Numerical Simulation Of Combustion Research Articles

Numerical Simulation of Combustion of Natural Gas Mixed with Hydrogen in Gas Boilers

Hydrogen mixed natural gas for combustion can improve combustion characteristics and reduce carbon emission, which has important engineering application value. A casing swirl burner model is adopted to numerically simulate and research the natural gas hydrogen mixing technology for combustion in gas boilers in this paper. Under the condition of conventional air atmosphere and constant air excess coefficient, the six working conditions for hydrogen mixing proportion into natural gas are designed to explore the combustion characteristics and the laws of pollution emissions. The temperature distributions, composition, and emission of combustion flue gas under various working conditions are analyzed and compared. Further investigation is also conducted for the variation laws of NOx and soot generation. The results show that when the boiler heating power is constant, hydrogen mixing will increase the combustion temperature, accelerate the combustion rate, reduce flue gas and CO2 emission, increase the generation of water vapor, and inhibit the generation of NOx and soot. Under the premise of meeting the fuel interchangeability, it is concluded that the optimal hydrogen mixing volume fraction of gas boilers is 24.7%.

The Combustion Numerical Simulation of a Liquid Slag Pulverized Coal Burner in the High Temperature Secondary Air

Taking a liquid slag pulverized coal burner as the research object, the combustion characteristics of the burner in different high temperature secondary air were simulated by Fluent commercial software, and the combustion characteristics of temperature field distribution and the change of component concentration were obtained. The simulation results show that the burner can form a front ignition zone, the air vortex low temperature zone, the central DC flame and the annular flame in the hot state. It can be found that increasing the secondary air temperature can improve the combustion intensity of the burner, promote the formation of CO, and form a high temperature reduction zone, which is conducive to inhibiting pollutant emissions. The research results provide theoretical support for the application of the burner in practice.

Numerical Modeling of Combustion and Detonation in Aqueous Foams

Combustible aqueous foams and foamed emulsions represent prospective energy carriers. This paper is devoted to the overview of model assumptions required for numerical simulations of combustion and detonation processes in aqueous foams. The basic mathematical model is proposed and used for the analysis of the combustion development in the wet aqueous foam containing bubbles filled with reactive gas. The numerical results agree with the recent experimental data on combustion and detonation in aqueous foams containing premixed hydrogen–oxygen. The obtained results allowed for distinguishing the mechanisms of flame acceleration, transition to detonation, detonation propagation, and decay.

Расчетная оценка влияния неравномерности распыла топлива на поле температур газа на выходе из камеры сгорания ГТД

This paper presents the results of numerical simulation of a gas flow with the combustion of atomized liquid fuel (the equilibrium combustion model pdf was used along with the model of a partially mixed mixture) in an annular combustion chamber of a gas turbine engine. Numerical modeling was carried out in the ANSYS Fluent computational complex. The purpose of the calculations was to assess the influence of the unevenness of the fuel spray specified in the design documentation and the coking of the parts of the front-line device on the radial and circumferential unevenness of the gas temperature field at the exit from the combustion chamber. The simulation used the previously verified turbulence model k-e with the functional dependence of the turbulent Schmidt number Sc on the gas temperature, which was implemented in the ANSYS Fluent computational complex using the user function (UDF). Since the fuel injector and the swirler represent a rather complex spraying scheme, which does not allow calculating the amount of fuel entering through the holes in the swirler cap, an installation was made and tests were carried out to determine the amount of the fuel-air mixture distributed over the holes in the swirler cap. The experimental values of the distribution of the air-fuel mixture through the holes in the swirler cap were further used to perform numerical simulation of combustion in the combustion chamber. Numerical modeling was carried out with sector non-uniformity equal to 0 %, 50 % (the maximum allowable according to the design documentation), and during coking of the swirler cap holes. As a result of the calculations, it was found that the sector irregularity of 50 % has an insignificant effect concerning the sector irregularity of 0 % on the radial irregularity of the gas temperature field at the exit from the combustion chamber, while the circumferential irregularity at the exit from the combustion chamber increased by 1.6 %. to the sectorial unevenness 0 %. When coking the holes of the swirler cap, the value of the radial diagram at the outlet from the combustion chamber increases by 1.2%, and the value of the circumferential irregularity increases by 4%.

