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The closed thermal power system employs the combustion of Li/SF6 as the heat source, which can provide power for UUV (Underwater Unmanned Vehicle). The startup and operation stability of the system can be significantly optimized by evaluating the combustion characteristics. Using the visual experimental system, the Li/SF6 combustion process is distinctly observed to be dominated by gas-phase combustion, and the flame is observed to be bright pink. The ignition temperature of Li/SF6 is 473.39 ± 2.00°C in the gaseous atmosphere for an initial pressure of 0.120 MPa and SF6 volume fraction of 75%. Furthermore, a computational model established by adopting the theory of minimum Gibbs free energy is used to estimate the combustion products of Li/SF6. Finally, the gaseous atmosphere of ignition of Li/SF6 is studied. O2 and N2 are not suitable to participate as combustion-supporting gases in the ignition of Li/SF6. Appropriately increasing the initial pressure can effectively reduce the ignition temperature of Li/SF6. To ensure the controlled combustion and safe operation of the closed thermal power system, the recommended initial SF6 volume fraction of the closed thermal power system is 75%. [ABSTRACT FROM AUTHOR]

The research effort in the microcombustor field has recently increased due to the demand for high-performance systems in microelectromechanical and micro power generation devices. To address rising concerns about pollutants from fossil sources, zero-carbon fuels such as hydrogen (H2) and ammonia (NH3) have been considered as an alternative in microcombustion processes. In a microcombustor, the surface area-to-volume ratio is much higher compared to conventional combustion systems, resulting in faster heat transfer rates and more intense combustion reactions. However, achieving efficient mixing of fuel and an oxidizer in a microcombustor can be challenging due to its small size, particularly for highly reactive fuels like H2. For NH3, challenges in microcombustion involve a low reactive, high ignition temperature (923 K vs. 793 K of H2) and high concentration of NOx combustion products. Therefore, studying the performance of these fuels in microcombustors is important for developing clean energy technologies. In this paper, to explore features of non-premixed NH3/air and H2/air combustion in micro-scale combustors, an Ansys Fluent numerical investigation was conducted on a Y-shaped microcombustor. Results show that for combustion with H2, stationary flames can be achieved even at lower equivalence ratios. Additionally, the pollutants generated from H2 in the flame are generally twice those of NH3. The overall efficiency of the microcombustor is two times greater for NH3 conditions than for H2 conditions. [ABSTRACT FROM AUTHOR]

In order to understand the pyrolysis and explosion characteristics of typical wood fiber dusts, the pyrolysis process, kinetic parameters, and pyrolysis gas types of the two dusts were calculated and analyzed using thermogravimetric-infrared coupler with redwood fiber dust and poplar fiber dust as the research objects. The results showed that the pyrolysis rate of mahogany dust was higher than that of poplar dust, and the activation energy was lower. The thermal weight loss of the two dusts was mainly reflected in the thermal decomposition at low temperature and combustion reaction at high temperature, and the pyrolysis products were mainly CO2, CO, H2O and a small amount of alkanes, alcohols, aldehydes, ketones and carboxylic acids, and the combustion products were mainly CO2 and CO, and the amount of CO2 of combustion products of mahogany fiber was higher than that of poplar fiber, while the pyrolytic combustion process of poplar fiber is relatively complex, with a high degree of incomplete combustion. The dust cloud minimum ignition temperature and maximum explosion pressure of the two wood fiber dusts were tested. Redwood fiber dust was more dangerous than poplar, and the mechanism was explained from the thermogravimetric-infrared test results. The results of this study could provide some data reference for the development of relevant policies and measures at sites involving such dusts. [ABSTRACT FROM AUTHOR]

In order to improve he reactivity of aluminum and high-temperature water vapor, aluminum-based polytetrafluoro-ethylene metastable intermolecular composites (Al/PTFE) with different ball milling time were prepared by mechanical ball milling. The micromorphology, crystal form and oxidation properties of the Al/PTFE were studied by scanning electron microscopy, laser particle size analyzer, X-ray diffraction, and synchronous thermal analyzer. The ignition performance of Al/PTFE in high-temperature water vapor was studied by a water vapor reactor. The micromorphology and composition of Al/PTFE combustion products were studied by scanning electron microscopy, laser particle size analyzer and X-ray diffraction analyzer. The rents show that the morphology of Al/PTFE composites changes from laky to massive with the increase of ball milling rime, and he particle size decreases with the increase of ball milling rime. The Al/PTFE composites prepared by 3 h ball milling show the best reactivity when reacted with Ugh temperature water vapor, and the D50 of the reaction product is 17.2 µm. The ignition delay time of Al/PTFE composites prepared by 3 h ball milling under high-temperature steam at 600 °C and 700 °C is 29 s and 15 s, respectively. The ignition temperature of the composites prepared in 3h are lower than those in both 1 h and 5h. [ABSTRACT FROM AUTHOR]

Regimes of continuous multifront detonation of two-phase mixtures of aviation kerosene and hot air are obtained for the first time and studied in a flow-type annular combustor 503 mm in diameter and 600 mm long. Air with a flow rate of 7.8–24 kg/s is preheated up to 600–1200 K by a firing method in the settling chamber by means of burning a stoichiometric H2–O2 mixture. Liquid kerosene is bubbled with air in the fuel injection system. The equivalence ratio of the fuel is 0.66–1.28. The influence of the air temperature on the region of continuous detonation, pressure in the combustor, and specific impulse is studied. Experiments with the air temperature in the interval 600–1200 K reveal regimes of continuous multifront detonation with one pair (frequency kHz) or two pairs (frequency kHz) colliding transverse detonation waves. Based on the stagnation pressure measured at the combustor exit, the thrust force and specific impulse are determined. It is shown that an increase in the air temperature assists in detonation burning of the two-phase kerosene–air mixture, but the degree of dissociation of combustion products increases, while the specific impulse of the thrust force decreases. The specific impulse increases if the amount of the fuel in the mixture is sufficiently small, and its maximum value with allowance for the energy of compressed air in receivers is approximately 2200 for the air temperature in the settling chamber equal to 600 K. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acidic hydrochar enhances dechlorination of waste PVC during co-HTT. • co-HTT of waste PVC improves energy content of HTT solid residues. • co-HTT solids showed higher ignition temperature and lower burnout temperatures. • co-HTT solids had low slagging, fouling and alkali indices. In this study, the chlorine mitigation from waste polyvinyl chloride (WPVC) during high temperature co-hydrothermal treatment (co-HTT) and the properties of the generated solid products were assessed. WPVC was co-fed with acidic hydrochar (AHC), which was produced via hydrothermal carbonization of pineapple waste in the presence of citric acid water solution. High temperature co-HTT experiments were performed at 300–350 °C, 0.25–4 h of reaction time, and 0–20 wt% AHC loading. Co-HTT solid products (co-HTT_SP) were characterized via proximate analysis, ultimate analyses, combustion analysis, and ash analysis. The results show that the addition of 5% AHC enhances the dechlorination efficiency (DE) of WPVC from 89.35% to 97.66% at 325 °C and 0.5 h. The highest DE, reaching 99.46%, was achieved at 350 °C and 1 h in the presence of 5 wt% AHC. Furthermore, loading 5% AHC improved the higher heat value (HHV) of the solid products from 23.09 to 31.25 MJ/kg at 325 °C and 0.5 h. The maximum HHV (34.77 MJ/kg) of a solid product was achieved at 350 °C, 4 h, in the presence of 5 wt% of AHC. The co-HTT solids shown low slagging indices, fouling indices, alkali indices, and medium chlorine contents. These findings support the viability of WPVC conversion into clean solid fuel via co-HTT. [ABSTRACT FROM AUTHOR]

