Ignition Experiments Research Articles

Characteristics and Typical Influential Factors of Wildfire Caused by High-Voltage Transmission Line Breakage Faults

In order to investigate the characteristics and typical influential factors of wildfires caused by accidental faults in high-voltage transmission lines, a bespoke platform was constructed for the purpose of conducting simulation experiments. Discharge and ignition experiments were conducted on a variety of substrates, including kidney fern fragments, cedar needle fragments, poplar sawdust, and eucalyptus leaf fragments, to investigate the effects of different gaps on the initiation and propagation of wildfires. The results demonstrate that the discharge-inducing ignition stages can be succinctly summarized as “two phases and two points” (the discharge induction period, the gap breakdown point, the arc induction period and the fault removal point) when a suitable gap is maintained between the simulated falling lines and the vegetation surface. In the event of direct contact, the removal of the fault is not possible. The potential for ignition of the aforementioned vegetation types by the discharge is as follows: cedar needles > eucalyptus leaf fragments ≈ poplar sawdust > kidney fern fragments. As the water content increases, eucalyptus leaf fragments can still be ignited, and the breakdown voltages required for discharge-inducing ignitions gradually decrease. In the case of different forest ground vegetation types, when ignited by the discharge between the falling lines and the vegetation under conditions of proper gap and moisture content, the resulting ignition and sustained flames will promote the formation of streamer channels and further aggravate the discharges and burning processes, potentially leading to the ignition of a wildfire.

Simulating Nonlinear Radiation Diffusion Through Quantum Computing

The recent success of the fusion ignition experiment at Lawrence-Livermore National Laboratory has renewed excitement for inertial confinement fusion. Designing such experiments relies on computational modeling using radiation hydrodynamic codes run on massively parallel supercomputers which simulate hydrodynamic flows, radiation diffusion, and thermonuclear burn. Constructing a quantum algorithm for radiation hydrodynamics that provides a quantum speedup is of great interest. A recent quantum algorithm that solves the Navier-Stokes equations of hydrodynamics with a quadratic speedup marks a first step towards this goal. Here we take the next step and present a quantum algorithm for nonlinear radiation diffusion that also has a quadratic speedup. To verify the algorithm we consider radiation striking a cold, optically thick target that generates a Marshak wave in the target. Results of numerical simulation of the quantum algorithm are compared with those of a standard partial differential equation solver and excellent agreement is found.

Characterization method of conductive film state of micro-cathode arc thrusters

Micro-Cathode Arc Thruster (μCAT) is an advanced electric propulsion system developed in the past decades to meet the maneuvering requirements of space microsatellites. However, the constraint on the its application is the short lifespan of the thruster. This is attributed to the conductive film, a key component of thruster discharge. In this study, we propose a measurement method for μCAT conductive film, and enables the evaluation of the evolution process of film thickness. The method is based on the four-probe resistivity testing theory and size effect fitting model, and establishes a method for characterizing the thickness and resistivity of μCAT conductive films. A comparison was made between the corrected resistivity test results of 1, 2, 5, and 10 μm film and the fitting results of the titanium film, revealing an error ofapproximately 10%. Additionally, a total of 2500 ignition experiments were conducted to verify the film thickness and resistance measurement of this method. This research serves as a valuable basis for the lifetime investigation of μCAT. Consequently, the thickness of the film progressively decreases with each discharge cycle, and the resistivity exhibits a corresponding increase due to the size effect. This method could be used as an effective method for exploring the μCAT lifespan and performance.

