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The microwave-to-plasma energy conversion efficiency and the ease of plasma self-ignition are critical factors affecting the applications for microwave plasma sources (MPSs). This study presents a novel MPS utilizing dielectric wedges for self-ignition and improved energy conversion. Firstly, we crafted a dielectric wedge with a gradient refractive index, guiding the electric field from air to dielectric materials and facilitating microwave propagation along the dielectric in a waveguide. Through electromagnetic simulation, we explored how the size and permittivity of the dielectric wedge affect the electric field distribution. Then, the MPS based on the dielectric wedge was designed. In this configuration, a dielectric tube encloses the discharge tube, connecting to dielectric wedges to guide electromagnetic waves to the plasma. We analyzed the MPS performance using the Drude model, evaluating microwave energy conversion efficiency across various electron densities and collision frequencies. The results were compared with a commonly used MPS based on a tapered waveguide, demonstrating the proposed MPS has wider applicability across different operation conditions. Finally, experiments under low pressures were conducted using various gases, showing an average energy conversion efficiency of approximately 40% higher than the tapered waveguide MPS. The experiments also indicate the proposed MPS has a greater capability of self-ignition at lower power levels. These findings highlight the efficacy of incorporating dielectric wedges to enhance MPS performance, making it conducive for broader industrial applications. [ABSTRACT FROM AUTHOR]

The samples including Li 0.1 Co 0.8 Fe 2. 1 O 4 (LCFO) spinel ferrite (SF) and LCFO SF/graphene oxide (GO = 10 wt%, 15 wt%, and 20 wt%) nanocomposite were fabricated via the self-ignition route by following the bath ultra-sonication method. Their structural, morphological, and compositional properties were analyzed using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray (EDX) spectroscopy, respectively. Moreover, the dielectric and magnetic properties at 300 K were studied using an impedance analyzer (IA) meter and vibrating sample magnetometer (VSM), respectively. All LCFO SF and GO-based LCFO nanocomposites exhibited a pure spinel matrix. The crystallite size was increased by the GO addition in the LCFO SF sample. The morphological analysis showed the non-uniform distribution of particles. The dielectric constant and loss exhibited behaviour consistent with Maxwell-Wagner interfacial polarization. The low tangent loss was observed at high frequency and ac conductivity analysis was increased with increasing the GO content. A slight enhancement in saturation magnetization was observed at 300 K with the addition of GO in LCFO SF. Hence, doping with GO offers a means to tune the dielectric, and magnetic response of the LCFO SF sample and is the best candidate for potential high-frequency application. [Display omitted] • The LCFO SF and LCFO/GO nanocomposites were prepared via the self-ignition route with an ultra-sonication technique. • The crystallite size was increased from 30 nm to 54 nm. • FTIR analysis along with XRD analysis also confirmed the spinel matrix. • SEM and TEM micrographs indicated the non-uniform distribution and agglomeration with the increasing GO. • The increase in GO leads to an improvement in the dielectric response. • The saturation magnetization was increased with the addition of GO. • The combination of LCFO SF with GO enhanced the dielectric, and magnetic properties, offering a candidate for high-frequency applications. [ABSTRACT FROM AUTHOR]

The work studies scenarios of self-ignition of hydrogen-air mixtures after a shock wave reflects from a destructible barrier made of sand or a solid wall. The experiments were carried out using a shock tube. The transverse dimensions of the diagnostic section were 40 × 40 mm. The initial pressure of the hydrogen-air mixture varied from 10 kPa to 50 kPa. The molar excess of hydrogen (equivalence ratio) was 0.3, 0.4 and 0.5. Typical oscillograms of pressure, a photomultiplier tube, and the results of high-speed visualization using the Schlieren method are presented. When the shock wave interacted with the destructible barrier, a thermodynamic unloading of shock-compressed mixture occurred in the direction of the scattering of fragments of the barrier. It was shown that under certain conditions, self-ignition of hydrogen could be prevented by using a destructible barrier. In this case, the prevention was recorded in a narrow range of Mach numbers of the incident shock wave, which are characterized by the occurrence of the so-called "weak" (or "mild") ignition of the hydrogen-air mixture. The conditions for strong ignition behind the reflected shock wave, as well as during the interaction of the reflected shock wave with the flame front behind the incident shock wave, were determined. The results of the presented experimental work are aimed at ensuring explosion safety when working with hydrogen in a confined space. [Display omitted] • The interaction of a shock wave with a sand barrier was studied. • Scenarios for self-ignition behind a reflected shock wave were determined. • Self-ignition can be prevented by placing a sand barrier instead of a solid wall. • The pressure ratios were determined during self-ignition. [ABSTRACT FROM AUTHOR]

In the study of self-ignition during pressurized hydrogen release, the morphology of the rupture disk alters the flow and mixing processes of the gas jet, as well as the development of shock waves, thereby affecting the occurrence of self-ignition. This study employs the LES method based on the RNG-SGS model, EDC model, and NUIMech1.1 H 2 combustion mechanism to investigate the flow mixing, shock wave development, and self-ignition phenomena under three different the rupture disk morphologies. The research findings indicate that as the growth trend of the rupture disk rupture ratio increases, the propagation speed of shock waves within the tube and the compression speed of the air and hydrogen-air mixing region accelerate, resulting in an earlier occurrence of self-ignition. A more complex rupture morphology leads to higher mixing rates between hydrogen and air and increased complexity of shock waves. Self-ignition initially occurs in the fuel-lean region of the boundary layer, followed by ignition at the center of the tube. The characteristic number of rupture disk is proposed to describe its impact on the self-ignition time. The competitive relationship between the two elementary reaction pathways of oxygen influences the development of the flame. • A CFD model for hydrogen release and self-ignition is established and validated. • The development process of multidimensional shock waves is described in detail. • The process of self-ignition and entire flame development is fully captured. • The reaction mechanism and HRR of self-ignition are analyzed. • The impact of rapture disk morphology on flow and self-ignition is fully obtained. [ABSTRACT FROM AUTHOR]

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice. • Hydrogen jet explosion can be induced by spark within 5D of the nozzle axis. • Comparing with spark ignition, self-ignition explosion had higher overpressure peak. • Self-ignition process was stable, but spark ignition was sensitive to the spark position. [ABSTRACT FROM AUTHOR]

