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We compared the reactivity of spherical particles composed of aluminum (Al) and silicon (Si) with spherical particles of Al with similar size (nominal diameter 1–2 μm). Both particles were synthesized using a liquid atomization technique such that both particles were encapsulated in a native oxide passivation shell. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) in inert and oxidative environments were performed coupled with X-ray Diffraction (XRD) for species identification. The results showed that incorporation of Si in the Al particles lowered the melting temperature by 85 °C and resulted in lower apparent activation energy for the oxidation reactions and more complete combustion at lower temperatures compared with pure Al powder. Results show promise for engineering fuel particles with minor alterations in metal formulation that promote more complete combustion and energy conversion.

The magnesium (Mg) particle surface can be used to regulate fluorination or oxidation reactions depending on the applied heating rate and Mg particle size. Magnesium particles are surrounded by a complex hydroxide shell composed of an inner layer of magnesium oxide (MgO) and outer layer of magnesium hydroxide (Mg(OH)2). As particles approach the nanoscale, the thick oxide shell (e.g., 22 nm) becomes an appreciable portion of the overall powder and can be exploited to regulate reactivity. In this study, the reactivity of 800 nm Mg particles (nMg) was compared to 44 µm Mg particles (µMg) when combined with Perfluoropolyethyer (PFPE), providing both fluorine and oxygen for Mg reactions. Experiments were performed at slow heating rates (10 °C/min) and separate experiments were performed at fast heating rates (6.0 × 105 °C/min). The slow heating rate studies used a differential scanning calorimeter (DSC) and thermogravimetric (TG) analyzer to examine reaction kinetics. The faster heating rate experiments used a hot wire to ignite a thermal run-away reaction. Powder X-ray diffraction (XRD) analysis of recovered residue at various temperatures corresponding to exothermic events in the DSC revealed reaction pathways for nMg + PFPE favoring oxidation reactions. For nMg powders, the outer Mg(OH)2 surface layer dehydrates at low temperatures (313 °C) creating highly reactive sites for surface oxidation reactions in the condensed phase leading to a higher conversion of Mg(OH)2 to MgO and greater consumption of Mg through oxidation reactions. For µMg, higher Mg(OH)2 dehydration temperatures (498 °C) stabilize µMg particles and the bulk of reactions occur at elevated temperatures and in the gas phase producing higher MgF2 concentrations. Under high heating rate conditions, MgF2 formation is favored over MgO formation for both particle sizes owing to the high reaction temperatures that promote gas phase reactions favoring MgF2 formation. Theoretical analysis using density functional theory (DFT) through cluster models for Mg(OH)2 and MgO surfaces further show that the Mg(OH)2 surface is more reactive with fluorine species than MgO, especially at elevated temperatures. The DFT results help explain the high heating rate reaction pathway that favors fluorination reactions independent of Mg particle size.

Processing and characterization of films synthesized with the blade casting method were studied. The films include 80 nm average diameter aluminum (nAl) particles combined with a solvent–binder system composed of acetone and dimethylformamide (DMF) co-solvent and Poly(vinylidene fluoride) (PVDF) binder. The nAl powder was stress-altered by annealing to 300 °C then quenching at two different cooling rates to induce elevated dilatational strain and stress within the nAl particles. Moreover, the annealing and quenching process dehydrated and dehydroxylated the surface enough to cause stress-altered particles to create more viscous slurries that produced a more porous film microstructure than untreated (UN) nAl powder. Density functional theory calculations revealed defective (i.e., dehydroxylated and dehydrated) sites on the stress-altered nAl particle surface may be responsible for the differences in nAl + PVDF reactivity that showed a higher enthalpy for aluminum-fluorine interface reactions for stress-altered nAl particles. Further, faster quenching created delamination at the core–shell interface and promoted greater energy conversion via a weaker, unsupported oxide shell that became less of a barrier for diffusion reactions. Results from this study provide insight on optimizing nAl particle properties for energy conversion using a method that could be applicable to a range of filler materials and influence bulk film properties.

To harness greater power from aluminum (Al) combustion, one approach is to chemically transform the aluminum oxide (Al2O3) passivation layer surrounding the Al core particle by exploiting surface r...

