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Numerical investigation of the effects of turbulence on the ignition process in a turbulent MILD flame

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Acta Mechanica Sinica 2021年第8期37卷 1299-1317,I0002页

作者： Xiang Qian Hao Lu Chun Zou Hanlin Zhang Shujing Shao Hong Yao State Key Laboratory of Coal Combustion School of Energy and Power EngineeringHuazhong University of Science and TechnologyWuhan 430074China

In this study,we conduct three-dimensional nonlinear large-eddy simulation to investigate the interaction between turbulence and reaction during the initial ignition process of a turbulent methane/hydrogen jet-in-hot-coflow flame under moderate or intense low-oxygen dilution(MILD)condition.Special focus has been placed on the spatial development of the flame and the temporal evolution of representative ignition spots that characterize the range of ignition behaviors observed in the case.Results show that the ignition process of the flame consists of four consecutive phases.ignition occurs initially with relatively lean mixtures,and compared to the corresponding homogeneous stagnant adiabatic combustion,the loss of radical species associated with flow transportation causes a delay in ignition.The initial ignition spots formed during the autoignition phase provide sufficient conditions for the stabilization of the flame,including the provision of a variety of key radicals.Results also show that the flow convection accompanying the hot coflow dominated the slow flame propagation,and the turbulent mixing is of great importance for rapid flame propagation.These findings will broaden our knowledge of MILD combustion and provide useful insights into advanced ignition contr.

关键词： MILD combustion ignition Large-eddy simulation

In depth fusion flame spreading with a deuterium-tritium plane fuel density profile for plasma block ignition

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Chinese Physics B 2012年第12期21卷 317-321页

作者： B.Malekynia S.S.Razavipour Department of Physics Gachsaran BranchIslamic Azad University

Solid-state fuel ignition was given by Chu and Bobin according to the hydrodynamic theory at x = 0 qualitatively. A high threshold energy flux density, i.e., E＊ = 4.3 × 10^12 J/m2, has been reached. Recently, fast ignition by employing clean petawatt-picosecond laser pulses was performed. The anomalous phenomena were observed to be based on suppression of prepulses. The accelerated plasma block was used to ignite deuterium tritium fuel at solid-state density. The detailed analysis of the thermonuclear wave propagation was investigated. Also the fusion conditions at x ≠ 0 layers were clarified by exactly solving hydrodynamic equations for plasma block ignition. In this paper, the applied physical mechanisms are determined for nonlinear force laser driven plasma blocks, thermonuclear reaction, heat transfer, electro,ion equilibration, stopping power of alpha particles, bremsstrahlung, expansion, density dependence, and fluid dynamics. New ignition conditions may be obtained by using temperature equations, including the density profile that is obtained by the continuity equation and expansion velocity. The density is only a function of x and independent of time. The ignition energy flux density, Et＊, for the x ≠ 0 layers is 1.95 × 1012 J/m2. Thus threshold ignition energy in comparison with that at x =0 layers would be reduced to less than 50 percent.

关键词： plasma block solid-state fuel ignition expansion

On the Use of Accurate ignition and Combustion Models in Internal Ballistics Gun Codes

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火炸药学报 2018年第2期41卷 117-121页

作者： Clive Wooclley QinetiQ Fort Halstead Sevenoaks Kent TN14 7BP United Kingdom

The desire for increased performance from guns is driving the charge designer towards charges that present challenges to numerical modelling.There is a pressing need for accurate,validated ignition and combustion models that can be used to predict the performance of advanced charges and ensure pressure waves are not developed or,if they are,then they can be managed.This paper describes efforts to model complex charge designs using a two-dimensional axi-symmetric multi-phase flow internal ballistics model.

