Air Ignition Research Articles

Investigating the influence of pressure on the ignition and oxidation behavior of EV33 alloy

The study investigates ignition and oxidation behavior of Mg-3Nd-3Gd-0.2Zr-0.2Zn (wt.%) (EV33 alloy) in air and varying pressure. EV33 exhibits easy ignition in air but not under specific pressure conditions. Surface microstructure evolution and detailed discussion of ignition mechanisms using oxidation mechanism and residual stress of oxide film are presented. Findings suggest a correlation between alloy ignition and oxide film rupture. Surface oxidation film rupture is the direct cause of ignition in magnesium alloys, and this phenomenon has been observed and documented for the first time. The residual stresses calculated under atmospheric conditions and at pressures of 0.05 MPa, 0.1 MPa, and 0.15 MPa (with air as the pressure medium) are as follows: 0.282 GPa, 0.561 GPa, 2.271 GPa, and 5.242 GPa.

Influence of Voltage Rising Time on the Characteristics of a Pulsed Discharge in Air in Contact with Water: Experimental and 2D Fluid Simulation Study

In the context of plasma–liquid interactions, the phase of discharge ignition is of great importance as it may influence the properties of the produced plasma. Herein, we investigated the influence of voltage rising time (τrise) on discharge ignition in air as well as on discharge propagation on the surface of water. Experimentally, τrise was adjusted to 0.1, 0.4, 0.6, and 0.8 kV/ns using a nanosecond high-voltage pulser, and discharges were characterized using voltage/current probes and an ICCD camera. Faster ignition, higher breakdown voltage, and greater discharge current (peak value) were observed at higher τrise. ICCD images revealed that higher τrise also promoted the formation of more filaments, with increased radial propagation over the water surface. To further understand these discharges, a previously developed 2D fluid model was used to simulate discharge ignition and propagation under various τrise conditions. The simulation provided the spatiotemporal evolution of the E-field, electron density, and surface charge density. The trend of the simulated position of the ionization front is similar to that observed experimentally. Furthermore, rapid vertical propagation (<1 ns) of the discharge towards the liquid surface was observed. As τrise increased, the velocity of discharge propagation towards the liquid increased. Higher τrise values also led to more charges in the ionization front propagating at the water surface. The discharge ceased to propagate when the charge number in the ionization front reached 0.5 × 108 charges, irrespective of the τrise value.

Experimental analysis of dual-stage ignition biomass downdraft gasifier based on various gasification media for the generation of high-quality producer gas

A dual-stage biomass ignition downdraft gasifier has been set-up with the four experimental approaches such as hot air ignition, hot air plus producer gas ignition, oxygen ignition and oxy-steam ignition approach. The experimental unit has been tested at electrical resistance loads of 15.24 kW, 23.62 kW, 27.43 kW, 32 kW and 38.86 kW. This unit provides a useful energy output of nearly 95.37 % in oxy-steam ignition approach at maximum load. The gasification medium is provided at the combustion zone as well as in pyrolysis zone for the complete and partial combustion in the respective regions through the installed nozzles. In the oxy-steam ignition approach, the enhanced quality of producer gas generates, which contains 94 % combustible gases in the producer gas. The Higher Heating Value (HHV) is 12.317 MJ/Nm3, whereas the biomass consumption rate is attained 21 kg/h at the highest resistive load with 1430–1590 °C grate temperature under the oxy-steam ignition approach. The proportion of tar is obtained 0.2 mg/Nm3 after the syngas cooling and cleaning arrangement with moisture content of 6 %, while a significant improvement of 21.26 % has been noted in efficiency under the oxy-steam ignition approach.

