Investigation Of Ignition Research Articles

Alpha heating and avalanche effect simulations for low density proton-boron fusion plasma

The initial interest in p-11B fusion, which produces three (3) alpha particles with total energy of 8.7 MeV, was regained the last few years, due to the important experimental measurements on alpha particle production and theoretical and numerical investigations. The re-evaluation of proton-boron fusion, as an important vector for “aneutronic” energy production, is based on the consideration of the “chain reactions alpha heating effect and the related avalanche effect”, as the important process, for the increase of the fusion species (p, 11B) temperatures, to temperatures corresponding to the optimump-11B fusion cross sections. Investigation of ignition and self-sustained conditions for low density (∼ 1020 m-3) proton-boron fusion plasmas is an interesting study topic for application in magnetic confinement. We use a multi-fluid, global particle and energy balance code, describing the temporal evolution of the physical parameters of the fusion medium, as a function of the initial conditions of density and temperature of the fusion species (p, 11B). For the establishment of the distinct contribution role of the avalanche effect in proton-boron fusion, we explore cases of low (<100 keV) and high (>100 keV) initial p-11B medium temperatures. For these temperature cases, density ratios np /nB > 1between the fusion species (p, 11B) are considered, for the optimization of Bremsstrahlung radiation losses. Simulations using the multi-fluid code in a low density p-11B medium with np /nB > 1, enable the evaluation of the initial temperatures range, which is necessary for the temporal increase of the alpha density, the rapid improvement in the p-11B fusion reaction rate (RR), the temperature rise of the fusion species (p, 11B) and the achievement of higher than 1 Q (Pf /P Brems) values, due to the manifestation of the avalanche effect.In the case of high initial fusion medium temperatures in the range: 150 keV ≤ T in ≤ 350 keV, the chain reactions alpha heating effect and the related avalanche effect contribute to the maintenance and the rise of the fusion species (p, 11B) temperature to high values, for ignition and self-sustained fusion (Q > 1).

Investigation of ignition and flame propagation in an axisymmetric supersonic combustor with laser-induced plasma

The ignition and flame propagation in an axisymmetric supersonic combustor were investigated. The laser-induced plasma was employed to ignite the supersonic inflow with a speed of Mach 2.5 and a total temperature of 1486 K. A direct-connect axisymmetric model scramjet with a fully transparent glass combustor was built, which enabled the circumferential and axial flame propagation in the cavity-based axisymmetric supersonic combustor to be visualized by the high-speed photography from the endoscopic and external views, respectively. An initial flame kernel is produced by the laser-induced plasma and propagates to the cavity leading edge along the axial direction. The establishment of the cavity shear-layer flame facilitates circumferential flame propagation. The circumferential flame propagation is coupled with the axial propagation, eventually generating a loop-shaped flame with a central-hole. Acceleration of the flame propagation can be observed, especially when the global equivalence ratio is increased. A plausible explanation for the flame propagation in the axisymmetric supersonic combustor was found using URANS numerical simulation. The axisymmetric cavity generates a low-speed loop-shaped recirculation region and thickened cavity shear-layer with an appropriate local equivalence ratio, resulting in the simultaneous axial and circumferential flame propagation. The increased temperature in the cavity and the thickened cavity shear-layer during the flame propagation produce a more intense heat release and mass transfer, leading to faster flame propagation.

INVESTIGATION OF IGNITION AND THERMAL DECOMPOSITION OF COAL FUEL, WASTE AND SAWDUST OF DIFFERENT DEGREES OF METAMORPHISM BASED ON MACHINE LEARNING METHODS

An experimental study of the thermal decomposition of coal fuel, waste, and sawdust of different degrees ofmetamorphism using a simultaneous thermal analyzer (STA) has been carried out. The heating rates in STA experiments were set at 5&amp;deg;C/min, 10&amp;deg;C/min, 20&amp;deg;C/min, and 30&amp;deg;C/min. A comparative analysis of machine learning algorithms for predicting the thermal decomposition of coal fuel is shows that a mathematical model based on an artificial neural network model can accurately simulate thermogravimetric (TG) mass loss curves for various fuels and refined products with an average coefficient of determination of 99&amp;#37;.

