Ignition Theory Research Articles

Progress in spontaneous ignition of hydrogen during high-pressure leakage with the considerations of pipeline storage and delivery

High-pressure pipeline storage presents a promising method for widespread and efficient hydrogen transfer. However, challenges arise in mitigating pressurized hydrogen leakage due to hydrogen embrittlement issues associated with conventional pipeline materials. Experimental findings indicate that pressurized hydrogen is prone to spontaneous combustion, even at relief pressures as low as approximately 2 MPa - well below the permissible pipeline pressure in most countries. Despite this, there remains a lack of consensus regarding the mechanism of spontaneous ignition from high-pressure hydrogen leakage, and current research in this area is deemed insufficient. This study aims to analyze and discuss the presumed mechanisms of spontaneous ignition comparatively, review the progress in the study of spontaneous ignition of hydrogen in high-pressure leakage based on diffusion ignition theory, and statistically compare and discuss the influences of significant factors existing in pipelines (e.g., macro size factors and internal structure) and/or pipe failures (e.g., rupture factors) on spontaneous ignition. It is hoped that this article will provide scholars involved in the development of hydrogen energy and the theories of spontaneous combustion with a systematic understanding of these phenomena.

Design method and experimental study on a novel self-sustaining internal combustion burner

Peak shaving represents a particular challenge with regard to coal-fired power plants, as methods to achieve stable, high-efficiency, and low-nitrogen-oxide combustion at ultralow loads remain unavailable. In this study, based on analysis of the ignition mechanism, heating mode, and theory of preheating method, we proposed a novel pulverized coal full-time self-sustaining internal combustion burner by combining the processes of plasma ignition, reverse jetting, and multi-stage ignition. A flame stability model for the burner's recirculation zone was established using the temperature change rate of the recirculation zone as a criterion. The ignition position of the stable self-sustained combustion of the pulverized coal gas stream was determined under various working conditions, and the length of the ignition core stage, a component of the burner inside which the pulverized coal gas stream achieves stable self-sustained combustion, was determined based on the calculated maximum ignition position; a self-sustaining internal combustion burner was then designed based on the ascertained length. Subsequently, we established an experimental system for the self-sustaining internal combustion burner and conducted tests in the load range of 25 %–100 %. Notably, the results of the pulverized coal self-sustained ignition position experiment were consistent with the computational results of the model. The self-sustaining internal combustion burner offers a quick start–stop feature, with the pulverized coal able to achieve stable self-sustained combustion after the plasma igniter shuts off. The resultant gas-phase products exiting the burner met the boiler's concentration requirements for enhanced nitrogen reduction, and the burner exhibited good anti-interference properties. The influence of the pulverized coal gas stream velocity and concentration on the self-sustained ignition was expounded. Under the experimental conditions, an optimal concentration range was ascertained for stable ignition of the pulverized coal gas stream, with the ignition position gradually advancing backward with increasing gas stream velocity. Together, our findings highlight the potential of the proposed burner design to support clean and efficient pulverized coal combustion in coal-fired power plants.

Near-infrared laser induced direct ignition of 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine by constructing diverse crystal structures

Although laser ignition is considered to be one of the most promising ways to detonate energetic materials due to its high safety and reliability, it is still a challenge to achieve direct ignition of energetic materials by a laser with low-power and near-infrared (NIR) band. In this paper, a molecular self-assembly strategy based on recrystallization was utilized to prepare 4,4′,5,5′-tetranitro-1H,1′H-[2,2′-biimidazole]-1,1′-diamine (DATNBI) crystals with various micro-nano structures. The characterization results suggest that DATNBI crystals with different degrees of roughness and defects by the induction of solvents and surfactants. The crystal defects can not only bring about the enhancement of light absorption of DATNBI in NIR band, but also advance its thermal decomposition, providing reliable support for direct laser ignition of DATNBI profit from the hot spot ignition theory. Combined with density functional theory, it is speculated that electrons of defect states achieve electron-hole recombination by laser radiation, thereby enhancing photothermal conversion. Compared with raw DATNBI, DATNBI crystals with rough surface and abundant defects can be directly ignited by a NIR laser and exhibits self-sustainable combustion. In summary, a direct NIR laser-ignitable energetic material has been prepared via appropriate crystal structure design.