Study of the reduced kinetic mechanism of methane/dimethyl ether combustion

The development of methane (CH4)/dimethyl ether (DME) combustion systems can reduce fossil energy consumption and pollutant emissions of gas turbines while enhancing fuel diversity. However, employing detailed kinetic mechanisms in the fluid dynamics calculations for the design and optimization of CH4/DME burner configurations is enormously costly for computational resources and time. Therefore, reduced kinetic mechanisms are essential for widespread implementation. In the current work, 1200 + iterations based on the genetic algorithm were performed with 30 target conditions, which extracted a reduced mechanism from the detailed CH4/DME chemical kinetic mechanism. It contained 35 species and 131 reaction steps that reasonably captured the detailed mechanism's main reaction path. Measurements from a shock tube verified that the reduced mechanism provides reasonable predictions of ignition delay times for pure methane, pure DME, and CH4/DME mixtures at T > 1300 K, 1050 K, and 1100 K, respectively. The addition of CH3O2 reaction schemes and modification CH3OCH2 related reactions extended the temperature range to T > 900 K, 700 K, and 760 K under stoichiometric and fuel-rich conditions. The accuracy of the reduced and optimized mechanism was also confirmed by other results obtained from laminar flames, counter-flow diffusion flames, and flow reactors. Accurate replication of the temperature and species profiles was achieved for the numerical simulation of the turbulent flames by the optimization mechanism, which also decreased nearly half the computational time compared to the detailed mechanism. Overall, there is a suitable balance between accuracy and computational efficiency, as shown by the reduced mechanism, promising potential computational cost savings for large-scale numerical combustion simulations.

The heating of a stream of particles by thermal counter radiation

Introduction. It is accepted that the depth of heating of the dust/gas/air mixture by the radiation of combustion products SR is equal to the length LR of the free path of radiation in the mixture. Numerical simulation of combustion of a gas-air mixture that has inert particles, taking into account the re-radiation of heat by heated particles of the fresh mixture, led to ratio SR >> LR. In this work, the analytical assessment of ratio χS = SR/LR is performed.One-dimensional problem model. The co-authors determined stationary temperature distribution over the flow of initially cold monodisperse particles suspended in vacuum. Particle velocity V is directed toward a heat-radiating, absolutely black surface that is permeable by particles. Simplifying assumptions are used: radiation consists of two oppositely-directed flows of electromagnetic energy; interaction between particles and radiation is described in the approximation of geometric optics; the temperature inside the particle is the same. Problem solving. It is shown that χS is determined by V=Vcp / (εT 0,5, σTb)3 , where cp, εT, σ, Tb are, respectively, heat capacity per unit volume of the suspended matter, integral emissivity of the particle material, the Stefan-Boltzmann constant, and the surface temperature. For ≤ 2.8, re-emission can be neglected: χS ≈ 1. At ≤ 1.2, temperature distribution regulates re-emission: χS ≈ 5 –1/(2 – εT) >> 1.Solution discussion. The analytical solution satisfactorily describes the available numerical solutions and experimental data for the case of combustion of a dust/gas/air mixture after specifying the parameters of a simplified model: the radiating surface should be understood as the flame front, Tb is the combustion temperature, and cp is the overall heat capacity of the mixture. The estimate ≤ 1.2 indicates the final high temperature of the gas suspension, the possibility of its autoignition far from the flame, and the need to change initial assumptions when simulating re-emission.Conclusions. Analytical evaluations make it possible to employ ratios SR >> LR and SR ≈ LR for the suspension over a thermal radiation source in vacuum. Conditions for the application of the results of simplified simulation of re-emission to the combustion of a dust/gas/air mixture are formulated.

Large‐eddy simulation of coal combustion in 15 MW pilot‐scale boiler‐simulation facility

AbstractHigh‐fidelity modeling provides a useful approach to investigate the multiscale multiphysics mechanism in the pulverized coal combustion. This research focuses on understanding the pulverized coal combustion in a pilot‐up facility: General electric (GE) 15 MW pilot‐scale boiler simulation facility (BSF). The heat flux to the boiler water wall, O2 concentration, and gas temperature are the quality of interest (QoI's) for this research, as they are the most important parameters for designing a full‐scale pulverized coal boiler. Even the heat flux in boiler is largely determined by the heat transfer mechanism, and other detailed multiphysics mechanisms, including multiphase turbulent flow, radiation heat transfer, ash deposition, coal devolatilization, and oxidation, also need to be accounted. This work applies large‐eddy simulation (LES) code on high‐performance computing facility to simulate pulverized coal combustion in BSF. The physics‐based submodel that contains the significant sensitivity for QoI's has been identified using the detailed impact factor analysis on this high‐fidelity modeling. Results indicate that the most sensitive submodel on QoI's is the wall‐heat‐transfer coupling with the ash‐deposition model, which allows us to prioritize to improve this submodel in the LES simulation. Thus, ash deposition and wall‐heat‐transfer processes have been modeled and integrated into coal combustion numerical simulation. The simulation results show quantitative agreement between the simulation with experimental data regarding gas temperature, O2 concentration, and heat‐flux profile across the exposed boiler walls. Another implication of this research is to demonstrate a positive societal impact of extreme computing and accelerate the development of new combustion technology using a capable exascale computing technique.