A numerical simulation of the ignition of a fuel (propane–air) mixture in a combustion chamber by a subcritical streamer discharge, initiated at the wall of the working channel of this chamber in the electric field with a strength lower than the breakdown one, on the basis of the gas dynamics equation defining the propagation of the combustion products in such a channel, the equation for the chemical kinetics of burning of a gas mixture in it, and the relation defining the formation and development of a streamer discharge in this mixture has been performed for different values of the initial pressure in the channel, the excess of the propane in the gas mixture, and the number of streamer-discharge initiators in the channel. The results of the numerical calculations were compared with the available results of the corresponding physical experiment and experiment on the ignition of an analogous gas mixture by a multipoint spark discharge. [ABSTRACT FROM AUTHOR]

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With a high demand for high-performance spacecraft, the development of new nanofluid fuels has become a major opportunity and challenge. As solid–liquid hybrid fuels, the combustion of nanofluid fuels is affected by various factors and the combustion performance needs to be improved. In this paper, the JP10/boron (B)-based nanofluid fuel droplets containing polytetrafluoroethylene (PTFE) with 10 mass% nB/PTFE content were prepared by a mechanical mixing method, and their combustion characteristics were investigated, especially the droplet behavior and flame characteristics. Additionally, the effects of nano-sized boron (nB) and nano-sized polytetrafluoroethylene (nPTFE) on the oxygen consumption and reaction characteristics of droplets at different combustion stages were also analyzed. The combustion process of the JP10/B-based nanofluid fuel droplets with nPTFE addition is mainly defined as four stages, namely ignition stage, mixed combustion stage, secondary combustion stage, and boron burning stage. The addition of a small amount of nPTFE to the JP10/B-based nanofluid fuel does not reduce the ignition delay time of the droplet, but the combustible gas products such as CO and CF4 generated by the reaction between nB and nPTFE in the mixed combustion stage can destroy the droplet strongly and enhance the combustion of JP10, so the combustion time of the JP10/B-based nanofluid fuel droplets with nPTFE addition in this stage is shortened by 10.1% compared with that of the JP10/B-based nanofluid fuel droplets. In addition, nPTFE destroys the boron surface oxide layer and improves the combustion efficiency of boron particles, and the maximum burning intensity of droplets can be increased by 47%. The particle size of condensate combustion products is reduced by 85% because the gases generated split the agglomerates into small fragments. [ABSTRACT FROM AUTHOR]

Spray ignition is widely encountered in energy and power engineering and is an important characteristic in combustor operation and design. Droplet ignition is an important part of spray ignition. Most present studies of droplet and spray ignition use numerical simulation, which sometimes cannot explicitly indicate the mechanism of ignition and is inconvenient for engineering applications. This paper reports experimental and analytical studies on ignition of a single droplet and spray under different flow conditions. Analytical results based on a one-dimensional model are compared with experimental results. The results reveal that the droplet ignition temperature decreases with an increase in the droplet size and increases with an increase in the relative gas velocity. The temperature of kerosene spray ignition by propane combustion products increases with an increase in the excess air and decreases with an increase in the droplet size. The obtained research results are useful for liquid-fueled combustor design and operation. [ABSTRACT FROM AUTHOR]

The paper presents the results of experimental investigations of the main characteristics of a typical indoor seat of fire at the stages of initiating the ignition of combustible materials and in the process of their burning. Wood material, wood fiberboard, linoleum, and plastic panels have been used as combustible materials. We registered the characteristics of the seat of fire, viz., the temperature in the zone of burning of combustible materials, the times of termination of their flame combustion, and thermal decomposition, the concentrations of gaseous products of pyrolysis and combustion of these materials. The possibility of indentifying the material dominating in the seat of fire has been substantiated. Reliable identification of such material makes it possible to optimize the process of suppressing the seat of fire. [ABSTRACT FROM AUTHOR]

To solve the problem of difficult ignition and poor combustion performance of boron particles, the effects of different particles and blending ratios on ignition and combustion characteristics of boron-based composite metal fuel were explored using a single particle experiment. The main combustion products were detected and analyzed by the energy dispersive spectrometer (EDS) and scanning electron microscopy (SEM). The combustion temperature distributions were measured by the two-color pyrometry method. The results show that the combustion process of boron and boron-based composite metal particles is mainly divided into two stages including ignition and combustion stage. The additin of aluminum, carbon nanotubes, and graphene reduces the ignition delay time and combustion time. The influence of ignition delay time is increased with the increase if blending ratios. Moreover, the addition of nano-aluminum has the greatest effect on the ignition delay time of the composite fuel. The addition of carbon nanotubes and graphene has the greatest effect on the combustion time. The temperatures of the boron nanoparticles are measured and mostly distributed at 1772K. The addition of nano-aluminum increases the combustion temperature of single particle to 1830K, while the addition of nano-iron decreases the combustion temperature of single particle to 1680K. The addition of graphene and carbon nanotubes has little effect on the combustion temperature. [ABSTRACT FROM AUTHOR]

Polyurethane material is used as an interior finish and wall cavity insulation. Flame-retardant products may be used for ignition, flame diffusion, and heat-release blocking. A large-scale test was conducted to understand the flame propagation characteristics of polyurethane with the addition of a flame retardant. The fire propagation properties and fire risks of four commonly used polyurethane materials were examined using three tests. Specifically, ignition properties, flame propagation behavior, and flashover occurrence were probed using full-scale tests, while heat release and fire characteristics were examined using cone calorimeter tests, and the toxicity of gaseous combustion products was assessed using gas toxicity tests. PIR F and PIR B, which contained flame retardants, featured slow flame propagation and a long-lasting residual flame, and PIR F released HCl and Br2 on combustion. Full-scale tests revealed that although external flame propagation was always accompanied by flashover, irrespective of whether the flame retardant was present, a delay or blockage of energy transfer to the inside was observed for flame-retardant-containing specimens. Apart from checking the safety at the material level, the importance of identifying the actual fire characteristics through a full-scale test was confirmed. [ABSTRACT FROM AUTHOR]

Spontaneous ignition of isolated n-heptane droplets with initial diameters of 20–100 μ m is simulated using air at 4 atm and 700–1200 K, which includes the typical operating conditions of recuperated microturbines. Because some fuel droplets in a combustor may be sprayed or carried to near the recirculation zone, the simulations use a mixture of pure air and hot combustion products as the oxidiser. The flame structures, evaporation times, and autoignition times in both physical and mixture fraction spaces for the different conditions are presented and compared. The variables examined include the air preheat temperature, amount of dilution with hot products, initial fuel droplet diameter, oxidiser temperature, and oxygen concentration. The results show that droplets in pure air at microturbine conditions fully evaporate before ignition, suggesting that a prevaporised concept is suitable for microturbines. The dilution with hot combustion products decreases the ignition delay time mainly by raising the oxidiser temperature. Low-temperature chemistry does not have a significant effect on droplet ignition because adding even a small amount of hot combustion products can increase the oxidiser temperature to higher than the temperatures favourable for low-temperature kinetics. The cool flame is only observed for 100 μ m droplets at low temperatures, but two-stage ignition is not observed. [ABSTRACT FROM AUTHOR]

Micron-sized iron particles are promising carbon-free fuels. Efforts have been made to understand the combustion process of pure iron particles. However, it is not well-established how important are the impurities and their influence on combustion. The ignition and combustion characteristics of iron particles with 6.18 wt.% silicon were studied both by online optical diagnostics and offline scanning electron microscope (SEM) and X-ray Diffraction (XRD) analysis in this work. It is found that the ignition delay time is proportional to d n with n = 1. 23 ∼ 1. 56 , indicating that the oxidation reaction is unlikely solely limited by internal ionic diffusion before ignition. Compared with pure iron particles, the silicon-containing iron particle has a lower peak temperature and less oxidized combustion products. The intensity-rising time in the first intensity peak stage scales (1 / X O 2 ) n with n = 0. 80 or 1. 38 , which implies an external diffusion controlled combustion regime. Silicon in the oxide layer likely reduces the internal diffusion rate of oxygen, which becomes a rate-limiting step after the first intensity peak. Meanwhile, the surface tension also decreases due to the silicon content, which may facilitate the gas bubble nucleation and burst. The particle could partially change back to the external diffusion regime when the oxide layer is broken by the bubble expansion. This mechanism allows the reaction rate to increase and particle temperature to rise again. This explanation is verified by plenty of holes in the combustion products as well as the fact that the rising time in the large peak stage is proportional to (1 / X O 2 ) n with n = 0. 37 or 0. 32. With the increase in the temperature of the ambient gas flow, evaporation was observed. The high ambient temperature is hypothesized to be a key factor to trigger the evaporation of silica. [ABSTRACT FROM AUTHOR]