LES/FGM investigation of ignition and flame structure in a gasoline partially premixed combustion engine

This paper presents a joint numerical and experimental study of the ignition process and flame structures in a gasoline partially premixed combustion (PPC) engine. The numerical simulation is based on a five-dimension Flamelet-Generated Manifold (5D-FGM) tabulation approach and large eddy simulation (LES). The spray and combustion process in an optical PPC engine fueled with a primary reference fuel (70% iso-octane, 30% n-heptane by volume) are investigated using the combustion model along with laser diagnostic experiments. Different combustion modes, as well as the dominant chemical species and elementary reactions involved in the PPC engines, are identified and visualized using Chemical Explosive Mode Analysis (CEMA). The results from the LES-FGM model agree well with the experiments regarding the onset of ignition, peak heat release rate and in-cylinder pressure. The LES-FGM model performs even better than a finite-rate chemistry model that integrates the full-set of chemical kinetic mechanism in the simulation, given that the FGM model is computationally more efficient. The results show that the ignition mode plays a dominant role in the entire combustion process. The diffusion flame mode is identified in a thin layer between the ultra fuel-lean unburned mixture and the hot burned gas region that contains combustion intermediates such as CO. The diffusion flame mode contributes to a maximum of 27% of the total heat release in the later stage of combustion, and it becomes vital for the oxidation of relatively fuel-lean mixtures.

Температура займання та самозаймання найпоширеніших деревних порід териконів

Екологічна небезпека шахтних породних відвалів в умовах урбанізованого середовища є високою. Для її оцінювання у кожному конкретному випадку потрібно проводити екологічний моніторинг для розроблення природоохоронних заходів з мінімізації негативних їх чинників. Наголошено на чинниках, які призводять до самозаймання вугільних відвалів, та на підставі наукових джерел детально описано хімізм досліджуваних процесів. Окиснення і горіння породних відвалів супроводжується значним виділенням водяної пари, яка є мінералоутворюючим середовищем для більшої частини мінералів: сульфатів, гідрокарбонатів, карбонатів, фосфатів, арсенатів. Окрім цього, внаслідок окиснення виділяється вуглекислота, нітроген оксид (IV), який з водою утворює нітратну кислоту. У разі нестачі кисню в осередках горіння в парогазових викидах міститися сірководень, вуглеводні, амоніак, оксид карбону (II). Акцентовано увагу на тому, що важливе значення в процесах окиснення належить сірці. Окиснення вугілля посилюється на дрібних частинках, через збільшення площі поверхні, що доступна для окиснення. Висвітлено, що найнадійнішим способом захисту від самозаймання вугільних відвалів є створення на їх поверхні рослинного покриву. Процес формування рослинного покриву є дуже важливим, адже при цьому відбувається як накопичення важких металів у рослинах, так і зв'язування субстрату їхніми коренями й кореневищами, що зменшує процес вивітрювання та вимивання породи, яка містить велику кількість важких металів. Встановлено показники температури займання та самозаймання зразків деревних порід відвалів вугільних шахт згідно з ДСТУ8829:2019. Дослідження показників займання та самозаймання твердих речовин і матеріалів здійснювали у весняний та літній періоди. Досліджуваними об'єктами були проби листя та деревина з терикону шахти Нововолинського гірничопромислового району (Волинська область, м. Нововолинськ). Встановлено, що для сосни звичайної температура займання становить: +225 °C, а самозаймання +475 °C. Температура займання берези повислої +260 °C, дуба звичайного +275 °C, козячої верби +280 °C, температура самозаймання – берези повислої +470 °C, дуба звичайного +475 °C, верби козячої +473 °C. Температура займання берези повислої, дуба звичайного, верби козячої ніж сосни звичайної робить їх перспективними породами дерев для запобігання самозайманню вугільних відвалів.

Experimental Investigation of the Effect Exerted by a Natural Fire on Wood Material

An experimental investigation of ignition of a wood material under the action of the forest fire front has been carried out in a laboratory to determine the conditions of ignition and combustion. The surface temperatures of samples were measured by means of thermocouples. The dependences have been derived showing the change of the surface temperature of samples exposed to the ground fire front.

Natural Buoyant Turbulent Diffusion Flame near a Vertical Surface

The structure and dynamics of a natural buoyant turbulent diffusion flame near a vertical surface with combustible gas exhaustion are numerically studied by using the FDS model and computer code. The flame is considered near the surface through which gaseous propylene is injected with a prescribed flow rate. Requirements are determined for the grid cell size in the near-wall region, which ensure sufficient spatial resolution of the boundary layer structure. It is shown that the predicted value of the total heat flux at the surface agrees with the measured results. Investigations of ignition and combustion of a vertical plate of non-charring thermoplastic (polymethylmetacrylate) with allowance for the material pyrolysis reaction show that the ignitor parameters determine the duration of the transient period, but weakly affect the growth of the heat release rate and the height of the pyrolysis region at the stage of developed burning. Significant effects of the ignitor shape, size, and temperature, as well as lateral entrainment of air on the velocity of the upward flame spread rate over the plate surface and on the shape of the pyrolysis front are revealed. The existence of critical parameters of the ignitor separating flame decay from developed burning is demonstrated. Three flame spread regimes with different pyrolysis front shapes are identified.

