Eddy Dissipation Concept Combustion Model Research Articles

Simulation of DME-O2 Combustion in a Hollow Cone Impinging Jet Combustor for Direct-Fired Supercritical CO2 Power Cycle

ABSTRACT Combustion is critical in the direct-fired supercritical CO2 power cycle. A hollow cone impinging jet combustor is designed. Instead of methane, dimethyl ether is used as the fuel for the direct-fired supercritical CO2 cycle, with a higher hydrocarbon ratio and oxygen. The dimethyl ether combustion process is simulated by Fluent, based on the k-ε turbulence model and Eddy-Dissipation Concept combustion model, combined with the dimethyl ether combustion mechanism. The effects of the CO2 recycling ratio, the excess oxygen coefficient, and in-combustor pressure are investigated to support improving combustion performance. The results indicate that the recycled CO2 intensifies the movement of the mixture in the combustor, reduces the peak temperature, and makes temperature distribution more uniform. As the excess oxygen coefficient increases, the peak temperature is enhanced, and the combustion is more sufficient. The effect of in-combustor pressure is complex. On the one hand, increasing in-combustor pressure reduces the jet penetration and inhibits the contact between dimethyl ether and O2, leading to a lower peak temperature. On the other hand, it prolongs the residence time of the high-temperature exhaust, making the reaction between dimethyl ether and O2 more sufficient. The optimal operating condition of the combustor is a CO2 recycling ratio of 0.95, an excess oxygen coefficient of 1.20, and an in-combustor pressure of 30 MPa. Moreover, the obtained combustion products parameters, such as temperature, component concentration, and mass flow rate, can guide the performance analysis for the direct-fired supercritical CO2 power cycle.

Colourless distributed combustion effects on a pre‐mixed coke oven gas flame

AbstractFuels consisting of high hydrogen concentration can be consumed under colourless distributed combustion (CDC) to suppress flashback tendency in premixed conditions. Higher NOX challenges can also be overcome through CDC. For those purposes, coke oven gas was consumed under CDC within the scope of this study. To achieve CDC, or diluents were introduced into the oxidizer so that oxygen concentration in the oxidizer would be decreased from 21% O2 to its lean blow‐off limits. Excess air ratios were determined as λ = 1.2 and λ = 1.5 along with a thermal power of 10 kW under premixed conditions. A commercial computational fluid dynamics code was used to predict temperature distribution and , CO, and emissions. 162‐step reactions created with GRI‐Mech 3.0 chemical kinetics was integrated to the eddy dissipation concept combustion model. The temperature and profiles predicted were compared with the experimental results. Consistency was achieved at ~95% for temperature profiles, and almost 100% for profiles between the measured and the predicted ones. According to the results, it is concluded that a more homogeneous temperature distribution with the ~21% decrease in the maximum temperature was observed, and there was about 96% decrease in level. It was also demonstrated that using as a diluent is more effective in terms of temperature distribution over the combustor and reduction, while dilution with is more effective in terms about 70% in decrease on CO.

Computational study of a high-pressure hydrogen storage tank explosion at different heights from the ground

A computational study was carried out to investigate the explosion of a 35-MPa, 72.4-L high-pressure hydrogen storage tank at different heights from the ground. The numerical simulations were carried out using OpenFOAM computational fluid dynamics code. The numerical simulation incorporates a k−ω shear stress transport turbulence model and an eddy dissipation concept combustion model with a one-step finite rate reaction. The prediction performance of the numerical approach was validated based on experimental results obtained from previous studies. The hydrogen tank explosion was investigated at different heights (h; 0.0, 0.2, 0.5, 0.8, and 1.0 m) from the ground and at h = 0.2 m from the ground with θ = 65°). The numerical predictions showed that tank height and position significantly affect the blast overpressure strength and propagation. The reflected pressure magnitude increased as the tank height decreased with respect to ground level. At farther distances, the explosion scenario of h = 0.2 m and θ = 65° showed stronger maximum overpressure and impulse hazards than the other height settings. The difference in maximum overpressure magnitude between the different explosion scenarios was insignificant at 4 m from the tank. Hydrogen gas auto-ignites closer to the ground, due to the compression effect attributed to the Mach stem phenomenon. Our results showed that blast effects in the radial direction are more hazardous than those in the axial direction.

