For capturing and recycling of CO_(2)in the internal combustion engine,Rankle cycle engine can reduce the exhaust pollutants effectively under the condition of ensuring the engine thermal efficiency by using the techn...For capturing and recycling of CO_(2)in the internal combustion engine,Rankle cycle engine can reduce the exhaust pollutants effectively under the condition of ensuring the engine thermal efficiency by using the techniques of spraying water in the cylinder and optimizing the ignition advance angle.However,due to the water spray nozzle need to be installed on the cylinder,which increases the cylinder head design difficulty and makes the combustion conditions become more complicated.In this paper,a new method is presented to carry out the closing inlet and exhaust system for internal combustion engines.The proposed new method uses liquid oxygen to solidify part of cooled CO_(2)from exhaust system into dry ice and the liquid oxygen turns into gas oxygen which is sent to inlet system.The other part of CO_(2)is sent to inlet system and mixed with oxygen,which can reduce the oxygen-enriched combustion detonation tendency and make combustion stable.Computing grid of the IP52FMI single-cylinder four-stroke gasoline-engine is established according to the actual shape of the combustion chamber using KIVA-3V program.The effects of exhaust gas recirculation(EGR)rate are analyzed on the temperatures,the pressures and the instantaneous heat release rates when the EGR rate is more than 8%.The possibility of enclosing intake and exhaust system for engine is verified.The carbon dioxide trapping device is designed and the IP52FMI engine is transformed and the CO_(2)capture experiment is carried out.The experimental results show that when the EGR rate is 36%for the optimum EGR rate.When the liquid oxygen of 35.80-437.40 g is imported into the device and last 1-20 min,respectively,21.50-701.30 g dry ice is obtained.This research proposes a new design method which can capture CO_(2)for vehicular internal combustion engine.展开更多
In composite solid propellants with high aluminum(Al)content and low burning rate,incomplete combustion of the Al powder may occur.In this study,varying lithium(Li)content in Al-Li alloy powder was utilized instead of...In composite solid propellants with high aluminum(Al)content and low burning rate,incomplete combustion of the Al powder may occur.In this study,varying lithium(Li)content in Al-Li alloy powder was utilized instead of pure aluminum particles to mitigate agglomeration and enhance the combustion efficiency of solid propellants(Combustion efficiency herein refers to the completeness of metallic fuel oxidation,quantified as the ratio of actual-to-theoretical energy released during combustion)with high Al content and low burning rates.The impact of Al-Li alloy with different Li contents on combustion and agglomeration of solid propellant was investigated using explosion heat,combustion heat,differential thermal analysis(DTA),thermos-gravimetric analysis(TG),dynamic high-pressure combustion test,ignition experiment of small solid rocket motor(SRM)tests,condensation combustion product collection,and X-ray diffraction techniques(XRD).Compared with pure Al,Al-Li alloys exhibit higher combustion heat,which contributes to improved combustion efficiency in Al-Li alloy-containing propellants.DTA and TG analyses demonstrated higher reactivity and lower ignition temperatures for Al-Li alloys.High-pressure combustion experiments at 5 MPa showed that Al-Li alloy fuel significantly decreases combustion agglomeration.The results from theφ75 mm andφ165 mm SRM and XRD tests further support this finding.This study provides novel insights into the combustion and agglomeration behaviors of high-Al,low-burning-rate composite solid propellants and supports the potential application of Al-Li alloys in advanced propellant formulations.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
