Based on the theory of forest burning link, the combustibility of the 6-year-old Chinese fir (Cunninghamia lanceolata) and macclure michelia (Michelia macclurei) mixed forest was determined in Youxi County, Fujian Pro...Based on the theory of forest burning link, the combustibility of the 6-year-old Chinese fir (Cunninghamia lanceolata) and macclure michelia (Michelia macclurei) mixed forest was determined in Youxi County, Fujian Province from 1988 to 1989. The results show that the daily mean moisture in the forest, moisture content of litter and the water reserves of the stand in mixed forest are 3%, 7.6% and 46.8% higher than that in pure stand respectively, the inflammables quantity and energy ratios of the stand biomass and total potential energy in mixed stand are 8.5% and 3.69% lower than that in pure stand respectively. Mixed forest can decrease the combustibility of stand.展开更多
Four bituminous coals and one anthracite were used in this study.On the basis of the similar volatile matter contents of the four bituminous coals,the effects of ash in coal on the microstructure,carbonaceous structur...Four bituminous coals and one anthracite were used in this study.On the basis of the similar volatile matter contents of the four bituminous coals,the effects of ash in coal on the microstructure,carbonaceous structure,and chemical composition of pulverized coal were studied.Thermogravimetric analysis was used to study the effect of the addition of anthracite on the combustibility of four different bituminous coals.The results showed that with the increase of ash content in pulverized coal,the microstructure of carbon particles in coal was not much different.However,the analysis results of Raman spectroscopy and X-ray diffraction pattern showed that as the ash content increased,the degree of graphitization of coal carbonaceous structure gradually decreased.The combustibility of the four bituminous coals were better than that of the anthracite.When bituminous coal and anthracite were mixed and burned,the combustibility of the mixed sample decreased as the ash content increased.展开更多
Representative coal samples were collected from different coal seams of the Chirimiri coalfield which covered the entire stratigraphic sequence. These samples were tested for Chemical analysis, Crossing Point Temperat...Representative coal samples were collected from different coal seams of the Chirimiri coalfield which covered the entire stratigraphic sequence. These samples were tested for Chemical analysis, Crossing Point Temperature (CPT), Petrography, Infrared studies (IR) and Differential Thermal Analysis (DTA). All the test results vindicated that the aforesaid parameters had a definite relationship with the stratigraphic disposition or the ranks of coal. The low rank coals found as younger seams in the stratigraphic sequence were more prone to spontaneous combustion whereas the higher rank coals found at the bottom of stratigraphic sequence were less prone to spontaneous combustion. Through combustibility characterisation by different tests, it was found that the upper Duman and Kaperti seams placed as younger seams in the stratigraphic sequence are highly prone to spontaneous combustion whereas the lower Karakoh and Sonawani seams seem to be least prone to spontaneous combustion.展开更多
Coal s volatile component, ash and fixed carbon content have different functions in different stages of a combustion process , but the traditional coal classification can precisely show its combustion property. In thi...Coal s volatile component, ash and fixed carbon content have different functions in different stages of a combustion process , but the traditional coal classification can precisely show its combustion property. In this experiment coal’ s evaluation indexes ( ignition index Di), ( bum off index Df) were used to qualitatively show the ignition property and combustion ending property of coal samples. Meanwhile, considering actual heating circumstances in calciner ( in cement plants), this thesis established the relationship among the ignition index, burn off index and coal s industrial analysis value,, whifh makes it possible for the user to predict the quality of coal before using it and is very valuable in practice.展开更多
This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for ...This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for identifying critical failure modes and their root causes,while BN introduces flexibility in probabilistic reasoning,enabling dynamic updates based on new evidence.This dual methodology overcomes the limitations of static FTA models,offering a comprehensive framework for system reliability analysis.Critical failures,including External Leakage(ELU),Failure to Start(FTS),and Overheating(OHE),were identified as key risks.By incorporating redundancy into high-risk components such as pumps and batteries,the likelihood of these failures was significantly reduced.For instance,redundant pumps reduced the probability of ELU by 31.88%,while additional batteries decreased the occurrence of FTS by 36.45%.The results underscore the practical benefits of combining FTA and BN for enhancing system reliability,particularly in maritime applications where operational safety and efficiency are critical.This research provides valuable insights for maintenance planning and highlights the importance of redundancy in critical systems,especially as the industry transitions toward more autonomous vessels.展开更多
Combustion dynamics are a critical factor in determining the performance and reliabilityof a chemical propulsion engine.The underlying processes include liquid atomization,evaporation,mixing,and chemical reactions.Thi...Combustion dynamics are a critical factor in determining the performance and reliabilityof a chemical propulsion engine.The underlying processes include liquid atomization,evaporation,mixing,and chemical reactions.This paper presents a high-fidelity numerical study of liquidatomization and spray combustion under high-pressure conditions,emphasizing the effects of pres-sure oscillations on the flow evolution and combustion dynamics.The theoretical framework isbased on the three-dimensional conservation equations for multiphase flows and turbulent combus-tion.The numerical solution is achieved using a coupling method of volume-of-fluid and Lagran-gian particle tracking.The Zhuang-Kadota-Sutton(ZKS)high-pressure evaporation model andthe eddy breakup-Arrhenius combustion model are employed.Simulations are conducted for amodel combustion chamber with impinging-jet injectors using liquid oxygen and kerosene as pro-pellants.Both conditions with and without inlet and outlet pressure oscillations are considered.Thefindings reveal that pressure oscillations amplify flow fluctuations and can be characterized usingkey physical parameters such as droplet evaporation,chemical reaction,and chamber pressure.The spectral analysis uncovers the axial variations of the dominant and secondary frequenciesand their amplitudes in terms of the characteristic physical quantities.This research helps establisha methodology for exploring the coupling effect of liquid atomization and spray combustion.It alsoprovides practical insights into their responses to pressure oscillations during the occurrence ofcombustion instability.This information can be used to enhance the design and operation ofliquid-fueled propulsion engines.展开更多
