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In view of the application limits of the modified eddy dissipation model (MEDM) in simulations of weakly turbulent flow, compressible flow, and internal flow, an improved eddy dissipation model (IEDM) is proposed. The IEDM model uses the dissociation reactions to obtain the correct combustion temperature instead of the specific heat compensation used in the MEDM model. This extends the application in compressible flow simulation. The simulation accuracy of the IEDM model for weakly turbulent flow is improved by using the accurate transport property and model. The maximum ε/k is limited to give a reasonable reaction rate near walls, and the expression for the model parameter A is also updated. Nine turbulent flames including seven jet flames and two opposed jet flames are simulated with the improved model. Compared with the experimental data of the jet flames, the peak temperature differences with the MEDM model and the IEDM model are 189 and 161 K, respectively, indicating the minor accuracy improvement of the IEDM model. Compared with the experimental data of the opposed flames, the peak temperature differences with the MEDM model and the IEDM model are 131 and 7 K, respectively, indicating the significant accuracy improvement of the IEDM model. [ABSTRACT FROM AUTHOR]

The relevance of the research is caused by the need for accurate reproduction of experimental measurements by mathematical models, since numerical simulation is widely used both for the development of new technologies for the combustion of solid fuels and for the modernization of existing boiler units. And as it is known, the parameters of a pulverized coal flame predicted by numerical simulation directly depend on the way the combustion chemistry in a turbulent flow is modeled. The main aim of the research is to study the accuracy of reproduction of experimental measurements for four approaches to the numerical simulation of ignition and burnout of combustible components of pulverized coal fuel in a turbulent flow. Objects: temperatures, concentrations of gas components (CO2, O2, CO and NOx), axial and tangential velocity components inside the IFRF 2.4 MW furnace. Methods: comparison of experimentally measured parameters of a pulverized coal flame and those predicted by numerical simulation. Numerical simulation was performed using the ANSYS FLUENT software package. The combustion of coal dust in the furnace is modeled as a two-phase turbulent flow system consisting of gas and discrete phases. Results. Numerical modeling of the combustion of pulverized coal in a turbulent flow has been carried out using four different approaches: equilibrium chemistry models with one and two mixture fractions; model of «eddy dissipation» and its combination with the kinetic model of combustion. A comparative analysis of the simulation results with the experimentally measured parameters of a pulverized coal flame established that all the studied approaches to modeling the pulverized coal combustion in a turbulent flow demonstrate a fairly good agreement with the experimental data. The «eddy dissipation» model in combination with the combustion kinetic model has the advantage in accuracy, and the equilibrium chemistry model with one mixture fraction has the advantage in the time of solution convergence.

Carbon monoxide is often produced during the incomplete combustion of volatile organic carbon compounds in industry. In the combustion chamber for oxidizing carbon monoxide emissions, a penta-coaxial port device can be used to improve the process of mixing the fuel and oxidizer. In this study, the conjugate heat transfer analysis was conducted by solving both Reynolds-averaged Navier–Stokes equations with the eddy dissipation model and solid heat conduction equation in the wall using Fluent 2019R2 to simulate the reaction flow of a volatile organic carbon compound burner and heat transfer of the stack insulation layer. The mass fractions of the O2, CO2, and CO gases; the temperature; and the velocity distribution in a combustion chamber were computed to investigate how various design parameters of the combustor, including air inlet size and stack height, and air inflow conditions affected the combustion performance. Results show that the size of the air inlet had only a minor effect on combustion efficiency and that the airstream forced by a fan significantly enhanced the combustion performance. In particular, increasing the height of the stack from 2 m to 4 m greatly increased combustion efficiency from 63% to 94%, with a 50% increase in the incoming air flow rate by natural convection, which demonstrates the importance of stack height in combustor design. [ABSTRACT FROM AUTHOR]

In view of the application limits of the modified eddy dissipation model (MEDM) in simulations of weakly turbulent flow, compressible flow, and internal flow, an improved eddy dissipation model (IEDM) is proposed. The IEDM model uses the dissociation reactions to obtain the correct combustion temperature instead of the specific heat compensation used in the MEDM model. This extends the application in compressible flow simulation. The simulation accuracy of the IEDM model for weakly turbulent flow is improved by using the accurate transport property and model. The maximum ε/k is limited to give a reasonable reaction rate near walls, and the expression for the model parameter A is also updated. Nine turbulent flames including seven jet flames and two opposed jet flames are simulated with the improved model. Compared with the experimental data of the jet flames, the peak temperature differences with the MEDM model and the IEDM model are 189 and 161 K, respectively, indicating the minor accuracy improvement of the IEDM model. Compared with the experimental data of the opposed flames, the peak temperature differences with the MEDM model and the IEDM model are 131 and 7 K, respectively, indicating the significant accuracy improvement of the IEDM model.