The development of efficient and reliable ignition systems for fuel mixtures is of interest for many practical applications associated with the use of combustion power plants. To increase the total flame surface, ensure the reliability of ignition, and increase the combustion rate in the chamber volume and the completeness of combustion of the combustible mixture, multipoint ignition of the fuel mixture using several pulsed spark discharges is used. Based on the data of a physical experiment, a comparison is made of the characteristics of combustion products in the working chamber when using different numbers of igniting spark discharges. The measurements were carried out at different ignition points of the mixture, initial mixture pressures, and fuel excess ratios in the mixture relative to the stoichiometric ratio. The values of the fuel excess coefficient used in the experiment are in a range the boundaries of which are the lower and upper concentration limits of ignition of the propane–air mixture. [ABSTRACT FROM AUTHOR]

The polyamine chelate complex of copper(II) hexafluorosilicate—[Cu(eda)(deta)]SiF6—(a flame retardant-hardener of epoxy resins) and CuSiF6-containing epoxy–amine composites—DGEBA/pepa-CuSiF6—with reduced combustibility and with the varied content of CuSiF6 were obtained in the DGEBA–pepa–CuSiF6 system (pepa—H2N[–C2H4NH–]nH, n = 1 (eda—NH2C2H4NH2) and n = 2 (deta—NH2C2H4NHC2H4NH2); DGEBA—bisphenol A diglycidyl ether). These samples were characterized by IR spectra, thermal analysis and flammability studies. The results of Thermogravimetric analysis (TGA) showed that thermal decomposition of [Cu(eda)(deta)]SiF6 is completed at 368 °C and the maximal temperature of the gaseous combustion products was 488 °C. TGA data for DGEBA/pepa-CuSiF6(22) confirm that the incorporation of [Cu(eda)(deta)]SiF6 into DGEBA significantly increases thermal stability and anti-flammability of CuSiF6-containing epoxy–amine composites. Ignition and self-ignition temperatures have been measured for all CuSiF6-containing epoxy–amine composites in accordance with ASTM D1929-16. Depending on the quantity of added CuSiF6, the tignition for this type of composite increases by 15–34 °C, and the tself-ignition increases by 25–58 °C compared to DGEBA/pepa. The flammability of the samples was evaluated by means of UL94 BH methods. The burning rate of the DGEBA/pepa-CuSiF6(66) and DGEBA/pepa-CuSiF6(88) epoxy–amine composites is severe slowed down (these samples do not propagate flame), while rburn. value for the unmodified epoxy–amine sample (DGEBA/pepa) is 25.13 mm min−1. [ABSTRACT FROM AUTHOR]

In the DGEBA–PEPA–CuSiF6 system (DGEBA is diglycidyl ether of bisphenol A, PEPA is polyethylenepolyamine), a new flame-retardant hardener for epoxy resins in the form of a chelate complex labeled as PEPA–CuSiF6 was synthesized and incorporated into the framework of DGEBA to make a range of CuSiF6-containing epoxy–amine composites (EA–CuSiF6) with reduced combustibility. The resulting EA–CuSiF6 composites were characterized using FTIR spectroscopy, thermogravimetric analysis (TGA), and temperatures of ignition and self-ignition measuring. TGA results showed that the thermal decomposition of PEPA–CuSiF6 ends at 368 °C, and after ignition of its organic component, the maximum temperature of the gaseous products of combustion reached 488 °C. TGA of EA–CuSiF6(22) sample confirms that the incorporation of PEPA–CuSiF6 into DGEBA significantly increases the thermal stability and reduces the flammability of the epoxy–amine composites. The combustibility of the epoxy–amine composite samples was investigated using "Ceramic tube" (CT) method. Results of CT measurement reveal that the maximal temperature of combustion gases for EA–CuSiF6(66) in comparison with unmodified epoxy–amine polymer (EAP) appreciably goes down and relative loss of the mass lessens. The measured ignition and self-ignition temperatures showed that depending on the amount of CuSiF6 added, tignition and tself-ignition for this type of composites increase by 15–34 °C and 25–58 °C, respectively, compared to EAP that does not contain additives. [ABSTRACT FROM AUTHOR]

The development of efficient and reliable ignition systems for fuel mixtures is of interest for many practical applications associated with the use of combustion power plants. To increase the total flame surface, ensure the reliability of ignition, and increase the combustion rate in the chamber volume and the completeness of combustion of the combustible mixture, multipoint ignition of the fuel mixture using several pulsed spark discharges is used. Based on the data of a physical experiment, a comparison is made of the characteristics of combustion products in the working chamber when using different numbers of igniting spark discharges. The measurements were carried out at different ignition points of the mixture, initial mixture pressures, and fuel excess ratios in the mixture relative to the stoichiometric ratio. The values of the fuel excess coefficient used in the experiment are in a range the boundaries of which are the lower and upper concentration limits of ignition of the propane–air mixture. [ABSTRACT FROM AUTHOR]

Potentially explosive atmosphere can occur not only in the production systems of the food, energy, chemical and petrochemical industries but also in the production processes of the mining industry. Gases, vapours, mists and dusts arise can escape in an uncontrolled way during production, processing, transportation and storage of flammable substances. In combination with oxygen, they create explosive atmospheres that, if ignited, lead to an explosion causing catastrophic damage to people's lives and property. To protect against the results of hazardous dust–gas mixtures explosions in a confined work space, where employees can stay, various control and protection mechanisms are used in the form of an active explosion-proof system. The article presents the results of tests on an active system for limiting the effects of ignition of gas and/or dust based on a highly efficient explosion suppression system—equipped with an ignition detection system, high-pressure fire extinguisher and a power supply and trigger system. Smokeless powder was used as the explosive charge and sodium bicarbonate as the suppressive material. Tests of the effectiveness of the active explosion suppression system were carried out on two devices: a small-size dry dust collector and a zone extinguishing system adapted for direct explosion suppression in closed working spaces. In both cases, the explosion suppression process took place through the action of extinguishing powder blown out of the fire extinguisher after membrane perforation by compressed combustion products. [ABSTRACT FROM AUTHOR]

The article presents the results of theoretical and experimental studies of the processes of wood particles ignition under heating conditions typical for furnace devices operating using the circulating fluidized bed technology. The characteristics and conditions of ignition processes under radiation, radiation-convective and radiation-convective-microwave heating are compared. According to the results of the experiments, it was found that the use of microwave energy to accelerate the ignition of wood biomass particles is most effective at moderate temperatures of the combustion medium (at T g ≤870 K). Such conditions, as a rule, are formed in furnace devices that operate using boiling and circulating layer technologies. Based on the results of the analysis of the regularities established in the experiments, a mathematical model of the processes of ignition of a particle of wood biomass under conditions of complex radiation-convective-microwave heating has been developed. Using the method of quasi-stationary "thermal" approximation developed by the authors, an approximate analytical solution of the essentially nonlinear problem of ignition of wood biomass particles under conditions of complex heating is obtained. A comparative analysis of the theoretical and experimental values of the ignition delay time showed their good agreement. The results of the performed studies illustrate the possibility of a sufficiently significant reduction in the ignition delay times of wood biomass particles when using microwave radiation in addition to "conventional" sources of heating fuel particles in the furnace space in the temperature range at which the minimum concentration of anthropogenic nitrogen oxides in fuel combustion products is ensured. [ABSTRACT FROM AUTHOR]

