Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The igniti...Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.展开更多
In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than thr...In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than three million degrees Celsius(Fig.1)[1-4].Inside the container was a tiny fuel capsule containing tritium and deuterium that imploded at more than 400 km·s^(-1)causing atoms to combine and releasing 5.2 MJ of energy[1-4].展开更多
Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignit...Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignition mechanism were analyzed,by investigating the flame ignition behaviors of AZ80(ZM5),EZ30K(ZM6)and WE43 Mg alloys.The results show that the rupture of the oxide films caused by liquid gravity was the key to causing ignition.According to thermodynamic calculations,compared with Mg,Al cannot be preferentially oxidized;while Nd can be preferentially oxidized through significant enrichment,resulting in a discontinuous Nd_(2)O_(3)inner layer in the ZM6 alloy;in contrast,Y has a strong preferential oxidation ability,which gives the WE43 alloy a continuous Y_(2)O_(3)inner layer and self-healing ability.In addition,the oxide film of the ZM5 alloy is loose and has poor mechanical properties,so it cannot effec-tively hinder diffusion and resist liquid gravity.Differently,the oxide films of the ZM6 and WE43 alloys are dense and have better mechanical properties,leading to higher ignition temperatures and longer igni-tion times.In addition,a criterion was proposed to predict the ignition time based on the law of energy conservation,and it was simplified to predict the ignition temperature.The errors between the predicted and measured values are within 11%.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
The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reachi...The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reaching 813.9℃ for the EV32–3Y(wt.%)alloy.Additionally,the calculated residual stresses of the Y_(2)O_(3) and Gd_(2)O_(3) films were 2.732 GPa and 2.569 GPa respectively,showcasing a distinct correlation between Y concentration and improved fire resistance.This enhancement can be attributed to the formation of denser oxide films,especially Y_(2)O_(3) and Gd_(2)O_(3),effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing.The study elucidates the vital role of Y addition in enhancing fire resistance,thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure.These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.展开更多
A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number...A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.展开更多
The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data ...The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data at three ignition positions.The venting mechanism was revealed by the simulated concentration distribution,temperature profile,and airflow velocity.The results show rear ignition results in the external methane mass distribution taking the form of"mushroom"and columnar flames in the external space,which can be expressed as a third-order polynomial relationship with distance;central ignition forms a relationship of the form y=AxB.Front ignition causes the temperature to show a tendency to repeated oscillations(rising,falling,and rising).Central ignition generates the maximum vented airflow velocity(V_(max)=320 m/s)upon vent opening.The results indicate that it is acceptable to apply numerical simulation of methane explosions in practice.展开更多
The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have ...The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.展开更多
During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different contr...During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different control for each cylinder.However,recent studies have paid insufficient attention to cylinders other than the first starting cylinder.This paper proposes a comprehensive control strategy based on experimental data from the direct-start process of the second,third,and fourth cylinders,aiming to enhance the characteristics of combustion and emission performance through the optimization of injection timing,equivalence ratio,and ignition timing.The research findings indicate that the second cylinder should inject fuel approximately 10 ms after the first cylinder ignites to mix thoroughly the fuel with air.The ignition timing of the second cylinder should be close to the highest point of the piston movement to minimize hindrance to the piston compression process.The third and fourth cylinders should adopt a delayed injection timing strategy to prevent the escape of injected fuel caused by low engine speed.The optimal ignition timing for the third cylinder is 20℃A BTDC,while the fourth cylinder should be ignited earlier due to its stronger airflow and faster formation of a mixture that can be ignited.As the fuel injection quantity increases,the power output of the three cylinders enhances,but at the same time,emissions also increase.Therefore,their optimal equivalence ratios are determined as 1.2,1.4,and 1.2,respectively,striking a balance between combustion and emission performances.展开更多
We investigate the influence of gold doping on the transport range of a relativistic electron beam in high-density deuterium–tritium(DT)fuel,which could be encountered in the double-cone ignition laser fusion.We deve...We investigate the influence of gold doping on the transport range of a relativistic electron beam in high-density deuterium–tritium(DT)fuel,which could be encountered in the double-cone ignition laser fusion.We develop the stopping power model to include gold doping and then analyze the influence of Coulomb collision and bremsstrahlung on the electron transport range with different gold doping ratios,consistent with the Geant4 simulations.When the gold doping ratio increases from 0.5%to 30%,the transport range of a 10 Me V electron beam is decreased by 9.6%and 18.5%via the bremsstrahlung.For the 1 Me V beam,the decrease of the range becomes 0.7%and 1.0%.We also investigate the transverse broadening of the electron beam and radiated photon energy reabsorption in a spherical target.When the gold doping ratio is 2%and the beam energy is increased from 1 Me V to 5 Me V,the bremsstrahlung photons cover 2.6%to 10.3%of the total beam energy.Meanwhile,the reabsorbed photon energy is reduced from 31.6%to 8.9%.展开更多
