One-dimensional laminar flame propagation with an enthalpy gradient

1961 ◽  
Vol 261 (1304) ◽  
pp. 53-78 ◽  
Keyword(s):  
Numerical Solutions ◽  
Laminar Flame ◽  
Plug Flow ◽  
Combustion Products ◽  
Radiative Heat Loss ◽  
Decomposition Products ◽  
One Dimensional ◽  
Combustible Gas ◽  
Gradient Parameter ◽  
Negative Gradient

Exact numerical solutions of the flame equations are presented for a class of one-dimensional pre-mixed steady flames propagating in the presence of an enthalpy gradient. It is shown that a positive enthalpy gradient increases the flame speed whereas a negative gradient decreases it to zero, the latter result occurring at a finite value of the dimensionless enthalpy-gradient parameter. The physical significance of the results is discussed quantitatively for the following cases: Flow of a combustible gas in to a hot plug : flow of a combustible gas in to a cold plug; the ‘sandwich burner’ (flame between two cooled plugs); radiative heat loss from the combustion products; burning of a condensed-phase propellant in an atmosphere with which the decomposition products can react chemically. It is shown that some of these conditions lead to the existence of two possible burning velocities, and to conditions under which the flame will be extinguished.

The heating of a stream of particles by thermal counter radiation

2021 ◽  
Vol 30 (2) ◽  
pp. 15-22
Author(s):  
N. L. Poletaev
Keyword(s):  
Heat Capacity ◽  
Temperature Distribution ◽  
Numerical Solutions ◽  
Combustion Products ◽  
Monodisperse Particles ◽  
Problem Model ◽  
One Dimensional ◽  
Simplifying Assumptions ◽  
Black Surface ◽  
Analytical Assessment

Introduction. It is accepted that the depth of heating of the dust/gas/air mixture by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the mixture. Numerical simulation of combustion of a gas-air mixture that has inert particles, taking into account the re-radiation of heat by heated particles of the fresh mixture, led to ratio SR >> LR. In this work, the analytical assessment of ratio χS = SR/LR is performed.One-dimensional problem model. The co-authors determined stationary temperature distribution over the flow of initially cold monodisperse particles suspended in vacuum. Particle velocity V is directed toward a heat-radiating, absolutely black surface that is permeable by particles. Simplifying assumptions are used: radiation consists of two oppositely-directed flows of electromagnetic energy; interaction between particles and radiation is described in the approximation of geometric optics; the temperature inside the particle is the same. Problem solving. It is shown that χS is determined by V=Vcp / (εT 0,5, σTb)3 , where cp, εT, σ, Tb are, respectively, heat capacity per unit volume of the suspended matter, integral emissivity of the particle material, the Stefan-Boltzmann constant, and the surface temperature. For ≤ 2.8, re-emission can be neglected: χS ≈ 1. At ≤ 1.2, temperature distribution regulates re-emission: χS ≈ 5 –1/(2 – εT) >> 1.Solution discussion. The analytical solution satisfactorily describes the available numerical solutions and experimental data for the case of combustion of a dust/gas/air mixture after specifying the parameters of a simplified model: the radiating surface should be understood as the flame front, Tb is the combustion temperature, and cp is the overall heat capacity of the mixture. The estimate ≤ 1.2 indicates the final high temperature of the gas suspension, the possibility of its autoignition far from the flame, and the need to change initial assumptions when simulating re-emission.Conclusions. Analytical evaluations make it possible to employ ratios SR >> LR and SR ≈ LR for the suspension over a thermal radiation source in vacuum. Conditions for the application of the results of simplified simulation of re-emission to the combustion of a dust/gas/air mixture are formulated.

The Influence of Singlet Oxygen and Ozone on the Combustion in Methane-Air Mixture

2013 ◽  
Vol 699 ◽  
pp. 111-118
Author(s):  
Rui Shi ◽  
Chang Hui Wang ◽  
Yan Nan Chang
Keyword(s):  
Singlet Oxygen ◽  
Chemical Kinetics ◽  
Mole Fraction ◽  
Ignition Delay ◽  
Delay Time ◽  
Ignition Delay Time ◽  
Laminar Flame ◽  
Combustion Products ◽  
Flame Speed ◽  
Air Mixing

