Laminar Flamelet Approach Research Articles

Numerical Predictions of Soot Formation in Kerosene/Air Jet Diffusion Flame

Soot volume fraction in a turbulent diffusion flame burning kerosene/air is simulated using steady flamelet approach. The soot inception model based on the formation rate of three and two ring aromatics is used, which further accounts for inception, coagulation, surface growth, and oxidation processes. The Favre-averaged governing equations of mass, momentum, and energy are solved in conjunction with k-? turbulence model in ANSYS-FLUENT. The fairly detailed reaction mechanism for kerosene/air is coupled to the turbulent flow field by steady laminar flamelet approach, while the soot is calculated using Moss-Brookes model. The predictions are found to match well with the measurements where no significant effects are observed with the inclusion of higher order hydrocarbon as precursors and surface growth.

Systematic study of the impact of chemistry and radiation on extinction and carbon monoxide formation at low scalar dissipation rates

In fire flames scalar dissipation rates in the reaction zone are low and radiation becomes important for extinction. The chemistry mechanism also strongly affects extinction and CO formation. The present study applies the unsteady laminar flamelet approach (or, equivalently, the conditional moment closure (CMC) method in mixture fraction domain, without transport in physical space). Six chemistry mechanisms are analyzed. In addition to adiabatic conditions, three radiation models are considered: RADCAL-based gray gas; weighted sum of gray gases (WSGG); and prescribed radiative fraction model. The oxygen mass fraction values for extinction are discussed, diluting the oxidizer by adding nitrogen. Carbon monoxide profiles are reported as well. The radiative fraction model is not capable of predicting the strong radiative effects at low scalar dissipation rates, while the RADCAL-based and the WSGG model are able to do so. The analysis of extinction and CO reveals strong sensitivity to the mesh in mixture fraction space, as well as to the shape of the conditional scalar dissipation rate profile. Results with the ARM2 mechanism and GRI3 are in very close agreement, so that significant time savings are possible, using ARM2.

REDIM reduced chemistry for the simulation of counterflow diffusion flames with oscillating strain rates

The dynamic behaviour and structures of laminar counterflow diffusion methane flames under oscillatory strain rates are investigated based on both detailed and reduced chemistry. It is known both from experiment and numerical studies that flame can deviate from its quasi-steady manner for high frequencies, which makes the well-known steady laminar flamelet model questionable. In this work, the Reaction-diffusion manifolds (REDIM) concept for simplified chemistry is applied to study the laminar counterflow diffusion flames with oscillating strain rates. In the construction of REDIM, one needs little knowledge of the studied system, and the REDIM reduced chemistry can cover both stable and unstable (extinction) regimes of the studied system. It is shown that the REDIM can capture both the steady and unsteady behaviours of the flame structures even for high frequencies, where the standard laminar steady flamelet approach is not appropriate.

Large Eddy Simulation on the Effects of Pressure on Syngas/Air Turbulent Nonpremixed Jet Flames

ABSTRACT The influence of increasing pressure on nonpremixed syngas/air turbulent jet flames is numerically investigated using large eddy simulations in conjunction with a steady laminar flamelet approach. The applicability of the steady flamelet approach is assessed through an extensive parametric study of laminar counterflow flames and tangential stretching rate analysis on target flame structures at different pressures. Two sets of large eddy simulations, exploring pressure values up to atm, are carried out. The first one (series A) is characterized by a constant jet Reynolds number, while the second one (series B) is characterized by a constant jet inlet velocity. Both campaigns show narrower flame brushes and reduced radical concentrations with increasing pressure. While for series A the flame length is not sensitive to pressure, a longer flame brush is noticed for series B, being mainly caused by the increased mass flow rate. The sensitivity of the local flame behavior to pressure, such as the OH layer thickness and position, is compared to the available experimental results, showing similar trends with a satisfactory agreement.

The capability of commercial CFD code to predict organic peroxide fireball characteristics.

Fireballs of liquid organic peroxides differ from those of liquid hydrocarbon fuels. Modified equations for predicting the fireball diameter, height, surface emissive power and the duration in dependence of the fuel mass are presented for di-tert-butyl peroxide. They base on 13 steel drum tests with fuel masses from 10 kg to 168 kg. Moreover, computational fluid dynamics simulations are performed using the laminar flamelet approach and a statistically turbulence treatment. Fireballs involving peroxide from 10 kg to 80 kg were simulated and their properties compared to the experimentally developed models. The deviations of each property are partially compensating each other leading to an adequate prediction of thermal safety distances for both, a time-independent and a time-averaged treatment. Simulations prove to be a good tool for predicting thermal radiation hazards of fireball scenarios.