Experiments and Theory on Droplet Ignition with Spark Discharges

ABSTRACT Ignition experiments were performed with individual n-decane droplets, initially, about 1 mm in diameter, which were suspended in quartz fibers and subjected to electrical discharges (sparks) of controlled power and duration. Experiments were performed with glow and arc discharges in air at 1 atm and approximately 300 K . Theory is developed to predict the probability of ignition of a fuel droplet as a function of time when it is exposed to an ignition spark. The theory considers the effect of random spark-to-spark fluctuations in the heat flux into the liquid on the time for the droplet surface temperature to be high enough to enable ignition. A Bayesian analysis is also performed to evaluate confidence intervals for parameters related to droplet ignition. Reasonable agreement between theory and experiment is demonstrated, suggesting that spark-to-spark fluctuations of the heat flux into a droplet may lead to a sigmoidal variation of the probability of ignition with respect to time.

Demonstration of shape analysis of neutron resonance transmission spectrum measured with a laser-driven neutron source

Laser-driven neutron sources (LDNSs) can generate strong short-pulse neutron beams, which are valuable for scientific studies and engineering applications. Neutron resonance transmission analysis (NRTA) is a nondestructive technique used for determining the areal density of each nuclide in a material sample using pulsed thermal and epithermal neutrons. Herein, we report the first successful NRTA performed using an LDNS driven by the Laser for Fast Ignition Experiment at the Institute of Laser Engineering, Osaka University. The key challenge was achieving a well-resolved resonance transmission spectrum for material analysis using an LDNS with a limited number of laser shots in the presence of strong background noise. We addressed this by employing a time-gated 6Li\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{6}{\ extrm{Li}}$$\\end{document}-glass scintillation neutron detector to measure the transmission spectra, reducing the impact of electromagnetic noise and neutron and gamma-ray flashes. Output waveforms were recorded for each laser shot and analyzed offline using a counting method. This approach yielded a spectrum with distinct resonances, which were attributed to 115In\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{115}\\,{\ extrm{In}}$$\\end{document} and 109Ag\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{109}{\ extrm{Ag}}$$\\end{document}, as confirmed through neutron transmission simulation. The spectrum was analyzed using the least-square nuclear-resonance fitting program, REFIT, demonstrating the possibility of using an LDNS for nondestructive areal-density material characterization.

Preparation of microstructure controllable CL-20/FOX-7 composite microspheres by microchannel recrystallization technology to enhance safety and combustion performance

Realizing the balance between high energy density and multifunctionality of energetic materials is a hot spot in current research, and its study is of great significance for the application of energetic materials. Regulating microstructure is widely recognized as an effective strategy for solving such problems. In this paper, four different microstructures of Hexanitrohexaazaisowurtzitane(CL-20)/1,1-diamino-2,2-dinitroethylene(FOX-7) composite microspheres, namely, hollow, porous irregular microspheres, porous microspheres, and layered porous microspheres, were prepared by microchannel recrystallization technology. The effects of crystal precipitation rate, binder mechanical properties, and purity of water phase on the microstructure of composite microspheres were systematically investigated. The four prepared samples were spherical particles with regular morphology and uniform particle size. The angle of repose and mechanical sensitivity tests showed that the CL-20/FOX-7 composite microspheres had good dispersibility and mechanical sensitivity. Ignition experiments show that hollow microspheres have the best energy release efficiency, while porous microspheres have higher energy density and more stable energy release efficiency. The results show that the combustion performance and safety of the composite microspheres can be effectively enhanced by adjusting the microstructure. Microchannel recrystallization technology can realize the controllable preparation of the microstructure of composite microspheres, which provides a reference for the design and preparation of other composite microspheres.

Hierarchical nanoarchitectonics of hollow hexanitrostilbene (HNS) microspheres to improve safety and combustion performance