Euler–Lagrange numerical simulation of a kerosene droplet mist ignition in air using analytically reduced chemistry

High altitude relight is a critical aspect of the aeronautical engine certification and may be addressed with the numerical simulation of two-phase ignition. However, such configurations are stiff and combined with local evaporation may lead to numerical issues. This paper provides several methods to perform two-phase ignition simulations using analytically reduced chemistry in the context of unstructured large Eddy simulation and Euler–Lagrange formalism. Firstly, an exponential formulation combined with a local and dynamic sub-cycling of the stiff chemistry is demonstrated to allow stable integration at the flow time step. Secondly, a particle-bursting method is applied to limit the impact of stiffness induced by the Lagrangian point-source approach in fine meshes. These methods are then applied in the simulation of ignition of a mono-disperse, multi-component kerosene spray in air. The use of the analytically reduced chemistry model enables us to describe in detail the chemical structure of the flame kernel during its formation. Moreover, local increase of fuel concentration is observed as the ignition proceeds which has a large influence on the combustion processes and the flame kernel development.

Validation of the Townsend criterion for ignition of volume gas discharges

An eigenvalue problem governing ignition of volume discharges is formulated in the drift approximation with account of photoionization and the presence of multiple ion species with various reactions. The Townsend ignition (self-sustainment) criterion is deduced by partial integration of this eigenvalue problem neglecting the photoionization, and, in the case of electronegative gases, also the detachment. The Townsend criterion is applied to three examples of discharge ignition in high-pressure air, two of them referring to negative coronas in concentric-cylinder and point-to-plane configurations and one to a configuration with weakly nonuniform electric field. The comparison of the results obtained from different forms of the Townsend criterion with those given by the accurate numerical solution of the full eigenvalue problem shows that the neglect of the diffusion of the charged particles produces an error in the ignition voltage of the order of or less. The effect of photoionization for these configurations is also weak as expected. The lower and upper estimates of the effect of negative ions over the ignition voltage are obtained from different forms of the Townsend criterion. A form of the Townsend criterion, which employs an effective attachment coefficient in air and takes into account, in an approximate way, also the detachment, gives a virtually exact value of the inception voltage in all the cases considered. Practical recommendations are given on when one can use the Townsend self-sustainment criterion, and when one should resort to a numerical solution of the general eigenvalue problem governing discharge inception.

Effects of K2SiF6 on Ignition and Heat Release Characteristic of Nano-Sized Aluminum Powders

ABSTRACT This study investigates the effect of potassium fluosilicate (K2SiF6) on the ignition and heat release characteristics of n-Al50, n-Al100, and n-Al800. It is found that K2SiF6 can effectively improve the ignition and heat release characteristics of nano-aluminum powder (n-Al). This is because K2SiF6 effectively increases the reaction rate. The heat release characteristics of the n-Al/K2SiF6 mixture are improved as the particle size of aluminum powder decreases and the heating rate increases. However, when the particle size reaches a certain level, the enhancement effect will become smaller and smaller. The study revealed that the addition of K2SiF6 influences the ignition delay time, reaction, and combustion products of the n-Al/K2SiF6 mixture. A small amount of K2SiF6 can greatly reduce the ignition delay time of nano-aluminum powder. With the increase of K2SiF6 content, the ignition delay time of n-Al50 decreases first and then increases, while the ignition delay time of n-Al100 and n-Al800 decreases continuously but the extent of this reduction progressively diminishes. The morphology and composition of the combustion products were analyzed. This paper found that K2SiF6 fluorinates the oxidized shell of aluminum, thereby promoting its ignition and combustion. The influence mechanism of K2SiF6 on n-Al ignition in air is discussed.

Effect of Phosphorus and Chlorine Containing Plasticizers on the Physicochemical and Mechanical Properties of Epoxy Composites

The possibility of using tris(2-chloroethyl) phosphate, tris(1-chloro-2-propyl) phosphate and tris(4-methylphenyl) phosphate as effective plasticizers for epoxy polymers has been studied. As a result of the research the optimum content of plasticizers (40 parts by mass) has been determined, which has the best effect on the strength and fire safety properties of epoxy composites. Modification of the epoxy polymer with presented plasticizers influences carbonization process increasing char yield and reducing the amount of volatile thermolysis products released into the gas phase, thus improving fire safety parameters of epoxy composites, reducing mass loss on ignition in air from 78 to 2–9% and increasing limiting oxygen index (LOI) values from 19 to 25–31% by volume, giving good fire protective properties to epoxy composites (UL-94 rating—V-0/V-1). The thermo-protective properties and the structure of the char formed by polymer combustion have been studied and the correlation between the thermo-protective properties of the char and the combustibility of the composite has been determined. Furthermore, the behaviour of the modified composite during high rate pyrolysis has been analyzed.