Accurate characterization of three-dimensional burning crack propagation remains pivotal yet challenging for energetic material safety,as conventional diagnostics and models inadequately resolve coupled crack-pressure...Accurate characterization of three-dimensional burning crack propagation remains pivotal yet challenging for energetic material safety,as conventional diagnostics and models inadequately resolve coupled crack-pressure dynamics in confined explosives.This study combines a novel spherical confinement system(with/without sapphire windows)with synchronized high-speed imaging and 3D reconstruction to overcome optical limitations in opaque explosives.Experimental analysis of centrally ignited HMX-based PBX-1 reveals:(1)burning cracks propagate radially with equatorial acceleration and polar deceleration,(2)systematic formation of 3–4 dominant crack branches across geometries,and(3)pressure evolution exhibiting gradual accumulation(subsurface cracking)followed by exponential growth(surface burn-through),with decay governed by cavity expansion.Building on Hill's framework,we develop a model incorporating cavity volume and fracture toughness criteria,validated against PBX explosive(95%HMX-based)experiments.The model demonstrates improved prediction of pressure trends compared to prior approaches,particularly in resolving laminar-phase accumulation and crackinduced surge transitions.Results establish structural cavity volume as a critical modulator of measured pressure and reveal direction-dependent crack kinematics as fundamental features of constrained combustion.This work provides experimentally validated insights into mechanisms of reaction pressure development and burning cracks pathways during constrained PBX explosive combustion.展开更多
Enhancing the output capacity of semiconductor bridge(SCB) through the application of composite nano-energetic films is a subject of wide concern. Furthermore, improving the safety, reliability, and production efficie...Enhancing the output capacity of semiconductor bridge(SCB) through the application of composite nano-energetic films is a subject of wide concern. Furthermore, improving the safety, reliability, and production efficiency of energetic semiconductor bridge(ESCB) is the primary focus for large-scale engineering applications in the future. Here, the Al/CuO nano-film ESCB was efficiently fabricated using 3D direct writing. The electrostatic safety of the film is enhanced by precisely adjusting the particle size of Al, while ensuring that the SCB can initiate the film with small energy. The burst characteristics of SCB/ESCB were thoroughly investigated by employing a 100 μF tantalum capacitor to induce SCB and ESCB under an intense voltage gradient. The solid-state heating process of both SCB and ESCB was analyzed with multi physical simulation(MPS). The experimental results demonstrate that the critical burst time of both SCB and ESCB decreases with increasing voltage. Under the same voltage, the critical burst time of ESCB is longer than that of SCB, primarily due to differences in the melting to vaporization stage. The MPS results indicate that the highest temperature is observed at the V-shaped corner of SCB. Due to the thermal contact resistance between SCB and the film, heat conduction becomes more concentrated in the central region of the bridge, resulting in a faster solid-state heating process for ESCB compared to SCB.The results of the gap ignition experiments indicate that at a 19 mm gap, an ESCB with a film mass of 10 mg can ignite nickel hydrazine nitrate(NHN) and cyclotrimethylenetrinitramine(RDX). This suggests that thermite ESCB can serve as a novel, safe, and reliable energy exchange element and initiator in largescale engineering applications.展开更多
Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show ...Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show that collective SRS in the plasma produced by ablating a polyimide film is detected for the ID beams,but is suppressed by adding a toe before the main pulse of the ID beams.The toe also strongly influences SRS of both the ID and DD beams excited in the plasma generated in the hohlraum.When a toe is used,the SRS spectra of the DD beams show that SRS tends to be excited in lower plasma density,which will result in a lower risk of super-hot electrons.Measurements of hot electrons support this conclusion.This research will help us produce a better pulse design for this new ignition path.展开更多
The semiconductor bridge(SCB)ignites through bridge film discharge,offering advantages such as low ignition energy,high safety,and compatibility with digital logic circuits.The study uses laser interferometry to inves...The semiconductor bridge(SCB)ignites through bridge film discharge,offering advantages such as low ignition energy,high safety,and compatibility with digital logic circuits.The study uses laser interferometry to investigate the gas dynamics of the bridge film after SCB plasma extinction.Interferometric images of the SCB film gas were obtained through a laser interferometry optical path.After the degradation model of digital image processing,clearer images were produced to facilitate analysis and calculation.The results show that the gas temperature at the center of the SCB film reaches a maximum of 1000 K,and the temperature rapidly decreases along the axial direction of the bridge surface to room temperature at 300 K.The maximum diffusion velocity of the plasma is 1.8 km/s.These findings provide critical insights for SCB design and ignition control.展开更多
Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of supr...Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.展开更多
Boron has high mass and volume calorific values,but it is difficult to ignite and has low combustion efficiency.This literature review summarizes the strategies that are used to solve the above-mentioned problems,whic...Boron has high mass and volume calorific values,but it is difficult to ignite and has low combustion efficiency.This literature review summarizes the strategies that are used to solve the above-mentioned problems,which include coatings of boron by using fluoride compounds,energetic composites,metal fuels,and metal oxides.Coating techniques include recrystallization,dual-solvent,phase transfer,electrospinning,etc.As one of the effective coating agents,the fluorine compounds can react with the oxide shell of boron powder.In comparison,the energetic composites can effectively improve the flame temperature of boron powder and enhance the evaporation efficiency of oxide film as a condensed product.Metals and metal oxides would react with boron powder to form metal borides with a lower ignition point,which could reduce its ignition temperature.展开更多
Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ig...Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ignition mechanism of EFIs directly igniting pyrotechnics.An oscilloscope,a photon Doppler velocimetry,and a plasma spectrum measurement system were employed to obtain information of electric characteristics,impact pressure,and plasma temperature.The results of the electric characteristics and the impact pressure were inconsistent with ignition results.The only thing that the ignition success tests had in common was that their plasma all had a relatively long period of high-temperature duration(HTD).It eventually concludes that the ignition mechanism in this research is the microconvection heat transfer rather than the shock initiation,which differs from that of exploding foil initiators detonating explosives.Furthermore,the methods for evaluating the ignition success of semiconductor bridge initiators are not entirely applicable to the tests mentioned in this paper.The HTD is the critical parameter for judging the ignition success,and it is influenced by two factors:the late time discharge and the energy of the electric explosion.The longer time of the late time discharge and the more energy of the electric explosion,the easier it is to expand the HTD,which improves the probability of the ignition success.展开更多
Hydrazine is toxic and carcinogenic, which greatly increases the difficulty of application and no longer meets the needs of green aerospace. As a green propellant, the Ammonium Dinitramide(ADN)-based liquid propellant...Hydrazine is toxic and carcinogenic, which greatly increases the difficulty of application and no longer meets the needs of green aerospace. As a green propellant, the Ammonium Dinitramide(ADN)-based liquid propellant has the advantages of higher specific impulse, being non-toxic,pollution-free, and easy storage. However, an ADN-based space engine in orbit has exposed the problems of high-temperature deactivation of catalysts and cold-start failure. An active ignition technology—electric ignition technology was explored in this paper to break through the technical bottleneck of catalyst deactivation and the inability to a cold start. An experimental system of a constant-volume combustor for the ADN-based liquid propellant based on the electric ignition method was established. The electric ignition and combustion characteristics of the ADN-based liquid propellant in a volume combustor with an electric ignition method were studied. The influencing mechanisms of the ignition voltage and the electrode structure on the electric ignition characteristics of the ADN-based liquid propellant were investigated. An elevation of the ignition voltage could facilitate the ignition process of the ADN-based liquid propellant, curtail electric energy input and heating effect, while exerting an adverse impact on the combustion process of the propellant.An increase in the ignition voltage enhanced the ignition process of the propellant while simultaneously suppressing its combustion process when utilizing mesh electrodes. Compared to the strip electrodes, the mesh electrodes increased the contact area between the electrodes and the propellant,increased the electric energy input power in the electric ignition process, and reduced the ignition delay time. The mesh electrodes could promote the combustion process of the propellant to a certain extent.展开更多
Plasma ignition technology has delivered good performance in the aerospace industry. In this study, a pre-combustion plasma jet igniter was designed, and its characteristics were examined from three aspects: the morph...Plasma ignition technology has delivered good performance in the aerospace industry. In this study, a pre-combustion plasma jet igniter was designed, and its characteristics were examined from three aspects: the morphology, temperature, and discharge characteristics and process of ignition. Images of the OH distribution were obtained by using an OH Planar Laser-Induced Fluorescence(OH-PLIF) experimental system. Results have shown that the proposed plasma jet had a higher OH concentration, longer length, and larger area than those of a traditional igniter. The stability of discharge of the igniter was improved as the equivalence ratio φ was increased, and reducing gas flow reduced the pulsation of the plasma jet. When the input current was increased from 15A to 35 A, the highest average temperature increased from 5127 K to 7987 K. An increase in the equivalence ratio reduced the region of arc ionization, but expanded the regions of the core combustion reaction and the outer flame. Herein, this study has obtained a deep understanding of the jet and ignition law and developed a new idea for the application of plasma in the ignition field.A pre-combustion plasma jet igniter can significantly improve the efficiency of ignition and shorten the ignition process compared with a traditional igniter.展开更多
During air injection into an oil reservoir,an oxidation reaction generates some heat to raise the reservoir temperature.When the reservoir temperature reaches an ignition temperature,spontaneous ignition occurs.There ...During air injection into an oil reservoir,an oxidation reaction generates some heat to raise the reservoir temperature.When the reservoir temperature reaches an ignition temperature,spontaneous ignition occurs.There is a time delay from the injection to ignition.There are mixed results regarding the feasibility of spontaneous ignition in real-field projects and in laboratory experiments.No analytical model is available in the literature to estimate the oxidation time required to reach spontaneous ignition with heat loss.This paper discusses the feasibility of spontaneous ignition from theoretical points and experimental and field project observations.An analytical model considering heat loss is proposed.Analytical models with and without heat loss investigate the factors that affect spontaneous ignition.Based on the discussion and investigations,we find that it is more difficult for spontaneous ignition to occur in laboratory experiments than in oil reservoirs;spontaneous ignition is strongly affected by the initial reservoir temperature,oil activity,and heat loss;spontaneous ignition is only possible when the initial reservoir temperature is high,the oil oxidation rate is high,and the heat loss is low.展开更多
基金supported by the National Key Research and Development Program of China(Grant No.2021YFB3501002)the National Natural Science Foundation of China(Grant No.52301059,No.52271009)the Shanghai Post-doctoral Excellence Program(Grant No.2023372).