Hollow structures have great potential in the field of energetic materials due to their excellent properties. In this study, nitrocellulose (NC) was used as a binder, and hollow-structured HNS/NC microspheres were prepared in the form of a suspension using the microjet droplet technology. The effects of spray velocity, suspension concentration, and receiving liquid temperature on the morphology, particle size, cavity structure, and pore size of the microspheres were systematically investigated. Subsequently, the effects of shell thickness and pore size on the dispersibility, specific surface area, crystal structure, thermal performance, mechanical sensitivity, and combustion performance of the microspheres were further studied. The results show that compared with the raw HNS, the hollow HNS/NC microspheres have good dispersibility, while retaining the crystal structure and chemical structure of the raw HNS, and have a lower activation energy, which is expected to achieve a rapid energy release reaction. In addition, compared with the solid HNS/NC microspheres, the hollow HNS/NC microspheres have a higher specific surface area (19.658 m2·g−1 vs 31.335 m2·g−1) and better safety performance (6 J vs 50 J). The ignition experiment results show that the hollow structure significantly enhances the combustion performance of HNS (305 ms vs 92 ms), improving the energy release efficiency. This preparation method is simple, efficient, and easy to scale up, providing a more universal and environmentally-friendly technical approach for the multi-structural design of energetic microspheres.

Ionization by XFEL radiation produces distinct structure in liquid water

In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×105 J/cm2), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O1+ and O2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory.

Dynamics of fuel-lean and stoichiometric methane-air explosion venting: Experiments and simulations

The computational explosion venting analyzer (EVA), a zero-dimensional (0D) model based on the conservation of mass and energy, is being developed to model centrally- and rear-ignited explosions. For this purpose, a series of explosion venting experiments in a cylinder with vent areas of 132.7, 86.6, 67.9 cm2 (corresponding to the vent area ratios of K=0.47,0.31,0.24, respectively) is performed. Two equivalence ratios of ϕ=0.8 and 1 are considered to represent the fuel-lean and stoichiometric methane-air mixtures, respectively. The dynamics of explosions is studied through the observation of flame propagation and pressure measurements. In rear ignition experiments, laminar, so-called “finger flame” propagation is observed, while in the case of center ignition, a flame initially expands spherically and then is pulled by the vent, acquiring a half-elliptical and half-spherical shape. The peak pressures obtained from rear ignition exceed their counterparts in the center ignition experiments. The EVA is compared with the experimental matrix. No turbulence is implemented in stoichiometric simulations, and slight turbulence has been accounted for in the lean mixture simulations. It is found that the large vent, generally, imposes more disturbances on the flame shape and the fuel-lean mixtures are more prone to the diffusional-thermal instabilities. It is shown that such a simple numerical tool, as the EVA is, can estimate a complicated problem such as pressure evolution resulted from a vented gas explosion.

Diagnosing hot-spot symmetry in surrogate ignition experiments via secondary DT-neutron spectroscopy at the NIF

Diagnosing hot-spot symmetry in surrogate ignition experiments via secondary DT-neutron spectroscopy at the NIF

Measurements of laser-plasma instabilities in double-cone ignition experiments relevant to the direct-drive conditions at Shenguang-II Upgrade laser facility

Experiments have been performed to investigate laser-plasma instabilities (LPIs) relevant to the direct-drive inertial confinement fusion (ICF) conditions at the Shenguang-II Upgrade (SG-II UP) laser facility during the double-cone ignition (DCI) experimental campaigns, with the overlapped laser intensity ranging from 6×1014Wcm−2 to 1.8×1015Wcm−2 . An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light. Across broad ranges of laser and plasma parameters, relevant to the direct-drive ICF conditions, the dominance of the stimulated Raman side scattering (SRSS) was confirmed, and its coexistence with the two-plasmon decay (TPD) was also observed. Significant SRSS scattered light was observed across an extremely wide range of emission angles, concentrated at large angles, and demonstrated to be robust throughout the parameter space. Time-resolved spectral measurements show distinctly different SRSS behaviors along different angles and a slightly higher threshold compared to the TPD. The overall SRSS energy loss was measured, indicating a scattered light energy fraction of up to 6%. These results are of crucial importance for the precise assessment of the LPIs in the DCI as well as other laser directly driven ICF schemes.

