Eddy Dissipation Concept Model Research Articles

Effects of Combustion Model and Chemical Kinetics in Numerical Modeling of Hydrogen-Fueled Dual-Stage HVOF System

The present work examines the effect of utilizing different combustion models and chemical kinetics in predicting the properties of gas and particle phases in a hydrogen-fueled, dual-stage high-velocity oxy-fuel (HVOF) thermal spray system. For this purpose, effects of two combustion models, eddy dissipation concept (EDC) and eddy dissipation model (EDM), on the temperature and velocity fields in the system are studied. The computations using EDC model are performed for detailed and reduced chemical kinetics and for a range of mixture from lean to rich. It is found that EDC with multi-step reaction mechanism predicts higher temperatures for the flow and particle in the warm spray system. In contrast to EDC, the EDM with one-step global reaction shows extra heat release outside the HVOF barrel for rich mixtures which leads to unphysical higher prediction of particle temperature. The simulations using EDC model with detailed and reduced chemical kinetics show some exothermic reactions in converging-divergent nozzle of the system. The heat release from these reactions has profound impacts on the flow and particle temperatures and affects the gas dynamic behavior of flow considerably. Finally, it is discussed that moving toward rich mixtures is more reliable way to control the particles temperature.

Computational analysis on oxygen MILD combustion using synthesis gas

In this paper, a possibility of the oxygen-syngas MILD combustion was assessed using the CFD analysis by applying the JHC (Jet-in Hot Co-flow) combustion system. The effect of the various syngas composition ratios was analyzed, and heating value of synthesis gas was controlled by ratio of CO and H2. The Ansys Fluent, commercial CFD code with RANS (Reynolds Averaged Navier-Stokes), modified k-ε equations and EDC (Eddy Dissipation Concept) model using 2D-axisymmetric computational domain was used in order to analyse oxygen-syngas MILD combustion. It was confirmed that the oxygen-syngas combustion can be formed in the MILD combustion under conditions of the oxygen concentration of 3 ~ 9 %, which is similar condition to the air-fuel MILD combustion region in the Adelaide and Delft flame. As the proportion of H2 in the composition of the synthesis gas is decreased, the region of the MILD combustion with Da < 1 is found to become wider due to the decrease in the Arrhenius reaction rate. At higher oxygen concentration in the co-flow, the region with Da <1 known as MILD regime tends to be decreased.

Numerical Investigation of Combustion Characteristics of a Wave Rotor Combustor Based on a Reduced Reaction Mechanism of Ethylene

To improve simulations of the flame and pressure wave propagation process and investigate the combustion characteristics of a wave rotor combustor (WRC), direct relation graphs with error propagation (DRGEP), quasi-steady-state assumption (QSSA), and sensitivity analysis were used to establish a reduced reaction mechanism comprised of 23 species and 55 elementary reactions, based on the LLNL N-Butane mechanism. The reduced reaction mechanism of ethylene was combined with an eddy dissipation concept (EDC) model to simulate the flame propagation characteristics in a simplified WRC channel. The effects of spoilers with different blockage ratios and hot-jets of different species on combustion characteristics of flame propagation and pressure rise in the WRC channel were investigated. When the heated inert air was used as hot-jet, the ignition delay time of WRC would increase, which indicated that the activity of the burned gas from the hot-jet igniter would affect the ignition delay time. The spoiler facilitates the coupling of flame and shock waves to reduce the coupling time and distance. With the blockage ratio of the spoiler increasing, the coupling time and distance would be reduced.

Study of combustion in CO2-Capturing semi-closed Brayton cycle conditions

The implementation of the Kyoto Protocol, the Paris Agreement, the directive 2018/410 of the European Union and other similar assessments, have placed greater demands related to the control of carbon dioxide emissions on the governments of the signatory countries. This fact has aroused interest not only in renewable energies, but also in new methods to produce power from fossil fuels without releasing greenhouse effect gases to the atmosphere. Within these new power generation methods, the ones where the combustion is performed with pure oxygen are particularly interesting, in order to reuse existing combined-cycle machinery. This article performs an analysis of combustion's phenomenology when it is achieved in conditions derived from semi-closed cycles with oxy-combustion for CO2 capture. The study was performed using Computational Fluid Dynamic (CFD) methods for reacting flows. Chemical reactions were modeled using the detailed GRI-Mech 3.0 mechanism and were taken into account in the CFDs using the Eddy Dissipation Concept model (EDC). The effect of different pressure ratios of the compression stage was analyzed. It was found that the coflow composition, apart from modifying the temperature field, also has an important impact on the boundary conditions that the High Pressure Turbine (HPT) may found at its inlet.