Supercritical combustion of gas-centered liquid-swirl coaxial injectors for staged-combustion engines

The combustion characteristics of gas-centered, liquid-swirl coaxial injectors typically used in oxidizer-rich staged combustion cycle engines are numerically investigated at supercritical conditions. Turbulence closure is achieved using large-eddy-simulation techniques, and turbulence/chemistry interaction is modeled by a steady laminar flamelet approach. Gaseous oxygen (GOX) at 687.7 K is injected into the center post while kerosene at 492.2 K is delivered tangentially into the outer coaxial annulus. The operating pressure is 25.3 MPa. Detailed flow structures and flame dynamics are explored. The entire flowfield can be divided into four regimes: propellant injection, flame initialization, flame development, and intensive combustion. The diffusion-dominated flame is anchored in the wake of the GOX post and further enhanced in the downstream taper region. The surface of the coaxial annulus and taper is covered by fuel-rich mixtures and thus protected from thermal flux in the flame zone. Effects of the recess length (from the end of GOX post to the entrance of taper region) on the flow and flame evolution are investigated in depth. The efficiency of propellant mixing and subsequent combustion is found to increase with increasing recess length. The kerosene film is nearly depleted before the exit of the recess region for cases with long recess length, and the flame spreads upwards in the taper region for cases with reduced recess length due to insufficient mixing between GOX and kerosene. In a fully recessed injector without fuel shielding, the injected kerosene behaves like a liquid jet in a crossflow. Two recirculating zones containing fuel-rich mixtures are formed between the injection slit and the headend. A broad flame region is established at the exit of the recess region. In a non-recessed injector, the occurrence of combustion is delayed to the taper region. The flame resides along the taper surface and the injector faceplate, with most of GOX convecting downstream unburned. Results obtained from the present study can also be used to characterize combustion responses to local flow oscillations.

Coal particle volatile combustion and flame interaction. Part II: Effects of particle Reynolds number and turbulence

Direct numerical simulation (DNS) is performed to characterize volatile combustion of isolated coal particles and closely spaced particle ensembles in laminar and turbulent flow. In part I of the paper the transient evolution of devolatilization and group flame effects were studied, Tufano et al. (2018). This analysis was limited to laminar flows and relatively low particle Reynolds numbers Rep. Here, we investigate the effect of large Rep and considerable levels of turbulence on the devolatilization and burning behavior of the particles. The complex physico-chemical interactions during PCC are characterized for laminar flow conditions first, before arrays of infinite particle layers are subjected to turbulence. Increasing Rep in laminar flow leads to delayed ignition of single particles with local extinction due to high upstream scalar dissipation rates and the formation of wake flame structures downstream of the particle. An attempt is made to recover the single particle results with a standard steady laminar flamelet approach, which is shown to work well at low Rep, but fails at high Reynolds numbers, where multi-dimensional effects occur and must be incorporated into flamelet modeling. It is found that applying standard film theory to model the effect of convection on devolatilization rates can lead to qualitatively wrong trends and up to 66% error in the peak devolatilization rate compared to the DNS results at Rep=8. The analysis of particle arrays in laminar flow shows a strong dependence of flame interactions on the values of Rep due to the different extent of the particle wakes. The occurrence of significant levels of turbulence introduces a wide range of additional chemical states due to the randomness of the turbulent fluctuations that can either act to increase or decrease the local strain, in turn weakening or enhancing particle interactions. For the studied conditions turbulence slightly promotes the mass release from the most upstream particle set, but considerably delays the volatile release from the downstream particles, which is explained by the different extents and degrees of interaction of the up- and downstream volatile flames. The present results are considered useful for the development of LES sub-grid scale combustion models for pulverized coal flames, such as flamelets and others.

Numerical study of fire spread using the level-set method with large eddy simulation incorporating detailed chemical kinetics gas-phase combustion model

A fire code has been developed for the purpose of modelling wildland fires via Large Eddy Simulation (LES) and the use of the level-set approach to track the flame front. Detailed chemical kinetics have been considered via the strained laminar flamelet approach for the combustion process which included the consideration of the yields of toxic volatiles such as CO, CO2 and soot production. Numerical simulations have been validated against an experimental study on the fire spread on a pine needle board under different slope angles. Peak temperatures and occurrence times during the propagation process were predicted with an overall average error of 11% and 3% respectively. This demonstrates that the flaming behaviour could be well predicted under different slope conditions. By incorporating the level set with the gas phase models, information including temperature field, toxic volatiles and soot particle concentrations can be realised in comparison to empirical fire spread models.