Numerical study of the impact of the EDC formulation and finite-rate chemistry mechanisms in CFD simulations of fire plumes

CFD simulations are presented for an in-depth study on different formulations (including implementation details) of the Eddy Dissipation Concept (EDC) turbulent combustion model, with infinitely fast chemistry as well as finite-rate chemistry with different reaction mechanisms. A turbulent line burner and a gaseous pool fire are chosen as first step in an extensive validation campaign for large eddy simulations of this kind, performed with OpenFOAM v1912. Artificial flame anchoring is necessary to establish a burning flame with finite-rate chemistry. Differences in mean temperatures, and the resulting flow fields, as obtained with the different formulations of the EDC combustion model, are explained by the impact of the reaction rates. CO is discussed as the most important of minor species as well. It is demonstrated that both the formulation of EDC and the choice of the chemistry mechanism can have a significant impact when the CFD mesh is not sufficiently fine, even though the flames studied are unsuppressed. This can lead to significant deviations from experimental data. This is a point of attention for future work, focusing on extinction and re-ignition phenomena.

A RANS/EDC Simulation of the Lifted Turbulent Non-Premixed Round Jet of CH4 Flame

The objectives of this work is to determine the average rate of reaction by numerical study of the reacting flow inside an axisymmetric free jet, and the validation of the eddy dissipation concept (EDC) combustion model implemented in ANSYS Fluent. The validation of the eddy dissipation concept combustion model involved the reproduction of a lifted, non-premixed, turbulent free jet flame described experimentally in Mahmud (2007). Three chemical mechanisms were used along the combustion model, namely the 2-step Westbrook and Dryer mechanism, the skeletal Jones-Lindstedt mechanism and the Hyer mechanism. Turbulence was modeled with the standard k-ε model The flame lift-off height and the temperature profiles are reproduced accurately by the Hyer model.

Investigation of reacting fuel jets in hot vitiated crossflow

Near-wall reacting jets can occur in different engineering applications, such as rocket combustion chambers and in gas turbine combustors and turbines. This work presents results of experimental investigations of reacting gaseous fuel jets (hydrogen, methane, propane) injected normally into a hot oxygen-rich cross-flow using OH laser-induced fluorescence and OH* chemiluminescence diagnostics. RANS CFD simulations with EDC combustion model are performed for comparison. To determine the surface heat fluxes, the inverse heat conduction method was applied using measured wall temperature data as input. It was observed, that hydrogen jets ignite directly at the injection location and caused a higher surface heat flux than the hydrocarbon jets, where jet-like diffusion flames emerged. With the latter fuels, a significant ignition delay length was observed. Operation with methane fuel showed the least stability, least reactivity and the lowest surface heat flux. Increasing the jet momentum ratio led to a reduced ignition delay length due to enhanced jet-crossflow interaction, and to a reduction of surface heat flux as the reacting jet detached more from the surface. CFD results using the Eddy-Dissipation Concept (EDC) combustion model predicted ignition delay lengths and reaction zone shapes in qualitative agreement with the experiment but with a trend of overestimating combustion temperatures.

Dynamic adjustment of the Eddy Dissipation Concept model for turbulent/combustion interactions in mixed combustion regimes

The Eddy Dissipation Concept (EDC) combustion model, in comparison with some other combustion models, has drawn attention, especially for the Moderate or Intense low oxygen Dilution (MILD) combustion. The original formulation of the EDC combustion model is not developed for the MILD combustion regime, and a revision of the model could be considered. In this study, the effect of the characteristic frequency on the EDC combustion model has been investigated, and some parametric studies on the ratios of length and time scales of the fine structures to the Kolmogorov scales have been performed. Results revealed that finding optimum model constants for all combustion field with a wide range of Damköhler numbers seems to be complicated. The variations in scales ratio of fine structure to the Kolmogorov eddies shows different consequence at low and high Damköhler number combustion regions which leads to a conclusion on difficulties for EDC model global optimization. As a solution, a localized modulation method based on some local variables such as the turbulence Reynolds number and Damköhler number has been developed and applied on the Adelaide Jet in Hot Coflow(JHC) and Delft Jet in Hot Coflow (DJHC), and in addition in supplementary material on Sandia/TUD piloted flame and Sydney bluff-body burners. These burners demonstrate combustion regimes with both low and high Damköhler numbers. Results have shown the better performance of the local approach in the simulation of the burners. The improvement is more perceptible at the sections far from the inlet, where Damköhler number is increased, in comparison with the standard (default) EDC model. The average of deviations from the measurements is decreased by more than 10% and even more by a decrement in oxidizer oxygen level.