Optical pressure sensing at MHz rates via collisional line broadening of carbon monoxide: uncertainty quantification in reacting flows

An optical method for high-speed line-of-sight pressure measurements using infrared laser absorption spectroscopy is presented with detailed uncertainty analysis related to thermodynamic and compositional variation in combustion environments. The technique exploits simultaneous sub-microsecond sensing of temperature and mole fraction to extract pressure from collisional line broadening at MHz rates. A distributed-feedback quantum-cascade laser near 5 upmu m in a bias-tee circuit is used to spectrally resolve multiple rovibrational transitions in the P-branch of the fundamental band of carbon monoxide, which may be seeded or nascent to reacting flows. A comprehensive approach for estimating collisional line broadening in complex combustion gas mixtures is presented. Uncertainty is quantified for a wide range of conditions, reflecting different fuels, equivalence ratios, reaction progress, and combustion modes (deflagration and detonation), which influence gas composition and temperature. The sensor was evaluated for accuracy and precision in both a high-enthalpy shock-tube facility in hydrocarbon–air ignition experiments and behind ethylene–oxygen detonation waves in a detonation-impulse tube facility at temperatures from 1500 to 3000 K and pressures from 0.5 to 10 bar. Pressure measurements were compared to measurements by piezoelectric pressure transducers and to theoretical estimates from normal-shock and Chapman-Jouguet simulations. The high-speed path-integrated optical pressure measurement offers an alternative to traditional electromechanical transducers that are constrained to values at wall boundaries and have proven unreliable in some harsh reacting flows.

Experimental study on non-isothermal oxidative characteristics and kinetics of methane in accelerating rate calorimetry tests

The non-isothermal oxidative characteristics and kinetics of natural gas have important effects on performance of gas reservoir combustion, which directly determines temperature distribution, playing a significant role in hydrogen generation boundary. In this paper, the non-isothermal oxidation of methane, as main component of natural gas, is in depth analysis, which is rarely studied. At first, the non-isothermal oxidative characteristics at different pressure, oxygen/methane ratio, and debris were investigated by accelerating rate calorimetry (ARC). Afterwards, the non-isothermal oxidation kinetic parameters were analyzed and calculated. The difference of onset self-exothermic, ignition temperature, and kinetics parameters under different conditions were extraordinarily emphasized, aiming achieving successful and stable gas reservoir combustion for high efficiency hydrogen production. The results indicated that there is no even self-exothermic phenomenon at depleted reservoir condition (7.1–9.8 MPa and 100–150 °C), and the minimum starting self-exothermic temperature ignition temperature of methane oxidation are 220.6 °C and 312.7 °C. The pressure did not have effect on oxidation temperature in methane oxidation while did in catalytic oxidation. It was observed that rock debris has catalytic effect on methane oxidation suggested by obviously lower onset self-exothermic temperature detected and significantly smaller activation energy calculated in oxidation process of methane with debris. Moreover, the oxidation reaction rate of methane with debris is lower than that of methane, assisting more methane undergoes a more thorough HTO reaction conducive to combustion and decreasing the possibility of explosion in the injection air ignition process. According to the results obtained by ARC tests, we suggested that the near-wellhole places of gas reservoirs should be better heated over 313 °C for successfully achieving stable combustion. Some new knowledge got from this study is conducive to achieve rapid and stable combustion, thus achieving high-efficiency hydrogen generation.

Accurate and precise measurement of uranium content in uranium trioxide by gravimetry: Comparison with isotope dilution mass spectrometry and its uncertainty estimation

Gravimetric measurement of U content in UO3 with ignition in air has been investigated. The ignition temperature, ignition time and aliquot sample mass are optimized as 900 °C, 60 min, and 1 g, respectively. The method is validated by isotope dilution mass spectrometry (IDMS) with uncertainty estimation. The obtained result by gravimetry is 0.78287 ± 0.00051 g/g (k = 2) and agreed with IDMS value. It has been found that U in UO3 can be measured accurately and precisely by gravimetry.

