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In order to investigate the acoustic oscillation characteristics of gas–liquid pintle rocket engines and elucidate the path by which spray combustion process provides energy to the combustor pressure oscillation, a LOX/GCH4 pintle engine with rectangular combustor was designed. By adding transverse velocity disturbance for the first time, the acoustic response of spray combustion process was simulated, and the effect of excitation amplitude on acoustic response was researched. Numerical results show that the adopted transverse velocity disturbance can excite the first-order transverse acoustic oscillation with same excitation frequency in the engine combustor. The acoustic response maintenance mechanism under extrinsic excitation is summarized for pintle engines. Besides, the temperature distribution inside the engine combustor tends to be uniform, and the low-frequency oscillation caused by the flame transverse swing gradually disappears. The amplitude of combustor pressure oscillation is dominated by excitement amplitude and phase difference between the pressure and heat release in combustion reaction region. In addition, the time-averaged combustor pressure can be amplified mainly by transverse velocity disturbance. The research work can provide a reference for related fire tests on the acoustic response of a subscale gas–liquid pintle engine. [ABSTRACT FROM AUTHOR]

Biomass combustion provides energy needs for millions of people worldwide. However, soot accumulation on the combustors' walls significantly reduces heat transfer efficiency. Herein, we demonstrate how microtextured surfaces minimize soot accumulation by enhancing soot oxidation. We investigate soot layers from the combustion of paraffin wax as a model for wood-based soot, and find that randomly microtextured glass obtained by sandblasting shows a 71% reduction in the time taken to oxidize 90% of surface soot coverage when compared to smooth glass at 530 °C. We also study grooved microtextures fabricated via laser ablation and find that grooves with widths between 15 and 50 µm enhance soot oxidation, while the expedited advantage is lost when the groove width is 85 µm. X-ray photoelectron spectroscopy validates the superior extent of soot removal on microtextures down to a sub-nanometer length-scale. The high density of sharp features such as peaks and edges on microtextures, and the conformality of the soot layer to the microtextures contribute to increased soot oxidation. We also demonstrate enhanced soot oxidation on microtextured stainless steel, the principal material of construction in biomass combustors. Microtextured surfaces that facilitate soot oxidation upon contact could significantly improve performance and longevity in various combustion applications. [ABSTRACT FROM AUTHOR]

The article presents experimental results of research concerning the action of weak electric and magnetic fields on physicochemical transformations in samples of hard coal with a previously destabilized microstructure. The actions of electric and magnetic fields are fundamentally different by many parameters. It has been shown that after treatment with a weak electric field, coal posted an electret potential with an anomalously continuous charge relaxation. Compared to untreated coal samples, the rate of methane emission from methane-saturated samples is maximum for long-flame coal and decreases as it approaches anthracite. The electric field stimulates the grinding of microparticles, a decrease in the maximum gas outlet temperature, a decrease in the enthalpy value in the formation of a new phase, and an increase in the chemical activity of treated coal samples. Fundamentally different results were obtained with magnetic stimulation of coals. In X-ray diffractograms of coal powders after magnetic treatment, the values of the maxima of the main peaks are the largest in comparison with the original samples and those treated with an electric field, which is consistent with an increase in the size of microparticles in a magnetic field. There is an increase in the heat of combustion and a decrease (by 5 times) in the loss of coal mass during heating. [ABSTRACT FROM AUTHOR]

The properties of azido-acetylenic derivatives of s-triazine containing various combinations of propynyloxy, propynylamino, N-methyl-propynylamino, and azido groups have been studied, and their enthalpy of formation in the condensed phase, density, and impact and friction sensitivities have been determined. Based on these data, the energy parameters of detonation, combustion, and adiabatic transformation for individual compounds and their compositions with the binder SKI-3 isoprene rubber have been calculated. The results of the integrated experimental and theoretical studies suggest a high heat of combustion of the investigated individual compounds and compositions based on them. [ABSTRACT FROM AUTHOR]

Space travel requires high-powered, efficient rocket propulsion systems for controllable launch vehicles and safe planetary entry. Interplanetary travel will rely on energy-dense propellants to produce thrust via combustion as the heat generation process to convert chemical to thermal energy. In propulsion devices, combustion can occur through deflagration or detonation, each having vastly different characteristics. Deflagration is subsonic burning at effectively constant pressure and is the main means of thermal energy generation in modern rockets. Alternatively, detonation is a supersonic combustion-driven shock offering several advantages. Detonations entail compact heat release zones at elevated local pressure and temperature. Specifically, rotating detonation rocket engines (RDREs) use detonation as the primary means of energy conversion, producing more useful available work compared to equivalent deflagration-based devices; detonation-based combustion is poised to radically improve rocket performance compared to today's constant pressure engines, producing up to 10 % increased thrust. This new propulsion cycle will also reduce thruster size and/or weight, lower injection pressures, and are less susceptible to engine-damaging acoustic instabilities. Here we present a collective effort to benchmark performance and standardize operability of rotating detonation rocket engines to develop the RDRE technology readiness level towards a flight demonstration. Key detonation physics unique to RDREs, driving consistency and control of chamber dynamics across the engine operating envelope, are identified and addressed to drive down the variability and stochasticity observed in previous studies. This effort demonstrates an RDRE operating consistently across multiple facilities, validating this technology's performance as the foundation of RDRE architecture for future aerospace applications. [ABSTRACT FROM AUTHOR]

A feasibility study was carried out for the transition of typical power engineering objects, differing in thermal capacities and electric powers, from traditional fuel (coal, natural gas, fuel oil) to the combustion of biomass, composite liquid fuel, and generator gas. Three options for producing generator gas during gasification of biomass, composite liquid fuel, and coal were studied cash flows were calculated for the transition of each of the power plants under consideration to alternative fuel and the payback period for such a transition. Relative indicators of the efficiency of the generator gas were determined taking into account a set of significant parameters: heat of combustion, fuel consumption, anthropogenic emissions, ash residue, maximum combustion temperature, minimum ignition temperature, combustion initiation delay time, cost, technical and economic indicators of storage, transportation and fuel combustion, fire and explosion safety. [ABSTRACT FROM AUTHOR]

