Simulation Of Combustion Process Research Articles

Numerical Simulation and Structural Optimization of Combustion Processes in a 750 t/d Waste Incinerator

This paper presents a numerical simulation and structural optimization study of the combustion process within the grate and boiler furnace of a 750 t/d waste incineration. The study focuses on adjusting the secondary air velocity, secondary air inclination angle, and the arrangement of secondary air nozzles. These adjustments aim to optimize parameters such as the temperature field, pollutant emission, flow field, particle residence time, and filling degree. The findings demonstrate that high-temperature zones, which lead to slagging problems, are likely to form beneath the front arch. The combustibles inside the furnace are thoroughly burnt, reflecting efficient combustion. The concentration of NOx in the flue gas at the furnace outlet generally ranges between 170 and 200 ppm. Optimal operating conditions are identified as a secondary air inclination angle of 20° with an air velocity of 55 m/s, and an angle of 30° with an air velocity of 55 m/s and 65 m/s, in conjunction with a relative arrangement of the nozzles. Under these conditions, the incineration furnace achieves its best operational state.

Simulation of the processes of spraying and combustion of kerosene and liquid oxygen in the chamber of a liquid-propellant rocket engine

The paper presents the results of simulation of spray and combustion processes in the liquid-propellant rocket engine chamber using the z77 reduced kinetic mechanism of chemical reactions and a hybrid method for determining spray parameters of a swirl atomizer. Simulation was carried out for the nominal operational conditions in a three-dimensional domain using the ANSYS Fluent software. The process of spraing liquid fuel components (T-1 kerosene and oxygen) by monopropellant injectors was simulated using a model of discontinuous phases. The simulation results (pressure, temperature and velocity) were compared with the data of analytical thermogasdynamic calculation results and experimental results for pressure in chamber and gas temperature near the wall. The difference between the simulation results and the experimental results does not exceed 8%. Thus, it was shown that it is possible to use the mechanism z77 and hybrid method for determining spray parameters of a swirl atomizer presented in this paper to obtain accurate simulation results of the kerosene T-1 and oxygen spray and combustion processes of the investigated liquid-propellant rocket engine.

Analysis of the Effect of More Fuel and Air Variations Excess Air on Combustion Process Simulation at a 10 kW Biomass Power Plant Using ASPEN PLUS

Abstract The utilization of biomass as an alternative energy can support the achievement of Net Zero Emissions. Each type of biomass fuel can provide different combustion effects from one another. This is due to the different heating values of each fuel. The calorific value is one of the things that affect the combustion performance of the biomass power plant. The main purpose of this study is to examine how different amounts of excess air used during the combustion process affect the outcomes. Combustion is a chemical reaction involving decomposition and gasification that simultaneously occurs in a space where a large amount of energy is released. The modeling and simulation of the decomposition and gasification processes were carried out using Aspen Plus. In this simulator, the decomposition process takes place in the Yields Reactor, while the gasification process occurs in the Gibbs Reactor. The biomass and ash components are characterized by their ultimate, proximate, and sulfur analysis. Then the excess air is varied to analyze its impact on the flame temperature from the reaction. The simulation findings emphasize crucial considerations for achieving complete combustion and reducing harmful gas emissions. Maintaining excess air close to the stoichiometric level ensures maximum combustion temperature at 1616.15 °C while minimizing excess air reduces NOx gas concentration. Approaching stoichiometric air level decreases CO gas and increases CO2, indicating more thorough combustion. However, excess air leads to lower adiabatic flame temperature due to nitrogen formation.

