Numerical Simulation Of Combustion Processes Research Articles

Numerical simulation of combustion processes

In this paper, we propose a numerical method for solving the problem of the propagation and combustion of a methane jet in an axisymmetric satellite air flow. Within the framework of the modified turbulence model and the Arrhenius law, mathematical and numerical models of the problem of a turbulent axisymmetric methane jet in an infinite cocurrent air flow at a finite reaction rate have been developed. By introducing functions and generalized Schwab-Zel'dovich functions, as well as the stream function, ten differential equations for the conservation of substances are represented by differential equations equivalent to them. The equations of the turbulent boundary layer of a multicomponent gas for an axisymmetric jet are transformed with the transition to dimensionless variables and the introduction of a stream function. The dimensionless equations of the turbulent boundary layer of reacting gases in von Mises coordinates are used for modeling. For the numerical solution of the combustion problem according to the Arrhenius law, an implicit finite-difference scheme was used, which provides the second order of approximation accuracy in longitudinal and transverse coordinates. This made it possible to significantly reduce the calculation time as a result of using a large calculation step for the longitudinal coordinate. In connection with the nonlinearity of the equations of conservation and transfer of substances, an iterative process was organized. Some results of the computational experiment are presented. Comparison of the results of calculating the change in the temperature of the axial flow according to the turbulence models modified by k − ε and Prandtl with experimental data. The adequacy of the results was verified by the implementation of the laws of conservation of mass, momentum and total enthalpy, as well as by comparing the results with experimental data from other authors with the largest 5% deviation. This means that the previously presented algorithm and calculation program can be used for practical purposes. The results obtained with both turbulence models were compared with experimental data. Analyzing the results, one can notice that the k − ε model coincides more qualitatively with the experiment than the Prandtl turbulence model.

RETRACTED: Numerical simulation of combustion process in different heating furnaces

The physical field of different heating furnaces and its related aspects were studied by numerical simulation method. Firstly, by studying the heating furnaces of different shapes, namely triangle furnace, square furnace and cylindrical furnace, it was found that: square furnace and cylinder furnace combustion was more full, high temperature range was larger, different furnace tube heat intensity distribution was more uniform, the amount of heat loss was lower, the outlet NOx emission was higher. By studying the cylindrical furnaces with different dip angles of 95°, 93°, 90°, 87° and 85°, it was found that with the decrease of the dip angle, the inner reflux decreases, the reaction rate decreases, the range of higher temperature increases, the heat absorption of the furnace tube was larger, and the NOx concentration at the outlet was lower.

Approach to combustion calculation using neural network

Numerical simulations of combustion processes in rocket engines requires a long run time of supercomputer systems even for a very short physical time. Therefore, creating digital twins of rocket engines needs enormous processor time, and is not very effective. This computational time surpasses the actual physical time of the process in many orders of magnitude. To speed up numerical simulations the paper presents a solution of the chemical kinetics problem using artificial neural network approach. Using the architecture of a multilayer neural network with bypass connections, namely residual network, it is possible to obtain a fast and reliable solution to the problem. The neural network is trained to predict the state of the system only one time step ahead. Using it in a recursive mode, it is possible to forecast for thousands of steps without loss of accuracy.

Numerical simulation of combustion process of petroleum coke partially substituting heavy oil in combustion space of float glass furnace

Numerical simulation of combustion process of petroleum coke partially substituting heavy oil in combustion space of float glass furnace

Modeling of transport processes in the cigarette principle combustion furnace

This paper presents numerical and experimental investigations of complex and interrelated physical and chemical phenomena that occur during combustion of baled soybean residue in the furnace with the cigarette type of combustion. The result of comprehensive research is reactive flow model of biomass combustion inside furnace. Model is described by set of PDE which define momentum, heat and mass transfer processes in porous and fluid system. The main aim of developed CFD model is numerical simulation of combustion process inside the cigarette furnace. It is also used to provide deeper insight in complex processes occurring during biomass combustion. Verification of proposed numerical model was performed through comprehensive experimental tests on the experimental-industrial plant of 1.5 MW boiler for heating the greenhouses in the Agricultural Corporation in Belgrade. The tests included measurement of flow rate and air and flue gas temperature input and output values on the furnace that are taken as the boundary conditions of the developed model. Comparison of the experimental results shows satisfactory agreement with numerical results (the maximum relative deviation of calculation and measurement temperatures are 10-45%), therefore the developed mathematical model could be used to analyse the effects of structural and parametric (fuel composition, power rate, air excess etc.) changes of the facility, from the standpoint of energy efficiency and ecology.