CFD modelling and performance increase of a pusher type reheating furnace using oxy-fuel burners

In conventional combustion systems which use air as oxidizer, a huge amount of the heat of formation is absorbed by the nitrogen in the air. In oxygen enriched or oxy-fuel combustion an O2/N2-mixture with a higher concentration of oxygen is used. Due to the lower amount of nitrogen in the oxidizer the flame temperature increases and radiative heat transfer is improved in the furnace. Therefore, the influence of additional oxy-fuel jet burners on the productivity of a pusher type reheating furnace is investigated in this paper. Due to the special arrangement of the billet in this type of furnace the billets can be treated as a fluid with a very high viscosity. Therefore, the periodic transient reheating of the billets and the gas phase combustion was calculated in one steady state calculation. The combustion in the gas phase is described by the steady laminar flamelet approach for air-fuel combustion and the eddy dissipation concept model is used in the simulation with the oxy-fuel burners. The results of the gas phase simulation with air as oxidizer was validated with measurements and showed an average deviation of 38 K. The calculated billet temperature was also compared to the measurements and showed deviation of 27 K which can be seen as a good agreement. With this model the influence of additional oxy-fuel burners is investigated. The investigation showed that with additional oxy-fuel burners the productivity of the furnace can be increased from 60 t/h to 68 t/h and furthermore the furnace efficiency increases from 62.9% to 65%. This shows the beneficial effect of using oxy-fuel combustion.

Computational analysis of a semi-industrial furnace fired by a flat flame burner under different O2/N2 ratios using the steady laminar flamelet approach

This paper uses computational fluid dynamics (CFD) to investigates a natural gas fired semi-industrial furnace with a thermal input of 250 kW which operates under different O2/N2 ratios in the oxidizer. The furnace is fired by a flat flame burner which is commonly used in industrial furnaces. The simulations were confronted with temperature measurements inside the furnace and with measurements of the surface temperature of the quarl. The main focus was on using models which are not computationally demanding. The steady laminar flamelet model (SFM) with a detailed mechanism was thus used to model the combustion. With the SFM the calculation time can be dramatically reduced compared to simulations with the eddy dissipation model (EDM) although using a detailed mechanism. The skeletal25 mechanism, consisting of 17 species and 25 reactions, was used in this investigation. Additionally the furnace was simulated with the two detailed mechanism GRI 3.0 and smooke46. The predicated temperature inside the furnace of the SFM and the skeletal25 were in good accordance with the measurements for all oxygen concentrations in the oxidizer. The predicted surface temperature of the quarl showed higher deviation from the measurements but also showed a reasonable standard of accuracy. Furthermore the investigation demonstrated that the two detailed mechanisms GRI 3.0 and smooke46 are also applicable for flat flame burners and oxygen concentrations up to 37 Vol% oxygen in the oxidizer, a finding which is in contrast to previous investigations with jet flames. For oxygen concentrations higher than 37 Vol% in the oxidizer the GRI 3.0 and the smooke46 mechanisms fails to predict the temperature field in the furnace. Only the skeletal25 mechanism was able to predict the temperature field correct for higher oxygen concentrations in the oxidizer.

Numerical modeling of soot formation in a turbulent C2H4/air diffusion flame

Soot formation in a lifted C 2 H 4 -Air turbulent diffusion flame is studied using two different paths for soot nucleation and oxidation; by a 2D axisymmetric RANS simulation using ANSYS FLUENT 15.0. The turbulence-chemistry interactions are modeled using two different approaches: steady laminar flamelet approach and flamelet-generated manifold. Chemical mechanism is represented by POLIMI to study the effect of species concentration on soot formation. P1 approximation is employed to approximate the radiative transfer equation into truncated series expansion in spherical harmonics while the weighted sum of gray gases is invoked to model the absorption coefficient while the soot model accounts for nucleation, coagulation, surface growth, and oxidation. The first route for nucleation considers acetylene concentration as a linear function of soot nucleation rate, whereas the second route considers two and three ring aromatic species as function of nucleation rate. Equilibrium-based and instantaneous approach has been used to estimate the OH concentration for soot oxidation. Lee and Fenimore-Jones soot oxidation models are studied to shed light on the effect of OH on soot oxidation. Moreover, the soot-radiation interactions are also included in terms of absorption coefficient of soot. Furthermore, the soot-turbulence interactions have been invoked using a temperature/mixture fraction-based single variable PDF. Both the turbulence-chemistry interaction models are able to accurately predict the flame liftoff height, and for accurate prediction of flame length, radiative heat loss should be accounted in an accurate way. The soot-turbulence interactions are found sensitive to the PDF used in present study.