关键词： internal ballistics ignition combustion moclelling guns modular charges pressure waves

Effect of CaO addition on ignition behavior in molten AZ31 and AZ91D Magnesium alloys

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Rare Metals 2006年第Z2期25卷 155-159页

作者： LEE Jin-Kyu JO Hyung-Ho KIM Shae K. Department of Advanced Material Engineering Sungkyunkwan University 300 Chunchun-dong Jangan-gu Suwon Gyunggi-do 440-746 KoreaAdvanced Material Center Korea Institute of Industrial Technology 7-47 Songdo-dong Yeonsu-gu Incheon 406-840 Korea dvanced Material Center Korea Institute of Industrial Technology 7-47 Songdo-dong Yeonsu-gu Incheon 406-840 Korea

Mg alloys have been widely used in automobile and electronic industries because of high specific strength, good castability, etc. However, molten Mg alloys will burn rapidly in air if not protected. To solve this problem, the molten metal should be protected from oxidation by blanketing the surface with flux or protective gases. SF6 gas is widely used for Mg alloys as a cover gas and has proved to be a successful inhibitor. However, the use of SF6 gas is limited because of its high cost and its significant impact on non-global warming potential. Therefore, SF6 gas is being replaced by alternative protection gases. Recent studies show that there has been another attempt by adding CaO into Mg alloys. The aim of this study is to evaluate the effect of CaO on the minimum amount of protective gas, which is necessary not to make ignition in the molten AZ31 and AZ91 Mg alloys.

关键词： AZ91 AZ31 CaO clean production ignition resistance

A new ignition hohlraum design for indirect-drive inertial confinement fusion

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Chinese Physics B 2016年第8期25卷 256-260页

作者：李欣吴畅书戴振生郑无敌谷建法古培俊邹士阳刘杰朱少平 Institute of Applied Physics and Computational Mathematics Beijing 100094 China

In this paper,a six-cylinder-port hohlraum is proposed to provide high symmetry flux on capsule.It is designed to ignite a capsule with 1.2-mm radius in indirect-drive inertial confinement fusion（ICF）.Flux symmetry and laser energy are calculated by using three-dimensional view factor method and laser energy balance in hohlraum.Plasma conditions are analyzed based on the two-dimensional radiation-hydrodynamic simulations.There is no Y_（lm）（l≤4） asymmetry in the six-cylinder-port hohlraum when the influences of laser entrance holes（LEHs） and laser spots cancel each other out with suitable target parameters.A radiation drive with 300 eV and good flux symmetry can be achieved by using a laser energy of 2.3 MJ and peak power of 500 TW.According to the simulations,the electron temperature and the electron density on the wall of laser cone are high and low,respectively,which are similar to those of outer cones in the hohlraums on National ignition Facility（NTF）.And the laser intensity is also as low as those of NIF outer cones.So the backscattering due to laser plasma interaction（LPI） is considered to be negligible.The six-cyliner-port hohlraum could be superior to the traditional cylindrical hohlraum and the octahedral hohlraum in both higher symmetry and lower backscattering without supplementary technology at an acceptable laser energy level.It is undoubted that the hohlraum will add to the diversity of ICF approaches.

关键词： ICE hohlraums ignition six-cylinder port

The catalytic effect of the Na and Ca-rich industrial wastes on the thermal ignition of coal combustion

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Chinese Journal of Chemical Engineering 2019年第10期27卷 2467-2471页

作者： Jun Cheng Fan Zhou Xiaoxu Xuan Jianzhong Liu Junhu Zhou Kefa Cen State Key Lab of Clean Energy Utilization Zhejiang UniversityHangzhou 310027China

The catalytic effects of four industrial wastes,namely,the soap residue(SR),brine sludge(BS),calcium carbide residue(CCR),and white lime mud(WLM),on coal thermal ignition were investigated.The acidity of palmitate anion associated with Na+in SR was lower than that of chloride anion combined with Na+in BS,which resulted in an improved the combustion of SR.The acidity of OH-anion combined with Ca2+in CCR was lower than that of CO32-anion combined with Ca2+in WLM,resulting in CCR exhibiting a better catalytic effect on coal ignition.The alkaline metal Na had lower initial ionisation energy than the alkaline earth metal Ca.Therefore,the Na-rich SR exhibited higher catalytic activity on coal ignition than Ca-rich CCR.The ignition temperature of coal with 0.5%SR decreased from 544 to 503°C.