Mechanistic study on the modification of Al NPs by PVDF with different interfacial binding methods to suppress agglomeration and promote combustion

The modification of aluminum nanoparticles (Al NPs) by polyvinylidene fluoride (PVDF) can significantly enhance their reaction characteristics and reduce combustion agglomeration. However, the impact and underlying mechanisms of changes in interfacial binding methods between them on the reaction process remain unclear. In this study, the oxidation and combustion processes, as well as the agglomeration behavior of Al NPs under three different interfacial binding methods (mixing, with oxygenation layer coating, and without oxygenation layer coating) between Al NPs and PVDF were investigated by utilizing ReaxFF molecular dynamics simulations, density functional theory calculations, and ignition experiments. The results indicate that changes in the interfacial binding method significantly affect the oxidation behavior of Al NPs, and PVDF molecules exhibit different decomposition pathways on the surfaces of Al and Al2O3. During the combustion stage, different interfacial binding methods determine distinct reaction modes between Al NPs and PVDF. Based on these findings, a reaction mechanism for Al NPs and PVDF is proposed. This study addresses the gap in the field of the impact of interfacial binding methods on the reaction processes between Al NPs and PVDF, laying a theoretical foundation for future research and providing guidance for the practical application of Al-based modified fuels.

Motor test data quality evaluation model based on critic-fluctuant weight assignment method

Abstract The article addresses the limitations of traditional weight analysis methods in handling ground ignition experiment data for solid rocket motors, particularly the anti-interference ability to noise factors. To address this issue, the specialized Critic-Fluctuant weight analysis method is proposed. This method calculates objective weight values based on fluctuation values and integrates noise standard scores into data quality assessment, enabling researchers to effectively and intuitively identify different levels of data quality. After comparing and analyzing the objective weights and data quality scores of 100 ground ignition test data sets, it is verified that Critic-Fluctuant has higher adaptability and accuracy than traditional CRITIC methods in ground ignition test scenarios. The article provides new insights and tools for researchers to deal with similar data characteristics.

Effective desensitization of composite materials HMX@PDA by insensitive DAAF: To improve safety performance

The sensitivity of energetic materials to external stimuli (mechanical, flame, etc.) limits their practical application. In order to improve the safety of HMX@PDA composite materials. In this study, HMX/DAAF@PDA composite microspheres with different mass ratios were prepared using a microfluidic self-assembly strategy, and the morphology, size, crystal structure, thermal behavior, flowability and mechanical sensitivity of the sample microspheres were analyzed. The results showed that the addition of DAAF did not change the crystal structure of the composites, and the HMX/DAAF@PDA composite microspheres showed high consistency and repeatability, concentrated particle size distribution, sphericity greater than 0.9 and good flowability. Meanwhile, the impact sensitivity of the sample was increased from 25 J to 50 J (S-3) and the friction sensitivity was increased from 160 N to 216 N. In addition, the ignition experiment and EXPLO5 calculation results show that the addition of insensitive DAAF can reduce the combustion of composite materials, thereby improving the application safety of the composites. This study provides a way for the design and preparation of high-energy insensitive composite explosives.

Constructing the combination bridge of aluminum hydride (AlH3) and polyvinylidene fluoride (PVDF) through the self-assembly of dopamine: Improving the stability and ignition properties of AlH3