Experimental Investigation of Ignition of Combustible Gas Mixtures by Friction Sparks

Experimental Investigation of Ignition of Combustible Gas Mixtures by Friction Sparks

Conditions of Stable Ignition of Coal-Water Slurry Containing Petrochemicals Based on Carbon Residue of Tire Pyrolysis

The results of experimental investigations of ignition of single droplets (radius of 0.5–1.5 mm) of coal-water slurry containing petrochemicals (CWSP) in a stream of air (oxidizer) with a temperature of 600–1200 K and velocity of 0.5–5 m/sec are presented. Carbon residue (particle sizes of 80–100 μm) from pyrolysis of used automobile tires, water, and exhausted engine, turbine and transformer oils were used as the main fuel components. The times of ignition delay and complete combustion of CWSP droplets were determined atvarying concentrations of the components in the ranges corresponding to modern combustion and burner devices. The conditions at which stable combustion of CWSP is initiated were determined.

Investigation of ignition and volatile combustion of single coal particles within oxygen-enriched atmospheres using high-speed OH-PLIF

To study devolatilization, ignition, and volatile combustion processes of single coal particles at a fundamental level, a flat flame burner was designed to provide oxygen-enriched exhaust gas environments at elevated temperatures and varying gas compositions. In one set of experiments coal particles were carried by a central jet using a gas mixture of the same composition as the flat flame. By this means a homogenous and connected flame was generated. At the instant when single coal particles transited this stationary flame, start of particle heat-up was well defined. This allows studying start of ignition more accurately compared to the other set of experiments where an inert carrier gas jet was used for transportation of coal particles. Heat-up and ignition were retarded temporally due to precedent mixing between inert gas and ambient flue gases. Coal particles with a high percentage of volatiles (36wt%) and a particle distribution ranging from 90 to 125µm were used. Coherent anti-Stokes Raman spectroscopy (CARS) measurements were performed to characterize ambient gas phase temperatures. By high-speed laser-induced fluorescence, imaging of OH-radicals ignition and volatile combustion was visualized for individual coal particles. Reaction zones surrounding each coal particle and the corresponding distances to coal particles were identified. This distance depended strongly on oxygen concentration of the ambient flue gas atmosphere. In addition to an improved phenomenological understanding the data may serve for model validation.

Numerical Investigation of Ignition in a Transient Turbulent Jet by Means of a PDF Method

A numerical investigation is carried out to study the ignition of a hydrogen/air mixture by a hot turbulent jet. A stand-alone probability density function method is used to model the turbulent reacting flow. In order to reduce the computational cost of chemical reactions, a reaction diffusion manifold technique is applied for an automatic mechanism reduction. The ignition delay time and the ignition length are investigated with respect to various inlet temperatures as well as the nozzle diameter and the jet inlet velocity. The simulation results reveal that immediately after a discharge of the hot exhaust gas from the nozzle, the hot gas cools down due to the strong turbulent mixing with the cold ambient mixture. However, further downstream where the turbulent mixing intensity is reduced, the heat release due to chemical reactions overcomes the heat dissipation, which eventually leads to ignition.

Experimental study of burning behaviors of intumescent coatings and nanoparticles applied on flaxboard

This article presents an experimental investigation of ignition and burning behaviors of intumescent coatings and nanoparticles applied on flaxboard using the cone calorimeter, single burning item (SBI) and reduced scale (one-third) ISO room. The effects of intumescent coatings and nanoparticles on time to ignition (TTI), mass loss rate (MLR), heat release rate (HRR), production of toxic gases (carbon monoxide and smoke) were investigated. The performance of intumescent coatings in under-ventilated condition was examined by performing tests in the one-third ISO room with reduced opening sizes. Results in the cone calorimeter and SBI indicated that (1) there is a substantial increase of TTI and decrease of MLR/HRR by intumescent coatings and (2) the addition of nanoparticles results in a further increase of TTI as well as a decrease of MLR/HRR owing to increased stability of the char. Tests in the one-third ISO room showed that although the intumescent coatings reduce the HRR the reduction is much less substantial than that in the cone calorimeter or SBI.