Surface modification is used to dramatically alter the thermal properties of a bulk metallic material. Thermal barrier coatings (TBCs) are typically applied using spray deposition or laser-based techniques to create a ceramic coating on a metal substrate. In this study, an effective TBC is created directly on a metallic substrate by inducing surface chemical reactions. Aluminum-zirconium (Al-Zr) substrates are used to induce surface-limited reactions that produce a 75-80% decrease in bulk thermal conductivity and diffusivity, respectively. The substrates are cylindrical disks 12.6 mm diameter and 2 mm thickness. Thermal properties are measured using laser flash analysis (LFA) at incrementally elevated temperatures. Focused ion beam (FIB) slicing of the substrate coupled with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) show that the substrate oxidized only along the outer 20 μm of the bulk surface. The layer thickness is significantly less than typical TBCs that can range from 50 to 300 μm yet the 20 μm coating still achieves a dramatic reduction in thermal transport properties. Additionally, thermal analysis reveals a sequence of exothermic reactions starting at 439 °C that include both intermetallic (i.e., ZrAl3) and oxidation (i.e., Al2O3 and ZrO) reactions suggesting continuous surface bonding at the coating-metal interface. The onset of exothermic activity coincides with the transition in thermal properties measured using LFA. These results show that surface oxidation reactions could be used to dramatically alter the thermal transport properties of a metal substrate.

Author(s): Williams, A; Shancita, I; Altman, I; Tamura, N; Pantoya, ML | Abstract: This study examines pressure build-up and decay in thermites upon impact ignition and interprets reactivity based on the holistic pressure history. The thermite is a mixture of aluminum (Al) combined with bismuth trioxide (Bi2O3) powder. Four different Al particles sizes were examined that ranged from 100 nm to 18.5 μm mean diameter and for each size, two different Al powder treatments were examined: stress-altered compared to untreated, as-received Al powder. Stress-altered Al powders have been shown to be more reactive, such that the stress-altered Al powder thermites offer a metric for analyzing thermite reactivity in terms of pressure development compared to untreated Al powder. In a binary thermite system, multiple phase changes and interface chemistry influence the transient pressure response during reaction. Results reveal three key pressure metrics that need consideration specifically for thermite combustion: (1) delay time to peak pressure, (2) peak pressure, and (3) decay after peak pressure. Our experiments show that a lower peak pressure corresponds with higher thermite reactivity because aluminum consumption of oxygen generated by decomposing solid oxidizer reduces the peak pressure. Faster rates of reaction consume oxygen at higher rates such that pressure development becomes more limited than less reactive thermites and the result is a lower peak pressure. This conclusion is opposite of traditional studies using metal fuels with a gaseous environment that typically show higher peak pressures correspond with greater reactivity.

Iodine containing oxidizers are especially effective for neutralizing spore forming bacteria by generating iodine gas as a long-lived bactericide. Metal iodates have been shown to be strong oxidizers when combined with aluminum fuel particles for energy generating applications. One method to produce metal iodates in situ is by using metal oxides and an energetic salt: aluminum iodate hexahydrate (Al(H2O)6(IO3)3(HIO3)2), which is called AIH. In this study, the thermal stability and reactivity of AIH with metal oxides commonly used in energetic formulations was investigated. Three metal oxides: bismuth(III) oxide (Bi2O3), copper(II) oxide (CuO), and iron(III) oxide (Fe2O3) were investigated because of their different oxygen release properties. Each metal oxide powder was combined with AIH powder. Thermal stability and reactivity were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) and reactive properties calculated to supplement experimental observations. Powder X-ray diffraction (XRD) was also used to identify the product species at various stages of heating corresponding to exothermic activity. Results show that AIH decomposition is entirely endothermic but, with the addition of metal oxide powder to AIH, exothermic reactions transform metal oxides into more stable metal iodates. This analysis provides an understanding of the compatibility of AIH with metal oxides and contributes to the development of novel energetic composites that have the advantages of both thermal and biocidal mechanisms for spore neutralization.

Automotive and transportation sectors will be inclined towards the renewable or green energy in the near future. One of the green energy sources discovered recently is biodiesel. Biodiesel is a source of clean alternative fuel for internal combustion engines, which reduces the exhaust emissions significantly. Like diesel, biodiesel also emits exhaust particulate matter (PM), which is responsible for the black soot coming out from the diesel engine. However, it is not clear that what will be the size of PM formed during the idle speed of a biodiesel fueled engine. In this study, the characteristics of the exhaust particulate during the idling speed of a biodiesel fueled single cylinder diesel engine is analyzed. Biodiesel showed a positive result in terms of the concentration of emitted PM. However, particle sizes were smaller in case of biodiesel than diesel. Further studies should be carried out to improve the properties of biodiesel to ensure that the emitted particle sizes are not toxic to human health.