• The chemical interactions between three typical pyrotechnics with cellulose as packing material have been studied. • The cellulose would interact with B/KNO 3 with exothermic reactions during the pyrolysis. • It is difficult for Mg/PTFE to undergo self-sustainable combustion at ambient pressure in presence of cellulose. • The cellulose has little effect on the flame temperature and reaction pathways of B/KNO 3. In order to study the effect of cellulose shell on the thermal behavior including pyrolysis gaseous products, ignition and combustion characteristics of typical pyrotechnics, three composites of pyrotechnics/cellulose were prepared in this paper. Various characterization techniques were used to investigate the prepared composites and their combustion condensed products (CCPs), including scanning electron microscopy (SEM), simultaneous thermal analysis (DSC-TG-FTIR), X-ray diffraction (XRD), bomb calorimetry, and home-made combustion diagnostic system. The results showed that the overall heat release of the black powder and Mg/PTFE decreased from 3108 J·g−1 and 1157.4 J·g−1 to 1045.4 J·g−1 and 810.4 J·g−1 in the presence of 33.3% cellulose, respectively. Moreover, the FTIR spectra showed that the cellulose did not change the reaction pathways of black powder and Mg/PTFE, which mainly include H 2 O, CO 2 , NO 2 for the black powder, and HF, H 2 O, CO 2 , CF 2 for Mg/PTFE. However, the condensed products of cellulose would interact with B/KNO 3 at a higher temperature, so that the heat release was largely increased by 339%. The cellulose has obviously impact on the energy release rate of Mg/PTFE in comparison to the other two composites. Moreover, the negative impact on ignition of Mg/PTFE composite is significant, when the content of cellulose reaches over 33.3%, resulting in difficult self-sustainable combustion at ambient pressure. The cellulose can largely reduce the maximum flame temperature of the black powder and Mg/PTFE, whereas it has little effect on B/KNO 3. The CCPs of the involved igniting pyrotechnics and their cellulose-based composites have different phases due to their strong thermal interactions with cellulose. [ABSTRACT FROM AUTHOR]

Acetylene is an effective additive to various rocket fuels. Acetam, an equilibrium highly concentrated solution of acetylene in liquid ammonia, is a promising fuel for use in liquid−propellant jet engines. To gain insights into the processes occurring in such systems and provide means for predicting their characteristics, the self-ignition of model acetylene−oxygen−argon mixtures is experimentally and theoretically studied. The experiments are performed behind reflected shock waves in a temperature range from 1100 to 1870 K at a total gas concentration of [M] ≈ 1.0 × 10−5 mol/cm3, with chemiluminescence signals from electronically excited C 2 * (λ ≅ 516 nm), CH* (429 nm), CO 2 *(363 nm), and OH* (308 nm) recorded. Numerical simulations within the framework of various detailed kinetic mechanisms closely reproduce the measured temperature dependences of the ignition delay time for the tested mixtures, but in some cases fail to satisfactorily describe the time profiles of the emission signals from C 2 *, CH*, CO 2 *, and OH*. The performed numerical simulations make it possible to explain the observed characteristic features of the emission profiles of electronically excited C 2 *, CH*, CO 2 *, and OH* during the self-ignition of C 2 H 2 –O 2 −Ar mixtures. Sensitivity analysis demonstrates that the existence and characteristics of the preignition stage in the CO 2 * and OH* emission signals are largely determined by the kinetic behavior of intermediate species, such as the ketene molecule and CH 2 radical. Based on the results obtained, a new detailed kinetic mechanism has been proposed for describing processes in the combustion products of acetylene-containing propellants, in particular chemiluminescent glow, which are of considerable interest for the development of new technologies for astronautics and aeronautics. • Results of shock-tube acetylene autoignition are presented. • A detailed kinetic mechanisms capable of describing acetylene ignition delay is developed. • The problems of simulation of chemiluminescence are discussed. • The importance of the kinetics of intermediate products are demonstrated. [ABSTRACT FROM AUTHOR]

An experimental study was carried out to investigate the combustion characteristics of plant-derived polyol liquor waste using thermogravimetric analyzer and vertical tube furnace tests. The research results showed that the waste liquor combustion reaction comprised four processes: evaporation, pyrolysis, combustion, and inorganic salt reaction, and that a wave peak exists for each process. The pyrolysis process, which is the most violent reaction, exhibited the maximum peak weight-loss rate and weight-loss ratio and had the lowest activation energy and frequency factor. The peak weight-loss rate of inorganic salt reaction process was less than that during the combustion process, but sodium alkali has catalytic effect at high temperature, which makes the activation energy and the frequency factor of inorganic salt reaction process less than that of the combustion process. The ignition temperature of the waste liquor in the vertical tube furnace was lower than the temperature in the thermogravimetric analyzer. The ignition temperature of pyrolysis volatiles measured in a vertical tube furnace was less than 700 °C but the ignition temperature of carbon combustion as measured with TG -- DTG was 718 °C. When the temperature inside vertical tube furnace was higher than 800 °C, the waste liquor combustion process becomes almost instantaneous (about 8 s) and is violent, which produces more residual carbon content in the combustion products as a longer holding time is necessary to ensure that the reaction is completed. [ABSTRACT FROM AUTHOR]

Reliable ignition of reactant mixtures containing combustion products is important to the function of many practical combustion devices. Prior work has considered the influence of CO 2 on ignition delay times and laminar flame speeds. This work examines the effects of dilution with CO 2 on forced ignition and development of ignition kernels in CH 4 /air mixtures. Ignition kernels were initiated by a high voltage spark discharge in CH 4 /air/diluent mixtures with a bulk velocity of 5 m/s and with 0. 7 ≤ Φ ≤ 0. 8. Ignition probabilities and kernel growth rates were determined from radiation intensity measurements collected using a Telops MS-IR FAST infrared camera. Nitrogen was used as an inert in a subset of conditions to facilitate identifying changes in chemistry associated with dilution by CO 2. Chemistry effects of diluents on ignition were isolated by examining undiluted, N 2 diluted, and CO 2 diluted flows with equivalent adiabatic flame temperatures. Dilution with CO 2 reduced the probability of ignition relative to undiluted and N 2 diluted conditions with the same adiabatic flame temperature. Ignition kernels diluted with CO 2 also tended to be smaller than those initiated in both undiluted and N 2 diluted mixtures, with reduced growth rates. [ABSTRACT FROM AUTHOR]

Zirconium-boron composite powders with the stoichiometric bulk composition corresponding to ZrB2 were prepared using high-energy milling in a shaker mill starting with elemental boron and zirconium. Milling times up to 3 hours were explored. The characterization of the prepared powders included measuring their particle size distribution, crystal structure, and assessment of particle structure and morphology. Reactions in the prepared powders were characterized using thermal analysis as well as custom ignition and combustion experiments. Composite powders consist of a Zr matrix with B inclusions mostly 100 nm or less in size. The homogeneity of mixing between boron and zirconium improves when the milling time increases from 1 to 2 hours; it is not affected by longer milling times. Boron and zirconium start reacting during milling; the degree of this reaction becomes appreciable when the milling time reaches 2 hours. In air, ignition of both pure zirconium and the prepared powders occurs in the same temperature range of ca. 400–700°C for the heating rates varied from 2000 to 20,000 °C/s. In fuel-rich conditions, ignition of the prepared powders is affected by the reaction between B and Zr, which occurs less readily for powders milled for 2 hours or longer. In air, particles of the prepared composite powders burn faster than either pure boron or zirconium. Flame temperatures for individual composite particles burning in air are reasonably close to those predicted as adiabatic flame temperatures for this composite-air system at stoichiometric and fuel-rich conditions. In combustion products of an air-acetylene flame, the burn rates of the prepared composites are lower than that of zirconium and are comparable to that of boron. Powders prepared by 1-hour milling burn faster than powders prepared using longer milling times. [ABSTRACT FROM AUTHOR]

