Thermal Regions of Combustion

Vulis, L. A.; Friedman, M. D.; Spalding, D. B.

doi:10.1115/1.3640688

Cited by 12 publications

(14 citation statements)

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“…The turbulence-chemistry interaction is modeled based on the Chalmers' partially stirred reactor (CPaSR) approach (Vulis, 1961;Chomiak and Karlsson, 1996), where the computational cell is divided into two zones: a reacting zone which is modeled as a perfectly stirred reactor (PSR) and nonreacting zone. The reactive volume fraction () is calculated as (6) where the residence time ( res ) is equal to the time step (t),  c is the chemical reaction time, and  mix is the mixing time…”

Section: Governing Equationsmentioning

confidence: 99%

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion

Marzouk

Huckaby

2010

Engineering Applications of Computational Fluid Mechanics

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ABSTRACT:We compare the performance and computational cost of 8 kinetic models (3 global and 5 elementary) that describe the finite-rate chemistry of syngas combustion. We apply them in simulating a turbulent jet flame with syngas diluted by 30% nitrogen. We model the turbulence by a modified k-epsilon model and the turbulence-chemistry interaction by the partially stirred reactor approach. To integrate the chemistry equations, we nominally use explicit fifth-order embedded Runge-Kutta ODE solver. But semi-implicit Bulirsch-Stoer and implicit Euler were also used. The computational time depends on the number of reaction steps and the ODE solver. Five models overpredict the maximum flame temperature (by 200 K-320 K). Two models underpredict it by 240 K and 580 K. The global model that is based on the Westbrook-Dryer (1981) model for hydrocarbon fuels gives the best agreement with measurements, and also has low computational demand. Therefore, it is recommended for modeling turbulent syngas flames.

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Section: Governing Equationsmentioning

confidence: 99%

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion

Marzouk

Huckaby

2010

Engineering Applications of Computational Fluid Mechanics

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“…However, mapping the reaction regimes for a single particle is crucial to understanding this difference and interpreting the flame structure in a suspension. The interplay between kinetic and diffusion reaction rates of heterogeneous chemical reactions leading to the processes of ignition and extinction was first investigated by Frank-Kamenetskii [4] and then analyzed further by Vulis [5]. Their analyses are adapted here in a simplified form to interpret the reaction behavior of a single particle injected into a hot oxidizing gas.…”

Section: Ignition and Combustion Of A Single Particlementioning

confidence: 99%

“…Unlike gas flames, the width of the flame reaction zone in particle suspensions can span a large temperature range and can be comparable to, or even exceed, that of the preheat zone [2]. The existence of diffusion micro-flames within a global flame-front (in effect, flames within the flame), which are insensitive to the bulk gas temperature, makes dust flames resistant to heat loss [1,3,4,5] and also serves to maintain a constant burning velocity with increasing fuel concentration in fuel-rich mixtures [6]. The ability of particles to ignite, together with low ignition temperatures, may result in much wider flame propagation limits for particle suspensions than for gaseous fuels.…”

Section: Introductionmentioning

confidence: 99%

Thermal structure and burning velocity of flames in non-volatile fuel suspensions

Soo

Kumashiro

Goroshin

et al. 2017

Proceedings of the Combustion Institute

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Flame propagation through a non-volatile solid-fuel suspension is studied using a simplified, time-dependent numerical model that considers the influence of both diffusional and kinetic rates on the particle combustion process. It is assumed that particles react via a single-step, first-order Arrhenius surface reaction with an oxidizer delivered to the particle surface through gas diffusion. Unlike the majority of models previously developed for flames in suspensions, no external parameters are imposed, such as particle ignition temperature, combustion time, or the assumption of either kinetic-or diffusion-limited particle combustion regimes. Instead, it is demonstrated that these parameters are characteristic values of the flame propagation problem that must be solved together with the burning velocity, and that the a priori imposition of these parameters from single-particle combustion data may result in erroneous predictions. It is also shown that both diffusive and kinetic reaction regimes can alternate within the same flame and that their interaction may result in non-trivial flame behavior. In fuel-lean mixtures, it is demonstrated that this interaction leads to certain particle size ranges where burning velocity increases with increasing particle size, opposite to the expected trend. For even leaner mixtures, the interplay between kinetic and diffusive reaction rates leads to the appearance of a new type of flame instability where kinetic and diffusive regimes alternate in time, resulting in a pulsating regime of flame propagation.

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“…Naturally, such analysis is only possible for those devices where these points may exist, i.e., if the maximum inclination of the heat generation curve is steeper than the curve of heat transfer. After Vulis [5] we call this condition critical, whereas we call the other case, where unstable points do not exist, noncritical.…”

Section: Statement Of the Problemmentioning

confidence: 99%

The mechanism of char ignition in fluidized bed combustors

Siemons¹

1987

Combustion and Flame

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Knowledge about ignition processes of coal in fluidized beds is of importance for the start-up and dynamic control of these combustors. Initial experiments in a transparent fluidized bed scale model showed the existence of a considerable induction period for the ignition of char, especially at low bed temperatures (e.g., 800-950K for bituminous coal). This paper focuses on char-ignition delay at these low temperatures. It is shown that temperature rise during ignition is not caused by coal particle diameter shrinkage but rather by an increase in reactivity. Analysis of the thermal ignition process leads to the conclusion that the process is noncritical, causing a gradual temperature rise without Semenov Jump. Consequences of this result for future research are expounded. Calculated values of the maximum inclination of the heat generation curve (heat release versus coal particle temperature) may be of use to the development of an adequate experimental device.

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Thermal Regions of Combustion

Cited by 12 publications

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A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion

Thermal structure and burning velocity of flames in non-volatile fuel suspensions

The mechanism of char ignition in fluidized bed combustors

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Thermal Regions of Combustion

Cited by 12 publications

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A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H2Combustion

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H2Combustion

Thermal structure and burning velocity of flames in non-volatile fuel suspensions

The mechanism of char ignition in fluidized bed combustors

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A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion

A Comparative Study of Eight Finite-Rate Chemistry Kinetics for Co/H₂Combustion