Small additions of hydrocarbons, such as propylene, which are widely studied as combustion and explosion inhibitors of hydrogen-air mixtures, sometimes exhibit specific properties. The known mechanism of the inhibitory effect of these additives is associated with the intensification of the termination of branching chains due to the addition of hydrogen atoms; however, conditions also exist in which these compounds, instead of inhibiting, have a neutral and even promoting effect. Such conditions and the reasons leading to the fact that inhibition is practically absent have not yet been studied. This article shows the results of numerical modeling, which make it possible to more fully outline the range of conditions where the addition of propylene practically does not inhibit hydrogen-air mixtures and outline possible reasons for this effect. The solution to three model problems is presented: self-ignition in a constant-volume reactor, laminar flame propagation, and gas ignition with a heated wire. The calculations are carried out with the detailed kinetic mechanism of chemical reactions NUIGMech 1.1 (2020). The objects of the study are three air mixtures containing hydrogen in amounts of 15, 29.6, and 50 vol % (lean, stoichiometric, and rich mixtures, respectively) without additives and with the addition of 1% propylene. [ABSTRACT FROM AUTHOR]

The ignition of lean hydrogen-air mixtures behind reflected shock waves at the temperature range of 902–1630 K and the pressure of 1 atm is studied experimentally and numerically. For the first time, reliable experimental data is obtained for temperatures below 1000 K, directly in the zone of change in the dominance of chain branching and chain termination reactions, which influence the formation of the ignition delay value. Expressions are formulated for ignition delay in two temperature intervals below and above 970–980 K, and the corresponding activation energy values are determined. Good agreement between the experimentally observed and calculated ignition delay values is demonstrated. The local sensitivity analysis allowed us to reduce the kinetic mechanism. • The new data on ignition of lean H 2 -air mixtures at the T of 902–1630 K and the P of 1 atm is presented. • Correlation expressions for ignition delay in two temperature intervals are formulated. • Good agreement between the experimentally observed and calculated ignition delay values is demonstrated. • The reactions determining the kinetic mechanisms of ignition delay formation of lean H 2 -air mixtures are identified. • Reduced kinetic mechanism is presented. [ABSTRACT FROM AUTHOR]

The paper is devoted to the comparative analysis of different CFD techniques used to solve the problem of high-pressure hydrogen release into the air. Three variations of a contemporary low-dissipation numerical technique (CABARET) are compared with each other and a conventional first-order numerical scheme. It is shown that low dissipation of the numerical scheme defines better resolution of the contact surface between released hydrogen and ambient air. As a result, the spatial structures of the jet and the reaction wave that arise during self-ignition are better resolved, which is useful for predicting the local effects of high-pressure hydrogen release. At the same time, the dissipation has little effect on the induction delay, so critical conditions of self-ignition can be reliably reproduced even via conventional numerical schemes. The test problem setups formulated in the paper can be used as benchmarks for compressible CFD solvers. [ABSTRACT FROM AUTHOR]

Induction and reaction times of hydrogen–air mixtures (ϕ = 0.5–2) have been measured behind reflected shock waves at temperatures of 1000–1600 K, pressures of 0.1, 0.3, 0.6 MPa in the domain of the extended second explosion limit. The measurements were performed in the shock tube with a completely transparent test section of 0.5 m long, which provides pressure, ion current, OH and high-speed chemiluminescence observations. The experimental induction time plots demonstrate a clear increasing of the global activation energy from high- to low temperature post-shock conditions. This trend is strongly pronounced at higher post-shock pressures. For a high-temperature range of T > 1200 K, induction time measurements show an activation energy for the global reaction rate of hydrogen oxidation of 64–83 kJ/mole. Detected reaction times exhibit a big scatter and a weak temperature dependence. The minimum reaction time value was nearly 2 µs. Obtained induction time data were compared with calculations carried out in accordance with the known kinetic mechanisms. For current and former shock-tube experiments within a pressure range of 0.1–2 MPa, critical temperatures required for strong (1000–1100 K), transient and weak auto-ignition modes behind reflected shock waves were identified by means of the pressure and ion-probe measurements in stoichiometric hydrogen-air mixture. The transfer from the strong volumetric self-ignition near the reflecting wall to the hot spot ignition (transient) was established and visualized below <1200 K with a post-shock temperature decreasing. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia have attracted increasing attention as carbon-free fuels. Ammonia is considered to be an effective energy storage and hydrogen storage medium. However, a small amount of unremoved NH3 is still present in the product during the decomposition of ammonia to produce hydrogen. Therefore, it is very essential to investigate the self-ignition of hydrogen-ammonia mixtures in order to accommodate the various scenarios of hydrogen energy applications. In this paper, the effect of NH3 addition on the self-ignition of high-pressure hydrogen release is numerically investigated. The RNG k-ε turbulence model, EDC combustion model, and 213-step detailed NH3/H2 combustion mechanism are used. CHEMKIN-Pro programs for zero-dimensional homogeneous and constant volume adiabatic reactor models are used for sensitivity analysis and ignition delay time of the chemical reaction mechanism. The results showed that the minimum burst pressure required for self-ignition increased significantly after the addition of ammonia. The maximum temperature and shock wave intensity inside the tube decreases with increasing ammonia concentration. The ignition delay time and H, HO2, and OH radicals reduce with increasing ammonia concentration. H and HO2 radicals are suggested as indicators for tracking the second and third flame branches, respectively. [ABSTRACT FROM AUTHOR]

The paper is devoted to the comparative analysis of different CFD techniques used to solve the problem of high-pressure hydrogen release into the air. Three variations of a contemporary low-dissipation numerical technique (CABARET) are compared with each other and a conventional first-order numerical scheme. It is shown that low dissipation of the numerical scheme defines better resolution of the contact surface between released hydrogen and ambient air. As a result, the spatial structures of the jet and the reaction wave that arise during self-ignition are better resolved, which is useful for predicting the local effects of high-pressure hydrogen release. At the same time, the dissipation has little effect on the induction delay, so critical conditions of self-ignition can be reliably reproduced even via conventional numerical schemes. The test problem setups formulated in the paper can be used as benchmarks for compressible CFD solvers.