Research on Structural Optimization of Regenerative Melting Aluminum Furnace

In order to predict the performance parameters of a regenerative melting aluminum furnace new designed based on the regenerative combustion technology, the computational fluid dynamics numerical simulation method was used to study its combustion characteristics. Flow field, temperature field and mass fraction of pollutant NO were numerically simulated for the furnace by using the k-ε turbulence model, Eddy-Dissipation Concept combustion model, P-1 radiation equation, and NO<SUB>X</SUB> pollutant model respectively of the ANSYS-Fluent software. The result shows a short circuit of the flue gas appears when the regenerative burner is arranged on the same side furnace wall, at the same time, the distribution of the temperature field is uneven. The researcher carried out structural transformation of the aluminum melting furnace. Compared with the furnace before modification, the furnace that the regenerative burners installed in the middle of both sides wall ensures temperature field distribution more uniform and reduction of the NO emissions at furnace outlet.

Numerical study of the pseudo-boiling phenomenon in the transcritical liquid oxygen/gaseous hydrogen flame

The interactions and effects of turbulent mixing, pseudo-boiling phenomena, and chemical reaction heat release on the combustion of cryogenic liquid oxygen and gaseous hydrogen under supercritical pressure conditions are investigated using RANS simulations. Comparisons of the present numerical simulation results with available experimental data reveal a reasonably good prediction of a supercritical axial shear hydrogen-oxygen flame using the standard k-ε turbulence model and the eddy dissipation concept combustion model with a 23 reaction steps kinetics for H2-O2 reaction. The present simulation qualitatively reproduced oxygen injection and its reaction with the co-flowing hydrogen, which is characterized by rapid flame expansion, downstream flame propagation, and expansion induced flow recirculation. Several turbulence models were used for numerical simulations. It is shown that the selection of an appropriate turbulence model for transcritical reacting flows is crucial and far more important than for subcritical reacting flows. It is indicated that the pseudo-boiling phenomena is the main reason for the considerable differences between the turbulence models in a transcritical flame. Also, it is demonstrated that the liquid oxygen core disappears faster in a non-reacting flow than in a reacting flow. The shear layer in the non-reacting flow is much stronger than reacting case; providing a large transfer of energy from the outer layer to the inner layer. At the supercritical injection conditions, the difference between the turbulence models is much less than the transcritical injection conditions.

Numerical and experimental investigations of geometrical parameters on GH2/GO2 injector

To study the influence of injector geometrical parameters on combustor flow fields, detailed numerical and experimental investigations of a single-element injector with gaseous hydrogen and gaseous oxygen (GH2/GO2) propellants were performed at atmospheric pressure. The flow field characteristics of three different injector forms: shear-coaxial, swirl-coaxial and dual-swirl were discussed. The simulations of the combustion process with the use of steady Reynolds-averaged Navier-Stokes (RANS) techniques on a base of the ANSYS software were conducted. The Realizable k-ε turbulence model and eddy-dissipation concept combustion model were employed taking into account reactions of chemical kinetics. Results from the simulations demonstrated the detailed flame structures of the combustion flow fields. Subsequently, an advanced, non-intrusive optical diagnostics approach was adopted, including high-speed imaging and OH* chemiluminescence. The results show that the swirl flow injector approach elicits a distinctly different ignition process, in which the heat load from the swirl flow results in substantial damage to the chamber wall. Finally, with the help of advanced imaging processing method, it verified the validation of the numerical simulated model and acquired a specific linear relationship between the optical data and numerical calculations.

Numerical study of hydrogen/methane buoyant fires using FireFoam

Hydrogen/methane buoyant fires with various hydrogen volume fractions ranging from 0% to 20% were numerically studied in this paper. The modified eddy dissipation concept combustion model for multi-fuels in the large eddy simulation (LES) framework was employed for combustion, and especially the infinitely fast rate based on “global” concept was improved. Combined with the weighted sum of gray gas model for emission/absorption coefficient, the finite volume discrete ordinates model was used to compute the radiative heat transfer. The predicted centerline temperature, velocity, and flame height are in good consistence with the measured data. Furthermore, the detailed analysis was conducted on the dependency of the parameters such as centerline temperature and velocity, flame height, and soot volume fraction on hydrogen volume concentration.