Effect of gas—phase carbon depletion by sooting on the structure of methane/air flamelets

The paper describes an approach to model soot formation/oxidation in non premixed turbulent flames, which in particular accounts for the effect of gas-phase carbon depletion due to sooting. The effect is relevant to combustion chambers fed with oxygen (rather than air), operating at high pressure and overall rich, such as rocket chambers. A scaled gas-phase elemental carbon mass fraction is introduced to this end and, in the framework of a laminar flamelet approach, a library is developed for use in turbulent combustion models. Due to the lack of reference data for rocket chambers conditions, the library is limited for the time being to nonpremixed methane/air flames at two values of pressure, 1 atm and 3 atm, for which experimental data are available. Results indicate a signicant effect of carbon depletion on the concentration of soot precursor acetylene in particular, and on the ensuing soot nucleation rate. The model is shown to correctly capture the decrease of the latter rate with gas-phase carbon depletion, thereby potentially enabling to extend the range of applicability of semi-empirical soot prediction models for nonpremixed turbulent combustion.

Nonlinear hydrodynamic and thermoacoustic oscillations of a bluff-body stabilised turbulent premixed flame

Turbulent premixed flames often experience thermoacoustic instabilities when the combustion heat release rate is in phase with acoustic pressure fluctuations. Linear methods often assume a priori that oscillations are periodic and occur at a dominant frequency with a fixed amplitude. Such assumptions are not made when using nonlinear analysis. When an oscillation is fully saturated, nonlinear analysis can serve as a useful avenue to reveal flame behaviour far more elaborate than period-one limit cycles, including quasi-periodicity and chaos in hydrodynamically or thermoacoustically self-excited system. In this paper, the behaviour of a bluff-body stabilised turbulent premixed propane/air flame in a model jet-engine afterburner configuration is investigated using computational fluid dynamics. For the frequencies of interest in this investigation, an unsteady Reynolds-averaged Navier–Stokes approach is found to be appropriate. Combustion is represented using a modified laminar flamelet approach with an algebraic closure for the flame surface density. The results are validated by comparison with existing experimental data and with large eddy simulation, and the observed self-excited oscillations in pressure and heat release are studied using methods derived from dynamical systems theory. A systematic analysis is carried out by increasing the equivalence ratio of the reactant stream supplied to the premixed flame. A strong variation in the global flame structure is observed. The flame exhibits a self-excited hydrodynamic oscillation at low equivalence ratios, becomes steady as the equivalence ratio is increased to intermediate values, and again exhibits a self-excited thermoacoustic oscillation at higher equivalence ratios. Rich nonlinear behaviour is observed and the investigation demonstrates that turbulent premixed flames can exhibit complex dynamical behaviour including quasiperiodicity, limit cycles and period-two limit cycles due to the interactions of various physical mechanisms. This has implications in selecting the operating conditions for such flames and for devising proper control strategies for the avoidance of thermoacoustic instability.

NO Prediction in Turbulent Diffusion Flame Using Multiple Unsteady Laminar Flamelet Modeling