This experimental investigation deals with the effects of fatty acid methyl ester (FAME) composition and the physicochemical properties of biodiesel on engine performance and emissions. FAME compositions have a considerable influence on the physical and chemical properties of biodiesel, such as density, viscosity, heating value, cetane number (CN), oxidation stability, and cold flow properties. The performance and emissions of a four-cylinder turbocharged diesel engine were studied under varying speeds and full load condition. For this investigation, 10% and 20% blends of Jatropha (Jatropha curcas), Alexandrian laurel (Calophyllum inophyllum), and palm biodiesels (JB, ALB, and PB, respectively) were used, and the results were compared with that of the B5 fuel (95% diesel and 5% palm biodiesel). The content of saturated fatty acid (methyl palmitate) for ALB and JB was found to be 23.3% and 20.4% higher respectively than that for PB. In total, PB showed 19.8% higher saturation than JB, while ALB showed 7.3% higher saturation than JB because of their higher content of longer chain saturated fatty acid (methyl stearate). The CNs of all three biodiesels increased with the increase of carbon chain length and saturation level, whereas iodine value and saponification value decreased with the increase of saturation level. An average of 2.8% and 4.5% brake power reduction were observed in the case of 10% and 20% biodiesel blends respectively. Brake specific fuel consumption increased in the range of 6%–20% compared with B5 fuel, whereas carbon monoxide and hydrocarbon emissions decreased significantly. Nitrogen oxide emissions increased in the range of 9%–23% for the 10% and 20% biodiesel blends with respect to B5 fuel.

Biological agent defeat formulations containing an iodinated binder offer a unique solution for sterilization and neutralization of the surrounding environment in the form of iodine gas generation. This study characterized the thermal reactivity of an iodinated binder: hexamethylene diamine (HMD) trimer (C20H30N4O2I4) when combined with aluminum and iron oxide (Al + Fe2O3) thermite. Laser ignition studies were performed to evaluate ignition time and energy, as well as in-situ monitoring of the reaction using a high-speed camera. Thermal analysis of HMD showed four stages of exothermic decomposition plus generation of gas phase iodine species released upon decomposition. Thermal analysis of HMD + Al + Fe2O3 is consistent with laser ignition studies that showed HMD aids ignition and reaction of the ternary mixture. Overall, HMD contributed to heating and ignition as well as provided a source for iodine gas in multiple stages of the thermal reaction.

Aluminum powder was thermally stressed by annealing and quenching, then the powder was non-uniformly dispersed in air and examined for dust combustion behavior as a function of stress-altering conditions. An explosion chamber with a powder injector, spark gap igniter, pressure sensor, spectrometer, and high-speed camera was used for experimentation. Aluminum powder was annealed to 573 K, held for 15 min, and quenched at a rate of 200 K/min (pre-stressed, PS) or 900 K/min (super-quenched, SQ). The untreated (UN), PS, and SQ Al powders were injected into the chamber, and pressure, temperature, and flame spreading behavior were analysed. SQ Al powder exhibited lower pressurization rates than that of PS Al, which was also lower than that of UN Al. Surface modifications to the stress-altered powders may affect their dispersion and suspension in the air environment, which affects flame spreading and pressurization rate. Specifically, annealing powders caused the removal of surface hydration that had two effects: increased the surface energy of the particles (confirmed with density functional theory calculations) and decreased surface roughness (suggested from previous work revealing loss of a nanostructure at the surface with annealing). These two surface modifications may inhibit powder dispersion such that pressurization rate is reduced compared with UN Al powder.

Biodiesel consists of long chain fatty acid esters derived from vegetable oils, animal fats, and used oils. Biodiesel contains different types, amounts, and configurations of unsaturated fatty acids, which are prone to oxidation. Biodiesel stability is affected by its interaction with atmospheric oxygen, light and temperature, storage conditions, and factors causing sediment formation. It can be classified broadly into three types: oxidation stability, thermal stability, and storage stability. Oxidative degradation occurs in biodiesel upon aerobic contact during storage, as well as upon contact with metal contaminants. Thermal instability focuses on the oxidation rate at higher temperatures, which is characterized by the formation of insolubles and increase in the weight of oil and fat. Storage stability is concerned with interaction between the physical and chemical characteristics of biodiesel with environmental factors, such as light, metal contamination, color changes, and sediment formation. Antioxidant concentration greatly influences engine performance and emission. The BSFC of biodiesel fuel with antioxidants is less than that of fuel without antioxidants. Moreover, an antioxidant can significantly reduce NOx formation during engine operation. Among the available synthetic antioxidants, only three antioxidants (TBHQ, PY, and PG) can significantly increase biodiesel stability. This article presents an overview of the stability of biodiesel, including the methods available for the prediction of its different stability properties. Feasible remedies to improve the stability of biodiesel and the effect of antioxidants in stabilized blends on engine performance and emission are also discussed.