文摘Magnesium and its alloys offer lightweight advantage and have extensive development prospects,particularly in aerospace.However,their flammability poses a significant barrier on the development of Mg alloys.The ignition resistance of these alloys often depends on the protectiveness of the oxide film formed on the surface.This paper elucidates the formation mechanism of oxide film from thermodynamics and kinetics,classifying oxide films based on their layered structure to assess their protective properties.Furthermore,it comprehensively reviews the impact of characteristics on the protective effectiveness such as compactness,continuity,thickness,and mechanical properties.The paper also introduces various characterization methods for the microstructure and properties of oxide film.The primary objective of this paper is to enhance the comprehension of oxide film concerning the ignition resistance of Mg alloys and to furnish references for future advancements and research in Mg alloys with heightened ignition resistance.
文摘In February 2024,192 lasers at the National Ignition Facility(NIF)in Livermore,CA,USA,began pouring 2.2 MJ of energy into a gold container smaller than the tip of a person’s little finger,heat-ing it to more than three million degrees Celsius(Fig.1)[1-4].Inside the container was a tiny fuel capsule containing tritium and deuterium that imploded at more than 400 km·s^(-1)causing atoms to combine and releasing 5.2 MJ of energy[1-4].
基金supported by the National Key Research and Development Program of China(No.2021YFB3501002)the National Science and Technology Major Project(No.J2019-Ⅷ-0003-0165)the National Natural Science Foundation of China(No.52301059).
文摘Oxide films hinder diffusion and resist external forces,which determines the flame ignition mechanism of magnesium alloys.The effects of the continuity,compactness and mechanical properties of oxide films on the ignition mechanism were analyzed,by investigating the flame ignition behaviors of AZ80(ZM5),EZ30K(ZM6)and WE43 Mg alloys.The results show that the rupture of the oxide films caused by liquid gravity was the key to causing ignition.According to thermodynamic calculations,compared with Mg,Al cannot be preferentially oxidized;while Nd can be preferentially oxidized through significant enrichment,resulting in a discontinuous Nd_(2)O_(3)inner layer in the ZM6 alloy;in contrast,Y has a strong preferential oxidation ability,which gives the WE43 alloy a continuous Y_(2)O_(3)inner layer and self-healing ability.In addition,the oxide film of the ZM5 alloy is loose and has poor mechanical properties,so it cannot effec-tively hinder diffusion and resist liquid gravity.Differently,the oxide films of the ZM6 and WE43 alloys are dense and have better mechanical properties,leading to higher ignition temperatures and longer igni-tion times.In addition,a criterion was proposed to predict the ignition time based on the law of energy conservation,and it was simplified to predict the ignition temperature.The errors between the predicted and measured values are within 11%.
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supported by the National Key Laboratory for Precision Hot Processing of Metals(Nos.6142909220102).
文摘The incorporation of Y significantly improves the fire resistance of the Mg-3Nd-2Gd-0.2Zr-0.2Zn(EV32)alloy.The findings indicate a significant increase in the ignition point of the alloy upon Y addition,notably reaching 813.9℃ for the EV32–3Y(wt.%)alloy.Additionally,the calculated residual stresses of the Y_(2)O_(3) and Gd_(2)O_(3) films were 2.732 GPa and 2.569 GPa respectively,showcasing a distinct correlation between Y concentration and improved fire resistance.This enhancement can be attributed to the formation of denser oxide films,especially Y_(2)O_(3) and Gd_(2)O_(3),effectively reducing the susceptibility of the oxide film to thermal stress-induced tearing.The study elucidates the vital role of Y addition in enhancing fire resistance,thoroughly investigating the mechanisms that impact both the formation of oxide films and ignition within the alloy structure.These findings not only contribute to a deeper comprehension of magnesium alloy performance under high-temperature conditions but also offer valuable theoretical guidance for enhancing its fire resistance through alloy design and application.