Space travel requires high-powered, efficient rocket propulsion systems for controllable launch vehicles and safe planetary entry. Interplanetary travel will rely on energy-dense propellants to produce thrust via combustion as the heat generation process to convert chemical to thermal energy. In propulsion devices, combustion can occur through deflagration or detonation, each having vastly different characteristics. Deflagration is subsonic burning at effectively constant pressure and is the main means of thermal energy generation in modern rockets. Alternatively, detonation is a supersonic combustion-driven shock offering several advantages. Detonations entail compact heat release zones at elevated local pressure and temperature. Specifically, rotating detonation rocket engines (RDREs) use detonation as the primary means of energy conversion, producing more useful available work compared to equivalent deflagration-based devices; detonation-based combustion is poised to radically improve rocket performance compared to today's constant pressure engines, producing up to 10 % increased thrust. This new propulsion cycle will also reduce thruster size and/or weight, lower injection pressures, and are less susceptible to engine-damaging acoustic instabilities. Here we present a collective effort to benchmark performance and standardize operability of rotating detonation rocket engines to develop the RDRE technology readiness level towards a flight demonstration. Key detonation physics unique to RDREs, driving consistency and control of chamber dynamics across the engine operating envelope, are identified and addressed to drive down the variability and stochasticity observed in previous studies. This effort demonstrates an RDRE operating consistently across multiple facilities, validating this technology's performance as the foundation of RDRE architecture for future aerospace applications. [ABSTRACT FROM AUTHOR]

The effect of different lower air inlet tube inclinations on the gas dynamics, including concentration, fluid flow profile, temperature, and heat transfer potency, to the bottom part of a rotary hearth furnace (RHF), were investigated. The lower air-inlet tube inclination was varied from 5° to 25° upwards with the horizontal to maximize the burner efficiency. The inlet tube configuration with the lower two air-inlet tubes inclined at 10° upwards emerged as the most efficient tube orientation in the present burner system. This air inlet configuration of the burner produced the maximum heat transfer efficiency in transferring the combustion heat produced in the freeboard region to the bottom pellet layer region. Moreover, it was also able to produce better CO post-combustion efficiency. [ABSTRACT FROM AUTHOR]

Fires involving solid combustible materials are, as a rule, eliminated by supplying water mist onto a burning surface. Problems of current importance include determination of optimum intensity and duration of water supply to ensure successful suppression of combustion in the case of fires of various strength. This paper offers a mathematical model of optimizing the process of fire suppression for solid combustible materials. Using the heat conduction equation, an analytical solution has been obtained to determine the time for water supply to the seat of fire for its suppression, which depends on the thermophysical properties of combustible materials, the power of the heat impact of the combustion source on these materials, the time of free fire development, and the intensity of water supply. The results of the performed calculations illustrate the efficiency of solving problems of optimizing the extinguishment of fire seats involving solid combustible materials. [ABSTRACT FROM AUTHOR]

Experiments on filtration combustion of car tires mixed with a solid coolant are carried out. The mass content of tire particles in a mixture varies from 10 to 70%. Particles of chemically inert sapphire (Al2O3) and sulfur-absorbing marble (CaCO3) are used as a heat carrier. Optimal conditions for the filtration combustion of car tires are determined (the tire content in a mixture is 50%, combustion temperature is approximately 1000°C, the mass burning rate is 0.40 kg/m3 of supplied air). It is established that the replacement of a solid inert coolant with marble has practically no effect on the combustion temperature. In this case, the composition of combustion products changes: the CO2 content in gaseous products increases (their combustion heat decreases from approximately 2.5 to 2.2 MJ/m3), the yield of liquid pyrolysis products decreases approximately from 45 to 40%, and the sulfur content in solid combustion products increases from 28 to 40%. [ABSTRACT FROM AUTHOR]

Coal combustion for energy has not only wasted the hydrogen-rich volatile matters but also results in CO2 emission causing serious environmental issues. An integrated coal pyrolysis and solvent extraction process under elevated temperatures in an inert atmosphere is implemented to convert as-mined coal from Wyoming Powder River Basin to functional carbon elements such as pyrolysis char (PC). This paper presents the development and fabrication of new carbon-based structural unit (CSU) using pulverized PC and two coal-derived pitches (mesophase pitch and tar pitch) to attain high compressive strength greater than 30 MPa, low thermal conductivity less than 0.30 W/m K, and low density less than 1.25 g/cm3. CSUs have the potential to overcome the current challenges with cement and concrete through pressurized fabrication followed by carbonization. This study aims to develop CSU with nearly 100% coal-derived carbon material for structural application in buildings. The effects of pressing pressures, carbonization temperatures, and binder contents on the density and mechanical and thermal properties of CSU samples are investigated. The study concludes that mesophase pitch produces a better performance of CSU samples, a combination of 100 MPa pressing pressure and carbonization temperature of 900 °C yields the highest compressive strength, and a 25% MP content is recommended for low-cost CSU fabrication. CSU has a much lower density, lower thermal conductivity, higher compressive strength, and higher strength-to-density ratio than normal concrete. [ABSTRACT FROM AUTHOR]