Al/NH_(4)CoF_(3)-Φ(Φ=0.5,1.0,1.5,2.0,and 3.0)binary composites and Al-NH_(4)CoF_(3)@P(VDF-HFP)ternary composites are fabricated via ultrasonication-assisted blending and electrostatic spraying.The effect of equivale...Al/NH_(4)CoF_(3)-Φ(Φ=0.5,1.0,1.5,2.0,and 3.0)binary composites and Al-NH_(4)CoF_(3)@P(VDF-HFP)ternary composites are fabricated via ultrasonication-assisted blending and electrostatic spraying.The effect of equivalence ratio(Φ)on the reaction properties is systematically investigated in the binary Al/NH_(4)CoF_(3)system.For ternary systems,electrostatic spraying allows both components to be efficiently encapsulated by P(VDF-HFP)and to achieve structural stabilization and enhanced reactivity through synergistic interfacial interactions.Morphological analysis using SEM/TEM revealed that P(VDF-HFP)formed a protective layer on Al and NH_(4)CoF_(3)particles,improving dispersion,hydrophobicity(water contact angle increased by 80.5%compared to physically mixed composites),and corrosion resistance.Thermal decomposition of NH_(4)CoF_(3)occurred at 265℃,releasing NH_(3)and HF,which triggered exothermic reactions with Al.The ternary composites exhibited a narrowed main reaction temperature range and concentrated heat release,attributed to improved interfacial contact and polymer decomposition.Combustion tests demonstrated that Al-NH_(4)CoF_(3)@P(VDF-HFP)achieved self-sustaining combustion.In addition,a simple validation was done by replacing the Al component in the aluminium-containing propellant,demonstrating its potential application in the propellant field.This work establishes a novel strategy for designing stable,high-energy composites with potential applications in advanced propulsion systems.展开更多
The presence of a surface oxide film(B_(2)O_(3))on boron(B)particles significantly compromises their combustion efficiency and kinetic performance in fuel-rich solid propellants.This study proposes an innovative conti...The presence of a surface oxide film(B_(2)O_(3))on boron(B)particles significantly compromises their combustion efficiency and kinetic performance in fuel-rich solid propellants.This study proposes an innovative continuous modification strategy combining non-thermal plasma(NTP)etching with fluorocarbon passivation.Characterization and kinetic analysis revealed that reactive plasma species—including atomic hydrogen(H),electronically excited molecular hydrogen(H_(2)^(*)),vibrationally excited molecular hydrogen(H_(2)v),and hydrogen ions(H^(+))—dominate the reduction of B_(2)O_(3)through lowering the transition energy barrier and shifting the reaction spontaneity.Subsequent argon plasma fragmentation of C_(8)F_(18)generates fluorocarbon radicals that form conformal passivation coatings(thickness:7 nm)on purified boron surfaces.The modified boron particles exhibit 37.5℃lower exothermic peak temperature and 27.2%higher heat release(14.8 kJ/g vs.11.6 kJ/g)compared to untreated counterparts.Combustion diagnostics reveal 194%increase in maximum flame height(135.10 mm vs.46.03 mm)and 134%enhancement in flame propagation rate(4.44 cm/s vs.1.90 cm/s).This NTP-based surface engineering approach establishes a scalable pathway for developing highperformance boron-based energetic composites.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
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
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
Gas injection-enhanced underground coal combustion for heat extraction represents a disruptive chemical fluidized extraction method of coal resources.Coal seam combustion dynamics provide crucial underpinnings for eng...Gas injection-enhanced underground coal combustion for heat extraction represents a disruptive chemical fluidized extraction method of coal resources.Coal seam combustion dynamics provide crucial underpinnings for engineering realization.This study establishes an experimental system for monitoring temperature field evolution during gas-assisted combustion in cylindrical coal cores,investigating the influence of moisture content(0%,16%,24%)on gas-assisted combustion kinetics.Results showed moisture content significantly influences combustion:higher levels(16%-24%)delay high-temperature expansion(0-1 h)due to evaporation energy absorption,but subsequently enhance efficiency through pore formation and oxygen diffusion,achieving 1120-1230°C peaks.Dry coal exhibits rapid initial combustion(peak temperature of 1130°C within 1 h)but weaker sustained reactions.The temperature field evolves from localized hotspots to an elliptical high-temperature zone,with axial expansion rates surpassing radial rates,driven by thermal buoyancy and convective heat transfer.Moisture’s dual role is revealed:initially as a thermodynamic inhibitor and later as a promoter by increasing pore diameter and oxygen diffusion coefficients.An optimal moisture content of 16%balances initial heat loss with enhanced reactivity,offering practical insights for optimizing gas injection and thermal recovery in underground coal combustion.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