Petroleum coke (petcoke) is a challenging fuel in terms of its complexity, high sulphur and nitrogen content, low volatile content, and undesirable emissions of SOx and NOx when used for power generation. To overcome these challenges, the oxy‐cracking process was recently proposed to convert the petcoke into a clean combustion fuel by reducing its sulphur and nitrogen contents, and consequently increasing its reactivity and combustibility. This work aimed to study the heating values and thermo‐oxidative behaviour of the oxy‐cracked petcoke, virgin petcoke, and their blends using thermogravimetric analysis (TGA). The results showed that the oxy‐cracked petcoke is oxidized at a temperature of 475 °C, which is easier and faster than the virgin petcoke, which is usually oxidized at around 540 °C. The heating value of the oxy‐cracked petcoke was not impacted and maintained constant ~30 MJ/kg, which is relatively similar to the virgin petcoke. The nitrogen and sulphur content in the oxy‐cracked petcoke is much lower than that of virgin petcoke. A significant improvement in the combustion performance parameters of the oxy‐cracked petcoke and their blends with virgin petcoke was achieved. For instance, the ignition temperature of the proposed fuel is reduced to 13 % compared to the virgin petcoke, which led to increasing the ignition index by two‐folds. Therefore, this approach might help in improving the thermal efficiency of petcoke by using oxy‐cracked products as an initiator in the combustion process. Highlights: The oxy‐cracked petcoke was proposed as an alternative fuel for power generation.The thermo‐oxidative behaviour of the oxy‐cracked petcoke blends was investigated.The heating values of virgin and oxy‐cracked petcoke were calculated.The combustion reaction characteristics of the proposed fuel were investigated.The reactivity indexes of the oxy‐cracked blend with virgin petcoke were evaluated. [ABSTRACT FROM AUTHOR]

Aluminum nitride (AlN) was synthesized by combustion of spherical Mg–Al alloy particles in air. Alloy powder was freely poured on a sample table, which formed a cone with a diameter of 1-2 cm. A commercial electro-thermal furnace was used to ignite the cone to start the synthesis. During the combustion, the temperature was measured and the actual burning process was recorded by a video camera. The morphology and phase makeup of the raw powders and the synthesized AlN powders were analyzed by scanning electron microscopy and X-ray diffraction. The thermodynamic properties and ignition temperatures were studied using differential scanning calorimetry and thermogravimetric analysis. Moreover, the effects of the Mg–Al alloy particle size (212.8 μm, 124.1 μm, 61.1 μm, and 29.5 μm) on the morphology of AlN were investigated. The results show that the combustion of Mg greatly promoted the nitridation of Al and that Al in both large and small alloy particles could be completely converted into AlN. The combustion products of the alloy consisted of two different layers: an upper white layer containing MgO and a lower black layer containing AlN. More AlN whiskers formed when small particles were used. However, very small Mg–Al alloy particles hindered the formation of AlN whiskers. [ABSTRACT FROM AUTHOR]

Combustion of two nanocomposite powders comprising equal mass fractions of aluminum and a metal fluoride, BiF3 or CoF2, is characterized experimentally. The powders were prepared by arrested reactive milling; earlier work showed that they are readily ignited upon heating and are insensitive to ignition by electrostatic discharge. Here, powder particles were ignited in air by passing through a focused CO2 laser beam. They were also ignited and burned in oxygen‐starved environments produced in the combustion products of an air‐acetylene and air‐hydrogen flames. Burn times and color temperatures of the particles were measured optically. Combustion products were collected and examined using electron microscopy. Correlations of burn times with particle sizes showed that the composites containing BiF3 burned faster than those containing CoF2. In air, the burn rates of both composite powders exceeded that of pure Al; in the oxygen‐starved environments the burn rates of the prepared composites were comparable to that of Al. The flame temperatures of the CoF2‐containing composite were limited by the Al boiling point while BiF3 containing composites burned at higher temperatures. Combustion mechanisms for the prepared materials are discussed qualitatively. [ABSTRACT FROM AUTHOR]

In the present work, two different methods were used to study the effect of mechanical activation on aluminothermic reduction of MoO 3. In the first method, a stoichiometric amount of Al + MoO 3 and 20% weight percent of aluminum oxide (as the heat absorber) was mixed and mechanically activated by milling process in a planetary ball mill under argon atmosphere. XRD patterns and SEM micrographs of the activated samples indicated that aluminothermic reduction of MoO 3 was done in the milling media after 5 h and increasing the milling time, decreased the remaining non reacted Al and MoO 3. In the second method, as received MoO 3 , was mechanically activated in different times in the range of 3 to 24 h. The effect of mechanical activation on molybdenum trioxide grain size was analyzed by Williamson-Hall method, and it was shown that, by increasing the activation time, the grain size and internal strain was reduced and increased, respectively. In the next step, the activated MoO 3 powders were mixed with stoichiometric amount of Al and 20 wt% Al 2 O 3 (as the heat absorber) and shaped in the form of cylindrical samples of 10 mm in diameter and height of 15–20 mm by applying 70 MPa uniaxial pressure. Aluminothermic reaction was initiated in the prepared pellets by using conventional microwave oven. The XRD patterns of the combustion products showed that, by mechanical activation of MoO 3 , the undesired phases of molybdenum dioxide (MoO 2) and aluminum molybdate Al 2 (MoO 4) 3 was decreased. The aluminothermic reduction of activated MoO 3 also was studied by non-isothermal Differential Scanning Calorimetry (DSC) with heating rate of 10 °C min−1 under argon atmosphere. The results showed that by mechanically activating MoO 3 for 24 h, the ignition temperature of reduction reaction decreased from 910 to 780 °C and the practical efficiency of the reaction increased from 82.9% (for the nonactivated MoO 3) to 92.5%. The comparing results between the milling mixture and the milling molybdenum trioxide indicated that the reaction in mixture cannot be completed during milling and a small amount of Al and MoO 3 remained in the activated powder. But for the activated MoO 3 , and after igniting in a conventional microwave oven the desired reaction went to completion. • It has been shown that. • Mechanical activation of MoO 3 , caused elimination of undesired phases of molybdenum dioxide and aluminum molybdate. • By mechanical activation of MoO 3 , the production of undesired phases of molybdenum dioxide (MoO 2) and aluminum molybdate Al 2 (MoO 4) 3 can be efficiently eliminated. • Mechanical activation decreases the ignition temperature of aluminothermic reduction of MoO 3. [ABSTRACT FROM AUTHOR]

The issues of obtaining fireproof textile materials that do not cause negative effects upon contact with human skin using surface treatment are covered. The basic formulations of the compositions most frequently used to produce fireproof fabrics are considered. The possibility of developing a composition with optimal properties based on well-known flame retardants by selecting the type and amounts of stabilizers has been studied. The optimal formulation of a flame-retardant impregnating composition is developed, providing resistance to ignition and safe when in contact with human skin. The results of experimental studies of fabrics treated with the developed composition are given, namely: assessment of ignition resistance, smoke-forming ability, toxicity of combustion products, toxicological and hygienic characteristics of the effects on a living organism. [ABSTRACT FROM AUTHOR]

This paper presents a review of studies of the combustion of composite propellants containing a combined fuel based on aluminum and boron. A method for studying the combustion of large particles of the combined Al + B fuel in air is described. Burning agglomerated Al/B particles 300–700 μm in diameter were obtained by ignition of miniature pieces of a composition containing 32% binder and 68% micron-sized aluminum and boron powders in the ratio Al/B = 81/19 placed in a burning metal-free sample. Agglomerates formed by the merger of many small particles burned in free fall in air. Procedures are described that were used to process video records of the combustion process and study condensed combustion products (combustion residues of agglomerates) in order to determine the burning time and analyze the transformation of the combined fuel into oxide. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simultaneous ignition occurred at a distance between the droplet centers of 3–5 mm. • At low temperatures, increasing the distance between droplets eliminates synergism. • The use of an oil additive (5%) reduced the ignition delay time of droplets by 15–20%. • The increase in air flow velocity contributed to the formation of a common flame zone. • The ignition delay in the droplet group increased with an increase in air flow velocity. Waste-derived slurries can be burned both in a fluidized bed and when injected into a boiler furnace. This paper is the first to analyze the dynamic characteristics of ignition and combustion of a group of three slurry droplets based on coal slime, water, and waste industrial oil in a low-temperature air flow with a temperature of 500–600 °C and velocity of 0.1–1.2 m/s. The distance between the droplet centers varied from 3 to 15 mm. The results of the study can develop innovative technologies for flare and fluidized bed combustion of fuel slurries at the boiler start-up stage. It was found that a distance of 3–5 mm between droplet centers provides almost simultaneous gas-phase ignition of all droplets. A further increase in the distance critically worsened the ignition and combustion and eliminated the synergy. An increase in the air flow velocity contributed to the appearance of a common flame zone but at the same time increased the ignition delay of droplets by a factor of 1.2–1.6. The negative effects of cooling and entrainment of combustion products by a low-temperature flow can be effectively reduced by adding 5 wt% of industrial oil to the slurry. Also, the use of oil reduced the droplet ignition delay time by 15–20%. At the stages of flame and heterogeneous combustion, the differences for droplets in a group increased (the stage durations differed by 1.5–3 times). For the low-temperature start-up of a boiler, it was found advisable to provide a droplet flow with a sufficient density to stabilize their ignition without significant flow deviations (dimensionless distance 1.5–2.5). [ABSTRACT FROM AUTHOR]