Light emission of Zr-based bulk metallic glass during high-speed cutting: From generation mechanism to control strategies

Light emission is a unique machining feature during high-speed cutting of Zr-based bulk metallic glass (BMG), which significantly deteriorates the machining quality and efficiency. However, its generation mechanism is still unclear. In this study, the light emission of Zr-based BMG during high-speed cutting was quantified photometrically, and its correlation with cutting energy was investigated. The chemical composition change and the formation process of luminescent particles were analyzed. The generation mechanism of light emission was subsequently revealed. It was found that the light emission is due to the spontaneous ignition in air of Zr-based BMG particles with large specific surface area, produced by ductile tearing of the bottom of the chip. The friction energy of the tool-chip interface flowing into the chips is the dominant factor that triggers particle combustion. Therefore, from the perspective of controlling tool wear, machining strategies with controllable light emission were proposed. In order to suppress light emission, the primary method is to decrease the cutting speed and feed. The second is to improve the chip removal ability and the wear resistance of the tool. Cutting oil is only effective for suppressing light emission at low cutting speeds, while liquid nitrogen is not suitable for cutting Zr-based BMG due to increased tool wear. The findings of this work contribute to a deeper understanding of the generation mechanism of cutting features in glassy metals, and provide guidance for high-speed cutting process optimization of Zr-based BMG.

Effect of particle morphology on reactivity, ignition and combustion of boron powders

Spherical boron powders with 2–20 µm sized particles were prepared by ball milling commercial boron in the presence of emulsion with hexane and acetonitrile serving as the continuous and droplet phases, respectively. A small amount of Fluorel®, a fluorocarbon serving as binder was dissolved in the acetonitrile. For comparison, an irregularly-shaped boron powder was prepared by milling commercial boron with the same acetonitrile/Fluorel® solution. Reactivity of the spherical boron powders was compared to those of milled and as received commercial powders with irregularly-shaped particles. Thermo-gravimetric measurements in Ar/O2 gas flow showed that milling boron with or without Fluorel® shifts the onset of boron oxidation to lower temperatures. The rate of initial oxidation was greater for the finer spherical powders compared to coarser spheres and to irregularly shaped milled powder. The milling did not appreciably change the activation energy of oxidation of boron and the observed accelerated oxidation was attributed to its increased specific surface area. Two of the finer prepared spherical powders could be ignited when coated on an electrically heated filament in the temperature range of ca. 600 – 1000 °C. Commercial powders, irregularly-shaped milled powder, and coarser spherical powders did not ignite. All boron powders aerosolized and ignited in an enclosed vessel in air generated similar pressures. In another experiment, blended boron and potassium nitrate powders were heated to ignition in room air using a laser beam. The ignition delays for the blends made with spherical powders were substantially shorter vs. similar blends with commercial powder. Combustion of the blends with spherical powders was more vigorous than with commercial boron. Particles were ejected more rapidly, and had shorter apparent burn times.

Methane-Air Plasma-Assisted Ignition Excited by Nanosecond Repetitively Pulsed Discharge: Numerical Modeling and Effect of Inert Gas.

Plasma-assisted ignition and combustion are promising approaches for controlling ignition enhancement and flame stabilization. The global loosely coupled plasma-assisted combustion kinetic model has been established by combining the ZDPlasKin and ChemKin codes, which is employed to numerically investigate the effects of the inert gas-diluted methane–air nanosecond repetitively pulsed (NRP) plasma on the ignition process. The results indicate that addition of the inert gas is conducive to increasing the chemical reactive species densities in the methane–air NRP discharge plasma. The addition of inert gases affects the generation pathways of plasma species and their corresponding contribution rates. Compared with the methane–air plasma, the dilution of inert gases shows obvious effects on reducing ignition delays, and the dilution of He and Ar decreases the ignition delays by 58.0 and 84.0%, respectively. CH3 + O2 = CH3O + O and H + O2 = O + OH are the dominant conducive reactions in the methane–air ignition chemistry. Moreover, the dilution of inert gases has considerable influences on the normalization sensitivity coefficients, especially for the reaction of H + O2 = O + OH.