关键词： Industrial waste Catalysis Coal combustion Thermal ignition

Irradiation uniformity at the Laser MegaJoule facility in the context of the shock ignition scheme

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High Power Laser Science and Engineering 2014年第2期2卷 1-12页

作者： Mauro Temporal Benoit Canaud Warren J. Garbett Rafael Ramis Stefan Weber Centre de Math'ematiques et de Leurs Applications ENS Cachan and CNRS 61 Av. du President Wilson Cachan Cedex France CEA DIF Arpajon Cedex France AWE plc Aldermaston Reading Berkshire United Kingdom ETSI Aeron'auticos Universidad Polit'ecnica de Madrid Madrid Spain ELI-Beamlines Institute of Physics Academy of Sciences of the Czech Republic Prague Czech Republic

The use of the Laser MegaJoule facility within the shock ignition scheme has been considered. In the first part of the study, one-dimensional hydrodynamic calculations were performed for an inertial confinement fusion capsule in the context of the shock ignition scheme providing the energy gain and an estimation of the increase of the peak power due to the reduction of the photon penetration expected during the high-intensity spike pulse. In the second part, we considered a Laser MegaJoule configuration consisting of 176 laser beams that have been grouped providing two different irradiation schemes. In this configuration the maximum available energy and power are 1.3 MJ and 440 TW. Optimization of the laser–capsule parameters that minimize the irradiation non-uniformity during the first few ns of the foot pulse has been performed. The calculations take into account the specific elliptical laser intensity profile provided at the Laser MegaJoule and the expected beam uncertainties. A significant improvement of the illumination uniformity provided by the polar direct drive technique has been demonstrated. Three-dimensional hydrodynamic calculations have been performed in order to analyse the magnitude of the azimuthal component of the irradiation that is neglected in twodimensional hydrodynamic simulations.

关键词： inertial confinement fusion shock ignition laser system

Experimental Investigation of Hydrocarbon-fuel ignition in Scramjet Combustor

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Chinese Journal of Aeronautics 2004年第2期17卷 65-71页

作者：宋文艳黎明蔡元虎刘伟雄白菡尘 DepartmentofAeroengine NorthwesternPolytechnicalUniversityShaanxiXi＇an710072China ChineseAerodynamicResearchandDevelopmentCenter SichuanMianyang622663China

The direct-connected supersonic combustor experiment is finished for kerosene fuel ignition in H_2/O_2 preheated impulse facility. The entrance parameter of combustor corresponds to scramjet flight Mach number 3.5. Kerosene ignition is realized by using hydrogen as pilot flame. Wall pressure distributions of combustion are measured and flame photographs of ultraviolet ray are got. Experiment indicates that it is very difficult for kerosene fuel to realize self-ignition at low entrance temperature (below 900K) in supersonic combustor. Hydrogen pilot flame is one of the efficient methods for realizing kerosene ignition.

关键词： supersonic combustor ignition impulse wind tunnel kerosene pilot flame

Non-equilibrium ignition criterion for magnetized deuterium–tritium fuel

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Nuclear Science and Techniques 2019年第4期30卷 132-142页

作者： E.Ghorbanpour A.Ghasemizad S.Khoshbinfar Department of Physics Faculty of Science University of Guilan

In this paper, non-equilibrium ignition conditions for magnetized cylindrical deuterium–tritium plasma in the presence of an axial magnetic field have been investigated. It is expected that temperature imbalance between ions and electrons as well as the axial magnetic field will relax the threshold of ignition conditions.Therefore, ignition conditions for this model are derived numerically involving the energy balance equation at the stagnation point. It has been derived using parametric space including electron and ion temperature(T_e, T_i), areal density(q R), and seed magnetic field-dependent free parameters of B/q, mB, and BR. For B/ρ 0.002 g cm^(-2), ρR> 0.25 g cm^(-2), and ρR > 0.02 g cm^(-2),respectively. The practical equilibrium conditions also addressed which is in good agreement with the corresponding one-temperature magnetized mode proposed in previous studies. Moreover, it has been shown that the typical criterion of BR ≥(6.13–4.64) × 10~5 G cm would be expectable. It is also confirmed that the minimum product of areal density times fuel temperature in equilibrium model is located in the range of T = 6–8 keV for all these free parameters, depending on the magnitude of the magnetic field. This is the entry point for the non-equilibrium model consistent with equilibrium model.

关键词： Magnetized plasma Two-temperature model Ion-electron non-equilibrium Axial magnetic field ignition criteria