Численное моделирование процессов горения водородовоздушной смеси в канале переменного сечения

Численное моделирование процессов горения водородовоздушной смеси в канале переменного сечения

Simultaneous improvement of exhaust emissions and fuel consumption by optimization of combustion chamber shape of a diesel engine

In order to achieve clean exhaust gas emissions and high fuel efficiency in diesel engines, a new combustion chamber concept called “egg-shaped piston bowl” was proposed and its effectiveness was validated by engine experiments using a single-cylinder research engine. Numerical simulations of combustion processes and exhaust gas emissions were carried out on different piston bowl geometries using GTT-CHEM code, which is a three-dimensional computational fluid dynamics code coupled with detailed chemical kinetics. In this code, a combustion model taking account of the auto-ignition process of a non-homogeneous mixture and a detailed phenomenological soot model was incorporated. In the detailed phenomenological soot model, particle inception from polycyclic aromatic hydrocarbons, surface growth/oxidation and particle coagulation processes were considered. In addition, to investigate the soot formation characteristics with different piston bowl geometries, experimental measurements by the two-color method were conducted with a constant-volume vessel under high-temperature and high-pressure conditions. As a result of the engine experiments and the numerical simulations, it was confirmed that simultaneous reduction in exhaust gas emissions and fuel consumption was able to be achieved by the egg-shaped piston bowl concept.

Numerical simulations of combustion process in a gas turbine with a single and multi-point fuel injection system

The paper presents a numerical study of a medium size model of industrial gas turbine combustor. The research was conducted using the RANS (Reynolds Averaged Navier–Stokes) approach with k–∊ model and LES (Large Eddy Simulation) with WALE (Wall Adapting Local Eddy viscosity) subgrid model. The simulations were performed in cold and reacting flow conditions. In the latter case, the combustion process was modelled using a steady flamelet model with chemical mechanisms of Smooke with 16 species and 25 elementary reactions, and the GRI-2.11 with 49 species and 277 elementary reactions including NO chemistry. In the first part of the paper, the numerical results were validated against experimental data including velocity field, temperature and species concentrations. The velocity components predicted for the cold flow agree very well with measurements. In the case of the simulations of the reacting flow, some discrepancies were observed in both the temperature field and species concentrations. However, the main flame characteristics were captured correctly. It turned out that the chemical kinetics had a larger impact on the results than the turbulence model. In the second part of the paper, we modified the fuel and air injection method and analysed how the changes introduced affect the flame dynamics. It was shown that: (i) depending on the distribution of air, the velocity, temperature and species composition in the upper part of the combustion chamber can be significantly altered; (ii) more substantial changes can be achieved by shifting the fuel injection points; their location outside the main recirculation zone leads to a dangerous situation resulting in overheating of the walls; (iii) it turns out that substantial differences in the flame characteristics in the upper part of the combustion chamber vanish approaching the outlet plane and the resulting mixture compositions are very similar.

3-D Modeling of Heat and Mass Transfer during Combustion of Solid Fuel in Bkz-420-140-7C Combustion Chamber of Kazkhstan

In this paper the results obtained by the numerical method of modeling of Ekibastuz coal burning in BKZ-420 combustion chamber of Kazakhstan Power Plant are presented. They are devoted to the numerical simulation of combustion processes in the furnace boiler BKZ-420. Boiler’s steam generates capacity equal 420 T/h. Boiler has six vertical pulverized coal burners arranged in two levels with three burners on the front wall of the boiler. High ash, low-grade coal from Ekibastuz burned in the furnace. Its ash content is 40%, volatile – 24%, humidity–5%, highest calorific value is 16750 kJ/kg. Milling dispersity of coal was equal to R90 = 15%.It was shown in this research that the most intense burning is observed in the central part of the chamber where the flow temperature reaches about 980 °C and it is seen that the temperature reaches a peak in the cross sections of the burners location. The combustion reaction there occurs more intensively.