МОДЕЛИРОВАНИЕ ПРОЦЕССА СГОРАНИЯ В ДИЗЕЛЬНОМ ДВИГАТЕЛЕ

The issues of combustion processes and the organization of the combustion workflow in diesel engines are relevant in view of the tightening of economic and environmental requirements for them. The problem of saving liquid fuels remains one of the most acute in the provision of fuel and energy resources. The development of highly efficient methods for organizing work processes when burning natural gas in a compressed or cryogenic state in the cylinders of internal combustion piston engines and determining ways to further reduce toxic emissions, increase fuel efficiency and reliability in promising gas engines is an urgent task. Mathematical modeling of liquid fuel combustion is a complex task, since it requires taking into account a large number of complex interrelated processes and phenomena. The article presents a simple 3-D model of cylinder diesel tractor engine D 144, the re- sults of numerical simulation of combustion of liquid and gaseous fuel in the cylinder of the diesel engine D-144. The article presents the results of modeling, including graphs of the dependence of nitrogen oxides, particles in outgoing gases, depending on the consumption of gaseous fuel in the form of pure methane. Additionally, tempe- rature and velocity contours are shown. The corresponding conclusions are made.

Numerical simulation of combustion of CH4 mixed H2 and rationality analysis of premixed ratio

Numerical simulation of combustion of CH4 mixed H2 and rationality analysis of premixed ratio

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ ГОРЕНИЯ СМЕСЕВОГО ТВЕРДОГО ТОПЛИВА, СОДЕРЖАЩЕГО БИДИСПЕРСНЫЙ ПОРОШОК БОРА

A problem of combustion of the composite solid propellants containing various powders of metals and non-metals is relevant in terms of studying the effect of various compositions of powders on the linear rate of propellant combustion. One of the lines of research is to determine the effect of the addition of a boron powder on the burning rate of a composite solid propellant. This work presents the results of numerical simulation of combustion of the composite solid propellant containing bidispersed boron powder. Physical and mathematical formulation of the problem is based on the approaches of the mechanics of two-phase reactive media. To determine the linear burning rate, the Hermance model of combustion of composite solid propellants is used, based on the assumption that the burning rate is determined by mass fluxes of the components outgoing from the propellant surface. The solution is performed numerically using the breakdown of an arbitrary discontinuity algorithm. The dependences of the linear burning rate of the composite solid propellant on the dispersion of the boron particles and gas pressure above the propellant surface are obtained. It is shown that the burning rate of the composite solid propellant with bidispersed boron powder changes in contrast to that of the composite solid propellant with monodispersed powder. This fact proves that the powder dispersion should be taken into account when solving the problems of combustion of the composite solid propellants containing reactive particles.

Numerical simulation of unsteady combustion at elevated pressure and initial temperature of the mixture for the model combustion chamber

The paper presents the results of investigation of combustion features of a fuel-lean methane-air swirling flame in a model combustion chamber using numerical simulation at an elevated pressure and initial temperature of the mixture. The equivalence ratio is 0.7, the initial temperatures of the mixture are 300 and 500 K, and the overpressure corresponds to 2 and 4 bars. Setting the increased pressure as the output boundary conditions in the numerical simulation of combustion in a model combustion chamber is shown to be efficient. It is found that a change in the initial temperature of the mixture from 300 to 500 K (at a fixed Reynolds number equal to 30000) leads to a significant change in the combustion regime. So, in the case of the initial temperature of the mixture equal to 300 K, the recirculation zone is formed only near the walls of the combustion chamber, and the flame has a compact shape, and is stabilized inside the premixer. With elevated initial temperatures of the mixture, a stagnation region is formed on the jet axis, and the flame displacement downstream relative to the premixer exists.