基金supported by the National Natural Science Foundation of China(Nos.12272408 and 11925207)the Natural Science Foundation for Distinguished Young Scholars of Hunan Province,China(No.2024J12057)。
文摘A numerical and experimental study was conducted to investigate the Laser Ablation(LA)ignition mode in an ethylene-fueled supersonic combustor with a cavity flameholder.Theexperiments were operated under a Mach number 2.92 supersonic inflow,with stagnation pressureof 2.4 MPa and stagnation temperature of 1600 K.Reynolds-averaged Navier-Stokes simulationswere conducted to characterize the mixing process and flow field structure.This study identifiedfour distinct LA ignition modes.Under the specified condition,laser ablation in zero and negativedefocusing states manifested two distinct ignition modes termed Laser Ablation Direct Ignition(LADI)mode and Laser Ablation Re-Ignition(LARI)mode,correspondingly.LA ignition in alocal small cavity,created by depressing the flow field regulator,could facilitate the ignition modetransforming from LARI mode to Laser Ablation Transition Ignition(LATI)mode.On the otherhand,the elevation of the flow field regulator effectively inhibited the forward propagation of theinitial flame kernel and reduced the dissipation of LA plasma,further enhancing the LADI mode.Based on these characteristics,the LADI mode was subdivided into strong(LADI-S)and weak(LADI-W)modes.Facilitating the transition of ignition modes through alterations in the local flowfield could contribute to attaining a more effective and stable LA ignition.
基金supported by the Young Scientists Fund of National Natural Science Foundation of China(Grant Nos.12202202 and 12202494)the National Key Research and Development Program of China(Grant No.2021YFC3100700)。
文摘The internal and external flow fields during vented explosions of methane were characterized through numerical simulation,and the capability of numerical simulation thereof was validated by previous experimental data at three ignition positions.The venting mechanism was revealed by the simulated concentration distribution,temperature profile,and airflow velocity.The results show rear ignition results in the external methane mass distribution taking the form of"mushroom"and columnar flames in the external space,which can be expressed as a third-order polynomial relationship with distance;central ignition forms a relationship of the form y=AxB.Front ignition causes the temperature to show a tendency to repeated oscillations(rising,falling,and rising).Central ignition generates the maximum vented airflow velocity(V_(max)=320 m/s)upon vent opening.The results indicate that it is acceptable to apply numerical simulation of methane explosions in practice.
文摘The utilization of graded Al powders offers the possibility to adjust the combustion performance of Al powders,while simultaneously safeguarding their energy properties.In this paper,a series of graded Al powder have been incorporated into the typical Al@AP composites through the spray drying technique.The thermal behavior,ignition and combustion characteristics were comprehensively evaluated and compared.The experimental results showed that with the varying inclusion of the graded Al,the heat of reaction exhibited a significant change,ranging from 9090 J·g^(-1) to 11036 J·g^(-1),which was strongly dependent on the particle size of Al.The combination of Al with diverse range of particle sizes in graded configuration serves to significantly enhance the decomposition of AP,resulting in the disappearance of the LTD stage and a conspicuous decrease of at least 11.7℃ in the peak temperature of the HTD.Furthermore,the maximum burning rate achieved by the Al-3@AP composite was 33.6 mm·s^(-1),which was exactly twice as high as that of the graded Al-1@AP composite with the lowest burning rate.Diffraction peaks corresponding to unburned Al were detected in the condensed combustion products of Al-1@AP,and the combustion images clearly indicated an incomplete combustion tendency for this sample.In contrast,a well-designed gradation of Al powders,such as a combination of fine Al powders with a particle size below 5μm,has proven to be the most conducive to enhancing the combustion efficiency of the composites.
基金supported by the National Natural Science Foundation of China(grant number 51576129).
文摘During the highly transient process of the direct-start in a four-cylinder GDI engine,each cylinder exhibits specific characteristics in terms of in-cylinder conditions and energy demands,necessitating different control for each cylinder.However,recent studies have paid insufficient attention to cylinders other than the first starting cylinder.This paper proposes a comprehensive control strategy based on experimental data from the direct-start process of the second,third,and fourth cylinders,aiming to enhance the characteristics of combustion and emission performance through the optimization of injection timing,equivalence ratio,and ignition timing.The research findings indicate that the second cylinder should inject fuel approximately 10 ms after the first cylinder ignites to mix thoroughly the fuel with air.The ignition timing of the second cylinder should be close to the highest point of the piston movement to minimize hindrance to the piston compression process.The third and fourth cylinders should adopt a delayed injection timing strategy to prevent the escape of injected fuel caused by low engine speed.The optimal ignition timing for the third cylinder is 20℃A BTDC,while the fourth cylinder should be ignited earlier due to its stronger airflow and faster formation of a mixture that can be ignited.As the fuel injection quantity increases,the power output of the three cylinders enhances,but at the same time,emissions also increase.Therefore,their optimal equivalence ratios are determined as 1.2,1.4,and 1.2,respectively,striking a balance between combustion and emission performances.