The geometrical diversion of combustible gas molecules notably affects their self-ignition in high-pressure tubes. This study investigates the propagation of shock waves and flame induced by a sudden pressure release of hydrogen in various Y-shaped tubes. The impact of the initial burst pressure, downstream tube length, and bifurcation angle (60°, 120°) were analyzed by recording the pressure signals, photoelectric curves, and jet fire evolution. The results showed that the gas diversion caused by the Y-shaped structure significantly reduces the maximum overpressure of the hydrogen jet, the intensity, and the velocity of the leading shock wave. Also, it was indicated that increasing the Y-shaped tube's length downstream of the bifurcation point could enhance the strength of leading and reflected shock waves after the Y-bifurcation, making self-ignition more likely to happen. Applying a 60°-bifurcation angle could create stronger leading and reflected shock waves during the propagation downstream of the bifurcation point, while a 120°-bifurcation angle could make a more substantial reflected shock wave propagating upstream. It leads to the re-ignition downstream of the bifurcation in the 60°-bifurcation tube after the flame quenching and stronger far-field jet fire outside the tube. • The impact of geometrical diversion of pressurized hydrogen was investigated. • The influence of tube length and bifurcation angle were analyzed. • The flame quenching and re-ignition were explored. • The evolution of double far-field jet fire was recorded. [ABSTRACT FROM AUTHOR]

This paper is a brief review and systematization of studies of flame acceleration and deflagration-to-detonation transition in circular smooth pipes, performed during the last several years at the A. V. Luikov Heat and Mass Transfer Institute of the National Academy of Sciences of Belarus. All stages of the flame acceleration process from initiation with a weak source to detonation are demonstrated and described. [ABSTRACT FROM AUTHOR]

In this paper the investigation of hydrogen release through two slits into air by means of numerical modelling in two-dimensional setup is carried out. Initial hydrogen pressure is varied in the range from 350 to 700 atm that corresponds to the conditions of hydrogen storage in high-pressure vessels. Besides, two main parameters that describe geometric configuration, the width of slits and the distance between them, are varied. Two modes of hydrogen release are possible at different values of the listed parameters: with and without hydrogen self-ignition. It is shown that the gas heating in the region of interference of two shock waves plays the key role in the process of self-ignition during hydrogen release through two slits. The types of ignition kernels formed with the variation in the main parameters are presented. The diagrams of hydrogen release modes are obtained in a wide range of the width of slits and the distance between slits. The regions of parameters are found in those diagrams in which the self-ignition takes place. In particular, it is shown that hydrogen self-ignites only when the slits are located relatively close to each other. With the increase in the width of slit this criterion weakens and starting from the certain width of slit hydrogen could self-ignite in the absence of the flow through the second slit. The obtained results could be interesting for the development of safe hydrogen storage systems as well as systems in which the combustion initiation takes place without the use of additional ignition devices. [ABSTRACT FROM AUTHOR]

The accidental release of high-pressure hydrogen into a tube can induce self-ignition, and special tube configurations can complicate their characteristics. Hence, this paper studies the shock waves and self-ignition in tubes with T-shaped structure. Results show that the shock wave intensity decreases after passing through the T-shaped region, and its intensity is lower in the branch pipeline. The flow field is extremely complex after shock waves enter the T-shaped region, accompanied by different shockwave structures (e.g. barrel shock and Mach disk), multiple reflections, and shock-shock interaction. In addition, the location of the bifurcation point affects not only the downstream velocity evolution but also the time of upstream pressure to reach the peak pressure. When the bifurcation point is the closest to the rupture disc, spontaneous ignition is least likely to take place. The flame intensity decreases after passing via a T-shaped zone. Besides, if the T-shaped zone is far from rupture disc, even extinguishment can occur. [ABSTRACT FROM AUTHOR]

Induction and reaction times of hydrogen–air mixtures (ϕ = 0.5–2) have been measured behind reflected shock waves at temperatures of 1000–1600 K, pressures of 0.1, 0.3, 0.6 MPa in the domain of the extended second explosion limit. The measurements were performed in the shock tube with a completely transparent test section of 0.5 m long, which provides pressure, ion current, OH and high-speed chemiluminescence observations. The experimental induction time plots demonstrate a clear increasing of the global activation energy from high- to low temperature post-shock conditions. This trend is strongly pronounced at higher post-shock pressures. For a high-temperature range of T > 1200 K, induction time measurements show an activation energy for the global reaction rate of hydrogen oxidation of 64–83 kJ/mole. Detected reaction times exhibit a big scatter and a weak temperature dependence. The minimum reaction time value was nearly 2 µs. Obtained induction time data were compared with calculations carried out in accordance with the known kinetic mechanisms. For current and former shock-tube experiments within a pressure range of 0.1–2 MPa, critical temperatures required for strong (1000–1100 K), transient and weak auto-ignition modes behind reflected shock waves were identified by means of the pressure and ion-probe measurements in stoichiometric hydrogen-air mixture. The transfer from the strong volumetric self-ignition near the reflecting wall to the hot spot ignition (transient) was established and visualized below

Self-ignition within a cylindrical tube that discharges high-pressure hydrogen results in flame formation. Because rectangular tubes are used to visualize fuel-flow dynamics, the influence of the tube cross-section on the self-ignition characteristics is investigated. As experimental investigation of the mechanisms underlying the self-ignition phenomenon in cylindrical tubes is difficult, three-dimensional numerical simulation is employed. Following the bursting of diaphragm by high-pressure hydrogen with a storage pressure of 9.0 MPa and a temperature of 300 K, initial self-ignition occurs at the center of the rectangular tube sidewall. This is because of the mixing of air and hydrogen induced by the bow-shock reflection-generated jet flow and resulting adiabatic shock compression-induced temperature increase. This temperature rise induces a secondary self-ignition at the tube corners. In the cylindrical tube, a solitary ring-shaped self-ignition occurs near the sidewall. The flame evolutions in rectangular and cylindrical tubes reveal similar flame-spreading trends, which indicates similar bow-shock reflection-induced self-ignition mechanisms. In this study, three-dimensional numerical simulations were performed to evaluate the release of hydrogen at 9.0 MPa through circular and rectangular tubes by the rupture of a diaphragm. The left and right figures show the hydrogen mass fraction and temperature distributions in the cross-section through the axis, respectively. The hydrogen mass fraction distribution indicates the mixing of hydrogen and air near the sidewall of the tube. The temperature distribution indicates the initiation of an exothermic reaction generated by the mixing of heated air and hydrogen induced by the shock wave. [Display omitted] • Examined self-ignition in high-pressure hydrogen jet owing to diaphragm rupture. • Examined the influence of cross-section shape of tube on self-ignition mode. • Self-ignition mechanism near diaphragm is not dependent on cross-section shape. • Flame growth behavior is influenced by the cross-section shape. • The effect of the cross-sectional shape of the tube on self-ignition is insignificant. [ABSTRACT FROM AUTHOR]