Research and method of air burst fracturing

At present, shale gas pressure fracturing volume development technology tends to be mature, shale gas backlog fracturing ends and enters the trial production stage. Due to the improper control of oil nozzle or its causes, the output drops sharply, or the drainage in the production process makes the funnel effect near the wellbore zone, resulting in the closure of the main fracture passage near the wellbore. However, the far-end complex sealing network structure produced by volume fracturing technology is still not fully closed, or secondary fractures occur in the absence of support for the original wellbore fractures or new complex fractures occur in the vicinity of the wellbore. The simple use of high-energy gas fracturing requires low cost, safety and simple and efficient characteristics, and the requirements for surface equipment are not too high. Existing methods mainly include well testing, sand washing by coiled tubing, gas lifting by coiled tubing, wellbore plugging removal, pumping and drainage by supplementary pressure well operator, etc. They can not fundamentally solve the need of closing or reopening new fractures in wellbore, and can not make new complex unclosed fractures near wellbore zone (without secondary fracturing). If the investment of surface equipment for secondary fracturing is similar to that of the first volume fracturing, and the investment is similar, the more complex situation will arise because of filtration and other reasons. At present, low concentration methane in air and wellbore is used to oxidize and exothermic to produce CO2 and H2O, and release energy at the same time. Temperature and pressure are the main means of energy in limited space. High energy gas formed after volume work can help to reopen the original fracture and form a new type of high energy gas fracturing method by means of air ignition and explosion, because the effect of high energy gas fracturing is not affected by stress, new cracks can be produced, and this crack can avoid overlapping with previous cracks. In particular, it can be pointed out that due to the improvement of thermal recovery of heavy oil and other means, the ground operation equipment has the commonality, and reasonable optimization of the construction plan can achieve the established purpose.

Distribution of Aluminum Clusters and Their Ignition in Air during Dispersion of Aluminum Nanoparticles in a Shock Wave

The dispersion of oxidized Al nanoparticles into clusters by rapid heating in a shock wave has been studied. Cluster distribution characteristics were calculated as a function of the parameters of the initial nanoparticle distributions and the nature of the interaction of deformation waves with the nanoparticle shell and core. The studies were carried out using the author’s proposed resonance mechanism for the dispersion of the liquid core of a nanoparticle by the shock pulse from the destruction of the solid oxide shell. The ignition of Al nanoparticles after dispersion in air was analyzed using the previously described kinetic oxidation mechanism with the evaporation of clusters taken into account. Initial distributions of nanoparticles and their ignition times are validated against published experimental data.

Synthesis and Study of Properties of Organic and Carbon Xerogels from Abies Bark Tannins

Methods of organic and carbon xerogels synthesis based on the use of condensed tannins isolated from abies bark were developed. Organic gels were synthesized by sol-gel condensation of tannins with formaldehyde in a solution of ethanol in the presence of catalysts (NaOH or HCl). The final gelation products were dried by alternating low (-18 – -40 °C) and room temperature to obtain tanninformaldehyde (TF) xerogels. FTIR study indicates that the formation of xerogels was accompanied by crosslinking reactions mainly due to the formation of carbon-carbon and alkyl ether bonds. Using the method of thermogravimetry, it was found that organic TF xerogels are thermally stable up to a temperature of 295 °C and they are resistant to ignition in air at temperatures up to 600 °C and can be used as thermo- and fire-retardant materials. Carbon tannin-formaldehyde xerogels were obtained by carbonization of organic xerogels at 800 °C in an argon atmosphere. The porous structure and surface morphology of organic and carbon xerogels was studied by BET- and SEM–methods. A significant development of the specific surface area (to 483–524 m2/g)as a result of the organic xerogels carbonization was established. Using SEM, it was shown that in carbon gels a spatially cross-linked structure of polymer chains consisting of 5-10 nmsized globule particles forming nanometer-sized pores is retained

Distribution of Aluminum Clusters and their Ignition in Air during Dispersion of Aluminum Nanoparticles in a Shock Wave