基金Project supported by the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDA25050300 and XDA25010100)the National Key R&D Program of China(Grant No.2018YFA0404801)+1 种基金the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(Grant No.20XNLG01)。
文摘We investigate the influence of gold doping on the transport range of a relativistic electron beam in high-density deuterium–tritium(DT)fuel,which could be encountered in the double-cone ignition laser fusion.We develop the stopping power model to include gold doping and then analyze the influence of Coulomb collision and bremsstrahlung on the electron transport range with different gold doping ratios,consistent with the Geant4 simulations.When the gold doping ratio increases from 0.5%to 30%,the transport range of a 10 Me V electron beam is decreased by 9.6%and 18.5%via the bremsstrahlung.For the 1 Me V beam,the decrease of the range becomes 0.7%and 1.0%.We also investigate the transverse broadening of the electron beam and radiated photon energy reabsorption in a spherical target.When the gold doping ratio is 2%and the beam energy is increased from 1 Me V to 5 Me V,the bremsstrahlung photons cover 2.6%to 10.3%of the total beam energy.Meanwhile,the reabsorbed photon energy is reduced from 31.6%to 8.9%.
基金supported by the National Natural Science Foundation of China(Grant No.12402445)the National Defense Foundation Stabilization Support Program(Grant No.JCKYS2024212108)the National Key Laboratory of Shock Wave Physics and Detonation Physics Foundation(Grant No.2024CXPTGFJJ06404)。
文摘Accurate characterization of three-dimensional burning crack propagation remains pivotal yet challenging for energetic material safety,as conventional diagnostics and models inadequately resolve coupled crack-pressure dynamics in confined explosives.This study combines a novel spherical confinement system(with/without sapphire windows)with synchronized high-speed imaging and 3D reconstruction to overcome optical limitations in opaque explosives.Experimental analysis of centrally ignited HMX-based PBX-1 reveals:(1)burning cracks propagate radially with equatorial acceleration and polar deceleration,(2)systematic formation of 3–4 dominant crack branches across geometries,and(3)pressure evolution exhibiting gradual accumulation(subsurface cracking)followed by exponential growth(surface burn-through),with decay governed by cavity expansion.Building on Hill's framework,we develop a model incorporating cavity volume and fracture toughness criteria,validated against PBX explosive(95%HMX-based)experiments.The model demonstrates improved prediction of pressure trends compared to prior approaches,particularly in resolving laminar-phase accumulation and crackinduced surge transitions.Results establish structural cavity volume as a critical modulator of measured pressure and reveal direction-dependent crack kinematics as fundamental features of constrained combustion.This work provides experimentally validated insights into mechanisms of reaction pressure development and burning cracks pathways during constrained PBX explosive combustion.
基金supported by the National Natural Science Foundation of China(Grant Nos.22275092 and 52372084)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX24_0709)+1 种基金the Fundamental Research Funds for the Central Universities(Grant No.30923010920)the State Key Laboratory of Transient Chemical Effects and Control,China,(Grant No.6142602230201).
文摘Enhancing the output capacity of semiconductor bridge(SCB) through the application of composite nano-energetic films is a subject of wide concern. Furthermore, improving the safety, reliability, and production efficiency of energetic semiconductor bridge(ESCB) is the primary focus for large-scale engineering applications in the future. Here, the Al/CuO nano-film ESCB was efficiently fabricated using 3D direct writing. The electrostatic safety of the film is enhanced by precisely adjusting the particle size of Al, while ensuring that the SCB can initiate the film with small energy. The burst characteristics of SCB/ESCB were thoroughly investigated by employing a 100 μF tantalum capacitor to induce SCB and ESCB under an intense voltage gradient. The solid-state heating process of both SCB and ESCB was analyzed with multi physical simulation(MPS). The experimental results demonstrate that the critical burst time of both SCB and ESCB decreases with increasing voltage. Under the same voltage, the critical burst time of ESCB is longer than that of SCB, primarily due to differences in the melting to vaporization stage. The MPS results indicate that the highest temperature is observed at the V-shaped corner of SCB. Due to the thermal contact resistance between SCB and the film, heat conduction becomes more concentrated in the central region of the bridge, resulting in a faster solid-state heating process for ESCB compared to SCB.The results of the gap ignition experiments indicate that at a 19 mm gap, an ESCB with a film mass of 10 mg can ignite nickel hydrazine nitrate(NHN) and cyclotrimethylenetrinitramine(RDX). This suggests that thermite ESCB can serve as a novel, safe, and reliable energy exchange element and initiator in largescale engineering applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.12205274,12275251,12105270,12205272,12305262,and 12035002)the National Key Laboratory of Plasma Physics(Grant No.JCKYS2024212803)+2 种基金the Fund of the National Key Laboratory of Plasma Physics(Grant No.6142A04230103)the National Key R&D Program of China(Grant No.2023YFA1608400)the National Security Academic Fund(Grant No.U2430207).