Deep learning methods for super-resolution reconstruction of temperature fields in a supersonic combustor

A general super-resolution (SR) reconstruction strategy is proposed to address the super-resolution reconstruction of temperature fields from low-resolution coarse temperature field data using convolutional neural networks. Two deep learning (DL) models were applied to augment the spatial resolution of temperature fields. One is the classical super-resolution convolutional neural network, and the other is the novel multiple path super-resolution convolutional neural network (MPSRC). Three paths with and without a pooling layer are designed in the MPSRC to fully capture spatial distribution features of temperature. Numerical simulations of combustion in a strut scramjet combustor at various Mach numbers are carried out to establish a dataset for network training and testing. The corresponding high-resolution temperature fields were successfully reconstructed with remarkable accuracy. The reconstruction performances of those models were comprehensively investigated and compared with the bicubic interpolation method. The results demonstrated that both DL methods can greatly improve the super-resolution reconstruction accuracy and the MPSRC can provide a better reconstruction result with a lower mean square error and a higher peak signal-to-noise ratio.

Investigation of Chemical Kinetic Model for Hypergolic Propellant of Monomethylhydrazine and Nitrogen Tetroxide

Abstract Hypergolic bipropellant of monomethylhydrazine (MMH) and nitrogen tetroxide (NTO) is extensively used in spacecraft propulsion applications and rocket engines. But studies on the chemical kinetic mechanism of MMH/NTO are limited. So, in this study by integrating the submechanisms of MMH decomposition, NTO thermal decomposition, MMH/NTO and intermediates, and small hydrocarbons, the comprehensive chemical mechanism of MMH/NTO bipropellant is proposed. The present chemical mechanism consists of 72 species and 406 elementary reactions. In two respects of ignition delay times and combustion flame temperatures, the present model has been validated against the theoretical calculation results and also compared with other kinetic models in the literature. The validations show that the predicted ignition delay times by the present kinetic model are highly consistent with the theoretical data and well describe the pressure-dependent characteristic. For combustion flame temperature, the present model also exhibits better predictions to the theoretical calculation results, which are also the same as the predictions by the MMH-RFNA model. Furthermore, the influences of initial temperature, chamber pressure, and NTO/HHM mass ratio (O/F) on the ignition delay time and combustion flame temperature are investigated. The auto-ignition behavior of MMH/NTO propellant is sensitive to initial temperature and chamber pressure, and the combustion flame temperature is more sensitive to the O/F. This study provides a detail chemical kinetics model for further mechanism simplification and combustion numerical simulation.

Numerical Simulation of Combustion in 35 t/h Industrial Pulverized Coal Furnace with Burners Arranged on Front Wall

Coal-fired industrial boilers should operate across a wide range of loads and with a higher reduction of pollutant emission in China. In order to achieve these tasks, a physical model including two swirling burners on the front wall and boiler furnace was established for a 35 t/h pulverized coal-fired boiler. Based on Computational Fluid Dynamics (CFD) theory and the commercial software ANSYS Fluent, mathematical modeling was used to simulate the flow and combustion processes under 75% and 60% load operating conditions. The combustion characteristics in the furnace were obtained. The flue gas temperature simulation results were in good agreement with experimental data. The simulation results showed that there was a critical distance L along the direction of the furnace depth (x) and Hc along the direction of the furnace height (y) on the burner axis. When x < L, the concentration of NO decreased sharply as the height increased. When y < Hc, the NO concentration decreased sharply with an increase in the y coordinate, while increasing dramatically with an area-weighted average gas temperature increase in the swirl combustion zone. This study provides a basis for optimizing the operation of nitrogen-reducing combustion and the improvement of burner structures.

Numerical Simulation of Combustion and Air Supply Process and Optimal Design of Traditional Top Combustion Hot Blast Stoves

The combustion performance and flue gas flow pattern of hot blast stoves significantly affect the temperature distribution of the combustion chamber and regenerator, as well as the air supply temperature and duration. In this study, a 3D fluid flow heat transfer model coupled with turbulence, combustion, heat radiation, and heat exchange models is established to study the combustion and air supply characteristics of a traditional hot blast stove. The results indicate that the nozzle arrangement on the traditional stove causes the flue gas to exhibit a high‐speed swirling flow. Due to the expansion of the flue gas and the centrifugal effect of the swirling flow, the “attachment” phenomenon of the fluid (i.e., a high edge velocity and a low center velocity) occurs in the combustion chamber, resulting in an unreasonable temperature distribution in the combustion chamber and regenerator. Accordingly, an improved design of a top combustion hot blast stove is proposed to solve this problem, and its performance is evaluated and compared with that of the original design via numerical simulations.