As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and com...As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and combustion zone was analyzed in the laboratory.The results showed that the decreased porosity of mixture resulted in the increased bed resistance by 160.56%when the bed depth increased from 600 to 1000 mm.After improving porosity of 1%by adding loosening bars with optimized size and distribution,the bed resistance decreased,and the productivity increased by 5%.The increase in bed depth increased the thickness of the wet zone from 120 to 680 mm and the resistance from 1.56 to 8.83 kPa.By using a three-stage intensive mixer and pre-adding water for granulation,the moisture of mixture was reduced by 0.6%,and the sintering productivity increased by 4%.Besides,the high bed resistance is mainly caused by the increase in the thickness of the combustion zone from 31.9 to 132.7 mm,and the bed resistance increased from 0.70 to 5.62 kPa.The bed resistance of the combustion zone at 900 mm was increased by 90.51%compared to 700 mm.After optimization of the distribution of coke breeze,the thickness of combustion zone at the lower layer decreased from 132.7 to 106.84 mm and permeability improved significantly.展开更多
Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different in...Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.展开更多
To study the influence of silicon(Si)on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(CL-20),NC/CL-20 composite explosives and Si/NC/CL-20 composite explosives were prepared by the electrostatic spraying ...To study the influence of silicon(Si)on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(CL-20),NC/CL-20 composite explosives and Si/NC/CL-20 composite explosives were prepared by the electrostatic spraying method.The morphology,structure and thermal decomposition properties of the samples were analyzed using scanning electron microscopy(SEM),X-ray energy spectroscopy(EDS),infrared spectroscopy(FT-IR),and simultaneous thermal analyzer(TG-DSC).Additionally,the combustion process of the samples was tested using a high-speed camera.The results show that the addition of nano-Si contributes to the formation of composite explosives with regular morphology and smaller particle size.The Si/NC/CL-20 composite explosive has better and more uniform sphericity,with an average particle size of 73.4 nm,compared to the NC/CL-20 composite explosive.The Si/NC/CL-20 composite explosive which produced by the electrostatic spraying method,achieves physically uniform distribution of the components including NC,CL-20,Si.The addition of Si promotes the thermal decomposition of CL-20.In comparison to the NC/CL-20 composite explosive,the activation energy of the Si/NC/CL-20 composite explosive decreases by 16.78 kJ/mol,and the self-accelerated decomposition temperature and the critical temperature of thermal explosion decreases by 3.12 K and 2.61 K,respectively.Furthermore,Si/NC/CL-20 composite explosive has shorter ignition delay time and faster combustion rate compared to the NC/CL-20 composite explosive,which shows that Si can improve the combustion performance of CL-20.展开更多
Hydrogen storage properties of LaN4.25Al0.75 alloy were experimentally investigated by XRD, PC isotherm curves, hydrogen absorption kinetics curves, XPS and its particle diameter. The structure of unit cell of LaNi4.2...Hydrogen storage properties of LaN4.25Al0.75 alloy were experimentally investigated by XRD, PC isotherm curves, hydrogen absorption kinetics curves, XPS and its particle diameter. The structure of unit cell of LaNi4.25Al0.75 alloy was deduced. The relationship between its structure and hydrogen storage performance of LaNi4.25Al0.75 alloy was analyzed. The results show that LaNi4.25Al0.75 alloy has rapid hydrogen absorption rate and good resistance to combustibility. It is also found that the function of the hydrogen absorption plateau pressure and temperature is ln peq=-4 820/T＋12.46, and the hydrogen absorption rate of the alloy decreases with increasing the temperature.展开更多
The current work includes a numerical investigation of the effect of biodiesel blends with different aluminum oxide nanoparticle concentrations on the combustion process in the cylinder of a diesel engine.IC Engine Fl...The current work includes a numerical investigation of the effect of biodiesel blends with different aluminum oxide nanoparticle concentrations on the combustion process in the cylinder of a diesel engine.IC Engine Fluent,a specialist computational tool in the ANSYS software,was used to simulate internal combustion engine dynamics and combustion processes.Numerical analysis was carried out using biodiesel blends with three Al_(2)O_(3) nanoparticles in 50,100,and 150 ppm concentrations.The tested samples are called D100,B20,B20A50,B20A100,and B20A150 accordingly.The modeling runs were carried out at various engine loads of 0,100,and 200 Nm at a rated speed of 1800 rpm.The combustion characteristics are improved due to the catalytic effect and higher surface area of nano additives.The results showed the improvements in the combustion process as the result of nanoparticle addition,which led to the higher peak cylinder pressure.The increases in the peak cylinder pressures for B20A50,B20A100,and B20A150 about B20 were 3%,5%,and 8%,respectively,at load 200 Nm.The simulation found that the maximum temperature for biodiesel blends diesel was higher than pure diesel;this was due to higher hydrocarbon values of B20.Also,nano-additives caused a decrease in temperatures in the combustion of biofuels.展开更多
To investigate the differences in combustion and energy release characteristics of metastable intermolecular composite materials composed of aluminum alloys and polyvinylidene fluoride(PVDF)with different compositions...To investigate the differences in combustion and energy release characteristics of metastable intermolecular composite materials composed of aluminum alloys and polyvinylidene fluoride(PVDF)with different compositions,two types of alloys were selected:Al-Mg and Al-Si.Pure aluminum powder of the same size was also chosen for comparison.The PVDF-coated metal particle composites and the mixtures of PVDF with metal particles were prepared using electrospray(ES)and physical blending methods(PM),respectively.A systematic study was conducted on the morphology,compositional structure,combustion performance,energy release characteristics,and thermal reactivity of the fabricated composites and their combustion products through scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),X-ray diffraction(XRD),combustion performance experiments,closed vessel pressure tests,and simultaneous thermogravimetric-differential scanning calorimetry(TG-DSC).The experimental results indicated that the PVDF-coated metal particles prepared by the electrospray method exhibited a distinct core-shell structure,with the metal particles in close contact with the PVDF matrix.Compared to the PM blended materials,the ES composites demonstrated superior combustion performance and energy release characteristics during combustion.Analysis of different metal fuel systems under identical preparation conditions revealed that Al-Mg and Al-Si fuels modulate the combustion and energy release properties of aluminum alloy-PVDF MICs through two distinct pathways.展开更多