Measurement, calibration, and verification on the critical ignition temperature of hot bridge wire electro-explosive device

To address the problem of the difference in temperature between the exposed and amorce-filled state of the bridge wire in the fiber optic thermometry, this paper proceeds from a mathematical model of the temperature rise of the hot bridge wire electro-explosive device (EED), the relationship between the critical ignition temperature and the current of hot bridge wire EED is discussed. Combining thermal ignition theory, the technique of measurement and calibration the critical ignition temperature of hot bridge wire EED is proposed, and the technique is validated by injection versus radiation. The results show that the critical ignition temperature of the tested hot bridge wire EED obtained by testing and calibration is 337.53 °C. The 50% ignition field strength of the hot bridge wire EED under radiation conditions obtained by the up-and-down method test is 1271 V m−1, while the equivalent ignition field strength determined from the critical ignition temperature under the same radiation conditions is 1345 V m−1, the error between the two is only 0.49 dB, which demonstrates the high accuracy of the proposed measurement and calibration technique.

CRITICISM OF THE “THEORY OF INCANDESCENT SURFACE IGNITION” BY Ya.B. ZELDOVICH. SELF-IGNITION OF INFINITE FUEL BY INCANDESCENT BODIES

The basic principles of thermal explosion were studied and outlined by 1980. It seemed that fundamental research had been completed, but in 1984 A.A. Filippov discovered that the “ignition” condition obtained by Ya.B. Zeldovich did not correlate with the data of the experiment on ignition of a gas mixture by incandescent cylinders. Since Zeldovich’s “Theory of Incandescent surface ignition” has long been the basis of the ignition theory, its analysis was carried out and an error was found. It is proved that the above-mentioned work is not related to ignition, but to the self-ignition of infinite fuel. It is shown that a thermal explosion of fuel from an incandescent body can develop not only as ignition, but also as self-ignition. The conditions of self-ignition of infinite fuel by a flat surface and a cylinder are given, as well as the probable condition of ignition of fuel between parallel walls of different temperatures.

Use of an electric heater as an idealized firebrand to determine ignition delay time of Eucalyptus globulus leaves

The Idealized-Firebrand Ignition Test (I-FIT) protocol was used to evaluate the piloted ignition delay times of fuel beds composed of leaves of Eucalyptus globulus (Labill.). The amount of fuel layer used for evaluation ranged between the fraction volume (α) of 0.03 to 0.07 which are values expected to be found in forest bed fuels. A theoretical model was developed to describe the heating and ignition of the fuel beds, based on the thermal ignition theory. The model, which was originally developed for pine needle beds, considers the penetration of radiation to the porous matrix. The model is able to accurately predict the ignition delay time for different values of α, but shows a poorer accuracy for the temperature evolution. This is explained by the large variability observed for the Eucalyptus leaves.

Ignition of Wildland Fuels Exposed to a Time-Decreasing Incident Heat Flux

ABSTRACT The effect of decreasing incident heat fluxes on the ignition delay time of dry pine needles is addressed in the present study. A customized modular instrument (I-FIT) that uses radiant heaters to simulate idealized firebrands ensures experimental repeatability for combustion experiments. Linear incident heat flux ramps are obtained by controlling the power of the heating element, thus simulating idealized firebrands. An analytical model based on the thermal ignition theory was developed and solved analytically using an integral approach. This model includes convective losses and in-depth penetration of radiation. Radiation was modeled using the P1 approximation. The theoretical model is complemented and validated by experimental data, showing increments of the ignition delay times when the negative slope steepness over time increases for the same heat flux. For given values of the initial incident heat flux on the sample, a critical slope is observed. For slopes steeper than this critical value, ignition is not attained.

Simulation on correlation of pulse ignition sensitivity for hot bridge wire EED

To solve the problem of testing the sensitivity under electromagnetic pulse radiation for a hot bridge wire electro-explosive device (EED), this paper simulated and analyzed the correlation between the critical ignition current under steady and pulse excitation. The simulation results showed that, under single pulse excitation, the critical ignition current of the EED decreases with the increase in the pulse width, and the variation law can be divided into three pieces: adiabatic, transition, and constant; while under pulse train excitation, due to the thermal cumulative effect, the critical ignition current is related to both material properties and excitation parameters. By analyzing the simulation results and considering the thermal ignition theory, the mathematical model of the critical ignition current under pulse excitation was established, and the mathematical model showed that under pulse train excitation, the critical ignition current is relevant not only to the single pulse excitation critical ignition current, pulse period, and duty cycle, but also to the ratio of single pulse and steady excitation critical ignition current and the thermal time constant. It was verified that the errors between the theoretical values obtained from the mathematical model and the results obtained from the simulation were within 2.5%.