The development of efficient catalytic methods for the synthesis of bio-based, full-performance jet fuels is critical for limiting the impacts of climate change while enabling a thriving modern society. To help address this need, here, linalool, a terpene alcohol that can be produced via fermentation of biomass sugars, was dehydrated, cyclized, and hydrogenated in a one-pot reaction under moderate reaction conditions. This sequence produced a biosynthetic fuel mixture primarily composed of 1-methyl-4-isopropylcyclohexane (p-menthane) and 2,6-dimethyloctane (DMO). The reaction was promoted by a catalyst composed of commercial Amberlyst-15, H+ form, and 10% Pd/C. Two other terpenoid substrates (1,8-cineole and 1,4-cineole) were subjected to the same conditions and excellent conversion to high purity p-menthane was observed. The fuel mixture derived from linalool exhibits a 1.7% higher gravimetric heat of combustion and 66% lower kinematic viscosity at −20 °C compared to the limits for conventional jet fuel. These properties suggest that isomerized hydrogenated linalool (IHL) can be blended with conventional jet fuel or synthetic paraffinic kerosenes to deliver high-performance sustainable aviation fuels for commercial and military applications. Sustainable aviation fuels offer the opportunity to both reduce CO2 emissions and produce fuels with superior properties to conventional petroleum-based fuels. Here, the bio-based monoterpene linalool is converted into an aviation fuel mixture primarily composed of p-menthane and 2,6-dimethyloctane at moderate temperatures and pressures using a combination of Amberlyst-15 and Pd/C catalysts. The resulting fuel is demonstrated to have a higher gravimetric heat of combustion, and a lower viscosity compared to petroleum derived Jet-A. [ABSTRACT FROM AUTHOR]

In order to reduce the risk of spontaneous combustion of coal left after long-term flooding in the goaf of the mine, in this paper, the inhibitory properties of different inhibitors on two kinds of water-immersed coals with different metamorphic degrees were studied in depth. The experiment selected Pingzhuang brown coal and Shaqu coking coal as research objects. The raw coal and water-immersed coal samples were compared and analyzed by thermogravimetric experiment method and Fourier transform infrared spectroscopy experiment method. The study showed that the activation temperature of brown coal and coking coal decreased by 7.91 and 2.25 °C respectively, and the activation energy decreased by 43.18 kJ/mol and 20.58 kJ/mol respectively. The natural tendency of coal was enhanced after water immersion, and water immersion had a greater impact on low-metamorphic brown coal. After adding four kinds of inhibitors, MgCl2, TEMPO, TPPI and PA to the two water-immersed coals, it was found that TPPI could significantly reduce the heat release rate of water-immersed brown coal, and the reduction value was 10.49 W/mg. The dry cracking temperature of water-immersed brown coal increased by 11.75 °C, and PA greatly increased the combustion activation energy of water-immersed coking coal by 25.77 kJ/mol. Meanwhile, it was found from the microscopic active groups that TTPI increased the content of water-immersed brown coal ether bonds by 4.84%. The absorption peak intensity of oxygen-containing functional groups such as C=O was significantly weakened. Similarly, PA also produced a large number of stable ethers in water-immersed coking coal, whose content increased by 5.21%, and the hydroxyl content decreased most significantly. The decomposition of TPPI into phosphoric acid after heating can inhibit the growth of active groups such as a large number of oxygen-containing functional groups in the water-immersed brown coal, thereby reducing the risk of spontaneous combustion. As a metal chelator, PA can reduce the catalytic effect of metal ions in water-immersed coking coal with fewer active groups, and inhibit coal spontaneous combustion by generating stable metal complexes to increase activation energy. This indicated that TTPI had the best inhibitory effect on water-immersed brown coal, while PA was more suitable for water-immersed coking coal. [ABSTRACT FROM AUTHOR]

The study of the elemental composition of labile humus substances passing into 0.1 M NaOH extract from typical chernozem under different cenoses indicated that, judging from the H : C ratio varying within 1.55–1.91, aliphatic structures predominate over cyclic components. Under the agrogenic impact, the processes demethylation, dehydrogenation, and oxidation of organic substances are developed in the chernozem. As a result, labile humic substances lose their aliphatic components and become enriched with oxidized nitrogen-containing cyclic structures. The intensity of this process increases in the series: permanent winter wheat > permanent corn > permanent bare fallow. At the same time, labile humic substances of the chernozem under permanent bare fallow are the least energy-intensive compounds as judged from the values of the heat of combustion found on the basis of elemental analysis data. Over the 23 years that have passed since the transfer of the permanent bare fallow to the unmanaged fallow overgrown by herbs, there have been no significant changes in the elemental composition of labile humus substances of typical chernozem, except for a tendency of their enrichment in newly formed aliphatic nitrogen-containing reduced and more energy-intensive compounds. [ABSTRACT FROM AUTHOR]

The fraction of methane in gas hydrates is approximately 12% (by weight). Theoretically, the combustion temperature of such a composition is rather low. Nevertheless, the measurements show that a much higher flame temperature can be ensured by organizing the process more appropriately. For this purpose, it is necessary to separate the dissociation and combustion regions (i.e., eliminate water heating). On the other hand, for combustion to be stable, some part of the combustion heat should be returned to the hydrate region to maintain the dissociation rate at a needed level. Stability of methane hydrate combustion is naturally determined by the ratio of heat release and heat transfer. This paper describes experiments on methane combustion above a layer of a dissociating gas hydrate, and a simple mathematical model is proposed for estimating diffusion combustion stability. Comparing the modeling results with experimental data allows one to determine the water vapor concentration and find the thermal balance of hydrate combustion. [ABSTRACT FROM AUTHOR]

Thermal insulation and hot oil adsorption have been paid increasing attention to industrial development. Decomposition and combustion of commercial heat insulation materials may happen in the continuously high temperature (≥ 200 °C) or/and instantaneously ultra-high temperature (≥ 250 °C). Nanofiber aerogel with versatile properties is a potential candidate for thermal insulation and hot oil adsorption. In this work, a novel three-dimensional polybenzimidazole nanofiber aerogel is designed and fabricated for thermal insulation and adsorption of high-temperature oil. Directional freeze casting and freeze-drying techniques are applied to build the three-dimensional structure. A nanofiber-corbelled porous-layer architecture is obtained by optimization with the adhesive effect of starch-derived carbon. Thanks to this architecture, the polybenzimidazole nanofiber aerogel owns suitable mechanical flexibility for delaying heat diffusion. Furthermore, the adsorption and thermal insulation at high temperatures are simultaneously achieved with its high porosity, low thermal conductivity, and thermal stability. This study proposes a promising path for aerogel preparation and applications on effective thermal insulation and hot oil adsorption. [ABSTRACT FROM AUTHOR]