This paper describes an experimental study investigating the effects of sinusoidal pulsed injection on the combustion mode transition in a dual-mode supersonic combustor.The results are obtained under inflow condition...This paper describes an experimental study investigating the effects of sinusoidal pulsed injection on the combustion mode transition in a dual-mode supersonic combustor.The results are obtained under inflow conditions of 2.9 MPa stagnation pressure,1900 K stagnation temperature,and Mach number of 3.0.It has been observed that,at the same equivalence ratio,the combustion mode and flow field structure undergo irreversible changes from a weak combustion state to a strong combustion state at a specific pulsed jet frequency compared to steady jet.For steady jet,the combustion mode is dual-mode.As the frequency of the unsteady jet changes,the combustion mode also changes:it becomes a transition mode at frequencies of 171 Hz and 260 Hz,and a ramjet mode at 216 Hz.Combustion instability under steady jet manifests as a transition in flame stabilization mode.In contrast,under pulsed jet,combustion instability appears either as a transition in flame stabilization mode or as flame blow-off and flashback.The flow field oscillation frequency in the non-reacting flow is 171 Hz,which may resonate with the 171 Hz pulsed jet frequency,making the combustion oscillations most pronounced at this frequency.When the jet frequency is increased to 216 Hz,the combustion intensity significantly increases,and the combustion mode transfers to the ramjet mode.However,further increasing the frequency to 260 Hz results in a decrease in combustion intensity,returning to the transition mode.The frequency of the flow field oscillations varies with the coupling of the pulsed injection frequency,shock wave,and flame,and if the system reaches an unstable state,that is,pre-combustion shock train moves far upstream of the isolator during the pulsed jet period,strong combustion state can be achieved,and this process is irreversible.展开更多
This study introduced an innovative numerical approach to examine combustion instability in Solid Rocket Motors(SRMs).The paper commenced with the derivation of a transient model for the solid propellant's condens...This study introduced an innovative numerical approach to examine combustion instability in Solid Rocket Motors(SRMs).The paper commenced with the derivation of a transient model for the solid propellant's condensed phase,followed by its numerical discretization.Subsequently,this model was integrated with gas phase computations of the chamber's internal flow field,encompassing fluid dynamics and combustion processes.The precision of the numerical method was validated by experimental data,and its reliability was confirmed through a grid independence analysis.The study then investigated the motor's stability under various operating conditions,revealing the impact of parameters such as the sensitivity coefficient of the burning rate to temperature and the nozzle throat diameter on the motor's stability.The results confirmed the bistable nature of combustion instability in specific regions.For instance,when the sensitivity coefficients of burning rate to ambient temperature(k_(1))ranged from 1.4 to 1.8,the SRM adopted in this study with a throat diameter of 0.12 m remained stable under small disturbances but triggered instability under large disturbances.Moreover,increasing the value of k_(1)and reducing the throat diameter can exacerbate combustion instability,leading to more pronounced nonlinear characteristics.The numerical method developed in this paper could effectively capture the nonlinear features of the combustion instability occurring in the motor,providing guidance for SRMs design.展开更多
The kerosene-fueled Scramjet with multi-cavity combustor has the potential to serve aspropulsion system for hypersonic flight.However,the impact of injection positions on combustionperformance and mechanism at high Ma...The kerosene-fueled Scramjet with multi-cavity combustor has the potential to serve aspropulsion system for hypersonic flight.However,the impact of injection positions on combustionperformance and mechanism at high Mach numbers remains uncertain.Therefore,a comparativestudy was conducted using numerical methods to explore multi-cavity Scramjet combustor perfor-mance at a flight Mach number 7.0 with different injection positions.The combustor is equippedwith 6 cavities arranged in three groups along the flow direction,each consisting of two cavities per-pendicular to the flow.It is shown that the injection location significantly influences combustionperformance:Front-injection yields higher combustion efficiency than post-injection,but post-injection is advantageous for the intake start.Additionally,regardless of injection positions,themainstream flow state near the cavities behind the injection can be categorized as supersonic flow,supersonic-subsonic coexistence flow,and subsonic flow.The optimal length from the downstreamto the trailing edge of the cavities behind the injection for achieving maximum combustion effi-ciency is determined.Further extension beyond this optimal length does not significantly increasethe combustion efficiency.In addition,the optimal length varies with different injection positions-specifically,it is about 60%longer with post-injection conditions than with front-injection con-ditions in this investigation.Moreover,significant secondary combustion within the cavities leadingto improved efficiency only occurs when mainstream flow state is either supersonic flow orsupersonic-subsonic coexistence flow.Also,with a well-optimized design,the kerosene-fueledmulti-cavity Scramjet can achieve enhanced combustion efficiency,which shows relatively smallvariation across a wide range of equivalence ratios.This might be caused by the effects of interac-tion among these multiple cavities.Therefore,these research findings can provide valuable insightsfor designing and optimizing the kerosene-fueled multi-cavity combustor in Scramjet at high Machnumbers.展开更多
Spontaneous combustion of lignite is closely related to the inherent minerals it contains, and the iron component has a remarkable influence on the combustion property of lignite. It is very important to study the inf...Spontaneous combustion of lignite is closely related to the inherent minerals it contains, and the iron component has a remarkable influence on the combustion property of lignite. It is very important to study the influence of iron component on the combustion reaction property of lignite to reveal autoignition mechanism of lignite and reduce autoignition of lignite. In this research, FeCl_(3) and Fe_(2)O_(3) were doped into demineralised lignite (SL+) by impregnation to research the effects of iron salts and iron oxides on the combustion properties of lignite. Based on the above, the effects of post-treatment method of the FeCl_(3)-doped coal samples, iron-salt hydrolysis products and heat-treated temperatures on the combustion property of lignite were researched, and the microstructures of the coal samples were characterised and analysed using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrate that doping with FeCl_(3) increases the combustion performance of lignite, thereby reducing the ignition temperature of lignite by approximately 112 ℃. In contrast, doping with Fe_(2)O_(3) has a weaker combustion-promoting effect. XRD and XPS characterisation indicates that iron species in the coal samples doped with iron salts are highly dispersed and exhibit the FeOOH structure, whereas iron species in the coal samples doped with Fe_(2)O_(3) exhibit the crystal form of α-Fe_(2)O_(3). Doping of lignite with FeCl_(3) and its hydrolysis product β-FeOOH reduces the ignition temperature of the coal samples. Iron species in the FeCl_(3)-doped coal samples after heat treatment at 300–500 ℃ increase the combustion property of the coal samples, whereas iron species after heat treatment at 600–900 ℃ have a much weaker or non-existent promoting effect on the combustion performance of the coal samples. The characterisation show a change in iron species in the coal samples with the rise in the heat treatment temperature. This change progresses from highly dispersed β-FeOOH below 300 ℃ to Fe_(3)O_(4) above 400 ℃. Fe_(3)O_(4) is gradually reduced, with part of it further reduced to elementary iron at the same time as grain growth. It is believed that the gradual agglomeration of Fe_(3)O_(4) and the appearance of elementary iron are the main reasons for the weakening or disappearance of the promoting effect on coal combustion.展开更多