Numerical investigation on the film cooling performance in a multi-elements splash platelet injector

A numerical simulation was performed to investigate the film cooling performance of a multi-element splash platelet injector. A 16-species, 41-reaction mechanism and an eddy-dissipation concept model were used for the simulation of turbulent combustion. The effects of typical film cooling parameters, such as injection slot height, slot geometry, mixture ratio, and injection position, were studied. An increase in slot height caused a direct decrease in velocity ratio and film coolant length and an increase in wall temperature in the combustion chamber head. Slot height, slot geometry, and mixture ratio exerted minimal influence on wall temperature. However, changes in slot geometry and injection position remarkably influenced the injector faceplate temperature. The size of the high-temperature zone of the faceplate increased with the change in slot geometry. When the injection position changed, the location and scope of the high-temperature zone also changed. Furthermore, two recirculation zones were observed near the injector post. These recirculation zones considerably affected film cooling performance, and the upper recirculation zone exerted an adverse influence on cooling performance in terms of faceplate temperature. Therefore, an appropriate design of the cooling slot should be selected to improve film cooling performance.

Large Eddy Simulation of a Pressurized, Partially Premixed Swirling Flame With Finite-Rate Chemistry

Finite-rate chemical effects at gas turbine conditions lead to incomplete combustion and well-known emissions issues. Although a thin flame front is preserved on an average, the instantaneous flame location can vary in thickness and location due to heat losses or imperfect mixing. Postflame phenomena (slow CO oxidation or thermal NO production) can be expected to be significantly influenced by turbulent eddy structures. Since typical gas turbine combustor calculations require insight into flame stabilization as well as pollutant formation, combustion models are required to be sensitive to the instantaneous and local flow conditions. Unfortunately, few models that adequately describe turbulence–chemistry interactions are tractable in the industrial context. A widely used model capable of employing finite-rate chemistry is the eddy dissipation concept (EDC) model of Magnussen. Its application in large eddy simulations (LES) is problematic mainly due to a strong sensitivity to the model constants, which were based on an isotropic cascade analysis in the Reynolds-averaged Navier–Stokes (RANS) context. The objectives of this paper are: (i) to formulate the EDC cascade idea in the context of LES; and (ii) to validate the model using experimental data consisting of velocity (particle image velocimetry (PIV) measurements) and major species (1D Raman measurements), at four axial locations in the near-burner region of a Siemens SGT-100 industrial gas turbine combustor.

Damkohler Number Analysis in Lean Blow-Out of Toroidal Jet Stirred Reactor

Lean blowout (LBO) prediction based on the local parameters in the laboratory toroidal jet-stirred reactor (TJSR) is investigated. The reactor operated on methane is studied using three-dimensional computational fluid dynamics (CFD); the results are compared with the experimental data. Skeletal chemical kinetic mechanism with the eddy dissipation concept (EDC) model is used. Flow bifurcation in the radial (poloidal) plane due to the interaction between counter-rotating vortices creates one dominating poloidal recirculation zone (PRZ) and one weaker toroidal recirculation zone (TRZ). The Damkohler (Da) number in the reactor is the highest in the stabilization vortex; it varies from about Da ∼ 2 at ϕ = 0.55 to Da ∼ 0.2–0.3 at LBO conditions. Due to the reduced turbulent dissipation rate in PRZ, the Da number is an order of magnitude higher than in TRZ. The global blowout event is predicted at the local Da = 0.2 in PRZ. Local blowout events in the regions of low Da can lead to flame instability and to a global flame blowout at a higher fuel–air ratio than predicted by the CFD. Local Da nonuniformity can be used for optimization and analysis of combustion system stability. Further research in the process parameterization and application to the practical combustion system is needed.

Towards predictive simulations of gaseous pool fires

Focusing on advancing predictive fire modeling, large eddy simulations using improved approaches related to thermophysical, turbulence, combustion and radiation modeling are presented. More specifically, the consideration of a non-unity Lewis number, the use of the Hirschfelder-Curtiss diffusion model, the inclusion of differential diffusion and Soret effects, the application of the dynamic Smagorinsky model with a variable turbulent Prandtl number, an eddy dissipation concept model for combustion and the weighted-sum-of-gray-gases model for radiation have been included in a modified version of fireFoam 2.2.x. A comprehensive comparison between the predictions of the modified code against the standard version of fireFoam and experimental data of a medium-scale 22.6 kW methanol pool fire is presented. Evaporation modeling is not yet included.