The steady laminar flamelet model (SLFM) (Peters, 1984, “Laminar Diffusion Flamelet Models in Non-Premixed Turbulent Combustion,” Prog. Energy Combust. Sci., 10(3), pp. 319–339; Peters, 1986, “Laminar Flamelet Concepts in Turbulent Combustion,” Symp. (Int.) Combust., 21(1), pp. 1231–1250) has been shown to be reasonably good for the predictions of mean temperature and the major species in turbulent flames (Borghi, 1988, “Turbulent Combustion Modeling,” Prog. Energy Combust. Sci., 14(4), pp. 245–292; Veynante and Vervisch, 2002, “Turbulent Combustion Modeling,” Prog. Energy Combust. Sci., 28(3), pp. 193–266). However, the SLFM approach has limitations in the prediction of slow chemistry phenomena like NO formation (Benim and Syed, 1998, “Laminar Flamelet Modeling of Turbulent Premixed Combustion,” Appl. Math. Model., 22(1–2), pp. 113–136; Heyl and Bockhorn, 2001, “Flamelet Modeling of NO Formation in Laminar and Turbulent Diffusion Flames,” Chemosphere, 42(5–7), pp. 449–462). In the case of SLFM, the turbulence and chemistry are coupled through a single variable called scalar dissipation, which is representative of the strain inside the flow. The SLFM is not able to respond to the steep changes in the scalar dissipation values and generally tends to approach to the equilibrium solution as the strain relaxes (Haworth et al., 1989, “The Importance of Time-Dependent Flame Structures in Stretched Laminar Flamelet Models for Turbulent Jet Diffusion Flames,” Symp. (Int.) Combust., 22(1), pp. 589–597). A pollutant like NO is formed in the post flame zones and with a high residence time, where the scalar dissipation diminishes and hence the NO is overpredicted using the SLFM approach. In order to improve the prediction of slow forming species, a transient history of the scalar dissipation evolution is required. In this work, a multiple unsteady laminar flamelet approach is implemented and used to model the NO formation in two turbulent diffusion flames using detailed chemistry. In this approach, multiple unsteady flamelet equations are solved, where each flamelet is associated with its own scalar dissipation history. The time averaged mean variables are calculated from weighted average contributions from different flamelets. The unsteady laminar flamelet solution starts with a converged solution obtained from the steady laminar flamelet modeling approach. The unsteady flamelet equations are, therefore, solved as a post processing step with the frozen flow field. The domain averaged scalar dissipation for a flamelet at each time step is obtained by solving a scalar transport equation, which represents the probability of occurrence of the considered flamelet. The present work involves the study of the effect of the number of flamelets and also the different methods of probability initialization on the accuracy of NO prediction. The current model predictions are compared with the experimental data. It is seen that the NO predictions improves significantly even with a single unsteady flamelet and further improves marginally with an increase in number of unsteady flamelets.

Initial phase modelling in numerical explosion applied to process safety

The utilisation of computational fluid dynamics (CFD) in process safety has increased significantly in recent years. The modelling of accidental explosion via CFD has in many cases replaced the classical Multi Energy and Brake Strehlow methods. The benefits obtained with CFD modelling can be diminished if proper modelling of the initial phase of explosion is neglected. In the early stages of an explosion, the flame propagates in a quasi-laminar regime. Proper modelling of the initial laminar phase is a key aspect in order to predict the peak pressure and the time to peak pressure. The present work suggests a modelling approach for the initial laminar phase in explosion scenarios. Findings are compared with experimental data for two classical explosion test cases which resemble the common features in chemical process areas (confinement and congestion). A detailed analysis of the threshold for the transition from laminar to turbulent regime is also carried out. The modelling is implemented in a fully 3D Navier–Stokes compressible formulation. Combustion is treated using a laminar flamelet approach based on the Bray, Moss and Libby (BML) formulation. A novel modified porosity approach developed for the unstructured solver is also considered. Results agree satisfactorily with experiments and the modelling is found to be robust.

CFD predictions of wake-stabilised jet flames in a cross-flow

This study describes an investigation into predicting the major flow properties in wake-stabilised jet flames in a cross flow of air using first- and second-order turbulence models, applied within a RANS (Reynolds-averaged Navier–Stokes) modelling framework. Standard and RNG (re-normalisation group) versions of the k-ε turbulence model were employed at the first-order level and the results compared with a second-moment closure, or RSM (Reynolds stress model). The combustion process was modelled using the laminar flamelet approach together with a thermal radiation model using the discrete ordinate method. The ability of the various turbulence models to reproduce experimentally established flame appearance, profiles of velocity and turbulence intensity, as well as the combustion efficiency of such flames is reported. The results show that all the turbulence models predict similar velocity profiles over the majority of the flow domain considered, except in the wake region, where the predictions of the RSM and RNG k-ε models are in closer agreement with experimental data. In contrast, the standard k-ε model over-predicts the peak turbulence intensity. Also, it is found that the RSM provides superior predictions of the planar recirculation and flame zones attached to the release pipe in the wake region.