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
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
Combustion catalyst is a key modifier for the performance of composite solid propellant.To exploit highefficiency combustion catalyst,a fascinating bimetallic metal-organic framework[MnCo(EIM)_(2)(DCA)_(2)]n(1)was con...Combustion catalyst is a key modifier for the performance of composite solid propellant.To exploit highefficiency combustion catalyst,a fascinating bimetallic metal-organic framework[MnCo(EIM)_(2)(DCA)_(2)]n(1)was constructed by an active dicyandiamide(DCA)linker,Mn^(2+),Co^(2+)centers,and an 1-ethylimidazole(EIM)ligand.1 possesses good thermal stability(Tp=205℃),high energy density(Eg=24.34 kJ/g,Ev=35.93 kJ/cm^(3)),and insensitivity to impact and frictional stimulus.The catalytic effects of 1 contrasted to monometallic coordination compounds Mn(EIM)_(4)(DCA)_(2)(2)and Co(EIM)_(4)(DCA)_(2)(3)on the thermal decomposition of AP/RDX composite were investigated by a DSC method.The decomposition peak temperatures of AP and RDX of the composite decreased to 335.8℃ and 206.4℃,respectively,and the corresponding activation energy decreased by 27.3%and 43.6%,respectively,which are better than the performances of monometallic complexes 2 and 3.The gas products in the whole thermal decomposition stage of the sample were measured by TG-MS and TG-IR,and the catalytic mechanism of 1 to AP/RDX was further analyzed.This work reveal potential application of bimetallic MOFs in the composite solid propellants.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
The main function of a hot blast stove is to deliver a high-temperature and stable hot blast to the blast furnace,which has an important impact on the blast furnace ironmaking process.To improve the combustion efficie...The main function of a hot blast stove is to deliver a high-temperature and stable hot blast to the blast furnace,which has an important impact on the blast furnace ironmaking process.To improve the combustion efficiency,a simulation model of the combustion part of an internal combustion hot blast stove was established by combining turbulence,combustion,and radiation models.Based on the original model,a new type of internal combustion hot blast stove is proposed.The results indicated insufficient combustion in the original structure and higher CO concentrations in the corners of the eyes at both ends of the combustor outlet,the recirculation area at the bottom of the combustion chamber was mainly concentrated in the middle part.With the new structure of the hot blast stove,the gas baffles with different inclination angles are added to the rectangular burner,at the outlet of the combustion chamber,the CO concentration is reduced to a certain extent,and the temperature distribution is more uniform.When the inclination angle of the gas baffle is 60°,the combustion chamber outlet section average temperature rises from 1686 K to 1693 K,the outlet flue gas average volume fraction of CO decreases the most,and the average volume fraction of CO decreases from 0.00708%to 0.00568%,which could reduce the CO content by about 20%.展开更多
Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficie...Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficiency and limited performance in aerospace propulsion.In this study,boron carbide(B4C)is investigated as an alternative fuel to pristine boron due to its favorable gas-phase combustion.Both metal oxide(nickel oxide(NiO))and metal fluoride(nickel fluoride(NiF_(2)))are selected as oxidizing modifiers to enhance the reactivity of B4C.A method combining laser ignition with optical diagnostics is employed to investigate the enhancing effects of different oxidizers on the ignition and combustion characteristics of B4C.Both NiO and NiF_(2)can significantly increase the combustion radiation intensity and reduce the time to maximum intensity of B4C.Differential scanning calorimetry,in-situ X-ray diffraction,and Fourier transform infrared spectroscopy were used for simultaneous thermal analysis of the B4C composite powders.Combined thermal analysis showed that the effects of NiO and NiF_(2)on promoting B4C combustion is mainly achieved via the formation of NimBn and the release of a large number of gas products.It is reasonable to speculate that the phase separation at the B2O3/NimBn interface forms new pathways for oxygen diffusion and reaction with the B core.The difference in the combustion mechanism of B4C with NiO and NiF_(2)lies in the gas phase products,i.e.,CO_(2)and BF3,respectively,thus leading to significant differences in their reaction processes.展开更多