Surface coating is an important method to solve the poor stability of aluminum hydride (AlH3). To overcome the difficulty of uneven coating of fluorine-containing polymers on the surface of AlH3, this study utilizes the adhesion properties of polydopamine (PDA) to establish a bridge between the oxide layer of AlH3 (Al2O3) and polyvinylidene fluoride (PVDF), so that Polyvinylidene fluoride (PVDF) was uniformly coated on the AlH3 surface, and a dual-core shell structure AlH3@PDA@PVDF composite was successfully prepared. Molecular dynamics simulations reveal significantly higher binding energy per unit area for γ-Al2O3@PDA/PVDF (1.2270 Kcal·mol−1·Å−2) compared to γ-Al2O3/PVDF (0.6644 Kcal·mol−1·Å−2), affirming that PDA can effectively enhance the interfacial interaction between AlH3 and PVDF. The morphology characterization and performance testing of raw AlH3 and AlH3@PDA@PVDF composite were carried out through SEM, XPS, FT-IR, DSC, VST, etc. The results indicate that through the interface modification of AlH3 by PDA, PVDF with a hydrophobic surface can be evenly coated on the surface of AlH3, causing the water contact angle (WCA) of the AlH3@PDA@PVDF composite to increase from 41° for the raw AlH3 to 124°. Furthermore, the total decomposition time of the AlH3@PDA@PVDF composite (2326 min) is improved by 1.8 times than that of the raw sample (1277 min), and its apparent activation energy (117.75 kJ·mol−1) was also higher than that of the raw sample (99.88 kJ·mol−1), indicating that coating with PDA and PVDF can improve the stability of AlH3. Ignition experiments demonstrate that the AlH3@PDA@PVDF composite has superior ignition reaction performance compared with the raw AlH3. Especially, adding a small amount of AlH3@PDA@PVDF composite can also significantly catalyze the thermal decomposition process of ammonium perchlorate (AP), reducing its high-temperature decomposition temperature from 405.37 °C to 352.20 °C.

Relative reactivity of methyl anisole isomers: An experimental and kinetic modelling study

Due to the current interest in biomass derived carbon neutral fuels and fuel additives for gasoline engines and to the growing need of understanding the fundamentals of gas phase combustion in the context of wildfires, this study investigates the combustion behavior of key components of biomass pyrolysis oils, namely the three methylanisole isomers (ortho-, meta- and para-methylanisole). Specifically, this study presents the first experimental ignition delay time measurements for such fuels using a shock tube and a rapid compression machine. Ignition experiments were carried out for stoichiometric fuel/air mixtures (φ = 1) at compressed pressure pc = 10 and 20 bar, covering a temperature range Tc = 880–1220 K. A kinetic model based on previous efforts in the area of oxygenated aromatic hydrocarbon fuels is proposed to reproduce and interpret the experimental findings, specifically focusing on capturing the observed different reactivity of the three isomers. To this aim, thermodynamic properties of primary intermediates and bond dissociation energies were calculated highlighting relevant differences originated from the relative position of the O–CH3 and –CH3 substituents. In addition, an isomerization pathway specific to the ortho isomer was theoretically investigated and found to motivate the observed higher reactivity with respect to the meta and para isomers

Polyethylene deflagration characterization and kinetic mechanism analysis

In this paper, the combustion process of polyethylene (C100H202) was simulated by experiment and Reaction Force Field molecular dynamics (ReaxFF MD) simulation, and the influence of density and temperature on the deflation of C100H202 was investigated. The flame propagation characteristics of C100H202 with different concentrations were studied by the Hartmann experiment system, and the pyrolysis characteristics of C100H202 under N2 and O2 atmospheres were studied by the TG test. The pyrolysis activation energy of C100H202 in N2 and O2 atmospheres is 72.160 kJ/mol and 92.356 kJ/mol, respectively, which is consistent with the reaction activation energy of 97.110 kJ/mol calculated by simulation. In addition, it is found through simulation that the increase in system density will increase the generation and consumption of intermediate products such as C2H4, which explains the phenomenon of more intense detonation when the concentration of C100H202 increases from 0.0002 g/cm3 to 0.0005 g/cm3 in dust ignition experiment from the molecular level. The results show that physical methods such as cooling down and releasing inert gas and chemical methods that consume functional groups have significant effects on the inhibition of hydrocarbon deflagrations from a microscopic point of view, and provide theoretical support for the study of the inhibition of hydrocarbon deflagrations.