Based on GRI3.0, we study the main chemical kinetics process about reactions of singlet oxygen O2(a1Δg) and ozone O3 with methane-air combustion products, inherit and further develop research in chemical kinetics process with enhancement effects on methane-air mixed combustion by these two molecules. In addition, influence of these two molecules on ignition delay time and flame speed of laminar mixture are considered in our numerical simulation research. This study validates the calculation of this model which cotains these two active molecules by using experimental data of ignition delay time and the speed of laminar flame propagation. In CH4-air mixing laminar combustion under fuel-lean condition(ф=0.5), flame speed will be increased, and singlet oxygen with 10% of mole fraction increases it by 80.34%, while ozone with 10% mole fraction increase it by 127.96%. It mainly because active atoms and groups(O, H, OH, CH3, CH2O, CH3O, etc) will be increased a lot after adding active molecules in the initial stage, and chain reaction be reacted greatly, inducing shortening of reaction time and accelerating of flame speed. Under fuel rich(ф=1.5), accelerating of flame speed will be weakened slightly, singlet oxygen with 10% in molecular oxygen increase it by 48.93%, while ozone with 10% increase it by 70.25%.

Influence of Heating Rates On the Toxicity of Evolved Combustion Products: Results and a System for Research

1983 ◽  
Vol 1 (6) ◽  
pp. 465-479 ◽  
Author(s):  
Shayne Cox Gad ◽  
Ann C. Smith
Keyword(s):  
Decomposition Rate ◽  
High Density Polyethylene ◽  
Combustion Products ◽  
Douglas Fir ◽  
High Density ◽  
Heating Rates ◽  
Decomposition Products ◽  
Sample Heating ◽  
Rate Of Heating

The significance of the rate of heating of materials to the nature and toxi cologic consequences of combustion products formed by natural and man-made products was evaluated using a system designed to allow exact control and reproducibility of this variable. Using this system, the decomposition products of Douglas Fir, Hem Fir, and a high density polyethylene were characterized in terms of gases evolved, lethality, and ability to incapacitate at sample heating rates of 20, 30, 40, and 50 °C per minute. For all three materials, the rate of heating was found to have marked influences on both the decomposition prod ucts and their toxicologic impact. This influence was not such as to be ex plainable as just a decomposition rate phenomenon.

scholarly journals Tornado-type stationary vortex with nonlinear term due to moisture transport

2010 ◽  
Vol 4 (1) ◽  
pp. 77-82 ◽  
Author(s):  
P. B. Rutkevich ◽  
P. P. Rutkevych
Keyword(s):  
Tropical Cyclones ◽  
Shooting Method ◽  
Nonlinear Term ◽  
Numerical Solutions ◽  
Variable Temperature ◽  
Slow Rotation ◽  
Nonlinear Phenomenon ◽  
One Dimensional ◽  
Stationary Vortex ◽  
General Possibility

Abstract. Tornado vortex is believed to be essentially nonlinear phenomenon; and the puzzle to choose the nonlinear term(s) responsible for its formation is still unresolved. In the present work we consider the nonlinear term associated with atmosphere humidity, by introducing variable temperature gradient depending on the vertical velocity of the fluid. Such term is able to yield energy to the system and is very suitable for such a problem. Other nonlinear terms are neglected, assuming slow rotation, or in other words a "weak" tornado approximation. We consider one-dimensional radial boundary problem, and use a modificaiton of shooting method to satisfy boundary conditions at large radii. Obtained numerical solutions of the nonlinear differential equation qualitatively agree with the observed atmosphere vortices (tornados, tropical cyclones). The obtained results show general possibility of existence of unstable motion even in convectively stable atmosphere stratification.

Diffusion-Limited Cell Dehydration: Analytical and Numerical Solutions for a Planar Model

1999 ◽  
Author(s):  
Alexander V. Kasharin ◽  
Jens O. M. Karlsson
Keyword(s):  
Analytical Solution ◽  
Numerical Solutions ◽  
Planar System ◽  
One Dimensional ◽  
Diffusion Limited ◽  
Dimensional Diffusion ◽  
Constant Diffusivity ◽  
A Cell ◽  
Cell Dehydration ◽  
The One

Abstract The process of diffusion-limited cell dehydration is modeled for a planar system by writing the one-dimensional diffusion-equation for a cell with moving, semipermeable boundaries. For the simplifying case of isothermal dehydration with constant diffusivity, an approximate analytical solution is obtained by linearizing the governing partial differential equations. The general problem must be solved numerically. The Forward Time Center Space (FTCS) and Crank-Nicholson differencing schemes are implemented, and evaluated by comparison with the analytical solution. Putative stability criteria for the two algorithms are proposed based on numerical experiments, and the Crank-Nicholson method is shown to be accurate for a mesh with as few as six nodes.