• The ceiling equilibrium wall-temperature is much lower than the combustion products. • The probability of pre-ignition occur is the highest nearby the open end of the tube. • The equilibrium temperature decrease along the tube when the divergent nozzle is utilized. • Wrapping flame at the open end will not be prevented if the convergent nozzle is utilized. • The convergent-divergent nozzle will reduce the wall-temperature near the open end. As the increase of wall-temperature during the long-duration operation, pre-ignition of the fresh mixture in the filling process often occur in the detonation tube, resulting in the failure of operation. An experimental work has been conducted to investigate the impact of nozzle on the wall-temperature of the detonation tube. In the present study, kerosene and oxygen enriched air were employed in the experiments, and an internally grooved semi-circle spiral, instead of traditional Shchelkin spiral was utilized to facilitate the deflagration to detonation transition (DDT) process. The theoretical results showed that the temperature of fresh mixture increase along the detonation tube during the filling process, and it is likely to be ignited near the open end. It was observed from the experimental results that the convergent section and the divergent section of the exit nozzle has different influence on the wall-temperature. The convergent nozzle will not prevent the wrapping flame near the open end of the detonation tube, and lead to the increase of equilibrium wall-temperature. The nozzle with a diverging section will eliminate the occurrence of wrapping flame during the operation, and the wall temperature near the open end are dramatically decreased. In addition, smaller expansion ratio of the nozzle will lead to lower equilibrium wall-temperature. [ABSTRACT FROM AUTHOR]

• The physical mixing effects of fuel molecules were evaluated through a micro-mixing TJI model framework. • The physical and chemical effects of both cold jet and hot jet revealed by comparing the HRR and IDT. • The low-carbon intermediate CH 3 /C 2 H 2 radicals in the cold jet have the most significant effect on shortening the IDT. • The flame instability with jet ignition were revealed by discussing the DL Instability and TD instability. The Equilibrium-PaSR and the Constant-volume reactor framework were used to construct the TJI combustion system with or without turbulence effects. Numerical investigations on micro-mixing and chemical kinetic effects of ultra-lean methane-air mixture ignited by turbulent jets were conducted. The results show that main chamber combustion (MCC) is commonly affected by the jet reactive stages and fuel mixed time. The higher mixing time leads to faster heat transfer and less temperature rise, which ultimately limits the fuel conversion. So PaSR 1 fuel reactivity has a stronger effect on t 50 (time of 50 % fuel conversion in MCC) than the micro-mixing effect. Besides, the methane content in the jet is particularly important for the overall combustion process in MCC. For the analysis of the chemical kinetic effects, it is known that the ignition of MCC at lower temperatures is more strongly affected by the chemical effects of the combustion products from the pre-combustion chamber (PCC). As the temperature increases, the chemical effect decreases slightly, and the physical effect presents an increasing trend. The low-carbon intermediate CH 3 /C 2 H 2 radicals in the cold jet have the most significant effect on shortening the ignition delay time (IDT). The ignition ability of the hot jet is closely related to the chemical effects of H/O/OH radicals, and the chemical effects of important low-carbon intermediate species are significantly reduced. For flame instability analysis, the combustion products can reduce the flame thickness of the mixture in MCC to increase the intensity of hydrodynamic instability. With the increase of [O + OH], the destabilizing effect of the thermal-diffusion instability of methane-air premixing gradually increases. [ABSTRACT FROM AUTHOR]

Ignition of fuel/oxidizer mixtures containing combustion products is important to the operation of advanced combustors. Previous work indicates that the presence of NO can reduce ignition delay times, yet the influence of NO on forced ignition is not clear. This work examines ignition kernels generated by spark discharges in CH 4 /air flows diluted with a mixture of NO and N 2. Differences in chemistry initiated by the presence of NO are examined by comparing mixtures diluted with only N 2 to mixtures diluted with both NO and N 2. Ignition probability and kernel growth rates are determined using measurements of infrared radiation emissions from the developing ignition kernels. The presence of NO in the unburned mixture does not affect ignition probability. However, the addition of small quantities of NO on the order of 300–1200 parts per million increases the size of ignition kernels relative to those generated in mixtures diluted with pure N 2 by up to 20%. Numerical modeling is performed to examine the role of low temperature chemistry on ignition behavior. The sensitivity of ignition kernel growth to the presence of NO is attributed to increased CH 4 oxidation rates caused by low-temperature chemistry activated in the early stages of kernel development. [ABSTRACT FROM AUTHOR]

Nano Silicon (Si) powder has become a new type of solid fuel in recent years because of its high energy density, large gas production, and low agglomeration behavior. Optimizing and improving its energy release performance is an important challenge. In this paper, DAP-4, an energetic molecular perovskite material with high energy and strong oxidation, was introduced as the oxidant to prepare DAP-4/Si composites, and its combustion properties were studied. The thermal decomposition, combustion performance, as well as their combustion product properties, were studied. The results showed the thermal decomposition properties of DAP-4/Si composites still keep stable (>370 °C), and the combustion properties of DAP-4/Si composites first increase with Si content and then reduced. It was confirmed that DAP-4/Si with the ratio of 6.5:3.5–6:4 had a better burning intensity than the other ratios. The combustion mechanism of DAP-4/Si composites was proposed based on the ignition and combustion characteristics of DAP-4/Si composites. This work may provide a further reference for the application of DAP-4 into solid propellant formulation. • (H 2 dabco)[NH 4 (ClO 4) 3 ] DAP-4/Si composites were prepared and characterized. • The combustion properties of DAP-4/Si composites were researched. • DAP-4/Si with the ratio of 6.5:3.5–6:4 had a better burning intensity than the other ratios. • The combustion mechanism of DAP-4/Si composites was proposed. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental study of the ignition and combustion of pyrotechnic compositions based on microsized and ultra-nanosized aluminum particles in a model two-zone gas generator using water as oxidizer. The flow of combustion products from the gas generator was video recorded, and the condensed products sampled behind the nozzle exit were studied by chemical and particle-size analyses. It was found that the replacement of microsized aluminum particles by ultra-nanosized particles in the samples led to a ≈17% decrease in the active aluminum content in the condensed phase, a 10-15% increase in the efficiency of the process in the gas generator (completeness of conversion of the pyrotechnic composition to combustion products), and a factor of about three decrease in the ignition delay. [ABSTRACT FROM AUTHOR]