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 Simulation and Industrial Experimental Research on the Coherent Jet with “CH4 + N2” Mixed Fuel Gas

Coherent jet technology is widely used in the electric arc furnace (EAF) steelmaking process to deliver more energy and momentum into the molten steel bath. Meanwhile, the characteristics of a coherent jet using pure CH4 as the fuel gas have been well investigated in previous studies. To reduce the consumption of CH4, coherent jet technology using “CH4 + N2” mixed fuel gas instead of pure CH4 was proposed and studied in detail by numerical simulation in the present work. The Eddy Dissipation Concept model, which has detailed chemical kinetic mechanisms, was adopted to model the fuel gas combustion reactions. Experimental measurements were carried out to validate the accuracy of the computational model. The present study shows that the jet characteristics of the main oxygen improve along with the increase of the CH4 ratio in fuel gas and with the increase of the flow rate of fuel gas. When the CH4 ratio in the fuel gas is 25 pct, the fuel gas flow rate only has a limited influence on the jet characteristics, unlike the rest of the fuel gas compositions, because a high N2 proportion deteriorates the combustion performance and leads to severe incomplete combustion. Moreover, a false potential core phenomenon was observed and explained in the present study. Based on the average values, the jet length of a coherent jet with 75 pct CH4 can achieve 89.8 pct of that with 100 pct CH4. Finally, an industrial experiment was carried out on a commercial 100t EAF using coherent jet with 75 pct CH4, showing that the average CH4 consumption was reduced from 3.84 to 3.05 Nm3 t−1 under the premise of no obvious changes in the other production indexes.

Assessment of On-the-Fly Chemistry Reduction and Tabulation Approaches for the Simulation of Moderate or Intense Low-Oxygen Dilution Combustion.

The current paper focuses on the numerical simulation of the Delft jet in hot co-flow (DJHC) burner, fed with natural gas and biogas, using the eddy dissipation concept (EDC) model with dynamic chemistry reduction and tabulation, i.e., tabulated dynamic adaptive chemistry (TDAC). The central processing unit (CPU) time saving provided by TDAC is evaluated for various EDC model constants and chemical mechanisms of increasing complexity, using a number of chemistry reduction approaches. Results show that the TDAC method provides speed-up factors of 1.4–2.0 and more than 10 when using a skeletal mechanism (DRM19) and a comprehensive kinetic mechanism (POLIMIC1C3HT), respectively. The directed relation graph with error propagation (DRGEP), dynamic adaptive chemistry (DAC), and elementary flux analysis (EFA) reduction models show superior performances when compared to other approaches, such as directed relation graph (DRG) and path flux analysis (PFA). All of the reduction models have been adapted for run-time reduction. Furthermore, the contribution of tabulation is more important with small mechanisms, while reduction plays a major role with large ones.

Modeling of coal combustion in the CFB by the EDC model with the global reaction mechanism

PurposeThis paper aims to shows the ability of the EDC model with a global reaction mechanism to describe reactions in the Eulerian simulation of a circulating fluidized bed (CFB).Design/methodology/approachThe eddy dissipation concept (EDC) model is embedded in an Eulerian-Eulerian approach to simulate homogeneous reactions.FindingsEDC_G is better than ED_FR in describing chemical reactions. The reaction of CH4 with O2 is faster than that of CO with O2, and NH3 is more liable to be converted than HCN. The combustion rate is higher than the Boudouard reaction rate of coal particles.N2O is mainly reduced by carbon, and NO is mainly converted by carbon into N2 and CO2.Originality/valueThe EDC model with a global reaction mechanism is embedded in a multi-fluid Eulerian approach to simulate the homogeneous reactions in the coal combustion in a CFB, including combustion of volatile gases, desulfurizing reactions and NOx reactions.