Numerical investigation of non-premixed and premixed rotational tubular flame: a study of flame structure and instability

Tubular flames are considered due to their advantages in the geometry of the flame. The major importance of tubular flame which makes it different from other flames is its uniform temperature distribution. Therefore, it reduces the possibility of the formation of thermal fluctuations and hot spots along the furnaces. In this paper, high-speed, non-premixed and premixed tubular flames are numerically investigated using computational fluid dynamics under various operational conditions. Methane/air and CO2-diluted methane/oxygen combustions are considered in both non-premixed and premixed modes. $$k - \omega \, SST$$ model, eddy dissipation concept combustion model, and P1 radiation model have been used as numerical models. Numerical results are validated against available experimental measurements in the non-premixed tubular flame using DRM22 kinetic mechanism for methane/air combustions and GRI-Mech 3.0 for methane/oxygen mixtures. The structure of the tubular flame in the combustion chamber and stability limits of tubular flame in terms of operating conditions have been studied in the present paper. Results show that premixed tubular flames establish more uniform radial temperature distribution and wider stable flame operating conditions. In addition, diluted methane/oxygen tubular flames have been shown broader stable condition limits than methane/air flames.

Generalisation of the eddy-dissipation concept for jet flames with low turbulence and low Damköhler number

Moderate or intense low oxygen dilution (MILD) combustion has been the focus of a range of fundamental experimental and numerical studies. Reasonable agreement between experimental and numerical investigations, however, requires finite-rate chemistry models and, often, ad hoc model adjustment. To remedy this, an adaptive eddy dissipation concept (EDC) combustion model has previously been developed to target conditions encountered in MILD combustion; however, this model relies on a simplified, pre-defined assumption about the combustion chemistry. The present paper reports a generalised version of the modified EDC model without the need for an assumed, single-step chemical reaction or ad hoc coefficient tuning. The results show good agreement with experimental measurements of two CH4/H2 flames in hot coflows, showing improvements over the standard EDC model as well as the previously published modified EDC model. The updated version of the EDC model also demonstrates the capacity to reproduce the downstream transition in flame structure of a MILD jet flame seen experimentally, but which has previously proven challenging to capture computationally. Analyses of the previously identified dominant heat-release reactions provide insight into the structural differences between a conventional autoignitive flame and a flame in the MILD combustion regime, whilst highlighting the requirement for a generalised EDC combustion model.

Numerical Study of Heptane Pool Fires on a Hollow Square Pan

Abstract Heptane pool fires with different mass burning rates ranging from 0.00123kg/s (corresponding to steady burning stage in experiments) to 0.0247kg/s (corresponding to fuel boiling burning stage) on a hollow square pan are numercally studied in this paper. The fireFoam, the large eddy simulation (LES)–based fire simulation code within OpenFOAM®, was employed with the modified Eddy Dissipation Concept combustion model[13] and PaSR based soot model[14]. The predictions achieved good qualitative and quantitative agreement with the experimental data[9]. Further analysis was conducted on the fire behaviour and in particular the fire merging phenomena. The dependency betwwen the key parameters such as flame height, centerline temperature and soot distributions on the mass burning rate was also discussed.

Numerical study of a tangentially fired boiler for reducing steam tube overheating

A comprehensive numerical and experimental study on a 200MW tangentially fired boiler firing metallurgical gases was conducted. A three-dimensional Computational Fluid Dynamics (CFD) model was developed to simulate the flow characteristics and combustion process inside the boiler. The eddy dissipation concept combustion model was applied to take into account detailed turbulent interactive reacting chemical reactions. Field experiments were also conducted on the original tangentially fired boiler under different operation conditions. Flame profiles videos were captured during experiments. A quick comparison of the experimental flame profile with numerical simulation results shows good agreement. Wall steam tubes overheating problem was observed, and the hot spots were identified based on a wide range of typical operation conditions. The effect of total fuel input and natural gas percentage on the furnace wall temperature were investigated.

Improvement study for the dry-low-NOx hydrogen micromix combustion technology

The dry-low-NOx (DLN) micromix combustion principle is developed for the low emission combustion of hydrogen in an industrial gas turbine APU GTCP 36-300. The further decrease of NOx emissions along a wider operation range with pure hydrogen supports the introduction of the micromix technology to industrial applications. Experimental and numerical studies show the successful advance of the DLN micromix combustion to extended DLN operation range. The impact of the hydrogen fuel properties on the combustion principle and aerodynamic flame stabilization design laws, flow field, flame structure and emission characteristics is investigated by numerical analysis using an eddy dissipation concept combustion model and validated against experimental results.