Due to increasing climate awareness and the introduction of much stricter exhaust emission legislation the internal combustion engine technology faces major challenges. Although the development and state of technology of internal combustion engines generally reached a very high level over the last years those need to be improved even more. Combining water injection with a diesel engine, therefore, seems to be the next logical step in developing a highly efficient drive train for future mobility. To investigate these potentials, a comprehensive evaluation of water injection on the diesel engine was carried out. This study covers >560 individual operating points on the test bench. The tests were carried out on a single-cylinder derived from a Euro 6d four-cylinder passenger car with the port water injection. Furthermore, a detailed pressure trace analysis (PTA) was performed to evaluate various aspects regarding combustion, emission, etc. The results show no significant effects of water injection on the combustion process, but great potential for NOx reduction. It has been shown that with the use of water injection at water-to-fuel rates of 25%, 50%, and 100%, NOx reduction without deterioration of soot levels can be achieved in 62%, 40%, and 20% of the experiments, respectively. Furthermore, water injection in combination with EGR offers additional reduction in NOx emissions. [ABSTRACT FROM AUTHOR]

The large-size single cell is a promising development trend for the lithium-ion battery (LIB) industry. LiFePO 4 is one of the favoured cathode materials, which is believed to have better safety features, while relatively little is known about the ejection of flammable gases and hot sparks during thermal runaway (TR). Similarly, the self-ignition mechanism, i.e., ignition of the released flammable gases by the ejected hot sparks, is also unclear. Relatively little is understood about the thermal radiation hazards of the jet flame. A series of gas analysis and combustion tests were conducted on a 280 Ah large-size cell with LiFePO 4 as cathode. In the unignited, or delayed ignition tests, involving cells with 100%, 75% and 30% state of charge (SOC), the composition and concentration of the gaseous products during TR were measured. The observation of the delayed ignition in one of the 100% SOC tests also led to caution about the gas explosion of LIB. This was followed by the quantified measurements of time-dependent flame heights, heat release rates and thermal radiation hazards. The self-ignition of the ejected electrolyte vapour and flammable gases by the ejected scorching sparks were captured and analysed. Two cycles of jet flames were observed and attributed to the successive TR of the two jelly rolls connected in parallel inside the cell. The evolution of the cell surface temperatures, heat release and mass loss rates were measured, which aided the analysis and can also support model validation by other researchers. The previously developed Multi-point Source (MPS) Radiation Model was adapted with the support of some measurements to estimate the thermal radiation hazards of battery. The adapted simple model can potentially be used to estimate thermal radiation hazards in practical applications where measurements are lacking. Self-ignition of the large-size LFP cell and the subsequent flame radiation hazard assessment. [Display omitted] • Self-ignition mechanisms of the large-size LFP cell were investigated. • A radiation model for the jet flame of the large-size LFP cell was developed. • A method is proposed to assess the radiation hazards of the LIB jet flame. [ABSTRACT FROM AUTHOR]

The detonation initiation characteristics of a single tube liquid-fueled pulse detonation combustor (PDC) is investigated at different inlet air temperatures in this paper. The inner diameter of the PDC is 62 mm. Gasoline and air are used as fuel and oxidant, respectively. The inlet air temperature is 288–523 K and the operating frequency of the PDC is 10~30 Hz. The experimental results show that the deflagration to detonation transition (DDT) distance, detonation initiation time, DDT time and jet ignition time decrease with the increasing operating frequency at the same inlet temperature. When the inlet temperature is 288 K, the DDT distance is shortened from 860.5 mm to 787.7 mm as the operating frequency increases from 10 Hz to 30 Hz. The detonation initiation time, the jet ignition time and the DDT time are reduced from 10.01 ms, 7.66 ms and 2.35 ms to 6.55 ms, 4.99 ms and 1.56 ms, respectively. When the inlet air temperature increases, the atomization and evaporation of the gasoline is improved, which also leads to the decrease in the DDT distance, the detonation initiation time, the jet ignition time and the DDT time. For example, when the inlet air temperature increases from 288 K to 523 K at the frequency of 10 Hz, the DDT distance is shortened from 860.5 mm to 747.2 mm and the detonation initiation time, the jet ignition time and the DDT time is reduced to 5.867 ms, 2.51 ms and 1.11 ms, respectively. Additionally, the self-ignition caused by high inner wall temperature occurs when PDC is operating at high frequency under high inlet air temperature. [ABSTRACT FROM AUTHOR]

The self-ignition delays of concentrated syngas mixtures are determined by the method of reflected shock waves in the temperature range T0 = 750–1150 K at pressures P0 ≈ 1 atm. The experiments are carried out using a shock tube setup equipped with a calibrated pressure sensor and spectral-optical measuring instruments. The time profiles, the pressure, radiation intensity of the chemiluminescent reactions O + H → OH+ hν (λ = (308 ± 2) nm) and CO + O → CO2 + hν (λ = (410 ± 3 nm)), and the thermal radiation reaction CO2 (λ = (4.35 ± 0.07 µm)) are recorded. The ignition of the mixture manifests itself as a sharp simultaneous increase in all signals; thus, the delay can be determined based on any of them. Specifically, the delay is determined from the pressure oscillograms as the time between the arrival of the reflected shock wave at the pressure sensor and the sharp pressure jump caused by the ignition of the mixture. Kinetic modeling is carried out using the NUIG1.1 mechanism and our own mechanism, which is a modification of the Keromnes mechanism. Sensitivity analysis shows that the branching reactions, H + O2 = O + OH (1), and chain termination, H + O2 (+M) = HO2 (+M) (2), play the most significant role in syngas ignition. It is established that with an increase in the proportion of CO in the composition of the syngas, the delay increases for two reasons: the contribution of the chain termination reaction CO + O (+M) = CO2 (+M) grows as does the rate constant of the main chain termination reaction (2), since CO is more efficient as a third body (M) than H2. The results of kinetic simulations are in good agreement with the experimental data, with the relative discrepancy being within 30%. [ABSTRACT FROM AUTHOR]