This study conducted a comprehensive characterization and analyses on the fire-resistant behaviors of novel fungal fibers grown with substrate containing Silica (Si) source at multiple scales. At micro-scale, the results of SEM showed that silica affected the physiological activities of fungi, with the extent of effects depending upon its concentration. Fourier-transform infrared (FTIR) spectra displayed the existence of Si–O–C chemical bonds in fungal fibers grown with Si source, indicating that Si source becomes a part of the structure of fungal fibers. Thermogravimetric analysis (TGA) and Microscale combustion calorimetry (MCC) of fungal fibers exhibit an early thermal decomposition of non-combustible components, which will potentially help release the thermal stress and mitigation of spalling when used in concrete. Compared with polypropylene (PP) fibers, fungal fibers have a lower thermal degradation rate, a higher residual weight, a lower heat release peak temperature, and less total heat of combustion; all of these indicate improved thermal stability and fire resistance, and a lower rate of function loss in case of a fire. Additionally, the thermal stability and fire resistance of fungal fibers were improved with the increase of Si source concentration in the nutrition medium. For example, addition of 2% Si source in the feeding substrate leads to a 23.21% increase in residual weight in TGA, and a 23.66 W/g decrease in peak heat release rate as well as a 2.44 kJ/g reduction in total heat of combustion in MCC. At laboratory scale, compared with PP fibers, fungal fibers grown with 2% Si source have a higher residual weight of 40.40%, a higher ignition temperature of 200.50 °C, and a declined flame height of 11.64 mm in real fire scenarios. Furthermore, only in the fungal fibers grown with Si source, partial burning occurred. In post-fire conditions, the microstructure of residual char from fungal fibers grown with higher content of Si source became denser, which would lead to a reduction of the fuel vapor release and heat transfer. FTIR spectra of residual char demonstrated that fungal fibers grown with Si source formed more stable chemical bonds with higher heat of chemical bond formation, contributing to improved thermal stability and fire resistance. Therefore, compared with traditional fibers used for fiber reinforced concrete, incorporating the new natural grown fibers will potentially further improve the fire resistance of concrete and mitigate the concrete spalling. [ABSTRACT FROM AUTHOR]

5 kinds of genuine medicinal materials, including Diding (Latin name: Corydalis bungeana Turcz), Purslane (Latin name: Portulaca oleracea L.), straw sandal board (Latin name: Hoya carnosa (L.f.) R. Br), June snow (Latin name: Serissa japonica (Thunb.) Thunb.), pine vine rattan (Latin name: Lycopodiastrum casuarinoides (Spring) Holub. [Lycopodium casuarinoides Spring]), were selected as the research objects. The combustion heat, thermo gravimetric parameters, and fat content, calcium content, trace element content, ash content of 5 kinds of genuine medicinal materials were measured. The combustion heat, differential thermal gravimetric analysis, fat content, calcium content, trace elements content, and ash content of 5 kinds of genuine medicinal materials were used to build a systematic multi-index evaluation system by gray pattern recognition and grey correlation coefficient cluster analysis, which can make up for the gaps in this area and provide scientific basis and research significance for the study of genuine medicinal materials quality. The results showed that the order of combustion heat of 5 kinds of genuine medicinal materials, including Diding, Purslane, straw sandal board, June snow, pine vine rattan, was Diding > June snow > straw sandal board > Purslane > pine vine rattan, the order of fat content (%) of 5 kinds of genuine medicinal materials was straw sandal board > Diding > pine vine rattan > June snow > Purslane, the order of calcium content (%) was pine vine rattan > June snow > Purslane > straw sandal board > Diding, the order of ash content was June snow > Purslane > straw sandal board > pine vine rattan > Diding. From the analysis of thermogravimetric analysis results and thermogravimetric combustion stability, the order of combustion stability of 5 kinds of genuine medicinal materials was June snow > pine Vine rattan > straw sandal board > Diding > Portulaca oleracea. The order of the content of 12 trace elements in 5 kinds of genuine medicinal materials, in terms of trace element content, June snow contains the highest trace elements in all samples. According to combustion heat, combustibility (combustion stability of genuine medicinal materials), fat, calcium, ash, trace element content, the comprehensive evaluation results of multi-index analysis constructed by gray correlation degree, gray correlation coefficient factor analysis, and gray hierarchical cluster analysis showed that the comprehensive evaluation multi-index order of 5 genuine medicinal materials, including Diding, Purslane, straw sandal board, June snow and pine vine rattan, was June snow > straw sandal board > Diding > Purslane > pine vine rattan. Therefore, the comprehensive evaluation results of the quality of genuine medicinal materials selected in this study were June snow the best, followed by straw sandal board. This research has important theoretical and practical significance for the multi-index measurement and comprehensive evaluation of genuine medicinal materials, and can provide scientific basis and research significance for the research of multi-index quality control of genuine medicinal material. [ABSTRACT FROM AUTHOR]