Aluminum-water(Al-H_(2)O)propellants represent an innovative class of solid propellants characterized by low cost and minimal signal signature.However,conventional formulations are hindered by significant aluminum(Al)...Aluminum-water(Al-H_(2)O)propellants represent an innovative class of solid propellants characterized by low cost and minimal signal signature.However,conventional formulations are hindered by significant aluminum(Al)agglomeration,leading to reduced combustion efficiency and substantial residues.This study introduces a method for modifying Al powder with Polyvinylidene Fluoride(PVDF)to enhance the performance of Al-H_(2)O propellants by mitigating agglomeration during combustion.Experimental methodologies,including thermogravimetric analysis under ambient-pressure nitrogen atmosphere and laser ignition tests,were employed to investigate the influence of varying PVDF content on the combustion characteristics of the propellants.Furthermore,the effect of PVDF on motor performance was systematically evaluated through laboratoryscale Solid Rocket Motor(SRM)tests.The results demonstrate that the addition of 7.5%PVDF significantly enhances the burning rate from 1.12 mm/s to 3.78 mm/s and reduces the mean particle size of condensed combustion products from 699μm to 527μm.Combustion efficiency rises from88.57%to 94.51%,while injection efficiency improves significantly from 30.45%to 70.45%.SRM tests further demonstrate an increase in combustion chamber pressure from 0.17 MPa to 0.58 MPa.A dynamic agglomeration model explains these improvements,attributing reduced agglomeration to enhanced aerodynamic forces and a thinner melting layer,while increased gas yield improves injection performance.This study highlights PVDF's potential in advancing Al-H_(2)O propellants by improving combustion and injection efficiency.展开更多
In this research study,magnesium-aluminum(Mg-Al)bimetallic oxide powders are synthesized via the sol-gel auto combustion method using diethanolamine(DEA)as the fuel.In order to subsequently determine the influence of ...In this research study,magnesium-aluminum(Mg-Al)bimetallic oxide powders are synthesized via the sol-gel auto combustion method using diethanolamine(DEA)as the fuel.In order to subsequently determine the influence of calcination temperatures upon the structure,chemical bonding,morphology,optical properties,and fluorescence properties of the as-synthesized and calcined Mg-Al bimetallic oxide powders,the researcher employed X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),transmission electron microscopy(TEM),UV–visible diffuse reflectance spectroscopy(UV-DRS),and photoluminescence spectroscopy(PL),respectively.It was apparent on the basis of the XRD and FT-IR analyses that those powders undergoing calcination at temperatures of 500℃,700℃,and 900℃contained the major phase magnesium aluminate(Mg Al_(2)O_(4))spinel with trace magnesium oxide(Mg O)and hydrotalcite(Mg_(6)Al_(2)(CO_(3))(OH)_(16)).When the calcination temperature rose to 1100℃,this resulted in a single phase MgAl_(2)O_(4)while MgO and(Mg_(6)Al_(2)(CO_(3))(OH)_(16))were no longer observed.UV-DRS analysis revealed that in optimized conditions,calcination resulted in better sample absorption and reflection levels when compared to the ultraviolet,visible,and infrared spectra observed in the case of the as-synthesized sample.The bandgap energy(E_(g))for calcined samples was in the range of 2.65 e V to 5.85 e V,in contrast to the value of 4.10 e V for the as-synthesized sample.Analysis of photoluminescence showed that for the as-synthesized samples and those calcined at low temperatures,visible light was emitted only in the violet,blue,and green regions with low intensity,while for samples calcined at higher temperatures,the emissions showed greater intensity and extended to the yellow and orange regions.Multiple defect centers were found in the bandgap which can explain these findings.展开更多
The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-heali...The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-healing function have problems such as irregular particle shape and uneven distribution of components,which affect the efficient play of self-healing function.In this paper,HMX-based energetic microspheres with self-healing function were successfully prepared by microchannel technology,which showed excellent self-healing effect in both Polymer-bonded explosives(PBXs)and Composite solid propellants(CSPs).The experimental results show that the HMX-based energetic microspheres with different binder contents prepared by microchannel technology show regular shape,HMX crystal particles are uniformly wrapped by self-healing binder(GAPU).When the content of GAPU in HMX-based energetic microspheres is 10%,PBXs show excellent self-healing effect and mechanical safety is improved by 400%(raw HMX vs S4,5 J vs 25 J).As a high-energy component,the burning rate of CSPs is increased by 359.4%,the time(burning temperature>1700℃)is prolonged by 333.3%,and the maximum impulse force is increased by 107.3%(CSP-H vs CSP-S4,0.84 mm/s vs 3.87 mm/s,0.06 s vs 0.26 s,0.82 m N vs 1.70 m N).It also has excellent storage performance.The preparation of HMX-based energetic microspheres with self-healing function by microchannel technology provides a new strategy to improve the storage performance of ECMs and the combustion performance of CSPs.展开更多
The soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment,so treating diesel engine exhaust is critical.At present,the most effective method for eliminating so...The soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment,so treating diesel engine exhaust is critical.At present,the most effective method for eliminating soot particles is post-treatment technology.Preparation of economically viable and highly active soot combustion catalysts is a pivotal element of post-treatment technology.In this study,different single-metal oxide catalysts with fibrous structures and alkali metal-modified hollow nanotubular Mn-based oxide catalysts were synthesized using centrifugal spinning method.Activity evaluation results showed that the manganese oxide catalyst has the best catalytic activity among the prepared single-metal oxide catalysts.Further research on alkali metal modification showed that doping alkali metals is beneficial for improving the oxidation state of manganese and generating a large number of reactive oxygen species.Combined with the structural effect brought by the hollow nanotube structure,the alkali metal-modified Mn-based oxide catalysts exhibit superior catalytic performance.Among them,the Cs-modified Mn-based oxide catalyst exhibits the best catalytic performance because of its rich active oxygen species,excellent NO oxidation ability,abundant Mn^(4+)ions(M^(n4)+/Mn^(n+)=64.78%),and good redox ability.The T_(10),T_(50),T_(90),and CO_(2)selectivity of the Cs-modified Mn-based oxide catalyst were 267°C,324°C,360°C,and 97.8%,respectively.展开更多
文摘Based on the theory of forest burning link, the combustibility of the 6-year-old Chinese fir (Cunninghamia lanceolata) and macclure michelia (Michelia macclurei) mixed forest was determined in Youxi County, Fujian Province from 1988 to 1989. The results show that the daily mean moisture in the forest, moisture content of litter and the water reserves of the stand in mixed forest are 3%, 7.6% and 46.8% higher than that in pure stand respectively, the inflammables quantity and energy ratios of the stand biomass and total potential energy in mixed stand are 8.5% and 3.69% lower than that in pure stand respectively. Mixed forest can decrease the combustibility of stand.