This paper studies the self-ignition of hydrogen flowing under pressure into a channel filled with an oxidizer medium containing neutral components, such as water vapor, helium, carbon dioxide, nitrogen, and argon. The work is carried out by the numerical modeling, taking into account the finite time of the rupture of the diaphragm dividing the high-pressure chamber and the channel. The calculations performed show that the ignition delay time of hydrogen increases with the H2O, He, CO2, or N2 concentration and when a certain concentration of the additive is reached, the hydrogen self-ignition does not occur. At the same time, it is demonstrated that self-ignition could develop in the form of two types of ignition kernels, occupying the entire channel cross section or localized near its wall. Furthermore, in some cases, the ignition kernel localized near the wall turns out to be unsteady and quenches before the hydrogen jet exits the channel. When the oxidant is diluted with argon, a qualitatively different scenario of the development of the process is observed, and with an increase in the argon content in the oxidizing medium, the self-ignition time decreases. Moreover, ignition occurs even at a very high content of argon in oxygen of up to 99.5%. This effect is related to the significantly lower heat capacity of argon compared to other neutral additives and, consequently, to the more intense heating of the oxidizing medium due to the hydrogen jet flowing into the channel. [ABSTRACT FROM AUTHOR]

The paper numerically studies the process of pressurized hydrogen release through a hole or a slit into a confined space filled with air. Based on the obtained results, three basic consequences of hydrogen release are demonstrated depending on the initial pressure of hydrogen and the distance to the obstacle: (i) hydrogen ignition before the interaction of the flow with the obstacle, (ii) hydrogen ignition after the flow interaction with the obstacle, (iii) jet flow without ignition. It is shown that ignition limits are wider when hydrogen is released through the slit compared to the case of hydrogen release through a small hole. A similar effect could be achieved by changing the geometry and volume of the vessel from which hydrogen is released. Results of this study can be applicable to the elaboration of hydrogen power engineering systems dedicated either to the combustion initiation or to the suppression of ignition of non-premixed hydrogen-air mixtures. • Self-ignition of hydrogen released into the confined space is studied numerically. • Three basic scenarios of hydrogen release are distinguished and demonstrated. • Mechanism of hydrogen jet ignition due to interaction with obstacle is revealed. • Diagrams of critical conditions for different scenarios are presented. [ABSTRACT FROM AUTHOR]

Accidental leakage of pressurized hydrogen into the pipeline is often accompanied by the non-premixed self-ignition flame, whilst the complex structure of pipeline affects the flame propagation. In this study, the propagation of self-ignition hydrogen flame in different three-way tubes is studied and the flame evolution near the two exits is compared. Effects of the tube length and the location of bifurcation points are investigated. Results show that the bifurcation structure has the attenuation effect on the intensity of flame and shock wave, and they attenuate more sharply in the branch pipeline. But the flame intensity can increase again downstream the bifurcation point in the trunk pipeline, and this increase is not continuous and decrease again as the tube length increases. In addition, the flame evolution can be different near two exits of the tube. As the bifurcation point moves downstream, the number of Mach disk and the time required to form the stable flame will increase near the exit of branch pipeline. Despite different flame evolution, the flame morphology and propagation are all controlled by the shock wave structures before the formation of the vortex, but the flame changes dramatically and grows rapidly to form the stable lift-off flame after the formation of the vortex. [ABSTRACT FROM AUTHOR]

Spontaneous ignition resulting from the accidental release of high-pressure hydrogen is an important safety issue, and the self-ignition flame can eventually induce a jet flame. However, the links between the self-ignition flame inside a tube and an external jet flame are unclear. Hence, this paper presents a study on how the self-ignition flame transforms into the jet flame in the near-field region of the nozzle. Effects of release pressure and tube length are investigated. Changes in release conditions can lead to changes in the flow characteristics of the self-combustible jet at the nozzle. Results show that the difference in the flow parameters is manifested in three aspects, which directly contribute to the diversity of transition forms. The expansion processes and shock structure govern the flame transition. The expansion process consists of two typical stages, which lead to two different flame morphologies. Besides, the presence of discontinuous surfaces in the shock wave structure can cause the self-ignition flame to extinguish or re-ignition in some transition processes, resulting in the flame appearing in different zones during different transitions. Finally, five forms of flame transition are proposed and their formation reasons are analyzed. Dominant factors and links between different transitions are eventually identified. [ABSTRACT FROM AUTHOR]

This paper presents a macrokinetics-based mathematical model for the numerical simulation of the fuel self-ignition period in a local volume of a hydrogen diesel engine with high pressure fuel injection equipment. A detailed kinetic mechanism of hydrogen oxidation with a special software were used to simulate hydrogen self-ignition in homogeneous chemical reactors for operating conditions of a real hydrogen diesel engine at the moment of the start of hydrogen gas injection. From the results of these simulations for constant-volume and constant-pressure reactors, an equation for the macrokinetics of hydrogen oxidation at high pressures was derived. Using this equation, various operation modes of a hydrogen diesel engine with heating of air and hydrogen were investigated by numerical methods. Ways to reduce the induction period and increase the engine reliability are indicated. [ABSTRACT FROM AUTHOR]

The dynamic mechanisms of self-ignition and flame propagation during high-pressure hydrogen release through a rectangular tube were experimentally investigated using pressure records, flame detection and high-speed photographs. Experimental results show that the minimum burst pressure for self-ignition decreases with an increase in axial distance to the diaphragm and then remains at an almost constant value. The self-ignition onset at the same location of the tube exhibits a certain randomness even if the intensity of the shock wave produced in the tube is similar. Multiple ignitions were observed at the early stage of hydrogen release. They usually had difficulty to sustainably develop and were extinguished owing to oxygen deficiency. At a subsequent stage, the ignition kernel appears again and grows rapidly in the axial and radial directions, finally converging to a complete flame across the tube width. It was found that the radial growth rate of the flame was lower than the axial growth rate. [ABSTRACT FROM AUTHOR]

The N47 engine debuted in March 2007 in the facelifted BMW 1 Series E87 and E81 and was also available in the BMW 1 Series E82 and E88, which were introduced the same year. The N47 engine replaced the M47 engine that had been in production for 8 years. The M47 construction underwent several modifications, so the injection system was changed, the cylinder head now consists of two parts, and the engine block is made of aluminium. Two main versions of the N47 engine are known: N47D16 (1.6 L) and N47D20 (2.0 L). In the case of both versions, several models with different performances were born. After the distribution of BMW passenger cars equipped with the N47D20 engine, it received a lot of negative criticism due to malfunctions. In this article, I would like to present the maintenance of the engine, which can be used to avoid the failure of passenger cars equipped with the N47D20 diesel engine with huge material damage. [ABSTRACT FROM AUTHOR]

In forensics, the investigation of intentional fires, generated by criminal violations of prevention rules, committed out of revenge, in order to hide other crimes, through vandalism, due to mental disorders or in the case of self-ignition in public in order to obtain claims. In forensics, fires and explosions are analysed according to the causes that produce them and according to the substances or devices that initiated and maintained their combustion or explosion.