Accurate evaluation of combustion enthalpy is of high scientific and industrial importance. Although ab-initio computation of the heat of reactions is one of the promising and well-established approaches in computational chemistry, reliable and precise computation of heat of combustion reactions by ab-initio methods is surprisingly scarce in the literature. A handful of works carried out for this purpose report significant inconsistencies between the computed and experimentally determined combustion enthalpies and suggest empirical corrections to improve the accuracy of the ab-initio predicted data. The main aim of the present study is to investigate the reasons behind those reported inconsistencies and propose guidelines for a high-accuracy estimation of heat of reactions via ab-initio computations. We show comparably accurate prediction of combustion enthalpy of 40 organic molecules based on a DSD-PBEP86 double-hybrid density functional theory approach and CCSD(T)-F12 coupled-cluster computations, with mean unsigned errors with respect to experimental data being below 0.5% for both methods. [ABSTRACT FROM AUTHOR]

Dioctyl sebacate (DOS), paraffin (PW), fluororubber (FR), and polyurethane (PU) are widely used as binders in aluminized propellants and explosives. In this study, ignition and combustion of aluminum powders coated with DOS, PW, FR, and PU are investigated. The flame speeds of the aluminum powders coated with DOS, PW, and PU are found to decrease with an increase in the content of these binders. The flame speed of the aluminum powder coated with FR is greater than those of the aluminum powders coated with DOS, PW, and PU. In this case, combustion improvement is due to the reaction between the alumina shell and FR. [ABSTRACT FROM AUTHOR]

In order to improve the thermal decomposition performances of ammonium perchlorate (AP), the laminated AP composite was prepared by ice-template induced self-assembly method. In this study, Iron-Konjac glucomannan (Fe3+-KGM) hydrosol rich in AP was selected as the freezing precursor. Through directional freezing of precursor and recrystallization of AP molecules, the laminated AP composite was obtained. The results showed that the thickness of the lamellar composite structure is about 10 to 30 μm, and the recrystallized AP particles are uniformly dispersed in the gel system. The oxygen bomb test results show that the micro-/nano-layered structure can significantly improve the sample's combustion heat value. Thermal analyses indicated that with the increasing Fe3+ content, the peak exothermic temperature of lamellar AP composite at different heating rates both showed a decreasing trend. With 10 wt% Fe(NO3)3·9H2O added, the decomposition peak temperature decreased from 433.0 to 336.2 °C at a heating rate of 5 °C/min, and the apparent activation energy (Ea) decreased dramatically from 334.1 kJ/mol to 255.4 kJ/mol. A possible catalytic thermal decomposition mechanism of lamellar AP composite catalyzed by Fe3+ was proposed. This work is beneficial to the structural design of other energetic materials. [ABSTRACT FROM AUTHOR]

Herein, we report a facile strategy to prepare polybenzoxazine/boron nitride composites foams with simultaneously improved thermal resistance, flame retardance, mechanical and dielectric properties using a sol–gel method. It is found that the boron nitride (BN) granules are uniformly dispersed and tightly encapsulated within the polymer matrix without any modification. Due to the reinforcement of BN, the compressive stress of the composites foams nearly double, giving the highest value of 14.61 MPa. Moreover, the low densities of the composites foams lead to low dielectric constant and dielectric loss at both low and high frequencies, e.g., the composite foam with 30 wt% BN (F/30BN) show dielectric constant and dielectric loss of 1.42 and 0.0818 (1 MHz), and 1.72 and 0.0013 (1 GHz), respectively. Additionally, the glass transition temperature and char yield of F/30BN reach 190.5 °C and 55.4%, which is 48.6 °C and 33.4% higher than the pristine polybenzoxazine foam. The incorporation of BN also imparts the composites foams with better flame retardancy by delaying combustion and slowing the heat release rate. [ABSTRACT FROM AUTHOR]

Recently, research on the preparation of porous Al-containing intermetallic compounds using combustion synthesis (CS) reaction in combination with a space holder process has been gradually increased, in order to improve the porosity and obtain the pore structures with controllable pore morphology and pore size. The reaction mechanism for the M–Al (M = Ti, Ni, Fe, Nb, and Cu) system is closely related to the state of aluminum (e.g., solid or liquid phase) and is greatly affected by processing parameters such as particle size, Al content, heating rate, compacting pressure, sintering temperature, content, and the type of pore-forming agents. Once the sintering temperature causes the appearance of one liquid phase in the reaction system, the remaining solid reactant quickly dissolves into the molten one to improve the surface contact and then generate considerable heat to complete the combustion reaction. Interestingly, the actual temperature change of the sample during the sintering process is accurately detected, and the transparent observation of the reaction state is also realized, which provides a new vision for further exploration of the reaction mechanism of other compounds. [ABSTRACT FROM AUTHOR]

Using ANSYS Fluent software, numerical simulation has been conducted for flow and burning processes in combustion chambers of gas-turbine power plants designed to recover oil-associated (casing-head) gas. The working process equations are considered in the Euler approach. The system of partial differential equations describing a threedimensional burning turbulent flow contains the laws of conservation of total mass, the mass of separate combustion product components, the combustion product momentum, the combustion product energy, the law of conservation of fuel composition elements, mixture fraction, turbulence kinetic energy. and dissipation of turbulence kinetic energy. The introduction of mixture fraction simplifies substantially the solution of the problem of turbulent mixing of the oxidizing agent and the fuel. Scalar quantities (density, temperature, and mass concentrations of components) are determined using the probability density function in accounting for the final chemical reaction rate of an unpremixed mixture. The flow velocity field is calculated using the "realizable" k–ε turbulence model. The results have been obtained for different schemes of component supply into the combustion chamber. A comparison of calculated and experimental data is given. [ABSTRACT FROM AUTHOR]

An analytical study has been made of the operating processes of burning of natural gas in the furnace of a steam water-tube boiler. The authors have determined the fields of the combustion-product temperature and of the heat-flux density in the furnace volume, and also the thermodynamic parameters of the reaction of combustion of methane and the enthalpy and entropy change of combustion products in the furnace with a secondary radiator and without it. The distribution of the entropy fields has been given and the regions of high entropy production near heat-transfer surfaces during the heat exchange of combustion products have been determined. To obtain optimum results, the authors used the model of minimum entropy generation in the thermodynamic system. An exergy analysis has been made of the operating processes of the chemical reactions of combustion and heat exchange of the combustion products with the tubular surfaces of the steam boiler. The influence of structural and regime parameters of the boiler furnace on the exergy loss has been shown. [ABSTRACT FROM AUTHOR]