基金financially supported by the Natural Science Foundation for Young Scientists of China (No.51804026)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (No.2017QNRC001)
文摘Four bituminous coals and one anthracite were used in this study.On the basis of the similar volatile matter contents of the four bituminous coals,the effects of ash in coal on the microstructure,carbonaceous structure,and chemical composition of pulverized coal were studied.Thermogravimetric analysis was used to study the effect of the addition of anthracite on the combustibility of four different bituminous coals.The results showed that with the increase of ash content in pulverized coal,the microstructure of carbon particles in coal was not much different.However,the analysis results of Raman spectroscopy and X-ray diffraction pattern showed that as the ash content increased,the degree of graphitization of coal carbonaceous structure gradually decreased.The combustibility of the four bituminous coals were better than that of the anthracite.When bituminous coal and anthracite were mixed and burned,the combustibility of the mixed sample decreased as the ash content increased.
文摘Representative coal samples were collected from different coal seams of the Chirimiri coalfield which covered the entire stratigraphic sequence. These samples were tested for Chemical analysis, Crossing Point Temperature (CPT), Petrography, Infrared studies (IR) and Differential Thermal Analysis (DTA). All the test results vindicated that the aforesaid parameters had a definite relationship with the stratigraphic disposition or the ranks of coal. The low rank coals found as younger seams in the stratigraphic sequence were more prone to spontaneous combustion whereas the higher rank coals found at the bottom of stratigraphic sequence were less prone to spontaneous combustion. Through combustibility characterisation by different tests, it was found that the upper Duman and Kaperti seams placed as younger seams in the stratigraphic sequence are highly prone to spontaneous combustion whereas the lower Karakoh and Sonawani seams seem to be least prone to spontaneous combustion.
基金Funded by Foundation for University Key Teacher by the Ministry of Mutation.
文摘Coal s volatile component, ash and fixed carbon content have different functions in different stages of a combustion process , but the traditional coal classification can precisely show its combustion property. In this experiment coal’ s evaluation indexes ( ignition index Di), ( bum off index Df) were used to qualitatively show the ignition property and combustion ending property of coal samples. Meanwhile, considering actual heating circumstances in calciner ( in cement plants), this thesis established the relationship among the ignition index, burn off index and coal s industrial analysis value,, whifh makes it possible for the user to predict the quality of coal before using it and is very valuable in practice.
基金supported by Istanbul Technical University(Project No.45698)supported through the“Young Researchers’Career Development Project-training of doctoral students”of the Croatian Science Foundation.
文摘This paper investigates the reliability of internal marine combustion engines using an integrated approach that combines Fault Tree Analysis(FTA)and Bayesian Networks(BN).FTA provides a structured,top-down method for identifying critical failure modes and their root causes,while BN introduces flexibility in probabilistic reasoning,enabling dynamic updates based on new evidence.This dual methodology overcomes the limitations of static FTA models,offering a comprehensive framework for system reliability analysis.Critical failures,including External Leakage(ELU),Failure to Start(FTS),and Overheating(OHE),were identified as key risks.By incorporating redundancy into high-risk components such as pumps and batteries,the likelihood of these failures was significantly reduced.For instance,redundant pumps reduced the probability of ELU by 31.88%,while additional batteries decreased the occurrence of FTS by 36.45%.The results underscore the practical benefits of combining FTA and BN for enhancing system reliability,particularly in maritime applications where operational safety and efficiency are critical.This research provides valuable insights for maintenance planning and highlights the importance of redundancy in critical systems,especially as the industry transitions toward more autonomous vessels.
基金supported by the National Natural Science Foundation of China(Nos.U23B6009 and 12272050)。
文摘Combustion dynamics are a critical factor in determining the performance and reliabilityof a chemical propulsion engine.The underlying processes include liquid atomization,evaporation,mixing,and chemical reactions.This paper presents a high-fidelity numerical study of liquidatomization and spray combustion under high-pressure conditions,emphasizing the effects of pres-sure oscillations on the flow evolution and combustion dynamics.The theoretical framework isbased on the three-dimensional conservation equations for multiphase flows and turbulent combus-tion.The numerical solution is achieved using a coupling method of volume-of-fluid and Lagran-gian particle tracking.The Zhuang-Kadota-Sutton(ZKS)high-pressure evaporation model andthe eddy breakup-Arrhenius combustion model are employed.Simulations are conducted for amodel combustion chamber with impinging-jet injectors using liquid oxygen and kerosene as pro-pellants.Both conditions with and without inlet and outlet pressure oscillations are considered.Thefindings reveal that pressure oscillations amplify flow fluctuations and can be characterized usingkey physical parameters such as droplet evaporation,chemical reaction,and chamber pressure.The spectral analysis uncovers the axial variations of the dominant and secondary frequenciesand their amplitudes in terms of the characteristic physical quantities.This research helps establisha methodology for exploring the coupling effect of liquid atomization and spray combustion.It alsoprovides practical insights into their responses to pressure oscillations during the occurrence ofcombustion instability.This information can be used to enhance the design and operation ofliquid-fueled propulsion engines.
基金supported by the Basic Science Center Project for the National Natural Science Foundation of China(No.72088101)the S&T Program of Hebei(No.23564101D).
文摘As the bed depth increases,sintering yield increases,but the productivity decreases.To reveal the reasons for the decrease in productivity and explore targeted solutions,the bed resistance of mixtures,wet zone,and combustion zone was analyzed in the laboratory.The results showed that the decreased porosity of mixture resulted in the increased bed resistance by 160.56%when the bed depth increased from 600 to 1000 mm.After improving porosity of 1%by adding loosening bars with optimized size and distribution,the bed resistance decreased,and the productivity increased by 5%.The increase in bed depth increased the thickness of the wet zone from 120 to 680 mm and the resistance from 1.56 to 8.83 kPa.By using a three-stage intensive mixer and pre-adding water for granulation,the moisture of mixture was reduced by 0.6%,and the sintering productivity increased by 4%.Besides,the high bed resistance is mainly caused by the increase in the thickness of the combustion zone from 31.9 to 132.7 mm,and the bed resistance increased from 0.70 to 5.62 kPa.The bed resistance of the combustion zone at 900 mm was increased by 90.51%compared to 700 mm.After optimization of the distribution of coke breeze,the thickness of combustion zone at the lower layer decreased from 132.7 to 106.84 mm and permeability improved significantly.
基金support from the National Natural Science Foundation of China(No.12002386).