The processes of ignition and combustion of i-CH-H and n-CH-H fuel blends in air are analyzed numerically. It is demonstrated that addition of hydrogen both to normal alkane ( n-CH) and to alkane with a branched structure ( i-CH) leads to an increase in the ignition delay time τ if the initial temperature of the mixture is lower than a certain value T and, vice versa, to a decrease in τind at T > T . The greater the fraction of hydrogen in the mixture, the greater the change in τind. At sufficiently high temperatures ( T > T ), addition of a small amount of alkane (≈2-10%) to hydrogen reduces the ignition delay time. The value of Tl depends on the pressure of the fuel-air mixture and, to a smaller extent, on the n-alkane type. The value of T also depends on the fraction of alkane in the fuel blend. If the initial pressure is sufficiently high (10 atm and more), addition of a small amount of i-CH or n-CH to the hydrogen-air mixture reduces the value of τind for all values of T . These features are caused by intense interaction of alkane and hydrogen oxidation kinetics. It is demonstrated that fuel blends consisting of hydrogen and n-CH ( i-CH) have a higher velocity of the laminar flame and wider limits of stable combustion than the hydrocarbons themselves. Nevertheless, a noticeable increase in the laminar flame velocity is observed only for the molar fraction of hydrogen in the fuel blend greater than 50%. In this case, it becomes possible to ensure stable combustion with a smaller fraction of NO in combustion products. [ABSTRACT FROM AUTHOR]

For the first time, for performing thermally coupled SHS processes, granular mixtures were used instead of powder ones. In this case, the rate of the heat transfer between the donor and the acceptor is virtually independent of the sample size and is determined only by the granule size. Therefore, an advantage of using a granular mixture is that the process optimized under laboratory conditions can be scaled without changing its characteristics and the properties of the desired synthesis product. The studied granular mixture comprised a mixture of (Ni + Al) granules (acceptor) and a mixture of (Ti + C) granules (donor), which differed in rate and temperature of combustion. It was determined that the ignition of the (Ni + Al) acceptor granules occurred in the combustion front. It was shown that using granular mixtures for performing coupled thermal reactions makes it possible to obtain the combustion products as a readily destructible sample, from which the desired product can be separated even if the melting point of the product of the interaction of the acceptor mixture is lower than the adiabatic combustion temperature. [ABSTRACT FROM AUTHOR]

For solving the low combustion efficiency caused by aggregation and further promoting the application of nano titanium powder (n-Ti), a new ternary composite high-substitute nitrochitosan/nano titanium/graphene oxide (NCh/n-Ti/GO) was prepared by a resonant acoustic mixing method. Herein the high-substitute nitrochitosan (NCh) was used as binder and oxidant to modify the surface of n-Ti powder, and GO was introduced as stabilizer and carrier. The energy release rate, laser ignition, combustion performance and sensitivity of NCh/n-Ti/GO were systematically studied in this work. The experiment results confirmed that GO plays a significant role in adjusting combustion performance and reducing the sensitivity of composite. Compared with n-Ti, NCh/n-Ti and NC/n-Ti, the introduction of GO can greatly increase the combustion time and reduce the flame propagation speed. In particular, NCh/n-Ti/GO (3 wt%) presentedan optimal linear flame morphology, the shortest ignition delay time and lowest pressurization rate. The combustion products were also determined and confirmed to be co-existence of TiO, a little TiN and unburned n-Ti powder. The introduction of GO can reduce the sensitivities to impact and electrostatic of composites greatly. The electrostatic sensitivity of NCh/n-Ti/GO (3 wt%) was 5.1 ± 0.1 mJ and decreased by 160% and 230%, compared with that of n-Ti and NCh/n-Ti. So the introduction of NCh and GO would be a good strategy to promote the combustion performances and safety of n-Ti powder. [ABSTRACT FROM AUTHOR]

• The core–shell energetic fibers are designed and fabricated through the coaxial electrospinning. • The combustion characteristics of core–shell energetic fibers increase by the increase of CL-20. • CSEF 50C films are deposited onto SCB in-situ displaying an excellent clearance ignition ability. Electrospinning has exhibited great potential in the fabrication of fibrous energetic materials for the past few years. Herein, the core–shell energetic fibers (defined as CSEF) were designed and fabricated through the coaxial electrospinning. The core stratum was Al/MoO 3 -PVDF and the shell stratum was CL-20-NC. The morphologies of CSEF performed a clear core–shell structure, and the constituent analyses demonstrated that the components did not change after the preparation. According to the relative content of CL-20, the samples were defined as CSEF 0C , CSEF 10C , CSEF 30C and CSEF 50C respectively. The clear core–shell structure of CSEF was confirmed through the morphologies. The total heat releases of CSEF were not affected by the variation of the content of CL-20 nearly, and the existence of CL-20 improved the thermal stability of Al/PVDF. The combustion propagation velocity of CSEF increased by the increase of CL-20 from 0.241 m/s (CSEF 0C) to 0.664 m/s (CSEF 50C). In addition, CL-20 decreased the ignition temperature and delay time of CSEF. The combustion products analyses demonstrated that CL-20 promoted the combustion performance of CSEF by leading to less sintering of the reactants. Furthermore, CSEF 50C films were fabricated and deposited onto a semiconductor bridge (SCB) in-situ (defined as CSEF 50C -SCB). CSEF 50C -SCB possessed larger flame and longer combustion duration, which displayed an excellent clearance ignition ability. The superior combustion performance of CSEF films assembled with SCB in-situ would exhibit the admirable application prospects for practice when combined the Micro-electromechanical systems (MEMS). [ABSTRACT FROM AUTHOR]

Stabilization methods of turbulent flames often involve mixing of reactants with hot products of combustion. The stabilizing effect of combustion product enthalpy has been long recognized, but the role played by the chemical composition of the product gases is typically overlooked. We employ a counterflow system to pinpoint the effects of the combustion product stoichiometry on the structure of turbulent premixed flames under conditions of both stable burning and local extinction. To that end, a turbulent jet of lean-to-rich, CH 4 /O 2 /N 2 -premixed reactants at a turbulent Reynolds number of 1050 was opposed to a stream of hot products of combustion that were generated in a preburner. While the combustion product stream temperature was kept constant, its stoichiometry was varied independently from that of the reactant stream, leading to reactant-to-product stratification of relevance to practical combustion systems. The detailed structure of the turbulent flame front was analyzed in two series of experiments using laser-induced fluorescence (LIF): joint CH 2 O LIF and OH LIF measurements and joint CO LIF and OH LIF measurements. Results revealed that a decrease in local CH 2 O+OH and CO+OH reaction rates coincide with the depletion of OH radicals in the vicinity of the combustion product stream. These critical combustion reaction rates were more readily quenched in the presence of products of combustion from a stoichiometric flame, whereas they were favored by lean combustion products. As a result, stoichiometric combustion products contributed to a greater occurrence of local extinction. Furthermore, they limited the capacity of premixed reactants to ignite and of the turbulent premixed flames to stabilize. In contrast, lean and rich combustion products facilitated flame ignition and stability and reduced the rate of local extinction. The influence of the combustion product stream on the turbulent flame front was limited to a zone of approximately two millimeters from the gas mixing layer interface (GMLI) of the product stream. Flame fronts that were separated from the GMLI by larger distances were unaffected by the product stream stoichiometry. [ABSTRACT FROM AUTHOR]

Aluminum (Al) powder as an additive can enhance the specific impulse of propellants. However, it is hard to completely burn due to its aggregates in the combustion of propellants. To improve the combustion of Al powder, calcium fluoride (CaF 2) was added to micron-sized Al powder to form the Al/CaF 2 mixture, whose thermal behaviors, ignition and combustion performance, and combustion products were investigated. Micron-sized Al powder with CaF 2 addition can decrease its ignition delay time and increase its self-sustaining combustion time. The corresponding values can be decreased by more than 65% and increased by more than 16%, respectively. Compared with micron-sized Al powder, an obvious gas-phase combustion occurs in the Al/CaF 2 mixture. The agglomeration mechanism of Al combustion in the Al/CaF 2 mixture were analyzed. On the one hand, the uneven distribution of oxidant leads to a pressure difference during combustion to accelerate Al agglomeration; on the other hand, the melting-agglomeration-combustion process occurs because the melting temperature and the ignition temperature of Al have a big difference. In addition, an improved Al combustion mechanism was established. • CaF 2 can decrease the ignition delay time and increase the self-sustaining combustion time of Al powder. • The addition of CaF 2 can cause an obvious gas-phase combustion of Al powder. • The presence of pressure difference causes Al agglomeration during combustion. • The process of Al agglomeration and gas-phase combustion was captured in detail. • The optimized gas phase combustion mechanism of Al powder was established. [ABSTRACT FROM AUTHOR]