Solution combustion synthesis (SCS) possesses many advantages for preparation of nanosized materials. In the process of SCS, a large amount of heat release results in the agglomeration of particles. Thus, the controllable synthesis of solution combustion is necessary. In this study, Ni–Al2O3 nanoparticles with various metal chlorides, i.e., LiCl, NaCl, KCl, MgCl2 and CaCl2, were prepared by SCS method and performed for CO methanation reaction in a slurry-bed reactor. All of the introduced metal chlorides could absorb reaction heat during the combustion process, among which the addition of NaCl minimizes the combustion temperature for its high heat capacity. Moreover, the molten NaCl exerts a steric hindrance effect that restrains the agglomeration of NiO particles, leading to the highest Ni dispersion and smallest Ni particles. MgCl2-added sample exhibits the lowest reducibility and Ni dispersion and the worst methanation activity. The performance shows that, under a harsh condition of 310 °C and 9200 mL (gcat h)−1, NaCl-added Ni–Al2O3 catalyst exhibits the optimal CO conversion, which keeps stable at ca. 87% in a 100-h test. This study offers a new strategy for nanosized catalyst preparation via SCS by introducing metal chlorides. [ABSTRACT FROM AUTHOR]

The main cause of the previously unexplainable most important features of gas-phase combustion was determined. It was shown that the sharp acceleration of combustion during heating and the high rates are primarily caused not by an increase in the rate constant of the limiting step, as was previously believed, but by an increase in the concentration of active intermediate particles with temperature as an exponential function of a positive exponential function of the Boltzmann factor. Such a character of the temperature dependence governs the transition from combustion to explosion and detonation. [ABSTRACT FROM AUTHOR]

Combustion of vapors of a flammable liquid whose temperature is below the flash point is under study. In this case, the flame propagates along the surface of the liquid due to being heated by combustion products. The velocities of an oxidizer moving towards the flame, which propagates at velocities comparable to the laminar burning rate of premixed hydrocarbon flames, are measured. The measurements show that the gas flow is laminar. There is a correlation established between the flash point of a flammable liquid and the flame propagation velocity. On the basis of the data obtained, it is assumed that the main mechanism of formation of a flammable mixture ahead of the combustion front is a diffusion mechanism. [ABSTRACT FROM AUTHOR]

The heat of combustion and the enthalpy of formation of 7,7′-bis(terfurazan[3,4-b:3,4′-d:3″,4″-f]azepine (I) and 1,1′-dioxide-7,7′-bis(terfurazan[3,4-b:3,4′-d:3″,4″-f] azepine (II), were experimentally determined. Product I was studied by X-ray diffraction analysis, and its crystallographic characteristics were determined. The efficiency of using compounds I and II as components of solid composite propellants was analyzed, and the type of compositions in which they are more effective than HMX was determined. [ABSTRACT FROM AUTHOR]

If a Li-ion cell fails and the electrolyte leaks out into air, a flammable premixed gas cloud can be formed. The electrolyte combustion energy is 65–70% of the total energy content of the cell. The main objective of this study is to determine the laminar burning velocity and the Markstein length for dimethyl carbonate and propane in a 20-liter explosion sphere with initial conditions at 100 kPa and 300 K. Five different stretch extrapolation models for the laminar burning velocity give practically the same result. The experimental results agree well with the previously published data and are slightly lower than the theoretical predictions. The laminar burning velocity for dimethyl carbonate is measured close to the saturation point under the initial conditions, which has not been previously reported. [ABSTRACT FROM AUTHOR]

In order to ensure the safety and reliability of weapons, it is very important to grasp the influence of the inside and outside diameters of the shell on the delay time. In this paper, a fluid–solid coupling model is established for a metal baffle-type delay element with a silicon-based delay composition. The combustion flow field of the delay element with the inside diameter of 3, 4, and 5 mm is simulated by the Star-CD software. Then a new method is proposed to calculate the delay time of the heat conduction delay element. The influence of the internal and external diameters on the delay time of the thermal conduction delay element is studied. The results show that the temperature of the ignition composition gradually increases due to the heat conductivity of the metal baffle after burning of the delay composition, and the highest temperature is reached at the centre of the ignition composition. The influence of the size of the inside and outside diameters on the delay time has a critical equilibrium point, which may be related to the balance between the combustion heat increment and the heat loss. [ABSTRACT FROM AUTHOR]

The heat of combustion and enthalpy of formation of bis(4 ″ -nitro[3,3 ′ :4 ′ ,3 ″ ]terfurazan-4-yl)-diazene (DNFNF) and (bis(4 ″ -azido-[3,3 ′ :4 ′ ,3 ″ ]terfurazan-4-yl)-diazene (DAzFNF) were first experimentally determined. It is found that the energy increment for replacing the nitro group with an azide group in the furazan cycle averages 290 kJ/mol and is close to the increment for replacing NO2 with N3 in trinitroethane. The dependence of the energy parameters of metal-free rocket propellants based on a mixture of ammonium perchlorate and DNFNF or DAzFNF with an active binder on the content of the high-enthalpy component in the formulation was studied by thermodynamic analysis. [ABSTRACT FROM AUTHOR]

The boundaries of stable combustion in a flow of an aluminum particle–air mixture in a wide range of changes in an air-to-fuel ratio (0.1–2.0) are experimentally determined. A characteristic feature of the relationship of a flame blowoff velocity with the air-to-fuel ratio is revealed: it has two maxima. Taking into account the principle of the flame stabilization mechanism, based on the equality of the flow velocity at which the flame is blown off to the flame front propagation velocity, it is concluded that there are two maxima in the relationship of the front velocity with the air-to-fuel ratio, which correspond to the maximum values of heat release and combustion temperature of the aluminum particle–air mixture with an air-to-fuel ratio of 0.2 and 1.0. Previously, these maxima were obtained by other researchers in thermodynamic calculations. [ABSTRACT FROM AUTHOR]