Simulation of fire combustion process in valve hall of DC converter power station

To investigate the fire danger of the valve hall, a 3D numerical model of the DC converter substation's valve hall is created by using the fire dynamics simulator (FDS) program and the fire burning process of the valve hall is simulated. In particular, the procedure of simulating the fire burning in the valve hall under various fire source positions is accomplished by varying certain parameters. The smoke spreading process, ambient temperature field, and heat release rate curve under various fire source placements are compared based on the results of the simulation calculations. The findings demonstrate that under various fire source locations, the valve hall's combustion process varies as well. This study compares the time for smoke to fill the entire valve hall, the maximum temperature within the valve hall, and the maximum fire source heat release efficiency in different fire scenes. The results indicate that in fire scenes where the fire source is closer to the middle position, the time for smoke to spread throughout the valve hall is shorter, and the fire source heat release rate is higher. Conversely, in fire scenes where the fire source is closer to the edge, the maximum temperature within the valve hall is higher. The numerical simulation of the valve hall in this DC converter station assessed the hazards under different fire scenes, aiming to maximize the safety of the valve hall. It provides reliable guidance for maximizing the safety of the valve hall and facilitating firefighting and rescue efforts, thus protecting personal safety and minimizing property damage.

Projection-based reduced order modeling of multi-species mixing and combustion

High-fidelity simulations of mixing and combustion processes are computationally demanding and time-consuming, hindering their wide application in industrial design and optimization. This study proposes projection-based reduced order models (ROMs) to predict spatial distributions of physical fields for multi-species mixing and combustion problems in a fast and accurate manner. The developed ROMs explore the suitability of various regression methods, including kriging, multivariate polynomial regression (MPR), k-nearest neighbors (KNN), deep neural network (DNN), and support vector regression (SVR), for the functional mapping between input parameters and reduced model coefficients of mixing and combustion problems. The ROMs are systematically examined using two distinct configurations: steam-diluted hydrogen-enriched oxy-combustion from a triple-coaxial nozzle and fuel-flexible combustion in a practical gas-turbine combustor. The projected low-dimensional manifolds are capable of capturing important combustion physics, and the response surfaces of reduced model coefficients present pronounced nonlinear characteristics of the flowfields with varying input parameters. The ROMs with kriging present a superior performance of establishing the input–output mapping to predict almost all physical fields, such as temperature, velocity magnitude, and combustion products for both test problems. The accuracy of DNN is less encouraging owing to the stringent requirement on the size of training database. KNN performs well in the region near the design points but its effectiveness diminishes when the test points are distant from the sampling points, whereas SVR and MPR exhibit large prediction errors. For the spatial prediction at unseen design points, the ROMs achieve a prediction time of up to eight orders of magnitude faster than conventional numerical simulations, rendering an efficient tool for the fast prediction of mixing and combustion fields and potentially an alternative of a full-order numerical solver.

Comparisons of Different Representative Species Selection Schemes for Reduced-Order Modeling and Chemistry Acceleration of Complex Hydrocarbon Fuels

The simulation of engine combustion processes, such as autoignition, an important process in the co-optimization of fuel-engine design, can be computationally expensive due to the large number of thermo-chemical scalars needed to describe the full chemical system. Yet, the inherent correlations between the different chemical species during oxidation can significantly reduce the complexity of representing this system. One strategy is to select a subset of representative species that accurately captures the combustion process at a fraction of the computational cost of the full system. In this study, we compare the performance of four different techniques to select these species. They include the two-step principal component analysis (PCA) approach, directed relation graphs (DRGs), the global pathway selection (GPS) approach, and the manifold-informed species selection method. A parametric study of the representative species selection is carried out on data from the simulation of homogeneous and perfectly stirred reactors by investigating seven cumulative variances and 47 different cut-off percentages for the two-step PCA, and 65 and 51 thresholds for the DRGs and GPS, respectively. Results show that these selection methods capture key important species that can accurately describe the chemical system and track each stage of oxidation. The two-step PCA is sensitive to the cumulative variance, and DRGs and GPS are sensitive to the choice of target variables. By selecting key representative species and reducing the number of thermo-chemical scalars, these three methods can be used to develop computationally efficient hybrid chemistry schemes.