Study on the Fluid Flow Characteristics of Coherent Jets with CO2 and O2 Mixed Injection in Electric Arc Furnace Steelmaking Processes

As an efficient oxygen supplying technology, coherent jets are widely applied in electric arc furnace (EAF) steelmaking processes to strengthen chemical energy input, speed up smelting rhythm, and promote the uniformity of molten bath temperature and compositions. Recently, the coherent jet with CO2 and O2 mixed injection (COMI) was proposed and demonstrated great application potentiality in reducing the dust production in EAF steelmaking. In the present study, based on the eddy dissipation concept model, a computational fluid dynamics model of coherent jets with COMI was built with the overall and detailed chemical kinetic mechanisms (GRI-Mech 3.0). Compared with one-step combustion reaction, GRI-Mech 3.0 consists of 325 elementary reactions with 53 components and can predict more accurate results. The numerical simulation results were validated by the combustion experiment data. The jet behavior and the fluid flow characteristics of coherent jets with COMI under 298 K and 1700 K (25 °C and 1427 °C) were studied and the results showed that for coherent jets with COMI, the chemical effect of CO2 significantly weakened the shrouding combustion reactions of CH4 and the relative importance of the chemical effect of CO2 increases with CO2 concentration increasing. The potential core length of coherent jet decreases with the volume fraction of CO2 increasing. Moreover, it also can be found that the potential core length of coherent jets was prolonged with higher ambient temperature.

Combustion characteristics of premixed hydrogen/air flames in a geometrically modified micro combustor

Main challenges for a fuel efficient micro scale combustion are rooted from size restriction of micro combustors which results with inappropriate residence time of fuel/air mixture and intensified heat losses due to relatively high surface to volume ratio of such devices. One way of increasing energy output of micro combustors is to optimize its geometry by considering simplicity and easy manufacturability. In this study, effect of combustor geometric properties on combustion behavior of premixed hydrogen/air mixtures was numerically investigated. For this purpose, an experimentally tested micro combustor’s geometric properties were modified by establishing a backward facing step which is varying distance from combustor inlet and has varying step height, and adding opposing cavities which are varying distance from combustor inlet and have constant length to depth ratio into the flow area. Modeling and simulation studies were performed using ANSYS Design Modeler and Fluent programs, respectively. Combustion behavior was analyzed by means of centerline and outer wall temperature distributions, amount of heat transferred through combustor wall, conversion ratio of input chemical energy to utilizable heat, and species distributions. Turbulence model used in this study is Renormalization Group (RNG) k-ε. Multistep combustion reaction scheme with 9 species and 19 steps was simulated using Eddy Dissipation Concept model (EDC). Results showed that backward facing step in the flame region alters reaction zone distribution, flame length and shape, and consequently temperature value and distribution throughout the combustor. Lastly cavity was found to slightly increase peak temperature value.

Comparative analysis of hydrogen/air combustion CFD-modeling for 3D and 2D computational domain of micro-cylindrical combustor

A computational study of a micro-cylindrical premixed hydrogen-air combustor using RANS is presented. The influence of the geometric dimensionality of the computational domain is studied by performing numerical simulations with 2D planar, 2D axisymmetric and 3D meshes. A commercial software package with a particular choice of several physical models (regarding turbulence, combustion, radiation) is used for this analysis. A mathematical model describing the hydrogen/air combustion in a cylindrical combustor is developed. The reaction scheme of combustion process with 9 species and 19 steps was simulated by usage Eddy Dissipation Concept (EDC) model. The obtained results from presented CFD model were compared with experimental and numerical data of other publications. The combustion characteristics of developed numerical model such as wall and fluid temperature, hydrogen mass fraction, velocity and pressure were investigated for different geometry types. It is established that the 2D approach to solving combustion problems leads to significant deviations of the obtained results from real ones and can be used only for a preliminary evaluation of the characteristics of the combustion process. Based on the developed model, it is established that the difference between the combustion products temperature at the combustor outlet for the three- and two-dimensional (2D-planar and 2D-axis) geometries is more than 25%, and for the range of the flame formation the temperatures differ by several times. The contours of pressure have minimal visual differences for the all hydrogen burning characteristics that are investigated in this work. The axial pressure profiles for all investigated geometries (2D-axis, 2D-planar and 3D) are almost similar in terms of trend and value.

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.

Validation of Turbulence/Chemistry Interaction Models for use in Oxygen Enhanced Combustion

In conventional air-fired combustion systems a huge amount of the heat of formation is absorbed by nitrogen. Oxygen enhanced combustion (OEC) systems uses an O2/N2 mixture with a higher concentration of oxygen than in the ambient air. As a consequence, higher flame temperatures as well as an improved radiative heat transfer in the furnace can be determined when OEC is used. Therefore, OEC is an option to increase the furnace efficiency especially in energy demanding high temperature processes like metal, glass or cement industries.The investigated furnace is cylindrical shaped with 1 m in diameter and a length of 4 m. It was tested for air-fuel combustion and several OEC test cases. A two-staged natural gas burner was arranged at the front surface. The burner allows three different methods to supply the O2/N2 mixture (premixed, air/oxy-fuel, oxygen lancing). Furthermore, the furnace was surrounded by a water cooled shell where the measurement of the total heat flux to the furnace wall was performed. Additionally, in-flame temperatures were determined at several radial and axial distances. Measured results were used to validate the CFD simulations carried out with the eddy dissipation (EDM), eddy dissipation concept (EDC) and steady flamelet model (SFM).