Investigation of ignition of particle-gas flow based on the hot-spot ignition model

Electric-spark ignition of flow of an aluminum particle-air mixture in a channel with a sudden expansion was studied experimentally using the model of hot-spot ignition. The critical radius of the initial site of ignition was determined, the dynamics of the process was studied, and the effect of turbulence intensity on the development of the hot spot was established.

Theoretical investigation of ignition and detonation of coal-particle gas mixtures

A mathematical model of ignition of a coal-particle gas suspension is developed within the framework of mechanics of reacting heterogeneous media. Some qualitative features are studied, which reveal different typical variants of heat dynamics of the mixture: heterogeneous ignition caused by the coke residue ignition reaction, homogeneous ignition induced by volatile oxidation in the gas phase, and hybrid ignition due to the simultaneous effect of surface and volume reactions. Verification of the model is performed using available experimental data on ignition delay times for coal-particle suspensions in air and oxygen behind reflected shock waves. The model is extended to detonation processes in the suspension, verified by experimental data on the relation between the propagation velocity and initial particle concentration. Stationary detonation regimes are studied, and specific features of detonation structures are discussed.

Investigation of Ignition of Liquid Propellant in Reservoir in Regenerative Liquid Propellant Gun Trials

It is important to understand the internal ballistic processes for the development of regenerative liquid propellant guns (RLPGs). A 30 mm RLPG test fixture was developed and firing trials were conducted to study the performance of the gun. During the trials, sometimes, combustion ignition in the reservoir took place resulting in substantial damage to the injection piston. This paper highlights the possible causes of this combustion and offers suggestions. regarding improvement in the design. An elaborate instrumentation set-up which could pinpoint the specific conditions leading to failures is suggested.

Investigation of ignition by composite sparks under high turbulence intensity conditions

In order to clarify the mechanism of ignition process by composite sparks under high turbulence intensity conditions, flame kernel development was observed and the effects of turbulence intensity and energy distribution of composite sparks on the minimum ignition energy were studied, using an ignition device which could vary energies of a capacitance component and the following glow discharge (subsequent component) independently. Mutual collision of jets emanating from four nozzles fitted on a combustion chamber provided turbulent fields with minimum, mean flow near the spark gap. Turbulence intensity ranges from 2.53 m/s to 9.87 m/s. In addition, a numerical simulation was made to study the mechanism of flame kernel development in its early stages. The experimental results indicate that the intitial stages of flame kernel development are the same as those in laminar conditions. Transformation of the laminar flame kernel into a turbulent flame kernel occurs earlier as turbulence intensity increases. The calculated results suggest that this tendency is associated with a degree of suppression of turbulence by a spherical shock wave initiated at the first onset of spark. Ignition ability was found to be much improved by the addition of the subsequent component to the capacitance component. This effect was pronounced in the case of turbulent mixtures of high intensity.

A Statistical Investigation of Ignition in a Fuel Spray using a Shock Tube.

In order to obtain a general aspect of the spontaneous ignition in a fuel spray injected in compressed air at high temperature, which takes place usually in diesel and pulse jet engines, an experimental method using a shock tube is developed. A shock wave driven by high-pressure He gas propagates in the air in the low-pressure tube and reflects at a shock tube end. Through application of the pressure of the shock wave at reflection, n-octane fuel is injected into the air behind reflected shock waves in the shock tube. The fuel injection space is optically separated into 5 regions in the vertical direction, and the induction period of spontaneous ignition in each region is separately observed. As the induction period fluctuates markedly, the measured results are treated statistically and analyzed on the basis of the stochastic ignition theory.

The use of the setchkin apparatus—mass spectrometry in the investigation of ignition and burning of flame retarded polystyrenes

AbstractA review is given of the possibilities for the use of the Setchkin apparatus combined with mass spectrometry in the investigation of the gaseous products of the thermo‐oxidative decomposition and burning of flame‐retarded polystyrenes, with simultaneous determination of the characteristics of ignition. Information on flame‐retardants in polystyrene, and their effect on the inhibition of burning in the gaseous phase were provided by mass fragmentation analysis of the main components of decomposition and burning.

Shock-tube investigation of ignition in methane-oxygen-argon mixtures

Shock-tube investigation of ignition in methane-oxygen-argon mixtures