Experimental investigations on high-pressure hydrogen release into obstructed tubes with varying obstacle positions are conducted to explore the dynamic mechanisms of shock propagation, self-ignition and flame evolution. High-speed photography, pressure sensor and light detector are used in the experiments. The results reveal that obstacle position significantly affects self-ignition by the multi-dimensional interactions and the turbulence-promoted mixing. The reflected shock results in an overpressure rise of twice that behind the leading shock. In addition, the intensity of reflected shock decreases when it propagates upstream. The critical burst pressure for self-ignition first decreases and then increases with a further obstacle position away from the burst disk. The lowest burst pressure for self-ignition is 2.08 MPa arising in the tube with obstacles located at 200 mm axially, half that of the smooth tube. In obstructed tubes, three possible self-ignition regions exist, including inclined obstacle walls, tube centerline and tube sidewalls. The patterns of self-ignition are determined by burst pressure and obstacle position. Besides, flame acceleration is observed in the obstructed, which is related to turbulence promoted by the shock-obstacle interaction. The farther obstacles from the burst disk results in more marked effects on flame acceleration. • The critical burst pressure decreases and then increases with obstacle position. • Three possible initial self-ignition regions exist in the obstructed tube. • Flame acceleration occurs behind the obstacles caused by the rising flame area. • Farther obstacle position causes a faster flame expansion and flame acceleration. • Dynamics of self-ignition and flame evolution in obstructed tubes are proposed. [ABSTRACT FROM AUTHOR]

Pure ammonia MILD combustion is studied numerically in a furnace. The effects of furnace wall temperature and dilution of inlet air with nitrogen on the characteristics of reaction zone (RZ), temperature distribution and exhaust emissions are investigated. The results show that lowering the furnace wall temperature and adding diluent to the inlet air, result in expansion of the RZ, reduction of fuel and oxidizer consumption rates, lower Damkohler, increased turbulent Reynolds and more similar RZ properties to the distributed combustion regime in the combustion regimes diagram. At a lower concentration of oxygen in the oxidizer, a higher threshold wall temperature is required for stable MILD combustion. Reducing the wall temperature and oxygen mole fraction in the oxidizer, increases the uniformity of temperature distribution. Analysis of exhaust emissions shows that reducing wall temperature and oxygen level in the oxidizer stream can significantly reduce NOx pollution, however, N 2 O emission rises. • Pure ammonia MILD combustion studied numerically in a furnace. • Reaction zone is defined based on NNH mole fraction distribution. • Higher minimum wall temperature is needed for stable combustion using diluted air. • Lower wall temperature and air dilution lead to more distributed reaction zone. • Air dilution and lower wall temperature result in lower NOx and higher N 2 O. [ABSTRACT FROM AUTHOR]

In this study, an experimental investigation is conducted to study the effects of CO addition (0%–7.5% vol.) on the self-ignition of pressurized hydrogen leakage. The result shows that more CO addition significantly decreases the likelihood of self-ignition inside the tube and the formation of self-sustained jet flame outside the tube. This can be mostly explained by the reduction of leading shock intensity inside the tube. Furthermore, CO addition effectively inhibits the flame propagation and development inside the tube. For pure hydrogen, the ignited flame quickly develops an intense flame spanning the tube width and eventually form a jet flame in ambient air. However, the H 2 –CO diffusion flame initiated approaching tube sidewall tends to propagate adjacent to the wall or be soon quenched with more CO addition. If the CO-weakened flame spouts to the tube exit, it may not survive the expansion at the tube exit and thus it is quenched. • The shock intensity is reduced in the presence of CO. • The critical pressure for self-ignition increases with CO addition concentration. • Shock intensity variation by CO addition is the main factor affecting self-ignition onset. • Small CO addition can effectively inhibit flame development inside the tube. • H 2 –CO flame spouting from the tube exit tends to be blown out. [ABSTRACT FROM AUTHOR]

Ignition within gas burner ejectors can lead to off design conditions and has significant influence on the burner behavior. Thus ignition in the ejector should be prevented. In the present study the influence of combustion reactions on the performance of gas burner injectors is investigated. To investigate if ignition is possible, simulated ignition delay times, using a detailed reaction mechanism, are compared to predicted mean residence times of the gas in the ejector. Gas burner ejectors are designed using one dimensional analytic equations, based on energy and momentum conservation equations and conventional isentropic equations. 1D results are compared to 2D computational fluid dynamics (CFD) simulations, to take into account non-ideal mixing effects along the ejector. Results are validated with experiments with air at room temperature. 1D results show very good agreement not only with CFD simulations for the case of non-reactive flows, but also with performed experiments.It is shown that the assumption of ideal mixing along the ejector and thus the comparison of the ignition delay time to the gas mean residence time, to predict ignition in the ejector, is not valid. Ignition in the ejector is possible, even if the ignition delay time is more than thirty times higher than the mean residence time. In addition to that, it is shown, that ignition and the choice of reaction mechanism have significant influence on the predicted gas burner ejector performance. Thus, the accurate prediction of ignition delay time and the use of a detailed reaction kinetic are mandatory to correctly predict the burner ejector behavior.