Comprehensive numerical study of the Adelaide Jet in Hot-Coflow burner by means of RANS and detailed chemistry

The present paper shows an in-depth numerical characterisation of the Jet in Hot Co-flow (JHC) configuration using the Reynolds Averaged Navier-Stokes (RANS) modelling with detailed chemistry. The JHC burner emulates the MILD combustion by means of a hot and diluted co-flow and high speed injection. The current investigation focuses on the effect of turbulent combustion models, turbulence model parameters, boundary conditions, multi-component molecular diffusion and kinetic mechanisms on the results. Results show that the approaches used to model the reaction fine structures, namely as Perfectly Stirred Reactors (PSR) or Plug Flow Reactors (PFR), do not have a major impact on the results. Similarly, increasing the complexity of the kinetic mechanism does not lead to major improvements on the numerical predictions. On the other hand, the inclusion of multi-component molecular diffusion helps increasing the prediction accuracy. Three different Eddy Dissipation Concept (EDC) model formulations are compared, showing their interaction with the choice of the C1ε constant in the k−ε turbulence model. Finally, two approaches are benchmarked for turbulence-chemistry interactions, the EDC model and the Partially Stirred Reactor (PaSR) model.

A Study of the Suitability of Combustion Chemistry in the EDC Model for the LES of Backdraft

구획실 내부의 고온 메탄연료에서 발생하는 백드래프트 현상에 대해 FDS v6를 이용한 LES를 수행하였다. EDC연소모델을 적용하였고 여기 필요한 화학반응기구에 대해서는 5가지를 검토하여 백드래프트에 대한 예측성능을 검토하였다. 구획실 내, 외부의 온도, 연료, 속도 및 압력분포에 대한 수치계산 결과고찰과 실험에서 얻어진 압력변화와의 비교를 수행하였다. FDS v6에서 기본적으로 제공하는 EDC 연소모델을 적용하면 LES 기법을 이용하여 백드래프트에 대한 수치계산이 가능함을 확인하였다. 그러나, 결합되는 화학반응기구에 따라서 백드래프트에 대한 예측성능이 큰 차이를 보였다. FDS에서 EDC 연소모델을 적용하여 백드래프트에 대한 LES를 수행할 경우에는 연료특성에맞는 화학반응기구의 적합성을 우선 검토하는 것이 필요함을 확인하였다.Large Eddy Simulation (LES) was peformed for the backdraft occurred in a compartment filled with high-temperaturemethane fuel using the Fire Dynamics Simulator (FDS) of version 6. The prediction performance of FDS, adopted the EddyDissipation Concept (EDC) combustion model with five different chemical reaction mechanisms, was evaluated. The temporaldistributions of temperature, fuel mass fraction, velocity and pressure were discussed with numerical results and the pressurevariation in time was compared with that of previous experiment. The FDS adopted the EDC model showed the possibilityof LES for the backdraft phenomena. However, the prediction performance of the LES with EDC model strongly dependedon the chemical reaction mechanism considered. It is necessary that the suitability of the chemical reaction mechanism shouldbe validated in advance for LES with the FDS v6 to be applied to the simulation of backdraft.

Effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air flames

In this study, effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air mixtures is numerically investigated. An experimentally tested micro combustor geometry is varied by establishing a cavity or a backward facing step or micro channels inside the combustor. Considering effect of combustor geometry on the amount of heat transferred through wall based on outer wall and combustor centerline temperature distributions, combustion behavior is analyzed. Emission behavior is examined by means of mixing conditions, combustion efficiency and maximum temperature value which are highly bound to geometric properties of a micro combustor. Turbulence model used in this study is Renormalization Group k-ε. For turbulence chemistry interaction, Eddy Dissipation Concept model is used. Multistep combustion reaction scheme includes 9 species and 19 steps. Numerical results obtained from this study are validated with published experimental data. Results of this study revealed that combustion in such combustors can be improved by means of quality of mixing process, residence time, combustor centerline and outer wall temperature distributions, conversion rate of input chemical energy to utilizable heat and emanated NOx levels from combustor outlet with proposed geometric variations.