A method for calculating the optimal ratio of the fuel and solid propellant in the gas generator of a high-velocity flying vehicle is proposed. A thermodynamic approach is used to describe the processes in the gas generator. The ratio of the solid propellant and fuel in the gas generator is determined by their physical and chemical properties. An increase in the density and heat of combustion of the solid propellant and in the fuel porosity leads to reduction of the volume fraction of the solid propellant in the gas generator. An increase in the density, specific heat, specific heat of sublimation, and temperature of sublimation of the fuel leads to an increase in the volume fraction of the solid propellant in the gas generator. [ABSTRACT FROM AUTHOR]

This paper presents a study of direct conversion of chemical energy into electrical energy during the combustion of a (80Zr + 20CuO)–(LiF + CaF2 + MgF2)–(15Zr + 85CuO) thin three-layer condensed energy system, which is a high-temperature galvanic cell. It is determined that this cell during combustion generates an electric signal with an amplitude of 1.6 V and a half-width of 15 s. Its formation mechanism is proposed. A time-resolving X-ray diffraction method is used to identify the phases formed. [ABSTRACT FROM AUTHOR]

The standard enthalpy of formation of 1,4-diethynylbenzene experimentally to be 500.6 ± 6.7 kJ/mol. Calculations show that 1,4-diethynylbenzene has a relatively high adiabatic combustion temperature (about 1970 K at a pressure of 5 atm) and very high heat of combustion in oxygen (42 MJ/kg); therefore, 1,4-diethynylbenzene can be used as the basis to develop an effective dispersing agent of solid fuel that provides an adiabatic combustion temperature of up to 2500 K at a heat of combustion far exceeding the values provided by HMX and the other azides of N-heterocycles previously proposed for this purpose. [ABSTRACT FROM AUTHOR]

This paper describes the experimental study of amplitude (with a frequency of up to 50 kHz) and integral characteristics of the self-magnetic field of high-temperature combustion products of hydrocarbon fuel, which flow out of the nozzle of a standard liquid-propellant engine (LPE) with simulation of the heat of a combustion chamber with injection of aluminum-magnesium alloy particles (c-phase) into the combustion chamber. It is determined that the amplitude of the magnetic field intensity generated by high-temperature (up to 3500 K) combustion products depends on the LPE operation modes and the presence of k phase particles in the particle flow. The magnetic field amplitude increases by 20% during the LPE burnout ≈0.2 s earlier than the pressure drop in the combustion chamber. The total volumetric electric charge generated by the combustion product flow with the c-phase is estimated. [ABSTRACT FROM AUTHOR]

Thermal decomposition of disubstituted salts of high-energy 5,5'-azotetrazole (sodium, ammonium, hydrazine, guanidine, aminoguanidine, and triaminoguanidine salts) under isothermal and nonisothermal conditions in solid and liquid phases is studied. The relationship between the basicity and the thermal stability of the 5,5'-azotetrazole salt is demonstrated. The boundary of possible existence of 5,5'-azotetrazole salts in terms of the basicity index pKa is determined. Gaseous and condensed products of decomposition are analyzed, and a mechanism of thermal decomposition of 5,5'-azotetrazole is proposed. The enthalpies of formation of some 5,5'-azotetrazole salts are determined, and the most reliable values are chosen on the basis of the analysis of the data obtained in the present study and those available in publications. [ABSTRACT FROM AUTHOR]

The heat of combustion and the standard enthalpy of formation of 3,4-bis(4-azidofurazan-3-yl)furoxan (DAzFF) and 4-azido-4″-nitro-3,3′:4′,′3′-terfurazan (AzNTF) were experimentally determined. Thermodynamic analysis was performed to investigate the efficiency of these compounds as potential components of metal-free solid composite propellants based on an active binder with the possibility of introducing an additional small amount of oxidizer with a high oxygen content, e.g., ammonium perchlorate. [ABSTRACT FROM AUTHOR]

A number of di-, tri-, and tetraazido-substituted azines as potential energetic dispersing agents of solid propellants for ramjet engines have been studied. The enthalpy of combustion and the enthalpy of formation of several azides (2,4,6-triazidopyrimidine, 2,4,6-triazidopyridine, 3,4,5-triazidopyridine-2,6-dicarbonitrile, and 3,4,5,6-tetraazidopyridine-2-carbonitrile) were experimentally determined. Eleven azides were compared with HMX in terms of the enthalpy of combustion in oxygen to CO2 and water (in the case of the presence of hydrogen in the component), as well as in terms of the temperature of the products of adiabatic conversion of the investigated components due to the high enthalpy of formation in the absence of an external oxidizer and the amount of gases released in this process. The enthalpy of combustion of all the investigated azides burned in air was found to be significantly higher than that of HMX, and for seven of the azides studied, the combustion temperature is significantly higher. As regards the gas release volume (24–31 mol/kg), the azides are inferior to HMX (41.9 mol/kg). Based on the combination of properties, the investigated azides can be considered as promising dispersing agents of solid propellants for ramjet engines. [ABSTRACT FROM AUTHOR]