STUDYING THE PROCESS OF HEATING OF A PIPE BILLET DURING GAS FORMING

2021 ◽  
pp. 156-161
Author(s):  
А.Ю. Боташев ◽  
Р.А. Байрамуков ◽  
Н.У. Бисилов ◽  
Р.С. Малсугенов
Keyword(s):  
Heat Transfer ◽  
Heat Balance ◽  
Heating Temperature ◽  
Fuel Mixture ◽  
Combustion Products ◽  
New Device ◽  
Combustible Gas ◽  
Ferrous Metals ◽  
Non Ferrous Metals ◽  
Propane Butane

Разработана и представлена схема нового устройства, осуществляющего штамповку деталей с нагревом трубной заготовки воздействием продуктов сгорания газообразной топливной смеси. В качестве топливной смеси может использоваться горючий газ - смесь воздуха с метаном или с пропан-бутаном. Представлены результаты исследования процесса нагрева трубной заготовки воздействием продуктов сгорания. Исследование проведено на базе уравнений конвективного теплообмена, теплового баланса и термодинамики. Получена зависимость для определения температуры нагрева трубной заготовки. Установлено, что температура заготовки зависит от материала и геометрических размеров заготовки, а также давления топливной смеси. Данное устройство обеспечивает нагрев до интервала горячей обработки стальных трубных заготовок диаметром более 150 мм при толщине стенки до 1,2…1,5 мм, а при диаметре более 300 мм - толщиной до 2,0…2,5 мм. Для нагрева трубных заготовок из цветных металлов и сплавов (например, алюминия и меди) требуется меньшее давление топливной смеси, чем для стали, благодаря этому обеспечивается нагрев заготовок значительно большей толщины, в частности, заготовок из алюминия толщиной до 6 мм We developed a diagram of a new device for stamping parts by heating a pipe billet by the action of combustion products of a gaseous fuel mixture. A combustible gas can be used as a fuel mixture - a mixture of air with methane or with propane-butane. We present the results of a study of the process of heating a pipe billet by the action of combustion products. We carried out the study on the basis of the equations of convective heat transfer, heat balance and thermodynamics. We obtained the dependence for determining the heating temperature of the pipe billet. We found that the temperature of the workpiece depends on the material and geometric dimensions of the workpiece, as well as the pressure of the fuel mixture. This device provides heating to the hot working interval of steel pipe billets with a diameter of more than 150 mm with a wall thickness of up to 1.2 ... 1.5 mm, and with a diameter of more than 300 mm - with a thickness of up to 2.0 ... 2.5 mm. To heat tubular billets made of non-ferrous metals and alloys (for example, aluminum and copper), a lower pressure of the fuel mixture is required than for steel, due to this, billets of a much greater thickness are heated, in particular, billets made of aluminum with a thickness of up to 6 mm

The Structure of Laminar Premixed H2-Air Flames at Elevated Pressures

2000 ◽  
Vol 214 (4) ◽  
Author(s):  
M. El-Gamal ◽  
E. Gutheil ◽  
J. Warnatz
Keyword(s):  
Laminar Flame ◽  
Flame Structure ◽  
Ideal Gas ◽  
Fortran Program ◽  
Laminar Flame Speed ◽  
Real Gas ◽  
One Dimensional ◽  
Rocket Propulsion ◽  
Elevated Pressures ◽  
Engine Combustion

In high-pressure flames that occur in many practical combustion devices such as industrial furnaces, rocket propulsion and internal engine combustion, the assumption of an ideal gas is not appropriate. The present paper presents a model that includes modifications of the equation of state, transport and thermodynamic properties. The model is implemented into a Fortran program that was developed to simulate numerically one-dimensional planar premixed flames. The influence of the modifications for the real gas behavior on the laminar flame speed and on flame structure is illustrated for stoichiometric H

scholarly journals Dissociation and recombination in the electrolyte flow model

2021 ◽  
Vol 2090 (1) ◽  
pp. 012076
Author(s):  
A Shobukhov ◽  
H Koibuchi
Keyword(s):  
Flow Model ◽  
Numerical Solutions ◽  
Stable Equilibrium ◽  
Steady State Solution ◽  
System Of Equations ◽  
Constant Flow ◽  
Dimensional Model ◽  
Electrolyte Flow ◽  
One Dimensional ◽  
Dilute Aqueous Solution

Abstract We propose a one-dimensional model for the dilute aqueous solution of NaCl which is treated as an incompressible fluid placed in the external electric field. This model is based on the Poisson-Nernst-Planck system of equations, which also contains the constant flow velocity as a parameter and considers the dissociation and the recombination of ions. We study the steady-state solution analytically and prove that it is a stable equilibrium. Analyzing the numerical solutions, we demonstrate the importance of dissociation and recombination for the physical meaningfulness of the model.

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