This paper reports on the experimental and numerical results of the hythane diffusion flame enriched by oxygen, realized in a coaxial burner characterized by a central jet of hythane injection with an internal diameter of d fuel = 6 mm and an annular jet of oxidant injection with a diameter of d ox = 18 mm. For velocity measurements, the Particle Image Velocimetry (PIV) technology is used. The numerical study is based on the K-ω-SST Turbulent Model and the Eddy Dissipation Model (EDM) for combustion. Firstly, a comparative study is carried out between experimental and numerical simulation of the flow dynamics in the hythane/Air + O 2 flame. Secondly, the numerical results show that the oxygen enrichment increases the temperature of the hythane flame and minimizes the formation of harmful gases into the environment. • Oxygen enrichment favors the flame temperature and reduces the hythane flame length. • The oxygen enrichment reduces the total volume of combustion products. • The oxygen enrichment minimizes the carbon monoxide production. • The mixture fraction characterizes the mixture quality between reactants. [ABSTRACT FROM AUTHOR]

Carbon monoxide is often produced during the incomplete combustion of volatile organic carbon compounds in industry. In the combustion chamber for oxidizing carbon monoxide emissions, a penta-coaxial port device can be used to improve the process of mixing the fuel and oxidizer. In this study, the conjugate heat transfer analysis was conducted by solving both Reynolds-averaged Navier–Stokes equations with the eddy dissipation model and solid heat conduction equation in the wall using Fluent 2019R2 to simulate the reaction flow of a volatile organic carbon compound burner and heat transfer of the stack insulation layer. The mass fractions of the O2, CO2, and CO gases; the temperature; and the velocity distribution in a combustion chamber were computed to investigate how various design parameters of the combustor, including air inlet size and stack height, and air inflow conditions affected the combustion performance. Results show that the size of the air inlet had only a minor effect on combustion efficiency and that the airstream forced by a fan significantly enhanced the combustion performance. In particular, increasing the height of the stack from 2 m to 4 m greatly increased combustion efficiency from 63% to 94%, with a 50% increase in the incoming air flow rate by natural convection, which demonstrates the importance of stack height in combustor design.

Thermal nitric-oxide (NOx) formation in industrial furnaces due to local overheating is a widely known problem. Various industries made significant investments to reduce thermal NOx by varying the operating conditions and designs of the furnace. It is difficult to find the optimal operating conditions that minimize NOx formation in the furnace by trial and error methods. The high temperature in the furnace complicates performing experiments in the furnace. Numerical modeling can provide significant information in such cases. Therefore, the objective of this paper is to obtain a numerical model of the furnace in such a way that the operating conditions can be varied and examined.In this paper, a three-dimensional steady-state finite element model for the anode baking industrial furnace is discussed. The COMSOL Multiphysics software is used for modeling the non-premixed turbulent combustion and the conjugate heat transfer to the insulation lining. The cfMesh software is used for obtaining the mesh. The results show that the simulated temperature agrees well with the measured data from our industrial partner in regions distant from the flames. The analysis shows that by decreasing the fuel mass flow rate and increasing the fuel pipe diameter by 45%, the peak in thermal NOx ppm generated in the furnace decreases by 42%. The model is limited by the use of a single-step chemistry mechanism with an eddy dissipation combustion model and a simplified approach for radiation, such as the P1 approximation model. The model can be further improved by considering a detailed chemistry mechanism model for combustion and a discrete ordinate model for radiation.