文摘Self-excited longitudinal combustion instabilities were investigated in a hypergolic liquid bipropellant combustor, which applied single dual-swirl coaxial injector. Hot-fire tests were conducted for four different injector geometries, while extensive tests on injection conditions were carried out for each injector geometry. The synchronous measurement of the pressure and heat release rate was applied, successfully capturing the process of the pressure and heat release rate enhanced coupling and developing into in-phase oscillation. By calculating Rayleigh index at the head and middle section of the chamber, it is shown that Rayleigh index of the middle section is even higher than that of the head, indicating a long heat release zone. When the combustion instability occurs, the pressure in propellant manifolds also oscillates with the same frequency and lags behind the oscillation in the combustor. Compared to the oscillation in the outer injector manifold, the oscillation in the inner injector manifold shows a higher correlation with that in the chamber in amplitude and phase. Based on numerical simulations of the multiphase cold flow inside the injector and combustion process in the chamber, it is found that injector geometries affect longitudinal combustion instability by changing spray cone angle. The spray with small cone angle is more sensitive to the modulation of longitudinal pressure wave in combustion simulations, which is more likely to excite the longitudinal combustion instability. Meanwhile, the combustion instability may be related to the pulsating coherent structure generated by the spray fluctuation, which is determined by injection conditions. Besides, a positive feedback closed-loop system associated with the active fluctuation and passive oscillation of the spray is believed to excite and sustain the longitudinal combustion instability.
基金National Natural Science Foundation of China(No.22275150)。
文摘To study the influence of silicon(Si)on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane(CL-20),NC/CL-20 composite explosives and Si/NC/CL-20 composite explosives were prepared by the electrostatic spraying method.The morphology,structure and thermal decomposition properties of the samples were analyzed using scanning electron microscopy(SEM),X-ray energy spectroscopy(EDS),infrared spectroscopy(FT-IR),and simultaneous thermal analyzer(TG-DSC).Additionally,the combustion process of the samples was tested using a high-speed camera.The results show that the addition of nano-Si contributes to the formation of composite explosives with regular morphology and smaller particle size.The Si/NC/CL-20 composite explosive has better and more uniform sphericity,with an average particle size of 73.4 nm,compared to the NC/CL-20 composite explosive.The Si/NC/CL-20 composite explosive which produced by the electrostatic spraying method,achieves physically uniform distribution of the components including NC,CL-20,Si.The addition of Si promotes the thermal decomposition of CL-20.In comparison to the NC/CL-20 composite explosive,the activation energy of the Si/NC/CL-20 composite explosive decreases by 16.78 kJ/mol,and the self-accelerated decomposition temperature and the critical temperature of thermal explosion decreases by 3.12 K and 2.61 K,respectively.Furthermore,Si/NC/CL-20 composite explosive has shorter ignition delay time and faster combustion rate compared to the NC/CL-20 composite explosive,which shows that Si can improve the combustion performance of CL-20.
基金Project (50276063) supported by the National Natural Science Foundation of China
文摘Hydrogen storage properties of LaN4.25Al0.75 alloy were experimentally investigated by XRD, PC isotherm curves, hydrogen absorption kinetics curves, XPS and its particle diameter. The structure of unit cell of LaNi4.25Al0.75 alloy was deduced. The relationship between its structure and hydrogen storage performance of LaNi4.25Al0.75 alloy was analyzed. The results show that LaNi4.25Al0.75 alloy has rapid hydrogen absorption rate and good resistance to combustibility. It is also found that the function of the hydrogen absorption plateau pressure and temperature is ln peq=-4 820/T＋12.46, and the hydrogen absorption rate of the alloy decreases with increasing the temperature.
文摘The current work includes a numerical investigation of the effect of biodiesel blends with different aluminum oxide nanoparticle concentrations on the combustion process in the cylinder of a diesel engine.IC Engine Fluent,a specialist computational tool in the ANSYS software,was used to simulate internal combustion engine dynamics and combustion processes.Numerical analysis was carried out using biodiesel blends with three Al_(2)O_(3) nanoparticles in 50,100,and 150 ppm concentrations.The tested samples are called D100,B20,B20A50,B20A100,and B20A150 accordingly.The modeling runs were carried out at various engine loads of 0,100,and 200 Nm at a rated speed of 1800 rpm.The combustion characteristics are improved due to the catalytic effect and higher surface area of nano additives.The results showed the improvements in the combustion process as the result of nanoparticle addition,which led to the higher peak cylinder pressure.The increases in the peak cylinder pressures for B20A50,B20A100,and B20A150 about B20 were 3%,5%,and 8%,respectively,at load 200 Nm.The simulation found that the maximum temperature for biodiesel blends diesel was higher than pure diesel;this was due to higher hydrocarbon values of B20.Also,nano-additives caused a decrease in temperatures in the combustion of biofuels.
基金the National Natural Science Foundation of China(NSFC,Grant Nos.52176114 and 52306145)Natural Science Foundation of Jiangsu Province(Grant No.BK20230929)+3 种基金China Postdoctoral Science Foundation(Grant No.2023M731693)Fundamental Research Funds for the Central Universities,Grant No.30924010505Jiangsu Funding Program for Excellent Postdoctoral Talentthe Center of Analytical Facilities,Nanjing University of Science and Technology for providing technical equipment support for this article。
文摘To investigate the differences in combustion and energy release characteristics of metastable intermolecular composite materials composed of aluminum alloys and polyvinylidene fluoride(PVDF)with different compositions,two types of alloys were selected:Al-Mg and Al-Si.Pure aluminum powder of the same size was also chosen for comparison.The PVDF-coated metal particle composites and the mixtures of PVDF with metal particles were prepared using electrospray(ES)and physical blending methods(PM),respectively.A systematic study was conducted on the morphology,compositional structure,combustion performance,energy release characteristics,and thermal reactivity of the fabricated composites and their combustion products through scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS),X-ray diffraction(XRD),combustion performance experiments,closed vessel pressure tests,and simultaneous thermogravimetric-differential scanning calorimetry(TG-DSC).The experimental results indicated that the PVDF-coated metal particles prepared by the electrospray method exhibited a distinct core-shell structure,with the metal particles in close contact with the PVDF matrix.Compared to the PM blended materials,the ES composites demonstrated superior combustion performance and energy release characteristics during combustion.Analysis of different metal fuel systems under identical preparation conditions revealed that Al-Mg and Al-Si fuels modulate the combustion and energy release properties of aluminum alloy-PVDF MICs through two distinct pathways.