基金Supported by National Natural Science Foundation of China(Grant No.51176082)Importation and Development of High-Caliber Talents Project of Beijing Municipal Institutions of China(Grant No.CIT&TCD20140311)Beijing Municipal Natural Science Foundation of China(Grant No.SQKZ201510016004)
文摘For capturing and recycling of CO_(2)in the internal combustion engine,Rankle cycle engine can reduce the exhaust pollutants effectively under the condition of ensuring the engine thermal efficiency by using the techniques of spraying water in the cylinder and optimizing the ignition advance angle.However,due to the water spray nozzle need to be installed on the cylinder,which increases the cylinder head design difficulty and makes the combustion conditions become more complicated.In this paper,a new method is presented to carry out the closing inlet and exhaust system for internal combustion engines.The proposed new method uses liquid oxygen to solidify part of cooled CO_(2)from exhaust system into dry ice and the liquid oxygen turns into gas oxygen which is sent to inlet system.The other part of CO_(2)is sent to inlet system and mixed with oxygen,which can reduce the oxygen-enriched combustion detonation tendency and make combustion stable.Computing grid of the IP52FMI single-cylinder four-stroke gasoline-engine is established according to the actual shape of the combustion chamber using KIVA-3V program.The effects of exhaust gas recirculation(EGR)rate are analyzed on the temperatures,the pressures and the instantaneous heat release rates when the EGR rate is more than 8%.The possibility of enclosing intake and exhaust system for engine is verified.The carbon dioxide trapping device is designed and the IP52FMI engine is transformed and the CO_(2)capture experiment is carried out.The experimental results show that when the EGR rate is 36%for the optimum EGR rate.When the liquid oxygen of 35.80-437.40 g is imported into the device and last 1-20 min,respectively,21.50-701.30 g dry ice is obtained.This research proposes a new design method which can capture CO_(2)for vehicular internal combustion engine.
基金the National Natural Science Foundation of China(Grant No.U2441263)for financial support of this work。
文摘In composite solid propellants with high aluminum(Al)content and low burning rate,incomplete combustion of the Al powder may occur.In this study,varying lithium(Li)content in Al-Li alloy powder was utilized instead of pure aluminum particles to mitigate agglomeration and enhance the combustion efficiency of solid propellants(Combustion efficiency herein refers to the completeness of metallic fuel oxidation,quantified as the ratio of actual-to-theoretical energy released during combustion)with high Al content and low burning rates.The impact of Al-Li alloy with different Li contents on combustion and agglomeration of solid propellant was investigated using explosion heat,combustion heat,differential thermal analysis(DTA),thermos-gravimetric analysis(TG),dynamic high-pressure combustion test,ignition experiment of small solid rocket motor(SRM)tests,condensation combustion product collection,and X-ray diffraction techniques(XRD).Compared with pure Al,Al-Li alloys exhibit higher combustion heat,which contributes to improved combustion efficiency in Al-Li alloy-containing propellants.DTA and TG analyses demonstrated higher reactivity and lower ignition temperatures for Al-Li alloys.High-pressure combustion experiments at 5 MPa showed that Al-Li alloy fuel significantly decreases combustion agglomeration.The results from theφ75 mm andφ165 mm SRM and XRD tests further support this finding.This study provides novel insights into the combustion and agglomeration behaviors of high-Al,low-burning-rate composite solid propellants and supports the potential application of Al-Li alloys in advanced propellant formulations.