Impact of methane addition on the performance of biodiesel fueled diesel engine

This study aims to investigate the impact of methane on performance and emission characteristics of diesel engine fueled by biodiesel. A combined chemical reaction model was developed including the reaction kinetics of biodiesel and methane with CO, NOx and soot formation mechanisms embedded. The developed skeletal reaction mechanism was first validated by performing ignition delay calculations against the detailed biodiesel reaction mechanism, then it was subject to 3D numerical simulations of combustion process in a diesel engine against the experimental results under various operating conditions, good agreement has been obtained. After the validation, it was used to investigate the effect of different methane percentage on the performance of the engine. The results indicate that under various engine load conditions, with the increase of methane addition, both CO and soot emissions are significantly reduced with negligible NOx emission change.

LHV predication models and LHV effect on the performance of CI engine running with biodiesel blends

The heating value of fuel is one of its most important physical properties, and is used for the design and numerical simulation of combustion processes within internal combustion (IC) engines. Recently, there has been a significant increase in the use of dual fuel and blended fuels in compression ignition (CI) engines. Most of the blended fuels include biodiesel as one of the constituents and hence the objective of this study is to investigate the effect of biodiesel content to lower heating value (LHV) and to develop new LHV prediction models that correlate the LHV with biodiesel fraction, density and viscosity. Furthermore, this study also investigated the effects of the LHV on CI engines performance parameters experimentally. To achieve the above mentioned objectives density, viscosity and LHV of rapeseed oil biodiesel, corn oil biodiesel and waste oil biodiesel at different blend fraction values (B0, B5, B10, B20, B50, B75, and B100, where ‘B5’ denotes a blend of 5% biodiesel and 95% mineral diesel, etc.) were measured as per EN ISO 3675:1998, EN ISO 3104:1996 and DIN 51900 standards. The engine experimental work was conducted on a four-cylinder, four-stroke, direct injection (DI) and turbocharged diesel engine by using rapeseed oil and normal diesel blends. Based on the experimental results, models were developed which have the capability to predict the LHV corresponding to different fractions, densities and viscosities of biodiesel. The models are shown to produce consistent results with experimentally measured ones and compared with previous researches’ models. Furthermore the effects of LHV on brake specific fuel consumption (BSFC) and thermal efficiency were analysed and it has been seen that for the neat biodiesel which its LHV is lower by 8% than diesel resulted in an increment of BSFC and thermal efficiency by 18% and 25% respectively.

Numerical simulation of HTPB combustion in a 2D hybrid slab combustor

A code for the numerical simulation of combustion processes in hybrid rockets, developed at the Space Propulsion Laboratory of Politecnico di Milano (SPLab), is presented. The code deals with Navier–Stokes equations solved with RANS approach, blowing effect, combustion kinetics and radiation. The equations are closed with k–epsilon turbulence model and well stirred reactor model. The P1 model, a simplification of the PN radiation model, is adopted. Specific simulation tools were developed using OpenFOAM®open source technology. The computational domain is 2D and split in two subdomains, simulating the reacting gas mixture on one side and the solid fuel grain on the other. The interface between the two regions plays a key role as the solid grain pyrolysis comes from a straight solution of the model without shortcuts. A propellant combination with polybutadiene and gaseous oxygen has been chosen and a reduced kinetic model for combustion of butadiene, considered as the major gaseous constituent coming from polybutadiene pyrolysis, has been developed for reactions occurring in oxygen atmosphere. The computational domain tries to replicate the real experimental setup and is split into three areas: pre-chamber, slab zone and post-chamber. High speed camera visualizations of the combustion processes allow to compare the flame height, obtained by the code and by experimental tests, along the grain for given boundary conditions.

Tracer method in numerical simulation of combustion processes

Fuel-rich laminar flat hydrogen-methane-air flames are studied numerically using the tracer method. It is found that, in the near-limit mixture, hydrogen has an advantage in the oxidation by oxygen. As the stoichiometric compositions are approached, this advantage decreases and then disappears. It is shown that H2*O and CO2* labeled additives participate in the reactions and the labels from these molecules move to other products. Small additives of CH4* in the mixture completely react to form HH*O, H2*O, CO, CO2, HH*, and H2*. Quantitative data on the distribution of the tracer atoms in products are given. The interaction of the hydrogen and methane oxidation schemes is studied. It is shown that in the presence of restriction on the interaction of these schemes, the laminar flame velocity increases by a factor of 5–7.