Flamelet modeling of coal particle ignition

This paper numerically investigates the ignition of a single coal particle during the devolatilization phase in a laminar entrained-flow reactor, for which experimental data are available from Molina and Shaddix [3]. Different numerical approaches are combined to evaluate the non-premixed flamelet approach for coal particle ignition. First, the particle trajectory and the particle heating are simulated with a Lagrangian–Eulerian approach using a detailed pyrolysis model. In a second step, these results are used as transient boundary conditions for a simulation fully resolving the flow, the mixing field and the chemical reactions around the particle. Finally, in combination with the boundary conditions the time-dependent scalar dissipation rate profiles from the resolved particle calculation are used in a flamelet calculation for the particle up- and downstream directions. Very good agreement is obtained in terms of ignition delay as well as temperature and chemical species distributions in the mixture fraction space when the resolved particle calculation and the unsteady flamelet calculation are compared in the downstream direction. Good agreement is obtained when the numerical results for the ignition time and the time-averaged OH distribution are compared with the available experimental data. The results show the capability of the laminar flamelet approach to correctly predict coal particle ignition during devolatilization using accurate scalar dissipation rate profiles.

Analysis of auto-ignition of heated hydrogen–air mixtures with different detailed reaction mechanisms

Auto-ignition processes of hydrogen, diluted with nitrogen, in heated air are numerically investigated by means of an unsteady laminar flamelet approach in mixture fraction space. The focus is on the auto-ignition delay time and the most reactive mixture fraction as obtained with five chemical mechanisms. Two strongly different levels of dilution, corresponding to experiments in the open literature, are considered. This concerns low-temperature chemistry at atmospheric pressure. The temperature of the air stream is much higher than the temperature of the fuel stream in the cases under study. We extensively investigate the effect of the co-flow temperature, the conditional scalar dissipation rate and the resolution in mixture fraction space for one case. With respect to the conditional scalar dissipation rate, we discuss the Amplitude Mapping Closure (AMC) model with imposed maximum scalar dissipation rate at mixture fraction equal to 0.5, as well as a constant conditional scalar dissipation rate value over the entire mixture fraction value range. We also illustrate that an auto-ignition criterion, based on a temperature rise, leads to similar results as an auto-ignition criterion, based on OH mass fraction, provided that the hydrogen is not too strongly diluted.

An assessment of large eddy simulations of premixed flames propagating past repeated obstacles

This paper presents an assessment of Large Eddy Simulations (LES) in calculating the structure of turbulent premixed flames propagating past solid obstacles. One objective of the present study is to evaluate the LES simulations and identify the drawbacks in accounting the chemical reaction rate. Another objective is to analyse the flame structure and to calculate flame speed, generated overpressure at different time intervals following ignition of a stoichiometric propane/air mixture. The combustion chamber has built-in repeated solid obstructions to enhance the turbulence level and hence increase the flame propagating speed. Various numerical tests have also been carried out to determine the regimes of combustion at different stages of the flame propagation. These have been identified from the calculated results for the flow and flame characteristic parameters. It is found that the flame lies within the ‘thin reaction zone’ regime which supports the use of the laminar flamelet approach for modelling turbulent premixed flames. A submodel to calculate the model coefficient in the algebraic flame surface density model is implemented and examined. It is found that the LES predictions are slightly improved owing to the calculation of model coefficient by using submodel. Results are presented and discussed in this paper are for the flame structure, position, speed, generated pressure and the regimes of combustion during all stages of flame propagation from ignition to venting. The calculated results are validated against available experimental data.

A fully-coupled simulation of vortical structures in a large-scale buoyant pool fire

A numerical study simulating the temporal vortical structures of a large-scale buoyant pool fire has been carried out using a fully-coupled Large Eddy Simulation (LES) model which incorporates all essential subgrid scale (SGS) turbulence, combustion, radiation and soot chemistry considerations. Based on the strained laminar flamelet approach, a scalar dissipation conditioned SGS combustion model is introduced to distinguish the highly non-equilibrating burn and extinguishment of flamelets commonly found in pool fires. Numerical results from the present model are validated and compared against a one-meter diameter methane pool fire experimental data and predictions from other LES field models. The predicted time-averaged velocity and temperature profiles have been found to be in good agreement with the experimental data and those numerical results. Qualitative comparisons of instantaneous velocity field against experimental data have revealed that the dynamic phenomena of large-scale vortical structures and its associated puffing behaviour of pool fire are well captured. Quantitative comparisons of velocity time history and pulsation frequency also show close agreement against experimentally evaluated quantities.