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(No.51706105)。
文摘Al/NH_(4)CoF_(3)-Φ(Φ=0.5,1.0,1.5,2.0,and 3.0)binary composites and Al-NH_(4)CoF_(3)@P(VDF-HFP)ternary composites are fabricated via ultrasonication-assisted blending and electrostatic spraying.The effect of equivalence ratio(Φ)on the reaction properties is systematically investigated in the binary Al/NH_(4)CoF_(3)system.For ternary systems,electrostatic spraying allows both components to be efficiently encapsulated by P(VDF-HFP)and to achieve structural stabilization and enhanced reactivity through synergistic interfacial interactions.Morphological analysis using SEM/TEM revealed that P(VDF-HFP)formed a protective layer on Al and NH_(4)CoF_(3)particles,improving dispersion,hydrophobicity(water contact angle increased by 80.5%compared to physically mixed composites),and corrosion resistance.Thermal decomposition of NH_(4)CoF_(3)occurred at 265℃,releasing NH_(3)and HF,which triggered exothermic reactions with Al.The ternary composites exhibited a narrowed main reaction temperature range and concentrated heat release,attributed to improved interfacial contact and polymer decomposition.Combustion tests demonstrated that Al-NH_(4)CoF_(3)@P(VDF-HFP)achieved self-sustaining combustion.In addition,a simple validation was done by replacing the Al component in the aluminium-containing propellant,demonstrating its potential application in the propellant field.This work establishes a novel strategy for designing stable,high-energy composites with potential applications in advanced propulsion systems.
基金supported by the National Natural Science Foundation of China(Nos.U2341249,12005076,22205112)the Fundamental Research Funds for the Central Universities(No.2025201012)。
文摘The presence of a surface oxide film(B_(2)O_(3))on boron(B)particles significantly compromises their combustion efficiency and kinetic performance in fuel-rich solid propellants.This study proposes an innovative continuous modification strategy combining non-thermal plasma(NTP)etching with fluorocarbon passivation.Characterization and kinetic analysis revealed that reactive plasma species—including atomic hydrogen(H),electronically excited molecular hydrogen(H_(2)^(*)),vibrationally excited molecular hydrogen(H_(2)v),and hydrogen ions(H^(+))—dominate the reduction of B_(2)O_(3)through lowering the transition energy barrier and shifting the reaction spontaneity.Subsequent argon plasma fragmentation of C_(8)F_(18)generates fluorocarbon radicals that form conformal passivation coatings(thickness:7 nm)on purified boron surfaces.The modified boron particles exhibit 37.5℃lower exothermic peak temperature and 27.2%higher heat release(14.8 kJ/g vs.11.6 kJ/g)compared to untreated counterparts.Combustion diagnostics reveal 194%increase in maximum flame height(135.10 mm vs.46.03 mm)and 134%enhancement in flame propagation rate(4.44 cm/s vs.1.90 cm/s).This NTP-based surface engineering approach establishes a scalable pathway for developing highperformance boron-based energetic composites.
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.
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supported by the Key Project of Chongqing Special Program for Technological Innovation and Application Development(CSTB2024TIAD-KPX0099)the Graduate Research Innovation Project of Chongqing,China(CYB240050),the Fundamental Research Funds for the Central Universities(2025CDJZKKYJH-14)the State Key Laboratory of Coal Mine Disaster Dynamics and Control for 2030 major project(2011DA105287-MX2030-202101).
文摘Gas injection-enhanced underground coal combustion for heat extraction represents a disruptive chemical fluidized extraction method of coal resources.Coal seam combustion dynamics provide crucial underpinnings for engineering realization.This study establishes an experimental system for monitoring temperature field evolution during gas-assisted combustion in cylindrical coal cores,investigating the influence of moisture content(0%,16%,24%)on gas-assisted combustion kinetics.Results showed moisture content significantly influences combustion:higher levels(16%-24%)delay high-temperature expansion(0-1 h)due to evaporation energy absorption,but subsequently enhance efficiency through pore formation and oxygen diffusion,achieving 1120-1230°C peaks.Dry coal exhibits rapid initial combustion(peak temperature of 1130°C within 1 h)but weaker sustained reactions.The temperature field evolves from localized hotspots to an elliptical high-temperature zone,with axial expansion rates surpassing radial rates,driven by thermal buoyancy and convective heat transfer.Moisture’s dual role is revealed:initially as a thermodynamic inhibitor and later as a promoter by increasing pore diameter and oxygen diffusion coefficients.An optimal moisture content of 16%balances initial heat loss with enhanced reactivity,offering practical insights for optimizing gas injection and thermal recovery in underground coal combustion.