基金supported by the Program of Key Laboratory of Cross-Domain Flight Interdisciplinary Technology,China(No.2023-ZY0205)。
文摘This paper describes an experimental study investigating the effects of sinusoidal pulsed injection on the combustion mode transition in a dual-mode supersonic combustor.The results are obtained under inflow conditions of 2.9 MPa stagnation pressure,1900 K stagnation temperature,and Mach number of 3.0.It has been observed that,at the same equivalence ratio,the combustion mode and flow field structure undergo irreversible changes from a weak combustion state to a strong combustion state at a specific pulsed jet frequency compared to steady jet.For steady jet,the combustion mode is dual-mode.As the frequency of the unsteady jet changes,the combustion mode also changes:it becomes a transition mode at frequencies of 171 Hz and 260 Hz,and a ramjet mode at 216 Hz.Combustion instability under steady jet manifests as a transition in flame stabilization mode.In contrast,under pulsed jet,combustion instability appears either as a transition in flame stabilization mode or as flame blow-off and flashback.The flow field oscillation frequency in the non-reacting flow is 171 Hz,which may resonate with the 171 Hz pulsed jet frequency,making the combustion oscillations most pronounced at this frequency.When the jet frequency is increased to 216 Hz,the combustion intensity significantly increases,and the combustion mode transfers to the ramjet mode.However,further increasing the frequency to 260 Hz results in a decrease in combustion intensity,returning to the transition mode.The frequency of the flow field oscillations varies with the coupling of the pulsed injection frequency,shock wave,and flame,and if the system reaches an unstable state,that is,pre-combustion shock train moves far upstream of the isolator during the pulsed jet period,strong combustion state can be achieved,and this process is irreversible.
基金supported by the National Natural Science Foundation of China(No.U2241250)。
文摘This study introduced an innovative numerical approach to examine combustion instability in Solid Rocket Motors(SRMs).The paper commenced with the derivation of a transient model for the solid propellant's condensed phase,followed by its numerical discretization.Subsequently,this model was integrated with gas phase computations of the chamber's internal flow field,encompassing fluid dynamics and combustion processes.The precision of the numerical method was validated by experimental data,and its reliability was confirmed through a grid independence analysis.The study then investigated the motor's stability under various operating conditions,revealing the impact of parameters such as the sensitivity coefficient of the burning rate to temperature and the nozzle throat diameter on the motor's stability.The results confirmed the bistable nature of combustion instability in specific regions.For instance,when the sensitivity coefficients of burning rate to ambient temperature(k_(1))ranged from 1.4 to 1.8,the SRM adopted in this study with a throat diameter of 0.12 m remained stable under small disturbances but triggered instability under large disturbances.Moreover,increasing the value of k_(1)and reducing the throat diameter can exacerbate combustion instability,leading to more pronounced nonlinear characteristics.The numerical method developed in this paper could effectively capture the nonlinear features of the combustion instability occurring in the motor,providing guidance for SRMs design.
基金financially supported by the National Key Laboratory of Ramjet,China(No.2022-020-003)the Fundamental Research Funds for the Central Universities,China(No.501QYZX2023146001)。
文摘The kerosene-fueled Scramjet with multi-cavity combustor has the potential to serve aspropulsion system for hypersonic flight.However,the impact of injection positions on combustionperformance and mechanism at high Mach numbers remains uncertain.Therefore,a comparativestudy was conducted using numerical methods to explore multi-cavity Scramjet combustor perfor-mance at a flight Mach number 7.0 with different injection positions.The combustor is equippedwith 6 cavities arranged in three groups along the flow direction,each consisting of two cavities per-pendicular to the flow.It is shown that the injection location significantly influences combustionperformance:Front-injection yields higher combustion efficiency than post-injection,but post-injection is advantageous for the intake start.Additionally,regardless of injection positions,themainstream flow state near the cavities behind the injection can be categorized as supersonic flow,supersonic-subsonic coexistence flow,and subsonic flow.The optimal length from the downstreamto the trailing edge of the cavities behind the injection for achieving maximum combustion effi-ciency is determined.Further extension beyond this optimal length does not significantly increasethe combustion efficiency.In addition,the optimal length varies with different injection positions-specifically,it is about 60%longer with post-injection conditions than with front-injection con-ditions in this investigation.Moreover,significant secondary combustion within the cavities leadingto improved efficiency only occurs when mainstream flow state is either supersonic flow orsupersonic-subsonic coexistence flow.Also,with a well-optimized design,the kerosene-fueledmulti-cavity Scramjet can achieve enhanced combustion efficiency,which shows relatively smallvariation across a wide range of equivalence ratios.This might be caused by the effects of interac-tion among these multiple cavities.Therefore,these research findings can provide valuable insightsfor designing and optimizing the kerosene-fueled multi-cavity combustor in Scramjet at high Machnumbers.
基金support from the National Natural Science Foundation of China(22368038,21968021,22308048)Science and Technology Plan Project of Inner Mongolia(2020GG0289)+1 种基金Natural Science Foundation of Inner Mongolia(2019MS02025)Science Fund for Distinguished Young Scholars of Inner Mongolia(2022JQ04).
文摘Spontaneous combustion of lignite is closely related to the inherent minerals it contains, and the iron component has a remarkable influence on the combustion property of lignite. It is very important to study the influence of iron component on the combustion reaction property of lignite to reveal autoignition mechanism of lignite and reduce autoignition of lignite. In this research, FeCl_(3) and Fe_(2)O_(3) were doped into demineralised lignite (SL+) by impregnation to research the effects of iron salts and iron oxides on the combustion properties of lignite. Based on the above, the effects of post-treatment method of the FeCl_(3)-doped coal samples, iron-salt hydrolysis products and heat-treated temperatures on the combustion property of lignite were researched, and the microstructures of the coal samples were characterised and analysed using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results demonstrate that doping with FeCl_(3) increases the combustion performance of lignite, thereby reducing the ignition temperature of lignite by approximately 112 ℃. In contrast, doping with Fe_(2)O_(3) has a weaker combustion-promoting effect. XRD and XPS characterisation indicates that iron species in the coal samples doped with iron salts are highly dispersed and exhibit the FeOOH structure, whereas iron species in the coal samples doped with Fe_(2)O_(3) exhibit the crystal form of α-Fe_(2)O_(3). Doping of lignite with FeCl_(3) and its hydrolysis product β-FeOOH reduces the ignition temperature of the coal samples. Iron species in the FeCl_(3)-doped coal samples after heat treatment at 300–500 ℃ increase the combustion property of the coal samples, whereas iron species after heat treatment at 600–900 ℃ have a much weaker or non-existent promoting effect on the combustion performance of the coal samples. The characterisation show a change in iron species in the coal samples with the rise in the heat treatment temperature. This change progresses from highly dispersed β-FeOOH below 300 ℃ to Fe_(3)O_(4) above 400 ℃. Fe_(3)O_(4) is gradually reduced, with part of it further reduced to elementary iron at the same time as grain growth. It is believed that the gradual agglomeration of Fe_(3)O_(4) and the appearance of elementary iron are the main reasons for the weakening or disappearance of the promoting effect on coal combustion.