As one of the most promising fossil energy substitutes, hydrogen energy is receiving increasing attention, and it has been greatly developed in recent years. However, hydrogen safety issues limit the large-scale application of hydrogen energy. Since 1922, the issue of self-ignition of high-pressure hydrogen discharge has gradually become the focus of attention of scholars in the field of hydrogen energy. Particularly fruitful research results have been obtained in the past 20 years, showing that the minimum discharge pressure of hydrogen self-ignition is approximately 2 MPa. In particular, the discharge tube shape and bursting disc rupture have a significant effect on the characteristics of hydrogen self-ignition. Moreover, the study of the hydrogen self-ignition mechanism under special working conditions has been extended by shock-induced ignition theory. Initial conditions mainly affect the critical pressure of hydrogen self-ignition by changing the formation, development and propagation of shock waves. Finally, the deficiencies and future research trends in research methods, self-ignition characteristics, and dynamic mechanisms are analysed. • Summarized the research results on the self-ignition of hydrogen discharge. • Introduced the deficiencies in the study of self-ignition of hydrogen discharge. • Discussed the urgency of multi-element gas self-ignition research. • Pointed out three fields that need further research. [ABSTRACT FROM AUTHOR]

The self-ignition of hydrogen/air is an important process in the micro thermophotovoltaic system. The transient numerical models of gas-phase reaction and catalytic reaction in the various catalytic micro combustors were built and verified. The self-ignition process of gas-phase reaction caused by catalytic reaction in the catalytic micro channel with conventional heat dissipation was studied. The self-ignition process could be divided into four stages, fuel diffusion stage - pure catalytic reaction stage - flame front moving stage - stable combustion stage. The ignition time and temperature limit at different inlet temperatures, inlet velocities and channel heights were analyzed. The results showed that the wall quenching effect, thermal effect and flame propagation effect are dominant at low temperature, medium temperature and high temperature respectively. The catalyst length and the mixture internal energy were the main factor at low inlet velocity and high inlet velocity respectively. The steady-state time was also studied in the various operation conditions. Finally, the catalytic combustion characteristics in the stable combustion stage were analyzed. The influence of inert section length, inlet temperature and inlet velocity on the maximum temperature and fuel conversion ratio were investigated. • Transient simulation of self-ignition process of H 2 /air in catalytic micro channel. • Studied effect of boundary parameters on ignition timing and temperature limit. • Obtained maximum temperature and conversion ratio at various working conditions. • Sensitivity analysis of ignition time and temperature were conducted. [ABSTRACT FROM AUTHOR]

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The article addresses the issues of the particular terminology for fire forensic investigations. Definitions for the basic parameters of a fire hazardous area, determining its susceptibility to ignition, and their relationship to the impulses initiating such areas’ combustion are analyzed.Two main tasks of forensic fire examinations are reviewed: establishing the technical cause of a fire, its organizational cause, and consequences. The author gives definitions for these tasks and the term “ignition source”.The paper’s relevance stems from the need to prevent mistakes in terminology when conducting a forensic fire investigation. The article may be of use for practicing experts and specialists in fire forensics’ theory and practice.

In many actual industrial scenes, the coal body and coal dust are not always in the tiled state, but in the inclined situation. A two – dimensional transient numerical model of coal oxidation reaction was established to study the self–ignition and smoldering characteristics of coal dust layers in the presence of inclination angle. The effects of gravity and thermal buoyancy were considered to solve the coupling problem of coal oxidation reaction and air flow. The results show that the growth coefficients of minimum ignition temperature of coal dust with thicknesses of 6.4 mm, 12.7 mm, 19.1 mm and 25.4 mm are 0.117 °C/°, 0.0467 °C/°, 0.033 °C/° and 0.033 °C/°, respectively. With the increase of hot plate temperature, the inclination of coal dust can greatly shorten the ignition delay time (IDT). The ΔIDT of coal dust inclination of 60° is 128 s/°C greater than that of 0°. The movement of high temperature point of coal dust in self–heating development stage is from the inside to the outside, and that in decaying stage is from the outside to the inside. In addition, some interesting phenomena in the process of coal self–ignition and smoldering have also been found. The influence of coal dust inclination on its self–heating is mainly reflected in the location of high temperature points and the spread of smoldering. This study is helpful to understand the characteristics of coal dust self–ignition and smoldering spread in inclined situation, and can guide the prevention of coal dust self–ignition. [ABSTRACT FROM AUTHOR]

Thermal runaway is a major safety concern for Lithium-ion batteries in manufacture, storage, and transport. Facing the frequent incidents in the air transport of massive batteries, more reliable fire prediction and protection strategies under low-pressures conditions are urgently needed. Herein, thermal runaway criticality of the open-circuit cylindrical battery piles (up to 9 cells with 30% SOC) under a hot boundary is investigated inside a novel low-pressure chamber (20–100 kPa). Characteristics battery temperatures for the safety venting and thermal runaway are measured to analyze the influences of pressure and cell number on battery failures. Results indicate that lowering the pressure could promote an earlier and stronger safety venting and weaken the intensity of the exothermic reactions inside cells, which is verified by the surface morphology of the electrodes. The overall fire risk is higher with higher pressure and larger battery-pile size, as indicated by the lower minimum boundary temperature for thermal runaway (255 °C~385 °C). Moreover, a simplified heat transfer model is established to explain the trend of thermal-runaway criteria and the influence of the low-pressure environment. This work delivers new insights into the effects of pressure and pile size on battery thermal runaway, which can help to improve the safe storage and transport of large-scale lithium-ion battery piles under varied pressure conditions. [ABSTRACT FROM AUTHOR]

Japan Aerospace Exploration Agency (JAXA) has planned High-Mach Integrated Control Experiment (HIMICO), which is a flight experiment under hypersonic conditions. The ramjet engine used in the experimental aircraft is designed for self-ignition of the fuel to occur due to high temperature caused by aerodynamic heating in hypersonic flow. We confirmed that self-ignition occurred under some test conditions in the combustion test. However, conditions of the incoming air and the injected fuel where self-ignition occurred were not clear. In this study, we develop a chemically reacting flow solver for investigating the self-ignition. Large-eddy simulations of the combustor of the HIMICO engine are performed using a detailed hydrogen-air reaction mechanism. The results show that qualitative prediction whether self-ignition occurs is possible by Large-eddy simulations using the solver. In the simulations, self-ignition occurs even under conditions where self-ignition did not occur in the test. On the other hand, it is found that the selection of the boundary condition of the injector outer walls has a great effect on the time to self-ignition. For improving the accuracy of prediction, it is necessary to consider turbulence and three-dimensional flow due to the intake and the effects of heat exchange on the injector outer walls. [ABSTRACT FROM AUTHOR]