Assessment of the EDC combustion model in MILD conditions with in-furnace experimental data

The paper presents a detailed experimental data set in a MILD combustion furnace. This laboratory scale furnace was especially designed to combine a small computational time with a kind of industrial operation. The in-furnace measurements are compared to the numerical results obtained with two turbulence–chemistry interaction models: the Eddy-Dissipation Model (EDFR) and the Eddy-Dissipation Concept (EDC). It is confirmed that the EDC model brings interesting improvements, compared to the EDFR model. First, it improves the prediction of the NOx emission thanks to the possibility to include in the reaction mechanism some radical species required to compute the NO reaction rates. Then, this model is able to capture the kinetic limitation responsible for the reaction delay and which impacts the reaction progress through the furnace. The effect of the operating conditions is correctly reproduced in a relative way, what is not the case with the EDFR model. However, due to its high sensitivity to the operating conditions the EDC model is not able to reproduce the shape and the position of the reaction zone with precision. In conclusion, the EDC model still needs to be optimized for MILD combustion modelling and requires detailed experimental data to this end, as proposed in this paper.

Numerical Simulation of the Acenaphthylene Compound in an Atmospheric Plasma Reactor to Treat Cooking Fumes

Acenaphthylene (chemical formula of C12H8, Acpy), also known as cyclopenta[de]naphthalene, is a polycyclic aromatic hydrocarbon (PAH) with 3 aromatic rings. The Acpy compound is a PAH on the Environmental Protection Agency's (EPA's) priority pollutant list. This study presents a simulation of an atmospheric plasma reactor (APR) using a method based on computational fluid dynamics (CFD). A commercial CFD tool was used to solve mass, momentum, and energy equations. The commercial FLUENT code was then used to simulate the Acpy compound using a 3D APR to treat the cooking fume exhaust emitted from a restaurant kitchen. The simulations in this study adopted the APR size and operating parameters from a self-designed atmospheric plasma reactor in a previous study (NSC95-2221-E020-021). An in-house reduced chemical mechanism was coupled with the CFD code for improved computational runtime. The reactivity of the system was considered with the RNG k-ε turbulence model and the classical Eddy Dissipation Concept combustion model. The simulation results were compared with the experimental temperature measurement and the removal efficiency of Acpy. The simulated average removal efficiency of Acpy was 61.3%.

Large Eddy Simulation of Vertical Turbulent Wall Fires

The objective of the present study is to evaluate the ability of wall-resolved large eddy simulations (LES) to accurately simulate wall fires. The boundary layer combustion configuration is a simplified vertical wall flame configuration in which gaseous fuel (propylene) is supplied across a porous wall and the fuel mass flow rate is prescribed. The focus of the study is on the flame-to-wall heat transfer. The LES performance is evaluated via comparisons with a previously developed experimental database.LES simulations are performed using FireFOAM (FireFOAM is an advanced fire modeling software developed by FM Global). The FireFOAM simulations use: a carefully-designed block-structured computational grid; the k-equation eddy viscosity model for turbulence; the Eddy Dissipation Concept (EDC) model for combustion; and the discrete ordinate method for thermal radiation transport. A number of modifications are introduced in the baseline FireFOAM modeling capability: the original turbulent eddy viscosity model is replaced by the wall-adapting local eddy-viscosity model – WALE – that provides correct near-wall behavior; the EDC combustion model is also enhanced to include laminar flame conditions.The wall flame configuration features low Reynolds number conditions and a transitional laminar-to-turbulent combustion regime; while these low Reynolds number conditions are believed to be representative of meter-scale wall fires, they represent a difficult challenge for LES simulations. The simulations are in good qualitative comparison with experimental data; quantitative agreement is fair. The main source of discrepancy is an overestimate of the size of the laminar flame base region and a reduced accuracy of LES combustion and radiation models under laminar-like conditions.

2D and 3D CFD modelling of a reactive turbulent flow in a double shell supercritical water oxidation reactor

In order to design and define appropriate dimensions for a supercritical oxidation reactor, a comparative 2D and 3D simulation of the fluid dynamics and heat transfer during an oxidation process has been performed. The solver used is a commercial code, Fluent 6.2®. The turbulent flow field in the reactor, created by the stirrer, is taken into account with a k–ω model and a swirl imposed to the fluid. In the 3D case the rotation of the stirrer can be modelled using the sliding mesh model and the moving reference frame model. This work allows comparing 2D and 3D velocity and heat transfer calculations. The predicted values (mainly species concentrations and temperature profiles) are of the same order in both cases. The reactivity of the system is taken into account with a classical Eddy Dissipation Concept combustion model. Comparisons with experimental temperature measurements validate the ability of the CFD modelling to simulate the supercritical water oxidation reactive medium. Results indicate that the flow can be considered as plug flow-like and that heat transfer is strongly enhanced by the stirring.