Use of tritium-rich fuel to improve the yield of layered deuterium/tritium inertial fusion capsules

In deuterium–tritium (DT) ice layered implosions, nearly all hot spot mass at peak burn comes from the dense fuel. Accurate prediction of the fuel mass ablation, including the enthalpy associated with mass inflow into the hot spot from the dense fuel, is essential to understanding the energetics and ignition of the hot spot in layered implosions. A recently published boundary layer analysis (Daughton et al., 2023) indicates a faster mass ablation rate than in previous analyses of layered implosions. Inclusion of this effect provides a better match to simulations and leads to a new ignition threshold where the temperature of the dense fuel plays a critical role. This analysis motivates possible new directions for improved capsule performance. Here, the authors present evidence in support of one such approach: the use of tritium-rich ice to decrease 14 MeV neutron scattering and heating of the dense fuel, resulting in less mass ablation and more robust burn of the hot spot. It is found from numerical simulations that despite a less favorable D:T ratio in the ice, the use of a 40:60 D:T ratio leads to an increase in capsule yield of 17% percent compared with that of a 50:50 D:T ratio fuel for capsules resembling those of the recent N210808 ignition experiment on the NIF (Abu-Shawareb et al., 2022) and an increase of 74% compared with that of a 60:40 D:T ratio fuel capsule. These results are potentially important for modeling all layered implosions, since some degree of DT fractionization may arise naturally during the beta layering process. In addition, this physics is important for the feasibility of high-gain capsule designs that seek to minimize tritium usage, as in some inertial fusion energy concepts.

Kinetics and hydrothermal combustion characteristics of ethanol in supercritical water

Supercritical hydrothermal combustion is a novel, clean, and efficient combustion method. In this work, a mechanism-based kinetic model of ethanol appropriate for high-pressure hydrothermal environment was developed. Combined with theoretical analysis and continuous ignition experiments, the transient ignition process, ignition temperature, and extinction temperature were discussed. A turbulent combustion model coupling detailed kinetics was constructed to analyze the co-flow diffusion hydrothermal flame. It was found that the ethanol kinetic model can well predict the reaction process, critical ignition temperatures, extinction temperatures, and diffusion combustion process of hydrothermal combustion. The ignition temperatures of 2.40–5.72 wt% ethanol ranged between 500–390 °C, and OH was a significant ignition indicator. As an auxiliary fuel, ethanol is superior to methanol. During co-flow hydrothermal combustion, the interfacial reaction between fuel and oxidant in jet core area had an important influence, and the local high-temperature flame was mainly distributed near the downstream of fuel jet.

Tuning the Ballistic Performance of a Single-Burning-Rate Grain Solid Rocket Motor via New Discontinuous Embedded Metal Wires

This work proposes a new effective method to realize variable thrust through discontinuous embedded metal wires in the solid rocket motor (SRM). We aimed to study the influence of discontinuous embedded metal wires on the performance of an SRM with a single-burning-rate grain. A model based on convection heat transfer, heat conduction, and heat radiation was established to calculate the heat transfer in the discontinuous embedded metal wires in the grain, to then obtain the burning rate ratio. Most importantly, a solid rocket motor was designed to verify the feasibility of variable thrust and of the present model prediction, with the embedded silver–nickel alloy wire divided into two segments in the grain. According to the SRM ignition experiment, the silver–nickel alloy wires raised the burning rate of the grain. The pressure varied regularly with changes in the discontinuous embedded metal wires. The theoretical burning rate ratio matched the experimental result well. Based on the verified model, the effects of the burning rate, pressure exponent, burning rate ratio, and number of wires on thrust were investigated. Burning rate, burning rate ratio, and pressure exponent were found to be positively correlated with thrust ratio. The thrust ratio could reach 12.5 when the burning rate ratio was 5. The ability to adjust thrust tended to increase with an increase in the number of wires. This study also provided a method to assess whether the consecutive embedded metal wires had been broken or not. The method using discontinuous embedded metal wires in the grain was proven to be feasible to realize multi-thrusts of single-burning-rate grain, which is a new idea for the design of a multi-thrust SRM.