Fluid dynamics and energy efficiency of submerged combustion process for treating wastewater with high salinity and COD concentration

Focusing on submerged combustion technology for the treatment of high salinity and high chemical oxygen demand (COD) wastewater, this study explores the characteristics of gas-liquid two-phase flow and heat transfer during the submerged combustion process, employing both experimental and numerical simulation methods.Consequently, the impact of essential parameters on the efficacy of submerged combustion in treating wastewater was analyzed. The experimental results show that increasing the fuel flow rate and immersion depth is beneficial to improve the temperature rise rate and shorten the evaporation time. With the increase of the organic solution flow rate and the initial COD value of the organic solution, the COD removal rate decreased, and the effect of the organic solution flow rate on the COD removal efficiency was more obvious. The use of a flat orifice plate or tapered orifice plate immersed tube structure can improve the thermal efficiency by over 10%. However, it is not conducive to the stability of the pressure in the combustor, increasing the fluctuation of the liquid level. Compared with that of traditional single-effect evaporation crystallization, the energy consumption of the submerged combustion device is decreased, and the total operation cost is reduced by 22.5%.

Simulation of alternative fuel combustion process in internal combustion engines

BACKGROUND: The tasks of improving fuel efficiency and environmental performance of engines are interrelated with the technical, economic, resource performance and reliability of their operation. AIM: In this regard, the aim is simulation of the alternative fuels combustion process. METHODS: To achieve this aim, the method for preparing a water-fuel emulsion mixed with diesel fuel has been developed and experimental studies have been carried out with the measurement of toxic components of exhaust gases from diesel engines. RESULTS: As a result of the research, the most optimal droplet sizes of water-fuel emulsions were revealed after 4–6 processing cycles with the smokiness reduction by 3 to 5 times, the NOx reduction by 2 to 3 times, the CO reduction by 20–30%, depending on the operating modes. CONCLUSIONS: As a result of the research, it was found that the use of alternative fuels makes it possible to expand the fuel balance and to improve environmental performance.

Tabulated Chemistry Combustion Model for Cost-Effective Numerical Simulation of Dual-Fuel Combustion Process

This study is dedicated to improving the efficiency of the flamelet-generated manifold (FGM) tabulated chemistry combustion modeling approach for predicting the combustion process in diesel-ignited internal combustion (IC) engines. The primary focus is on reducing table generation time and memory requirements. To accurately predict dual-fuel combustion processes, it is important to model both premixed and non-premixed combustion regimes. However, attempting to include both regimes in a single FGM lookup table leads to significant increases in the table size and generation time. In response, this work proposes a dual-table configuration, with each table dedicated to a specific regime. The solution is then interpolated from these tables based on the calculated combustion regime indicator during the computational fluid dynamics (CFD) simulation. This approach optimizes computational efficiency while ensuring an accurate representation of dual-fuel combustion. Additionally, to establish a cost-effective and accurate 3D CFD simulation workflow, the dual-table FGM methodology is coupled with the partially averaged Navier–Stokes (PANS) turbulence model. The feasibility of the proposed FGM methodology is tested utilizing six chemical kinetics mechanisms with different levels of detail. The results of this study demonstrated that the dual-table approach significantly accelerates table generation time and reduces memory requirements compared to a single table that includes both combustion regimes. Furthermore, 3D CFD simulation results of the dual-fuel combustion process are validated against available experimental data for three engine operating points. The in-cylinder pressure traces and rate of heat release obtained from the 3D CFD simulations employing the FGM PANS methodology show good agreement with experimental measurements, confirming the accuracy and reliability of this modeling approach.

Is monolithic configuration superior to random packing in a fixed bed reactor for CLC like processes?