A Theoretical Description of the Ignition Conditions for TC17 Alloy in Oxygen-Enriched Atmospheres

ABSTRACT Titanium alloys can be ignited under extreme conditions including high pressure, high temperature, and high-speed friction. A theoretical description of the ignition conditions for titanium alloys is critical for their safe use in aerospace industries. In this study, a chemical-absorption-controlled ignition model for bulk TC17 alloy in oxygen-enriched atmospheres was developed based on Semenov’s thermal ignition theory. The adsorption coefficient, reaction order, and activation energy for the ignition of TC17 alloy were obtained by fitting the model with the experimental critical oxygen pressure and critical ignition temperatures. The fitting results showed that the chemical-absorption-controlled ignition model fitted better with the experimental data compared with the diffusion-controlled ignition model, implying that the ignition process was controlled by chemical absorption rather than oxygen diffusion through the oxidation layer. Moreover, the activation energy for the ignition of TC17 alloy bars was obtained to be 50.01 kJ/mol, which was only less than one-fourth of that of non-isothermal oxidation (231.98 kJ/mol), indicating that the ignition requires much lower activation energy than oxidation. The chemical-absorption-controlled ignition model successfully predicted the ignition temperature of TC17 alloy bars with different diameters with the relative error within 4.41%, demonstrating the validity of the model.

Understanding the role of fire retardants on the discontinuous ignition of wildland fuels

This work reports on a theoretical and experimental study on the role of fire retardant treatments on the discontinuous ignition of wildland fuels. The effect of the concentration of fire retardant in the solution applied to the vegetation is as expected to increase the ignition delay time. We found that the fire retardant modifies the fuel bed effective thermophysical properties, delaying the thermal response of the specimen when subjected to an incident heat flux. Nevertheless, the critical heat flux remains unaltered within the experimental error. We followed a proven approach based on the thermal ignition theory and testing which however has not been previously employed to study fire retardants on wildland fuels. To carry this out, we performed experiments on the I-FIT apparatus, which yields repeatable results and controlled boundary conditions. The theoretical model shows a good agreement with the experimental results, delivering simple expressions for pencil-and-paper calculations of the ignition delay time and analytical tools to evaluate effective fuel properties. These results will help CONAF and other forest services around the world to gain insight on the optimal concentrations and delivery methods for these types of products during wildfire response.

Trigeminal Neuralgia - where are we today?

Introduction: Trigeminal neuralgia (TN) is one of the most crippling facial pain syndromes, which has a significant impact on quality of life. This chronic disorder presents as brief shock-like paroxysmal severe, stabbing pain with rapid onset in the distribution of trigeminal nerve (CNV). The aim of this article was to review the recent literature about the epidemiology, pathogenesis, diagnosis, treatment methods and the important advances in all these fields.Etiology and pathomechanism: The best known and tested theory on the genesis of the trigeminal neuralgia seems to be a nerve compression at the nerve root entry-zone. However there are other theories like the trigeminal convergence-projection theory, the bioresonance hypothesis or the ignition theory that are trying to explain the etiology of TN. Treatment: Available treatment methods consist mainly of medications and surgical procedures. Surgical treatment may be divided into 2 categories: destructive and non-destructive. Among these interventions we can distinguish percutaneous rhizotomy stereotactic radiosurgery and microvascular decompression. All of them are very efficacious, however MVD is approved as the gold standard in the treatment of TN. Botulinum neurotoxin type A injections are not the first line for treatment, but it may be an attractive alternative for classic pharmaceutical or surgical therapy, as it’s safe and effective. Acupuncture is also proposed in recent studies as a valuable treatment option, even though there is little well-designed research.Conclusion: Much remains to be learned about the diagnosis, pathomechanism and methods of treatment of neuropathic pain and the efficacy of each of them. Further evidence-based studies are needed, as the amount of reliable materials is still not sufficient and lots of them have yet to be examined.