False diffusion in numerical simulation of combustion processes in tangential-fired furnace

Numerical simulation serves as one of the most important tools for analyzing coal combustion in Tangentially Fired Furnaces (TFF) with NUMERICAL FALSE DIFFUSION as one key problem that degrades the simulation accuracy, especially for complex flow patterns. False diffusion often completely compromises the accuracy, leading to erroneous predictions. This paper reviews various methods to reduce the numerical diffusion. In computational fluid dynamics (CFD), false diffusion originates from a truncation error of the Taylor series approximation of the derivative and multidimensional discretization effects. Higher-order upwind convective schemes were designed to reduce truncation errors, while grid line adjusting methods were developed to reduce crossflow diffusion. This paper compares numerical and experimental results for isothermal flows to evaluate these methods. Results with the standard upwind scheme in a rectangular Cartesian mesh are compared with results in body-fitted meshes for comprehensive combustion processes in a TFF. Analysis of the false diffusion effect in the x, y, z directions and the artificial viscosity distribution in a rectangular mesh shows where the false diffusion overtakes the real physical diffusion and where the mesh must be refined or grid line must be adjusted to improve TFF combustion simulations.

The geometry of reaction trajectories and attracting manifolds in composition space

In numerical simulations of combustion processes, the use of dimension reduction to simplify the description of the chemical system has the advantage of reducing the computational cost, but it is important also to retain accuracy and adequate detail. Most existing dimension reduction methods assume the existence of low-dimensional attracting manifolds in the full composition space and try to approximate or directly identify the low-dimensional attracting manifolds. However, questions remain about the geometry of the reaction trajectories in the full composition space, the existence of the low-dimensional attracting manifolds in low-temperature regions, and the minimum dimension of the attracting manifold required for describing a particular chemical system. This paper tries to address some of these issues by studying the reaction trajectories starting from a wide range of different initial compositions for both H2/air and CH 4/air mixtures. Along each trajectory, we study the tangent bundle of the trajectory, the eigenvalues of the Jacobian matrices, and the singular values of the sensitivity matrices (i.e. sensitivity with respect to initial composition). It is shown that the dimension of the affine space containing a trajectory (or of the tangent bundle along a trajectory) is much smaller than the dimension of the full composition space. Even at low temperatures, the Jacobian matrices still have a significant number of large (in magnitude) negative eigenvalues, which implies the existence of fast time scales and low-dimensional attracting manifolds (even at low temperatures). The geometrical significance of sensitivity matrices is explored. Based on the sensitivity matrices, a new method is proposed to determine the minimum dimension of the attracting manifold required for describing a chemical system with prescribed accuracy, and to identify the ‘principal subspace’ which is an approximation to the tangent space of the attracting manifold.

Radiant Image Simulation of Pulverized Coal Combustion in Blast Furnace Raceway

Abstract The relationship between two-dimensional radiant image and three-dimensional radiant energy in blast furnace raceway was studied by numerical simulation of combustion process. Taking radiant image as radiant boundary for numerical simulation of combustion process, the uneven radiation parameter can be calculated. A method to examine three-dimensional temperature distribution in blast furnace raceway was put forward by radiant image processing. The numeral temperature field matching the real combustion can be obtained by proposed numeric image processing technique.

508 2サイクル水素エンジンにおける燃焼過程の数値シミュレーション(環境とエネルギー)

508 2サイクル水素エンジンにおける燃焼過程の数値シミュレーション(環境とエネルギー)

B162 噴霧燃焼数値解析における気相-油滴間熱移動とパーセルモデルの検証(OS-5 燃焼研究における可視化,計測およびモデル化手法の進展II)

To examine the evaporative cooling effects due to droplet group combustion, we conducted direct numerical simulations of combustion processes of n-decane polydisperse spray entering into a gaseous flat-flame stabilized in a laminar 2D counterflow configuration. Firstly, we investigated the effects of energy exchange between droplets and gaseous phase and the latent heat. The latent heat had stronger influence on the evaporative cooling effect in the droplet group combustion region. Secondly, parcel model on numerical simulations of spray combustion were examined. We found that the use of the parcel approach has a risk of causing a delay of combustion reaction, since the partial fuel vapor pressure increases at limited locations, which suppresses the global droplet evaporation rate.

403 ハイタン燃料直接噴射2ストローク機関における燃焼過程の数値シミュレーション(エンジンシステム(1))

403 ハイタン燃料直接噴射2ストローク機関における燃焼過程の数値シミュレーション(エンジンシステム(1))

903 HCCIエンジンにおける燃焼過程の数値解析(エンジンシステムI)

903 HCCIエンジンにおける燃焼過程の数値解析(エンジンシステムI)