基金supported by the National Natural Science Foundation of China(Nos.U2441284 and 22375164)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2024042)。
文摘Aluminum-water(Al-H_(2)O)propellants represent an innovative class of solid propellants characterized by low cost and minimal signal signature.However,conventional formulations are hindered by significant aluminum(Al)agglomeration,leading to reduced combustion efficiency and substantial residues.This study introduces a method for modifying Al powder with Polyvinylidene Fluoride(PVDF)to enhance the performance of Al-H_(2)O propellants by mitigating agglomeration during combustion.Experimental methodologies,including thermogravimetric analysis under ambient-pressure nitrogen atmosphere and laser ignition tests,were employed to investigate the influence of varying PVDF content on the combustion characteristics of the propellants.Furthermore,the effect of PVDF on motor performance was systematically evaluated through laboratoryscale Solid Rocket Motor(SRM)tests.The results demonstrate that the addition of 7.5%PVDF significantly enhances the burning rate from 1.12 mm/s to 3.78 mm/s and reduces the mean particle size of condensed combustion products from 699μm to 527μm.Combustion efficiency rises from88.57%to 94.51%,while injection efficiency improves significantly from 30.45%to 70.45%.SRM tests further demonstrate an increase in combustion chamber pressure from 0.17 MPa to 0.58 MPa.A dynamic agglomeration model explains these improvements,attributing reduced agglomeration to enhanced aerodynamic forces and a thinner melting layer,while increased gas yield improves injection performance.This study highlights PVDF's potential in advancing Al-H_(2)O propellants by improving combustion and injection efficiency.
基金financial supported from the Thailand Research Fund,Office of the Higher Education Commission(Grant number MRG6280220)。
文摘In this research study,magnesium-aluminum(Mg-Al)bimetallic oxide powders are synthesized via the sol-gel auto combustion method using diethanolamine(DEA)as the fuel.In order to subsequently determine the influence of calcination temperatures upon the structure,chemical bonding,morphology,optical properties,and fluorescence properties of the as-synthesized and calcined Mg-Al bimetallic oxide powders,the researcher employed X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),scanning electron microscopy(SEM),transmission electron microscopy(TEM),UV–visible diffuse reflectance spectroscopy(UV-DRS),and photoluminescence spectroscopy(PL),respectively.It was apparent on the basis of the XRD and FT-IR analyses that those powders undergoing calcination at temperatures of 500℃,700℃,and 900℃contained the major phase magnesium aluminate(Mg Al_(2)O_(4))spinel with trace magnesium oxide(Mg O)and hydrotalcite(Mg_(6)Al_(2)(CO_(3))(OH)_(16)).When the calcination temperature rose to 1100℃,this resulted in a single phase MgAl_(2)O_(4)while MgO and(Mg_(6)Al_(2)(CO_(3))(OH)_(16))were no longer observed.UV-DRS analysis revealed that in optimized conditions,calcination resulted in better sample absorption and reflection levels when compared to the ultraviolet,visible,and infrared spectra observed in the case of the as-synthesized sample.The bandgap energy(E_(g))for calcined samples was in the range of 2.65 e V to 5.85 e V,in contrast to the value of 4.10 e V for the as-synthesized sample.Analysis of photoluminescence showed that for the as-synthesized samples and those calcined at low temperatures,visible light was emitted only in the violet,blue,and green regions with low intensity,while for samples calcined at higher temperatures,the emissions showed greater intensity and extended to the yellow and orange regions.Multiple defect centers were found in the bandgap which can explain these findings.
基金support given by the Fundamental Research Program of Shanxi Province(Grant No.202203021212152)。
文摘The self-healing function is considered one of the effective ways to address structural damage and improve interfacial bonding in Energetic composite materials(ECMs).However,the currently prepared ECMs with self-healing function have problems such as irregular particle shape and uneven distribution of components,which affect the efficient play of self-healing function.In this paper,HMX-based energetic microspheres with self-healing function were successfully prepared by microchannel technology,which showed excellent self-healing effect in both Polymer-bonded explosives(PBXs)and Composite solid propellants(CSPs).The experimental results show that the HMX-based energetic microspheres with different binder contents prepared by microchannel technology show regular shape,HMX crystal particles are uniformly wrapped by self-healing binder(GAPU).When the content of GAPU in HMX-based energetic microspheres is 10%,PBXs show excellent self-healing effect and mechanical safety is improved by 400%(raw HMX vs S4,5 J vs 25 J).As a high-energy component,the burning rate of CSPs is increased by 359.4%,the time(burning temperature>1700℃)is prolonged by 333.3%,and the maximum impulse force is increased by 107.3%(CSP-H vs CSP-S4,0.84 mm/s vs 3.87 mm/s,0.06 s vs 0.26 s,0.82 m N vs 1.70 m N).It also has excellent storage performance.The preparation of HMX-based energetic microspheres with self-healing function by microchannel technology provides a new strategy to improve the storage performance of ECMs and the combustion performance of CSPs.
基金supported by National Key R&D Program of China(2022YFB3506200,2022YFB3504100)National Natural Science Foundation of China(22072095,22372107,22202058)+3 种基金Excellent Youth Science Foundation of Liaoning Province(2022-YQ-20)Shenyang Science and Technology Planning Project(22-322-3-28)Liaoning Xingliao talented youth Top talent program(XLYC2203007)University Joint Education Project for China-Central and Eastern European Countries(2021097).
文摘The soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment,so treating diesel engine exhaust is critical.At present,the most effective method for eliminating soot particles is post-treatment technology.Preparation of economically viable and highly active soot combustion catalysts is a pivotal element of post-treatment technology.In this study,different single-metal oxide catalysts with fibrous structures and alkali metal-modified hollow nanotubular Mn-based oxide catalysts were synthesized using centrifugal spinning method.Activity evaluation results showed that the manganese oxide catalyst has the best catalytic activity among the prepared single-metal oxide catalysts.Further research on alkali metal modification showed that doping alkali metals is beneficial for improving the oxidation state of manganese and generating a large number of reactive oxygen species.Combined with the structural effect brought by the hollow nanotube structure,the alkali metal-modified Mn-based oxide catalysts exhibit superior catalytic performance.Among them,the Cs-modified Mn-based oxide catalyst exhibits the best catalytic performance because of its rich active oxygen species,excellent NO oxidation ability,abundant Mn^(4+)ions(M^(n4)+/Mn^(n+)=64.78%),and good redox ability.The T_(10),T_(50),T_(90),and CO_(2)selectivity of the Cs-modified Mn-based oxide catalyst were 267°C,324°C,360°C,and 97.8%,respectively.