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supported by the National Natural Science Foundation of China(Grant No.22175025)State Key Laboratory of Explosion Science and Safety Protection(Grant No.YBKT22-03)+1 种基金the Natural Science Foundation of Chongqing(Grant No.CSTB2023 NSCQ-LZX0098)the Chongqing Municipal Education Commis-sion(Grant No.KJZD-M202301404).
文摘Combustion catalyst is a key modifier for the performance of composite solid propellant.To exploit highefficiency combustion catalyst,a fascinating bimetallic metal-organic framework[MnCo(EIM)_(2)(DCA)_(2)]n(1)was constructed by an active dicyandiamide(DCA)linker,Mn^(2+),Co^(2+)centers,and an 1-ethylimidazole(EIM)ligand.1 possesses good thermal stability(Tp=205℃),high energy density(Eg=24.34 kJ/g,Ev=35.93 kJ/cm^(3)),and insensitivity to impact and frictional stimulus.The catalytic effects of 1 contrasted to monometallic coordination compounds Mn(EIM)_(4)(DCA)_(2)(2)and Co(EIM)_(4)(DCA)_(2)(3)on the thermal decomposition of AP/RDX composite were investigated by a DSC method.The decomposition peak temperatures of AP and RDX of the composite decreased to 335.8℃ and 206.4℃,respectively,and the corresponding activation energy decreased by 27.3%and 43.6%,respectively,which are better than the performances of monometallic complexes 2 and 3.The gas products in the whole thermal decomposition stage of the sample were measured by TG-MS and TG-IR,and the catalytic mechanism of 1 to AP/RDX was further analyzed.This work reveal potential application of bimetallic MOFs in the composite solid propellants.
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.
文摘The main function of a hot blast stove is to deliver a high-temperature and stable hot blast to the blast furnace,which has an important impact on the blast furnace ironmaking process.To improve the combustion efficiency,a simulation model of the combustion part of an internal combustion hot blast stove was established by combining turbulence,combustion,and radiation models.Based on the original model,a new type of internal combustion hot blast stove is proposed.The results indicated insufficient combustion in the original structure and higher CO concentrations in the corners of the eyes at both ends of the combustor outlet,the recirculation area at the bottom of the combustion chamber was mainly concentrated in the middle part.With the new structure of the hot blast stove,the gas baffles with different inclination angles are added to the rectangular burner,at the outlet of the combustion chamber,the CO concentration is reduced to a certain extent,and the temperature distribution is more uniform.When the inclination angle of the gas baffle is 60°,the combustion chamber outlet section average temperature rises from 1686 K to 1693 K,the outlet flue gas average volume fraction of CO decreases the most,and the average volume fraction of CO decreases from 0.00708%to 0.00568%,which could reduce the CO content by about 20%.
基金The National Natural Science Foundation of China(Grant Nos.523B2063 and 52376089)。
文摘Boron-based fuels,recognized for their high energy density and potential in energetic applications,encounter challenges such as long ignition delays and incomplete combustion,which result in reduced combustion efficiency and limited performance in aerospace propulsion.In this study,boron carbide(B4C)is investigated as an alternative fuel to pristine boron due to its favorable gas-phase combustion.Both metal oxide(nickel oxide(NiO))and metal fluoride(nickel fluoride(NiF_(2)))are selected as oxidizing modifiers to enhance the reactivity of B4C.A method combining laser ignition with optical diagnostics is employed to investigate the enhancing effects of different oxidizers on the ignition and combustion characteristics of B4C.Both NiO and NiF_(2)can significantly increase the combustion radiation intensity and reduce the time to maximum intensity of B4C.Differential scanning calorimetry,in-situ X-ray diffraction,and Fourier transform infrared spectroscopy were used for simultaneous thermal analysis of the B4C composite powders.Combined thermal analysis showed that the effects of NiO and NiF_(2)on promoting B4C combustion is mainly achieved via the formation of NimBn and the release of a large number of gas products.It is reasonable to speculate that the phase separation at the B2O3/NimBn interface forms new pathways for oxygen diffusion and reaction with the B core.The difference in the combustion mechanism of B4C with NiO and NiF_(2)lies in the gas phase products,i.e.,CO_(2)and BF3,respectively,thus leading to significant differences in their reaction processes.
