume bomb calorimeter that enabled the additional measurement of pressure. The previously developed method of dispersing powder ensured nearly 100% combustion efficiency. The contribution of the combustion energy to heating the gas inside the calorimeter bomb was determined by analyzing the measured pressure traces and found to be measurably lower than 100%. The energy loss was attributed to radiant heat transfer from burning metal particles to the bomb wall. Aluminum powders with median size ranging from 4 μm to 100 μm were studied. The estimated fraction of radiative loss depended on the particle size. Radiative loss saturated at nearly 50% for larger particles and gradually reduced with the particle size decrease below 20 μm. We related the observed radiative loss to a recently introduced process that occurs during metal combustion, namely condense-luminescence. The results shown here have important implications for the role of radiant energy exchange in metal particle combustion and will transform future approaches to harnessing metal oxidation energy for a multitude of applications.
Direct demonstration of complete combustion of gas-suspended powder metal fuel using bomb calorimetry
(2022) Tran, Quan (TTU); Altman, Igor; Dube, Pascal; Malkoun, Mark; Sadangi, R; Koch, Robert; Pantoya, Michelle L. (TTU)
Off-the-shelf calorimeters are typically used for hydrocarbon-based fuels and not designed for simulating metal powder oxidation in gaseous environments. We have developed a method allowing a typical bomb calorimeter to accurately measure heat released during combustion and achieve nearly 100% of the reference heat of combustion from powder fuels such as aluminum. The modification uses a combustible organic dispersant to suspend the fuel particles and promote more complete combustion. The dispersant is a highly porous organic starch-based material (i.e. packing peanut) and allows the powder to burn as discrete particles thereby simulating dust-type combustion environments. The demonstrated closeness of measured Al heat of combustion to its reference value is evidence of complete metal combustion achieved in our experiment. Beyond calorific output under conditions simulating real reactive systems, we demonstrate that the calorimeter also allows characterization of the temporal heat release from the reacting material and this data can be extracted from the instrument. The rate of heat release is an important additional parameter characterizing the combustion process. The experimental approach described will impact future measurements of heat released during combustion from solid fuel powders and enable scientists to quantify the energetic performance of metal fuel more accurately as well as the transient thermal behavior from combusting metal powders.
Establishing calibration-free pyrometry in reactive systems and demonstrating its advanced capabilities
(2023) Jaramillo, Nicholas R. (TTU); Ritchie, Cole A. (TTU); Pantoya, Michelle L. (TTU); Altman, Igor
A calibration-free multi-color pyrometry data analysis approach for determining the temporal change in the reciprocal temperature by only comparing the photomultiplier tube (PMT) responses to the system light emission is introduced. For Arrhenius reactions, analyzing the reciprocal temperature is particularly relevant for evaluating reactivity. The high accuracy of the proposed method is provided by eliminating the calibration step, which is made possible by considering the ratio of PMT signals as a function of time. The developed methodology is applicable to systems with continuous light emission spectra of the thermal nature that originate from condensed particulates. A demonstration of the data analysis approach was performed using aluminum powder burning in air. Four PMTs detected light emission during combustion that enabled analysis of six detector combinations to obtain a time-dependent signal ratio. Based on the temperature-dependent nature of light emission, the PMT response ratio provided the value of the reciprocal temperature change. All six detector combinations generated precisely coinciding results within time periods where the light emission trace behavior was relatively smooth that validated the data processing approach. It was also found that a non-smooth behavior of light emission led to significant deviations between outputs of different PMT combinations. This inconsistency between outputs was an indication of multi-temperature light emission whereas consistency between outputs corresponds to the single-temperature emission behavior. Using the calibration-free data processing approach, we isolated time periods where multi-temperature radiation is essential. Then, we further decoupled contributions from non-monotonic light emission signals and resolved two distinct temperatures responsible for observed radiation peculiarities.
Thermite and intermetallic projectiles examined experimentally in air and inert gas environments
(2022) Croessmann, Charles Luke (TTU); Cagle, Colton (TTU); Dube, Pascal; Abraham, Joseph; Altman, Igor; Pantoya, Michelle L. (TTU)
Intermetallic (aluminum and zirconium) and thermite (aluminum and molybdenum trioxide) projectiles were launched using a high velocity impact ignition testing system. The experiments were designed to simulate reactivity in high (argon) and low (air) altitude environments. The projectiles were launched into a chamber that included a steel target plate for projectile penetration before impacting a rear witness plate. The chamber was semi-sealed and instrumented for quasi-static pressure data. The results provide an understanding of energy release from the projectile materials and of the environmental influence on performance. The transient pressure traces provide insight into reaction kinetics. A bifurcation in transient pressure rise was an indication of a shift in reaction kinetics from the inherent reactive material to metal oxidation with the environment. The bifurcation was delayed by about 0.15 ms for the intermetallic relative to the thermite, evidence that the thermite reaction proceeded faster upon impact than the intermetallic. The two-step process (impact ignition of the reactive material followed by metal oxidation) was shown to produce higher energy conversion efficiencies than projectiles composed of pure fuel (i.e., aluminum) reported previously. Both reactive materials showed energy conversion efficiencies greater than 30% (for air) and 50% (for argon), and an explanation of underestimated efficiency and energy losses is provided. These results have implications for advancing formulations for ballistic applications. Structural reactive materials can be used to modify the effective reactivity of metal-containing formulations in varied atmospheric environments.