文摘Stimulated Raman scattering(SRS)under a new ignition path that combines the advantages of direct-drive(DD)and indirect-drive(ID)schemes is investigated experimentally at the Shenguang-100 kJ facility.The results show that collective SRS in the plasma produced by ablating a polyimide film is detected for the ID beams,but is suppressed by adding a toe before the main pulse of the ID beams.The toe also strongly influences SRS of both the ID and DD beams excited in the plasma generated in the hohlraum.When a toe is used,the SRS spectra of the DD beams show that SRS tends to be excited in lower plasma density,which will result in a lower risk of super-hot electrons.Measurements of hot electrons support this conclusion.This research will help us produce a better pulse design for this new ignition path.
基金supported by the Anhui Zhongchuang Energy New Energy Technology Co.,Ltd.,Entrusted Project.
文摘The semiconductor bridge(SCB)ignites through bridge film discharge,offering advantages such as low ignition energy,high safety,and compatibility with digital logic circuits.The study uses laser interferometry to investigate the gas dynamics of the bridge film after SCB plasma extinction.Interferometric images of the SCB film gas were obtained through a laser interferometry optical path.After the degradation model of digital image processing,clearer images were produced to facilitate analysis and calculation.The results show that the gas temperature at the center of the SCB film reaches a maximum of 1000 K,and the temperature rapidly decreases along the axial direction of the bridge surface to room temperature at 300 K.The maximum diffusion velocity of the plasma is 1.8 km/s.These findings provide critical insights for SCB design and ignition control.
基金financial support from the LASERLAB-EUROPE Access to Research Infrastructure Activity (Application No. 23068)carried out within the framework of EUROfusion Enabling Research Projects AWP21-ENR-01-CEA02 and AWP24-ENR-IFE-02-CEA-02+3 种基金received funding from Euratom Research and Training Programme 2021–2025 under Grant No. 633053supported by the Ministry of Youth and Sports of the Czech Republic [Project No. LM2023068 (PALS RI)]by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA25030200 and XDA25010100)supported by COST (European Cooperation in Science and Technology) through Action CA21128 PROBONO (PROton BOron Nuclear Fusion: from energy production to medical applicatiOns)
文摘Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering(SSRS)instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion.Nonetheless,SSRS remains to date one of the least understood parametric instabilities.Here,we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme(I×10^(16)W/cm^(2)),showing significant SSRS growth in the direction perpendicular to the laser polarization.Modification of the focal spot shape and orientation,obtained by using two different random phase plates,and of the density gradient of the plasma,by utilizing exploding foil targets of different thicknesses,clearly reveals a different dependence of backward SRS(BSRS)and SSRS on experimental parameters.While convective BSRS scales with plasma density scale length,as expected by linear theory,the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization.Our analysis therefore demonstrates that under current experimental conditions,with density scale lengths L_(n)≈60–120μm and spot sizes FWHM≈40–100μm,SSRS is limited by laser beam size rather than by the density scale length of the plasma.
基金funded by Shaanxi Provincial Key Research and Development Program of China(Grant No.2021ZDLGY11)partially supported by NSAF Project of China(Grant No.U2030202)。
文摘Boron has high mass and volume calorific values,but it is difficult to ignite and has low combustion efficiency.This literature review summarizes the strategies that are used to solve the above-mentioned problems,which include coatings of boron by using fluoride compounds,energetic composites,metal fuels,and metal oxides.Coating techniques include recrystallization,dual-solvent,phase transfer,electrospinning,etc.As one of the effective coating agents,the fluorine compounds can react with the oxide shell of boron powder.In comparison,the energetic composites can effectively improve the flame temperature of boron powder and enhance the evaporation efficiency of oxide film as a condensed product.Metals and metal oxides would react with boron powder to form metal borides with a lower ignition point,which could reduce its ignition temperature.