This work investigated the ignition and combustion process of single micron-sized iron particles in the hot gas flow of burned methane-oxygen-nitrogen mixture. The particle emission intensity was recorded by a high-speed camera in different flame conditions. Particle temperature was derived through two-color pyrometry method employing an ICCD camera equipped with a stereoscope. Based on scanning electron microscopy (SEM) image, the microstructure change of iron particles was investigated. Results showed that the temperature of burning particle rose rapidly and was much higher than the ambient temperature. The fresh iron particles mainly went through several stages in hot gas flow: heating, melting, rapid combustion and cooling. Some of them became bright again after cooling. According to the above combustion process, combustion parameters including ignition delay time, accelerated burning time, total burning time and second stage of combustion time were defined. All the above defined parameters were almost linearly increasing with the increase of particle size under the same oxygen concentration. For iron particles with roughly the same size, the ignition delay time, accelerated burning time and total burning time decreased as the effective oxygen concentration increased especially for particle size larger than 40 µm. The second stage of combustion time for particles with similar size were almost the same under different oxygen concentrations. After combustion, most of the particles change from irregular shape to spherical or ellipsoidal shape, and some of them showed hollow shell structure. A phenomenon of nano-sized particles releasing during the iron particles combustion had been identified. The frequently observed luminous tail was attributed to coming from the thermal radiation of the formed nanoparticles, which was supported by the SEM sampling analysis of the combustion products. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ignition delay and burnout times of OCWF can be controlled by surface roughness. • To change the combustion characteristics, steel is processed by 100-μm abrasives. • Laser surface processing allows controlling the ignition and combustion characteristics. • Laser processing of steel intensifies the fuel droplet combustion on its surface. The ignition and combustion of single organic coal-water fuel (OCWF) droplets made of coal (30%), waste engine oil (35%), and water (35%) during conductive heating on the surfaces of the machine steel modified with abrasive materials and laser radiation were studied experimentally. The experimental conditions (material and temperature of the heating surfaces) corresponded to the operating conditions of modern furnace chambers of boilers at thermal power plants. It is found that the ignition delay and burnout times during conductive heating of OCWF droplets on steel surfaces can be controlled by changing the surface roughness parameters. On the example of 7-mg OCWF droplets with a radius of about 1.2 mm, it is shown that for processing of heating surfaces, it is necessary to use the abrasive materials with an average grit size of 100 μm to decrease the ignition and burnout times. The abrasive materials with an average grit size of more than 100 μm have an insignificant effect on the ignition delay and burnout times of OCWF droplets. However, such processing significantly increases the deposition of solid combustion products (ash deposits) with an increase in the surface roughness. Laser processing of steel surfaces is of particular interest in the implementation of passive ways of controlling the ignition and combustion characteristics of OCWF droplets. This way of changing the surface texture allows controlling the ignition delay and burnout times in a wide range of the heating source temperatures, as well as reducing the intensity of the solid product deposition on the heating surface during the OCWF combustion. The positive effect from laser processing of heating surfaces to intensify the fuel droplet combustion consists in increasing the velocity of vapor flows from combustible fuel components due to the droplet dispersion. This, in turn, intensifies the formation of a combustible vapour-gas mixture and increases the velocities of flame propagation together with the dispersion products of fuel droplets along the textured surface. [ABSTRACT FROM AUTHOR]

In this work, the effect of in-vacuum low-temperature auto-ignition of a W–Cu 2 O nanopowders mixture obtained by natural oxidation of W–Cu composite nanopowders is demonstrated. The powder is obtained via electrical explosion of wire technique and consists of bimetallic particles instead of Cu and W mixture. The evolution of the phase composition has been studied using in situ X-ray diffraction technology during heating. The structural investigation shows that particles have a core-shell structure, increasing a contact surface between reactants. The ongoing reactions are described, and studies of the structure of powders and combustion products are given. Combustion occurs in the solid-phase temperature range, which is confirmed by the thermal imaging data. • Nanostructured composite powders W–Cu 2 O with a "core-shell" structure were obtained. • The effect of auto-ignition of nano-composite powder W–Cu 2 O is described. • The maximum combustion temperature is 860 °C, which is in the solid-phase region. [ABSTRACT FROM AUTHOR]

• An equilibrium constants database established according to minimizing Gibbs energy. • Development of a combustion products equilibrium model by the constants database instead of fitting functions. • Model accuracy greatly improved compared with that of fitting functions. • Analysis of temperature, O 2 concentration, fuel types, etc., on the equilibrium mole fraction of combustion products. As international concern that regards N O x emissions from the shipping industry increases, it is challenging and urgent to reduce ships' N O x emissions. According to the extended Zeldovich, the determination of the equilibrium concentration of combustion products is crucial for the prediction of N O formation in internal combustion engines. In the present work, an equilibrium constants database of related chemical reactions is established based on the theory that the total Gibbs energy reaches its minimum when a reaction achieves equilibrium. Afterward, a combustion product equilibrium model with twelve species considered is established based on the equilibrium constants database. The accuracy of the model is significantly improved compared with the commonly used ones which calculate the equilibrium constants through fitting function. The errors of the model are within 2% compared with STANJAN which is widely used for chemical equilibrium analysis. The model results are comparable to STANJAN. Afterward, the effects of the temperature, pressure, fuel–air equivalence ratio, O 2 concentration, N 2 concentration, A r concentration and fuel type on the equilibrium mole fractions of the combustion products are investigated. The equilibrium concentration of combustion products is significantly affected by the temperature, O 2 concentration and fuel–air equivalence ratio, but slightly influenced by the pressure and A r concentration. The existence of O and N in the fuel slightly reduces the N O equilibrium mole fraction of the combustion products at the same temperature, pressure and fuel–air equivalence ratio. However, the ratio of molar carbon hydrogen in the fuel and the existence of O and N in the fuel have a significant impact on the C O 2 mole fraction of the combustion products. [ABSTRACT FROM AUTHOR]

A micro-sized B-Al alloy has application potential to be an energetic material for metal fuel. To understand the combustion mechanism of micro-sized B-Al compound powder and explosives containing B-Al (30 wt.%), the ignition and combustion characteristics of B-Al compound powder without and with HMX (cyclotetramethylenetetranitramine) under different pressures (0.4, 0.8, 1.2, 1.5 and 1.8 MPa) and atmospheres (60% O + 2 40 % N 2 , 80% O + 2 20 % N 2 and 100% O 2) were studied via a laser ignition experimental system. The images and characteristic parameters of the ignition and combustion process with different conditions for the B-Al compound powder without and with HMX were obtained. The effects of atmosphere and pressure on the ignition and combustion characteristics of the B-Al compound powder without and with HMX were discussed through a comparative analysis. For the condensed combustion products (CCPs), the phase crystal structures were analysed with X-ray diffraction (XRD), the micro-morphology of the surface was observed with scanning electron microscopy (SEM), and the micro-area elementary composition was analysed with X-ray energy dispersive spectrum (EDS). The results show that whether the increase in pressure or oxygen concentration, the ignition delay time (t id) and combustion time (t ct) of samples without and with HMX decrease, while the maximum spectral intensity (I max) and the maximum combustion temperature (T max) increase. According to the flame morphology, the combustion of the B-Al compound powder is weaker, while that of the B-Al powder with HMX is more intense, and the flame area is larger, which produces a large amount of smoke and presents a deflagration phenomenon. Specially, for various B-Al powder (B/Al = 3/7, 1/1 and 7/3) with HMX under high pressures (1.2, 1.5 and 1.8 MPa), the higher ratio of B leads to shorter combustion time and stronger spectral intensity. Unreacted B, Al and their final oxides, B 2 O 3 and Al 2 O 3 , were detected in the CCPs of both samples without and with HMX. In addition, the CCPs like BN, AlN and Al 5 O 6 N were also detected. The experimental results can help us better understand the chemical reaction mechanism and energy release characteristics of HMX-based explosives containing B-Al. [ABSTRACT FROM AUTHOR]