Mathematical modeling the ignition of several gas hydrate particles

Gas hydrates are regarded as a high-potential type of alternative fuel for the power industry, transportation, space, and special-purpose equipment. Due to their high conversion rates and safe long-distance transportation by all means of transport, gas hydrates can be widely used as primary and secondary fuels. No one has yet developed a general theory of safe and effective gas hydrate ignition under different thermal conditions reproducing those of promising applications. There are no prediction models for an array of particles with different shapes and porosities. This research aims at studying such conditions. Using the experimental data obtained, we have developed a physical and mathematical model for numerical studies of gas hydrate ignition behavior. Here we consider the most promising compositions of methane-based hydrates. The ignition delay times are determined for the emerging gas-vapor mixture when two and three hydrate particles are heated in variable arrangement schemes and at different distances between them. We also determine how the key factors—size, number, and distance between hydrate particles, temperature of external gaseous medium, component composition of particles, as well as their shape and porosity—influence the ignition speed in the systems of interest. Approximations are obtained to predict the gas hydrate ignition characteristics as a function of the key factors and to extend the modeling results to the thermal conditions of the current and future power plants.

A Mathematical Theory of Ignition by an Incandescent Surface

A Mathematical Theory of Ignition by an Incandescent Surface

A chemically assisted ignition mathematical model based on the theory of thermal ignition

A chemical ignition mathematical model was established based on the analysis of the process of chemical ignition and thermal ignition theory . Then, the model was solved by the method of nets on a computer to explore the mechanism for in-situ combustion ignition with chemical additives. Also, the development course of in-situ combustion ignition was reviewed. In addition, the ignition process by chemical methods was analysed. It was shown that the mathematical model was able to calculate some parameters such as the critical duration of the outer source action and critical energy for ignition. The heat flux that ignites an oil layer is greater than 2.35, when its dimensionless initial activation energy ɛ and initial temperature θ0 are 0.026 and 11. Moreover, the ignition process and temperature distribution of oil sands were described with the model. The results are of great theoretical significance for understanding chemically assisted ignition mechanism in-depth, controlling ignition parameters and guiding chemical additives formulation design and optimization, etc.

Research progress on the self-ignition of high-pressure hydrogen discharge: A review

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.

DEVELOPMENT OF REQUIREMENTS AND SIMULATION OF THE PROCESS OF IGNITION OF EXPLOSION-HAZARDOUS MIXTURE BY A LOW VOLTAGE MEASURING CIRCUIT

The current lack of literature on the safe use of low-voltage measuring circuits in coal mines leads to the fact that they are trying to make unreasonable demands or simply prohibit their use under any far-fetched pretext. At the same time, measuring low-voltage circuits are an important integral component of diagnostics and information content of mining equipment control systems. This is due to the fact that the theory and models of the ignition of a methane-air mine atmosphere (MMA) solve problems in a narrow setting and cannot be used in the general mine case. The article identifies the conditions and parameters for the ignition of the MMA from the low-voltage measuring circuit (NVC),developed criteria for the ignition of the form the NVC, the existing model of the possible ignition process of the MMA from the NVTs is finalized. Currently, there are two theories of ignition of the HCV: thermal and ionic. From the author's point of view, the thermal model of VSH ignition from the electric discharge of the NSC is based on the analysis of the propagation of the temperature wave from some heat source in an inert environment. The thermal ignition model of VHS does not take into account many details of the physics of the combustion mechanism, such as the chain nature of individual acts of chemical interaction, the activation energy of molecules in the formation of active centers, and it is based on postulating some electric discharge. An assessment of the intrinsic safety and the possibility of self-expansion of the NVC flame core has been carried out. The approbation of research at three foreign conferences and the interest of foreign colleagues in them are shown. The article contains links to the state budget topics of the National Academy of Sciences of Ukraine and the numbers of state registration of Ukraine.