文摘Exploding foil initiator(EFI)is a kind of advanced device for initiating explosives,but its function is unstable when it comes to directly igniting pyrotechnics.To solve the problem,this research aims to reveal the ignition mechanism of EFIs directly igniting pyrotechnics.An oscilloscope,a photon Doppler velocimetry,and a plasma spectrum measurement system were employed to obtain information of electric characteristics,impact pressure,and plasma temperature.The results of the electric characteristics and the impact pressure were inconsistent with ignition results.The only thing that the ignition success tests had in common was that their plasma all had a relatively long period of high-temperature duration(HTD).It eventually concludes that the ignition mechanism in this research is the microconvection heat transfer rather than the shock initiation,which differs from that of exploding foil initiators detonating explosives.Furthermore,the methods for evaluating the ignition success of semiconductor bridge initiators are not entirely applicable to the tests mentioned in this paper.The HTD is the critical parameter for judging the ignition success,and it is influenced by two factors:the late time discharge and the energy of the electric explosion.The longer time of the late time discharge and the more energy of the electric explosion,the easier it is to expand the HTD,which improves the probability of the ignition success.
基金supported by the National Natural Science Foundation of China (No. 52176097)。
文摘Hydrazine is toxic and carcinogenic, which greatly increases the difficulty of application and no longer meets the needs of green aerospace. As a green propellant, the Ammonium Dinitramide(ADN)-based liquid propellant has the advantages of higher specific impulse, being non-toxic,pollution-free, and easy storage. However, an ADN-based space engine in orbit has exposed the problems of high-temperature deactivation of catalysts and cold-start failure. An active ignition technology—electric ignition technology was explored in this paper to break through the technical bottleneck of catalyst deactivation and the inability to a cold start. An experimental system of a constant-volume combustor for the ADN-based liquid propellant based on the electric ignition method was established. The electric ignition and combustion characteristics of the ADN-based liquid propellant in a volume combustor with an electric ignition method were studied. The influencing mechanisms of the ignition voltage and the electrode structure on the electric ignition characteristics of the ADN-based liquid propellant were investigated. An elevation of the ignition voltage could facilitate the ignition process of the ADN-based liquid propellant, curtail electric energy input and heating effect, while exerting an adverse impact on the combustion process of the propellant.An increase in the ignition voltage enhanced the ignition process of the propellant while simultaneously suppressing its combustion process when utilizing mesh electrodes. Compared to the strip electrodes, the mesh electrodes increased the contact area between the electrodes and the propellant,increased the electric energy input power in the electric ignition process, and reduced the ignition delay time. The mesh electrodes could promote the combustion process of the propellant to a certain extent.
基金co-supported by the National Natural Science Foundation of China(No.52306123)the Postdoctoral Science Foundation,China(No.2023M734277)the Natural Science Basic Research Program of Shaanxi,China(No.2021JQ-046)。
文摘Plasma ignition technology has delivered good performance in the aerospace industry. In this study, a pre-combustion plasma jet igniter was designed, and its characteristics were examined from three aspects: the morphology, temperature, and discharge characteristics and process of ignition. Images of the OH distribution were obtained by using an OH Planar Laser-Induced Fluorescence(OH-PLIF) experimental system. Results have shown that the proposed plasma jet had a higher OH concentration, longer length, and larger area than those of a traditional igniter. The stability of discharge of the igniter was improved as the equivalence ratio φ was increased, and reducing gas flow reduced the pulsation of the plasma jet. When the input current was increased from 15A to 35 A, the highest average temperature increased from 5127 K to 7987 K. An increase in the equivalence ratio reduced the region of arc ionization, but expanded the regions of the core combustion reaction and the outer flame. Herein, this study has obtained a deep understanding of the jet and ignition law and developed a new idea for the application of plasma in the ignition field.A pre-combustion plasma jet igniter can significantly improve the efficiency of ignition and shorten the ignition process compared with a traditional igniter.
基金supported by the National Natural Science Foundation of China (No.51974334)Hainan Province Science and Technology Special Fund (ZDYF2022SHFZ107)local efficient reform and development funds for personnel training projects supported by the central government,Heilongjiang Postdoctoral Scientific Research Fund (LBH-Q21012)。
文摘During air injection into an oil reservoir,an oxidation reaction generates some heat to raise the reservoir temperature.When the reservoir temperature reaches an ignition temperature,spontaneous ignition occurs.There is a time delay from the injection to ignition.There are mixed results regarding the feasibility of spontaneous ignition in real-field projects and in laboratory experiments.No analytical model is available in the literature to estimate the oxidation time required to reach spontaneous ignition with heat loss.This paper discusses the feasibility of spontaneous ignition from theoretical points and experimental and field project observations.An analytical model considering heat loss is proposed.Analytical models with and without heat loss investigate the factors that affect spontaneous ignition.Based on the discussion and investigations,we find that it is more difficult for spontaneous ignition to occur in laboratory experiments than in oil reservoirs;spontaneous ignition is strongly affected by the initial reservoir temperature,oil activity,and heat loss;spontaneous ignition is only possible when the initial reservoir temperature is high,the oil oxidation rate is high,and the heat loss is low.