In this paper, the effect of the combustion and turbulence Sub-Grid Scale (SGS) model on simulation of a pool fire turbulence field has been studied in open source Cumputational Fluid Dynamic (CFD) software, OpenFOAM. Two combustion models: Eddy Dissipation Model (EDM) and infinite fast chemistry, with the one-equation and Smagorinsky SGS model, are evaluated for a large-scale pool fire. In general, fast kineticbased combustion models predict excessive heat release rate. The mean squared of the velocity uctuations is over-predicted. In this simulation, the turbulence models have no significant effect on the results. In fact, the effect of the combustion model is dominant. The EDM combustion model is more compatible when used with the one-equation SGS model and improves the results compared to other cases. In addition, the infinite fast chemistry combustion model is not a suitable model for fire simulation. [ABSTRACT FROM AUTHOR]

In this study, the NG + H 2 /air + O 2 turbulent flame is numerically investigated using the Computational Fluid Dynamics CFD code. The modulation of combustion and radiation is performed respectively by the Eddy Dissipation Model and the Discrete Ordinate Model. The turbulence modeling is carried out by Shear Stress Transport (SST/k-ω) turbulence model. The H 2 amount in the fuel mixture varies under constant volumetric fuel flow between 0 and 60% and the oxidant is composed by 80% air and 20% pure oxygen. The results obtained show the hydrogen addition to Natural Gas improves the mixing between the reactants, reduces their residence time and reduces the length and thickness of the flame. On the other hand, the hydrogen enrichment minimizes the CO 2 and CO production and increases the NO x level. • The hydrogen addition to fuel improves the mixing between the reactants and favors the flame temperature. • The hydrogen enrichment reduces the flame length and thickness. • The hydrogen addition minimizes the CO 2 and CO production and increases the NO x. [ABSTRACT FROM AUTHOR]

This paper reports an experimental and numerical investigation of a methane-air diffusion flame stabilized over a swirler coaxial burner. The burner configuration consists of two tubes with a swirler placed in the annular part. The passage of the oxidant is ensured by the annular tube; however, the fuel is injected by the central jet through eight holes across the oxidizer flow. The experiments were conducted in a combustion chamber of 25 kW power and 48 × 48 × 100 cm3 dimensions. Numerical flow fields were compared with stereoscopic particle image velocimetry (stereo-PIV) fields for non-reacting and reacting cases. The turbulence was captured using the Reynolds averaged Navier-Stokes (RANS) approach, associated with the eddy dissipation combustion model (EDM) to resolve the turbulence/chemistry interaction. The simulations were performed using the Fluent CFD (Computational Fluid Dynamic) code. Comparison of the computed results and the experimental data showed that the RANS results were capable of predicting the swirling flow. The effect of the inlet velocity ratio on dynamic flow behavior, temperature distribution, species mass fraction and the pollutant emission were numerically studied. The results showed that the radial injection of fuel induces a partial premixing between reactants, which affects the flame behavior, in particular the flame stabilization. The increase in the velocity ratio (Rv) improves the turbulence and subsequently ameliorates the mixing. CO emissions caused by the temperature variation are also decreased due to the improvement of the inlet velocity ratio.

This paper presents a CFD simulation of premixed combustion tests, and centers around a comparison between the classical Eddy Dissipation Model (EDM) and the more sophisticated Turbulent Flame Closure (TFC) model. The chosen tests relate to hydrogen-air deflagration experiments in the THAI and ENACCEF facilities, featuring respectively slow and fast dynamics. Validation of the models is accomplished by comparing model predictions against important measured combustion parameters (flame velocity and spatial propagation, pressure history, spectra, etc.). We follow CFD Best Practice Guidelines, in particular by conducting systematic mesh and time-step sensitivity studies. Both default models predict combustion evolution reasonably well in all tests studied. For the ENACCEF dual compartment experiments, the flame propagation features several dynamical phases, and the TFC model using the progress variable approach reproduces better than the EDM the flame velocity evolution, which leads to better estimation of the temporal gradient of pressure. The better performance of the TFC model comes however at the expense of a larger computational effort, i.e. larger meshes and smaller time steps. This observed trend in 2D geometries is likely to be enhanced in 3D settings. [ABSTRACT FROM AUTHOR]