Numerical Analysis of Entropy Production during Hydrogen-Air Burner Combustion Process

Entropy production during hydrogen-air diffusion in the combustion chamber (СС) was studied. A two-dimensional axisymmetric combustion chamber is considered in this paper. The numerical simulation of combustion has been done by Fluent software. The entropy production per unit volume for heat conduction and convection, mass diffusion, viscous dissipation, and the chemical reaction was calculated by user-defined function (UDF) post-processing, while the entropy production for heat transfer radiation was determined by post-processing with the help of calculated data of temperature. The results reveal that the radiation entropy production cannot be omitted when second law analysis of thermodynamic is adopted in high-temperature conditions such as boilers, heat exchangers, furnaces, etc; in these devices, thermal radiation is the basic mode of heat transfer. The effects of parameters such as Boltzmann number and Reynolds number on entropy production and entropy production number are analyzed. It is shown that the total entropy production number first decreases with the increase Reynolds and Boltzmann numbers; and then gradually increases. The results provide a theoretical reference for the improvement of thermodynamic efficiency for heat transfer and energy utilization.

Numerical simulation of combustion in a biomass briquette chain boiler

A bed and furnace integrated model of biomass briquette chain boilers was built on basis of theories of computational fluid mechanics, heat transfer, thermodynamics, and chemical reaction kinetics. The combustion in the biomass briquette chain boilers was characterized under five working parameters (air-preheating temperature, fuel bed thickness, grate advancing speed, particle diameter, air supply mode) through experimental design, numerical simulation, and mathematical programming. Finally, these parameters were optimized with the ant colony algorithm. It was found that the combustion efficiency and economic benefits were both optimized at the air-preheating temperature of 553.22 K, fuel bed thickness of 0.16 m, particle diameter of 0.02 m, and uniform centered air supply. This study offers some theoretical basis and method for the optimized design and operation of biomass briquette chain boilers.

Numerical simulation of combustion and emission of blast furnace gas boiler

Taking an 110t/h full-fired blast furnace gas boiler as the research object, the numerical simulation method is used to calculate the combustion process in the furnace. The influence of flow field on combustion is analyzed, and the influence of air preheating temperature and oxygen concentration on combustion and NOx emission is discussed, which provides a theoretical basis for optimal design and reasonable operation of blast furnace gas boiler. The results indicate that with the increase of air preheating temperature and oxygen concentration, the CO consumption rate is increased, the in-furnace maximum temperature and average temperature are increased to different extents, the temperature distribution is basically unchanged, and the NOx concentration at the furnace outlet is also increased. The NOx concentration multiplies as the oxygen concentration increases.

Numerical simulation of hydrogen combustion in oxidizer supersonic flow in flowpaths of various configurations

The paper deals with the numerical simulation of the combustion of a hydrogen-air mixture in a supersonic flow in channels of various configurations. Axisymmetric and plane type flows are considered. The simulation is based on solving the complete system of Navier-Stokes equations with closure using a turbulence model and detailed chemical kinetics. To validate the results, Beach-Evans-Schexnayder and Burrows-Kurkov experimental data are used. The influence of various kinetic mechanisms, models of turbulence, and boundary conditions on the solution obtained is considered. The boundaries of the methods are shown.

Валидация методов расчета горения водорода в сверхзвуковом потоке модельного воздуха по экспериментальным данным Бича — Эванса — Шекснайдера

This paper deals with numerical simulation of combustion of a hydrogen-air mixture in a supersonic flow. The simulation is based on solving the complete system of Navier-Stokes equations with closure using the turbulence model and detailed chemical kinetics. The mixing and combustion of a hydrogen-air fuel mixture is considered in the experimental formulation of Beach-Evans-Schexnayder. The effect of various kinetic mechanisms, turbulence models, TCI models, and boundary conditions on the solution is studied qualitatively and quantitatively. The relative errors of mass concentration of water for control sections are determined, and the methods’ boundaries are shown. Conclusions are drawn on the influence of turbulent mixing mechanisms and chemical kinetics on the combustion of hydrogen.