The detonation initiation characteristics of a single tube liquid-fueled pulse detonation combustor (PDC) is investigated at different inlet air temperatures in this paper. The inner diameter of the PDC is 62 mm. Gasoline and air are used as fuel and oxidant, respectively. The inlet air temperature is 288–523 K and the operating frequency of the PDC is 10~30 Hz. The experimental results show that the deflagration to detonation transition (DDT) distance, detonation initiation time, DDT time and jet ignition time decrease with the increasing operating frequency at the same inlet temperature. When the inlet temperature is 288 K, the DDT distance is shortened from 860.5 mm to 787.7 mm as the operating frequency increases from 10 Hz to 30 Hz. The detonation initiation time, the jet ignition time and the DDT time are reduced from 10.01 ms, 7.66 ms and 2.35 ms to 6.55 ms, 4.99 ms and 1.56 ms, respectively. When the inlet air temperature increases, the atomization and evaporation of the gasoline is improved, which also leads to the decrease in the DDT distance, the detonation initiation time, the jet ignition time and the DDT time. For example, when the inlet air temperature increases from 288 K to 523 K at the frequency of 10 Hz, the DDT distance is shortened from 860.5 mm to 747.2 mm and the detonation initiation time, the jet ignition time and the DDT time is reduced to 5.867 ms, 2.51 ms and 1.11 ms, respectively. Additionally, the self-ignition caused by high inner wall temperature occurs when PDC is operating at high frequency under high inlet air temperature.

This study is devoted to the numerical analysis of the process of the hydrogen release at a pressure of 60 atm through an opening diaphragm into a channel filled with oxygen with additives of substances neutral from a chemical point of view: nitrogen, water vapor, carbon dioxide, and helium It is shown that at a certain content of additives, there is no self-ignition of hydrogen during the release. Qualitative regularities are obtained showing that in the case of adding water vapor to the atmosphere of oxygen, the effect of slowing down and ultimately suppressing self-ignition is most pronounced compared to the action of other additives listed below in order of decreasing effect: helium, carbon dioxide, and nitrogen Two scenarios of the development of combustion in the channel are demonstrated and described. In both cases, self-ignition occurs at the side wall of the channel, and then intense combustion develops either in the entire cross section of the channel, or inside the kernel, localized at the channel wall and propagating in the flow in the direction of the exit from the channel. [ABSTRACT FROM AUTHOR]

The regularities of the ignition and combustion of peat of different permeabilities in conditions of natural air convection are investigated. The initial initiation temperatures are determined for peat samples of different particle size distributions. It is shown that with an increase in the permeability of peat samples, the temperature and combustion rate increase, and a more complete consumption of oxygen occurs with the increase in the concentration of carbon monoxide and carbon dioxide in the gaseous products. The gaseous products of peat combustion under conditions of natural air convection contained mainly CO, CO2, and O2. The methane content did not exceed 0.5; and hydrogen, 2 vol %. [ABSTRACT FROM AUTHOR]

Accelerated adoption of hydrogen gas for energy storage requires improved safety for hydrogen storage. In particular, control of self-ignition of hydrogen vented through tubes by pressure relief devices (overpressure protection devices), such as rupture disks, is needed. We clarify the process of self-ignition in tubes of various lengths during venting of high-pressure hydrogen and observe flame behavior at the tube exit. The importance of distance from the rupture disk for flame front evolution is revealed. Specifically, in a tube longer than a critical value, the self-ignited flame undergoes a quenching process, possibly due to steam formation, before it exits the tube. A tube that is too short does not give the gas sufficient time for hydrogen and air mixing to initiate self-ignition. Finally, at slightly longer tube lengths, the hydrogen ignites, but the flame does not fully develop before it exits, and the vortex formed by expanding gas extinguishes it. • Examined self-ignition in high-pressure hydrogen jet owing to diaphragm rupture. • Visualization of flame growth behavior in a tube. • Visualization of flame behavior out of a tube. • The longer a tube, the more flames develop in the tube. • When a flame develops in a tube, a jet flame is more likely to form outside the tube. [ABSTRACT FROM AUTHOR]

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

The most influential factor for self-ignition of high-pressure hydrogen is known to be the strength of the shock. Thus, the self-ignition can be suppressed by weakening the shock strength, which is possible by reducing the area where the hydrogen is ejected in this study. To confirm the possibility of this method, experiments were done by controlling the burst pressure of up to 302 bar and the ratio of the opening area. The experimental results showed that the minimum burst pressure of self-ignition is increased exponentially as the opening area is reduced. This confirmed that reducing the opening area under the same burst pressure conditions has an effect on the suppression of self-ignition. However, it was also found that the minimum shock speed that causes self-ignition gradually decreases as the opening area becomes smaller, which results from an increasing in mixing. The CFD simulation results showed that the volume of the flammable region in the tube was increased and the hydrogen-air mixing efficiency also increased when the opening area became smaller. The results suggest that reduction of the opening area can suppress a self-ignition by weakening the shock strength, but it should be noted that an increase in mixing effect also occurs. Image 1 • The self-ignition of hydrogen can be effectively suppressed by reducing the opening area. • The burst pressure for self-ignition increases exponentially with the reduction of opening area. • The small opening area ratio results in weaker shock strength, but stronger air/hydrogen mixing. • Strong mixing was observed to increase the possibility of self-ignition even with weak shock wave. [ABSTRACT FROM AUTHOR]

This study investigates two-dimensional REB 6 nanostructures formation from a reaction mixture of RE 2 O 3 –B 2 O 3 –Mg–NaCl composition (RE is Ce, La, Nd, or Eu). The reaction mixture is sealed in a metal cup and is preliminarily heated in argon to reach the flash point. A combustion wave forms on the top surface of the pellet after self-ignition at ~650 °C. This wave quickly propagates through the sample and increases the sample temperature to 800–950 °C, converting the raw mixture into the final product. Processing of the final product leads to the formation of pure hexaboride phases of RE, the particles of which are in the form of nanosheets with a thickness of 50 nm (or less) and a BET surface of 23.8–50.8 m2/g. In addition, CeB 6 nanosheets were tested as a catalyst in NaAlH 4 dehydrogenation/hydrogenation processes. The results demonstrated that the catalytic activity of CeB 6 nanosheets increases with higher portions of NaCl. [ABSTRACT FROM AUTHOR]

In forensics, the investigation of intentional fires, generated by criminal violations of prevention rules, committed out of revenge, in order to hide other crimes, through vandalism, due to mental disorders or in the case of self-ignition in public in order to obtain claims. In forensics, fires and explosions are analysed according to the causes that produce them and according to the substances or devices that initiated and maintained their combustion or explosion. [ABSTRACT FROM AUTHOR]