Combustion of Magnesium Wires with Oxygen and Water Vapor

ABSTRACT The combustion of magnesium with water is an attractive power source because of the high combustion enthalpies and safety of the materials. For space propulsion, wire-shaped magnesium, which is easy to be fed to the combustion chamber, is considered to be used as a fuel. This study aims to obtain the combustion characteristics of magnesium wire with water for use in spacecraft and oxygen for comparison to combustion behavior. We used a 0.5 mm diameter wire with a length of 40 or 50 mm as fuel. An electric current heated the wire in an enclosed combustion chamber pressurized at 10–100kPa by the oxidizers. The wires continued to be heated until they broke, and then the behaviors were divided into cases where they self-combusted and cases where combustion did not occur. This result revealed the critical conditions of sustainable combustion, which is the same as the ignition temperature in thermal ignition theory. In the case of water vapor, the wire breakage temperature was lower than that in the oxygen case, suggesting that the gaseous products altered the oxide film of the wire. The spectroscopic measurements obtained several excitation spectra and the combustion temperature, which is calculated from a continuous spectrum. In the reaction with water, the measured combustion temperature was lower than the melting point of MgO. As a result, the oxides were deposited on the surface and formed a characteristic fibrous shape rather than dispersed.

A simplified analytical model for radiation dominated ignition of solid fuels exposed to multiple non-steady heat fluxes

Heat fluxes from fires are strongly time-dependent. Historically, the thermal ignition theory in its classical form has neglected this time dependency until recent years, where theories have been developed to include time-varying incident heat fluxes. This article proposes a simplified general model formulation for the heating of solid fuels exposed to four different heat flux behaviors, considering the penetration of radiation into the medium. The incident heat flux cases developed where: Constant, Linear, Exponential and Polynomial, which represent different situations related to structural and wildland fires. The analytical models consider a spatially averaged medium temperature and exact and approximate solutions are presented, based on the critical ignition temperature criterion, which are valid for solids of any optical thickness. The results were validated by comparison with various models presented in the literature, where the model granted in this work was capable to adjust to all of them, especially when high heat fluxes are involved. Therefore, the proposed model acquires a significant engineering utility since it provides a single model to be used as a general and versatile tool to predict the ignition delay time in a manageable way for solid fuels exposed to different fire conditions.

Development of a pyrolysis model for poly(vinylidene fluoride-co-hexafluoropropylene) and its application in predicting combustion behaviors

Pyrolysis and combustion behaviors of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), a promising polymer matrix in lithium-ion polymer battery, are experimentally and numerically investigated. A pyrolysis reaction scheme consisting of three high order consecutive reactions was established based on the thermogravimetric analysis (TGA) measurements and parameterized combining a modified numerical model and Genetic Algorithm (GA). The results show that in the heating rate range of 5–20 K min−1 the peak temperature of pyrolysis increases from 739 to 770 K. After deriving the pyrolysis kinetics, the thermodynamics was further determined by inversely modeling the measured mass loss rate in cone calorimeter tests. By fitting the measured heat release rate, the effective heat of combustion of each gaseous component, the global effective heat of combustion (9.56 MJ kg−1) and the flame heat flux (15 kW m−2) were quantitatively estimated. Reliability of the fully developed model was validated by alternative experimental results which were not utilized in parameterization, and good agreement was found. The collected ignition times in cone calorimeter tests were well predicted by the numerical model employing the measured critical mass flux, 2.87±0.32 g m−2 s−1. By invoking the ignition theory proposed for thermally intermediate solid and the measured ignition data, thermal diffusivity of PVDF-HFP, critical heat flux and critical temperature were assessed to be 3.00 × 10−7 m−2 s−1, 17.13–24.34 kW m−2 and 763.34–794.13 K, respectively.

Закономерности возгорания метана и угольной пыли от электрического источника в горных выработках

Fires and explosions pose the greatest threat in underground mines that use high-voltage electrical grids. The paper presents data on explosions of combustible methane and coal dust mixtures in Russian mines. It is shown that there always exists a high risk of fire resulting from a malfunction in the electrical grid. The research aims at determining the type and parameters of an electric arc, spark or open flame generated at the breaking points of electric conductors which initiate the ignition of a combustible medium. It was found that the commonly known ionic and thermal theories of ignition do not match the present state of knowledge. The methodology consisted in investigating patterns of electric charge generation and transfer up to the point of the mains failure. Regularities of energy processes in the atomic and molecular structure of the conductor material are presented. For the first time ever the concept of transformation of the electromagnetic energy generated in the alternator into photon packets of high-frequency energy is justified. An electron of the conductor atom absorbs a quantum of the generated energy, converts the generated frequency into a high-frequency photon packet and radiates it into the electric grid. It has been found that an electric arc or a spark, acting as a source of ignition for a combustible medium, is an electromagnetic emission of energy in the visible range.