The high enthalpies of combustion of atomic clusters Aln, Bn, and Cn (n = 1, 2, …, 7), AlnCm and BnCm (n = 1, …, 5 and m = 1, …, 5), AlnBm (n + m ≤ 7), and AlnHm and BnHm (n = 1, …, 4 and m ≤ 12) have been assessed. The specific energy release, the final adiabatic temperature, and the effectiveness of the combustion products of fuel mixtures based on kerosene, dimethyl ether, and ethyl alcohol with small additions of such clusters have been determined under the assumption of attaining a thermodynamic equilibrium in their combustion products. An analysis has been made of the potentials of small aluminum- and boron-containing clusters for use in improving thermochemical properties of the fuels. It has been shown that adding such clusters to traditional fuels in the amount of 10% of the fuel mass can increase the specific energy release of the fuel by 2 MJ/kg, the effectiveness of combustion products of the fuel by 10%, and their final temperature by 200 K. [ABSTRACT FROM AUTHOR]

An oxygen-diluted partially premixed/oxygen-enriched supplemental combustion (ODPP/OESC) counterflow flame is studied in this paper. Flame images are obtained through experiments and numerical simulations with the GRI-Mech 3.0 chemistry. The oxygen dilution effects are revealed by comparing the flame structures and emissions with those of a premixed flame and partially premixed flame (PPF) at the same equivalence ratio (ϕ = 0.95 and ϕ = 1.4). The results show that both PPF and ODPP/OESC flames have distinct double flame structures; however, the location of the premixed combustion zone and the distance between premixed/nonpremixed combustion zone are significantly different for these two cases. For the ODPP/OESC flame, the temperature in the premixed combustion zone is lower and the premixed zone itself is located farther downstream from the fuel nozzle, which leads to reduction of NO and CO emissions, as compared to those of the PPF. Therefore, by adjusting the distribution of the oxygen concentration in the premixed and nonpremixed combustion zones, the ODPP/OESC can effectively balance the chemical reaction rate in the entire combustion zone and, consequently, reduce emissions. [ABSTRACT FROM AUTHOR]

An experimental prototype of an engine of a new type for water transport-pulse detonation hydroramjet-was designed, built, and tested for the first time. Firing test of the prototype with a 2-L combustor was performed on a specially designed test stand with a thrust-measuring frame capable of producing an approach water stream in the form of a submerged jet with a velocity up to 10 m/s. The specific impulse was experimentally measured, ranging from 370 s at high operation frequency (20 Hz) to 1200 s at low operation frequency (1 Hz); i.e., the measured specific impulse of the pulse detonation hydroramjet exceeded that of the best modern liquid rocket engines. [ABSTRACT FROM AUTHOR]

An underwater explosion test is used to determine the detonation properties of metallized explosives containing aluminum and boron powders. An oxygen bomb calorimeter (PARR 6200 calorimeter, Parr Instrument Company, USA) is used to obtain the heat of combustion of the metal mixtures. As the content of boron powders is increased, the heat of combustion of the metal mixtures increases, and the combustion efficiency of boron decreases. The highest value of the combustion heat is 38.2181 MJ/kg, with the boron content of 40%. All metallized explosive compositions (RDX/Al/B/AP) have higher detonation energy (including higher shock wave energy and bubble energy) in water than the TNT charge. The highest total useful energy is 6.821 MJ/kg, with the boron content of 10%. It is 3.4% higher than the total energy of the RDX/Al/AP composition, and it is 2.1 times higher than the TNT equivalent. [ABSTRACT FROM AUTHOR]

We have investigated under laboratory conditions the effect of the combustion site modeled by a steppe combustible on wood specimens of different profiles (flat and cylindrical specimens) with the use of IR diagnostics. Experiments were carried out with the use of a JADE J5330SB infrared imager in the spectral range of 2.64-3.25 μm. The temperature profiles on the surface of wood specimens of different forms (flat and cylindrical specimens) have been obtained and the heat-stressed parts under the action of the model combustion site imitating a low-intensity low forest fire have been determined. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the transition from layer-by-layer to convective combustion and to explosion for charges of advanced high-density explosives in a constantvolume chamber at a pressure of up to ≈60 MPa. Approximation of the results of the experiments with good correlation revealed a common parameter for explosives that characterizes the kinetics of convective combustion and made it possible to rank explosives according to their capability of transition from combustion to explosion. The results can be useful for computational modeling of explosion under accidental heating conditions. [ABSTRACT FROM AUTHOR]

The authors present the results of experimental studies of the basic properties of fuel granules that have been produced from wood raw material treated in different temperature regimes. The authors have established the influence of the temperature of pretreatment of the raw material on the hygroscopicity, swelling, flame-maintenance efficiency, and heat of combustion of fuel granules. A comparative analysis of the energy efficiency of torrefacted pellets and regular fuel granules has been made. [ABSTRACT FROM AUTHOR]

The modes of operation of a flow reactor with an inert inner body were investigated. A numerical study of the combustion of a methane-air mixture was performed. The parameter ranges of possible modes of reactor operation were determined depending on the dimensionless parameters of heat exchange of the mixture with the inert body and the side surface and the mixture flow parameter. The existence of non-uniqueness regions of operation modes is shown. The influence of the inert inner body on the distribution of the regions of possible modes of reactor operation is considered. [ABSTRACT FROM AUTHOR]

The combustion of various propellants containing ammonium nitrate (AN) is studied. It is shown that the effect of AN on the burning rate depends on the heat of combustion of the starting propellant, the amount of AN, and the pressure at which combustion occurs. Thus, AN slightly increases the burning rate of low-calorific value propellants and significantly reduces that of high calorific value formulations. It is shown that combined catalysts can considerably increase (by a factor of up to ≈6 at a pressure of 2-4 MPa) the burning rate of propellants containing 50-70% of AN, and reduce the pressure dependence of the burning rate. [ABSTRACT FROM AUTHOR]

Results of experimental studies on pyrolysis of brown coals of the Lelchitsy deposit, which were conducted on Laboratory setups in stationary and moving layers for producing high-caloric energy carriers, are presented. The yield of the pyrolysis products is determined; the chemical composition of solid, liquid, and gaseous products of thermochemical treatment is considered. [ABSTRACT FROM AUTHOR]