Distribution of Aluminum Clusters and their Ignition in Air during Dispersion of Aluminum Nanoparticles in a Shock Wave

Software for numerical simulation of the combustion of aluminum particles suspended in air

This paper presents a computer model for studying the processes of ignition and combustion of air suspended aluminum particles, based on a system of differential equations of the gas phase balance and the probability density function for temperature and particle size. The model is implemented as software for a two-dimensional non-steady state case. A new implicit difference scheme consisting in two - and three-point approximations for the first and second derivatives is proposed and implemented. A set of calculations is performed and the results of the reacting mixture characteristics distribution, the areas of the maximum heat release and their relationship with the most air suspension probable state are presented.

Epoxy composites with increased operational characteristics, filled with dispersed mineral fillers

The aim of this work is to increase the physicochemical, deformation and strength properties and to reduce the combustibility of composites on the base of epoxy resin by introducing a oligo(resorcinophenyl phosphate) with terminal phenyl groups Fyrolflex - modifier of polyfunctional action, and disperse mineral fillers – diorite and chromite. Result of the studies established that the optimum amount of modifier in the composition of the epoxy resin is 40 mass parts, which provides an increase in the operational properties of the composites: the breaking stress at bending increases by 2 times, the breaking stress at compression increases by 28%, the impact strength increases twice, while the modulus of elasticity and hardness of composites slightly decrease. The addition of modifier into the epoxy polymer provides an increase in heat resistance from 86 to 132–156 °C, also it improves the thermal stability of the composite, which manifests itself in a shift from the initial temperature to higher temperatures (from 200 to 230 °C), while it is noticed furthermore that yield of carbonized Structures was risen from 40 to 54%, providing less release of volatile pyrolysis products into the gas phase, which leads to the decrease in flammability of the epoxy composite and it can be shown in the reduction of its loss in mass while cauterizing in air from 78 to about 4.7% and an increase in the oxygen index from 19 to 28% by volume what transfers the material into class with low flammability. The rational content of diorite and chromite (100 parts by weight of chromite and 50 parts by mass of diorite) is chosen as a filler, which ensures an increase in physical and mechanical characteristics and a reduction in the cost of production: the breaking stress increases by 15–30% and the elastic modulus at bending increases 3.5–4.5 times, the breaking stress increases by 35%, and the tensile modulus by 50–240%, the hardness increases by 68–95%, while the impact strength remains at the level of the unfilled plasticized composite. In addition, it is proved that the addition of both diorite and chromite provides an increase in the thermal and heat resistance of epoxy composites, also lowers combustibility of the epoxy composite: the weight loss at ignition in air is reduced to 1.2–2.2% and the oxygen index rises from 28 to 30–35% by volume, thus the material does not support combustion in air and belongs to the class of hardly flammable. The study was carried out with the financial support of a grant for young scientists of the SSTU named after Gagarin Yu.A. (project SGTU-287).

Effects of Vibrational Excitation on Nanosecond Discharge Enhanced Methane–Air Ignition

A zero-dimensional model of nonequilibrium plasma-assisted methane–air ignition at atmospheric pressure is presented to study the effects of vibrationally excited species on ignition enhancement. It is found that the vibrationally excited species , , and especially can be generated efficiently when the reduced electric field strength is below 100 Td in a stoichiometric methane–air mixture. The results show that vibrationally excited species could not effectively enhance ignition via kinetic pathways due to their fast relaxation, but instead via thermal pathways through gas heating. Despite this, the thermal enhancement is much less effective than the kinetic effects due to plasma, indicating that the production of vibrationally excited species consumes the energy deposited in the plasma, and thus limits the production of more active particles, such as O, , and . A sensitivity analysis is conducted to further understand the detailed chemistry of the ignition enhancement involving vibrational excitation. The results show the reactions and have significant inhibitive effects on ignition enhancement in discharge conditions with a fixed plasma energy. The reactions involving the production of O and show promotive effects in enhancing ignition because they accelerate the radical production through chain branching reactions. Finally, the calculated ignition delay times at different temperatures show that the ignition enhancement by nanosecond discharge and the promotive effect of N are more significant at low temperatures.