The aim of this study is to investigate the effect of the polymethyl acrylate (PMA) additive on the formation of particulate matter (PM) and nitrogen oxide (NOX) emission from a diesel coconut and/or Calophyllum inophyllum biodiesel-fueled engine. The physicochemical properties of 20% of coconut and/or C. inophyllum biodiesel-diesel blend (B20), 0.03 wt% of PMA with B20 (B20P), and diesel fuel were measured and compared to ASTM D6751, D7467, and EN 14214 standard. The test results showed that the addition of PMA additive with B20 significantly improves the cold-flow properties such as pour point (PP), cloud point (CP), and cold filter plugging point (CFPP). The addition of PMA additives reduced the engine's brake-specific energy consumption of all tested fuels. Engine emission results showed that the additive-added fuel reduce PM concentration than B20 and diesel, whereas the PM size and NOX emission both increased than B20 fuel and baseline diesel fuel. Also, the effect of adding PMA into B20 reduced Carbon (C), Aluminum (Al), Potassium (K), and volatile materials in the soot, whereas it increased Oxygen (O), Fluorine (F), Zinc (Zn), Barium (Ba), Chlorine (Cl), Sodium (Na), and fixed carbon. The scanning electron microscope (SEM) results for B20P showed the lower agglomeration than B20 and diesel fuel. Therefore, B20P fuel can be used as an alternative to diesel fuel in diesel engines to lower the harmful emissions without compromising the fuel quality.

To achieve reductions in vehicle idling, strategies and actions must be taken to minimize the time spent by drivers idling their engines. A number of benefits can be obtained in limiting the idling time. These benefits include savings in fuel use and maintenance costs, vehicle life extension, and reduction in exhaust emissions. The main objective of idling reduction (IR) devices is to reduce the amount of energy wasted by idling trucks, rail locomotives, and automobiles. During idling, gasoline vehicles emit a minimum amount of nitrogen oxides (NOx) and negligible particulate matter (PM). However, generally a large amount of carbon monoxide (CO) and hydrocarbons (HC) are produced from these vehicles. Gasoline vehicles consume far more fuel at an hourly rate than their diesel counterparts during idling. Higher NOx and comparatively larger PM are produced by diesel vehicles than gasoline vehicles on the average during idling. Auxiliary power unit (APU), direct-fired heaters, fuel cells, thermal storage system, truck stop electrification, battery-based systems, engine idle management (shutdown) systems, electrical (shore power) solutions, cab comfort system, and hybridization are some of the available IR technologies whose performances for reducing fuel consumption and exhaust emissions have been compared. This paper analyzes the availability and capability of most efficient technologies to reduce fuel consumption and exhaust emissions from diesel and gasoline vehicles by comparing the findings of previous studies. The analysis reveals that among all the options direct fired heaters, APUs and electrified parking spaces exhibit better reduction of fuel consumption and exhaust emissions than others.

The ever-increasing demand for energy has accelerated the research and development of renewable energy sources, which can eventually decrease the dependence on fossil fuel reserve. Biodiesel, a renewable energy source, has received considerable attention as an alternative fuel for the last few decades. In this study, biodiesels produced from two feedstocks were analyzed with a fatty acid methyl ester (FAME) composition, Fourier transform infrared (FT-IR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy (1H and 13C), in order to improve their physicochemical properties and determine the relationships among them. Here, the physicochemical properties of biodiesels produced from C. nucifera, and P. pinnata oils and their 5%, 10%, 20%, and 30% (by volume) blends were compared with pure diesel (B0), according to ASTM D6751 standards. All of the biodiesels and their blends satisfied the conditions to be an alternative fuel, compared to diesel but pure C. nucifera biodiesel, and their blends yielded more property improvement through their physicochemical property analysis and had the lowest carbon residue content. FAME composition, FT-IR and NMR spectra analysis were used to show the better properties of C. nucifera biodiesel and its blends through high ester content, transmittance, and conversion rate, respectively, than P. pinnata biodiesel and thus can be considered for commercial use in diesel engines.

This experiment evaluates the effects of non-oxidative biodiesel (low oxygen content biodiesels) characteristics and their engine performances. Biodiesels produced from different feedstocks typically contains 10% to 15% oxygen by weight, which enhances the combustion quality and reduces the emissions of hydrocarbons (HCs) and carbon monoxide (CO). However, it produces a higher amount of nitrogen oxides (NOx) due to an increasing number of combustion products, resulting in a higher cylinder temperature. In addition, lean air–fuel mixtures can contribute to higher NOx emissions because biodiesel is more oxygenated than diesel. In this study, biodiesels produced from different feedstocks by a transesterification process were used to reduce the oxygen content by dipping an iron bar in the biodiesels, which absorbs oxygen and gets oxidized. Then, the oil characteristics, such as the percentage of saturated and unsaturated fatty acids, thermal degradation, stability and existing functional groups, were analyzed using fatty acid methyl ester (FAME) composition analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy analysis of neat biodiesel and non-oxidative biodiesel. Herein, Pongamia and Moringa biodiesels, containing normal and reduced weight percentages of oxygen, were evaluated to improve the quality and stability of biodiesels used in the diesel engine, which will also reduce the NOx emissions. Non-oxidative biodiesels had some positive effect on their properties, which can further reduce the NOx emissions. Herein, non-oxidative Pongamia and Moringa had quite similar characteristics and the former was observed to perform better in the reduction of NOx and other emissions as well.