The present work deals with modeling and simulation of a pilot-scale bubbling fluidized bed gasifier (BFBG) for the gasification of high ash Indian coal. Taking into account different stages of coal gasification, such as drying, volatilization, gasification and combustion processes, a two-dimensional model with quadrilateral cells is developed using FLUENT 12.0 software. The model incorporates exchange of mass, momentum and energy between gaseous phase (phase 1) and solid phase (phase 2) using Eulerian-Eulerian approach. The solid phase is described by kinetic theory of granular flows. Four heterogeneous and four homogeneous reactions covering six species in gaseous phase (CO, CO2, H2, N2, O2 and H2O) and coal in solid phase are considered for the above process. The kinetics for the homogeneous reactions are described using eddy dissipation model available in FLUENT while that for heterogeneous reactions, a user-defined function (UDF) with Arrhenius kinetics is written in C language. The validation of the above model has been done using experimental data generated in a pilot-scale BFBG at Center Institute of Mining and Fuel Research (CIMFR), Dhanbad, India. The computed exit gas compositions as well as temperature profile inside the gasifier are in good agreement (within an error band of ±10%) with experimental data. The flow behaviors and volume fraction profiles of gas and solid phases in the bed zone and freeboard zone of the gasifier have also been predicted using this model. [ABSTRACT FROM AUTHOR]

The aim of this study is to predict the NOx emissions from marine diesel engines by using computational fluid dynamics (CFD). ANSYS program is the simulation software that was used for performing this study. The commercial code of eddy dissipation model (EDM) is the code that was used for simulating the combustion process. The simulation is carried out between 330 CAD and 485 CAD. The principle steps of simulation are illustrated and explained. The result of simulation is validated with result of the experiment that was carried out on direct injection diesel engine. [ABSTRACT FROM AUTHOR]

Abstract: This work compliments our recently published work of implementing the eddy dissipation turbulent combustion model in OpenFOAM [1]. The major update proposed herein is linking the EdmFoam1.5 solver with radiation modeling libraries in OpenFOAM. The new solver was validated against experimental data for jet and swirling Sydney flame (SM1). Each case was modeled with/without radiation modeling. The results have a fair agreement in general. In jet flame cases, the radiation modeling has a good impact on refining the predicted results. However it has not the same great effect on the swirling flame case. A review of the EDM applications in different reacting flow problems is also presented and discussed. [Copyright &y& Elsevier]

Abstract: A two-dimensional axisymmetric RANS numerical model was solved to investigate the effect of increasing the turbulence intensity of the air stream on the NOx and soot formation in turbulent methane diffusion flames. The turbulence–combustion interaction in the flame field was modelled in a k − ε/EDM framework, while the NO and soot concentrations were predicted through implementing the extended Zildovich mechanism and two transport equations model, respectively. The predicted spatial temperature gradients showed acceptable agreement with published experimental measurements. It was found that the increase of free stream turbulence intensity of the air supply results in a significant reduction in the NO formation of the flame. Such phenomenon is discussed by depicting the spatial distribution of the NO concentration in the flame. An observable reduction of the soot formation was also found to be associated with the increase of inlet turbulence intensity of air stream. [Copyright &y& Elsevier]

Abstract: Accidental releases of flammable gases may lead to major fires with extensive effects on the surroundings, mainly due to the intense thermal load emissions. In this paper, a computational approach based on fluid dynamics techniques was attempted aiming at the estimation of resulting thermal radiation emissions and overpressure in large scale cloud fires. In particular, the work dealt with the simulation of Coyote series trials, which conducted in 1981 by Lawrence Livermore National Laboratory (LLNL) and involved the release, dispersion, ignition and combustion of unconfined natural gas clouds in the open-air. In the computations, the CFD code CFX 5.7 was utilized which, in addition to the standard three-dimensional Navier–Stokes equations, incorporates the model for turbulence modeling, the Eddy Dissipation model for combustion and P1 model for radiation transport modeling. Computational thermal radiation histories were compared with experimental data from totally four trials showing a reasonably good agreement for several locations in the field. Discrepancies were laid on overestimation of the thermal load receipted at a certain location, nevertheless within a factor-of-two of the observed values. Moreover, positive peak overpressures were sufficiently low to indicate that the combustion of the cloud yielded a flash fire rather than an explosion. [Copyright &y& Elsevier]