In light of the geometric deficiencies and diffusion constraints of conventional packed-bed reactors, the potential application of monolithic configurations in fixed-bed reactors was explored using the structure-resolved CFD approach. This work delves into how geometric features of fixed beds influence flow patterns and related transport phenomena. To assess the performance of mass transfer and heterogeneous reactions in different configurations, we conducted simulations of fixed-bed chemical looping combustion (CLC) processes, in which a simplified model of non-catalytic gas-solid reactions is implemented to reduce the computational costs. Our findings highlight the importance of face contact between reaction tube and the monolithic structure, which effectively eliminates the inherent wall effects of random packing and enhances the radial heat conduction. More uniform geometry in the monolithic configuration naturally suppresses violent interstitial channeling flow in the random packing. Notably, the honeycomb configuration demonstrates an exceptionally low pressure drop, about two orders of magnitude smaller than that of the Raschig ring packing, and the designable monolithic configurations offers the potential to further reduce the pressure drop with enlarged voidage. Open-cell foams exhibit excellent convective and radial heat transport properties, promote homogeneous flow fields, and demonstrate superior performance in conjugate transport and heterogeneous reactions.

Effect of variable geometry turbocharger on the performance of the opposed piston engine – An experimental approach

The increasing trend of low-carbon policy obligates engine manufacturers to implement new solutions to meet demanded emission reduction. Thus, a growing interest has been in reviving the 2-stroke, opposed-piston engine concept to improve engine thermal efficiency. Although such an engine offers advantages over classic, 4-stroke engines, its application was limited only to the marine sector. Also, recent research activities were mostly limited to scavenging and combustion process simulations due to the lack of available test engines and challenging experimental setup requirements.The authors tested a prototypical 2-stroke, axially opposed-piston engine under various variable turbocharger geometry settings. The author's previous paper on experimental tests with a fixed vane turbocharger influenced the current research activities. The experimental research of a unique axial opposed-piston engine with a wobble-plate mechanism, combined with variable turbocharger geometry application, signified the novelty of such research. The engine test stand accurately measured instantaneous intake and exhaust pressure, in-cylinder pressure and temperature, brake thermal efficiency, and emission. The study demonstrated that the axial opposed-piston engine provides high efficiency of 49.2%. However, the variable turbine geometry actuation increases its efficiency to 51.2% at high load conditions, contributing to CO, HC, and soot emission reduction by 25.1%, 52.5%, and 14.7%, respectively.

Effect of dual port-direct injection of syngas in a rotary engine

Using syngas as a primary fuel for internal combustion engines with spark ignition is a bridge technology for transitioning from carbon-based to hydrogen-based energy sources. There are two different ways of syngas delivery into combustion chamber: port injection or direct injection. In this study, the combination of these methods is considered for integration benefits of each injection technology and promotion of syngas utilization in rotary engines. In the novel concept of syngas dual injection, part of the fuel is delivered by a port injector during the induction stroke, while another part is directly injected during the compression stroke. The ratio of fuel mass delivered by port and direct injection is changed within the range of 0.0 (direct injection only) to 1.0 (port injection only) and chosen as a key parameter of concentration stratification. This study aims to investigate the optimal fuel injection strategy with numerical simulation of mixture formation, ignition, and combustion processes. It was shown that dual injection strongly influences turbulence intensity and mixture heterogeneity. The turbulence lengthscales generally increase with dual injection ratio growth. The direct injection case demonstrates maximum performance characteristics. However, the case with a small portion of directly injected fuel (10%–25%) increases fuel conversion efficiency by 5%–7% and decrease fuel consumption by 4%–6% with lower level of CO emission. The results show that the dual injection strategy provides flexibility in controlling the combustion process and emission reduction.

Simulation of the harmful emissions formation in the exhaust gases of marine diesel of multi-fuel systems

Currently, the world community is increasingly struggling with harmful effects on the environment, the biosphere and the atmosphere in various fields of industry. One of the pollutants is marine transport. The main type of environmental pollution from marine power plants is harmful emissions of CO, CO2, NO sulfur compounds and other components contained in diesel exhaust gases. The main regulatory document determining the compliance of marine power plants with international environmental requirements is the international convention MARPOL 73/78, developed by the International Maritime Organization (IMO). One of the ways to solve this problem is the use of additional components for fuels on ships, such as water, hydrogen, natural gas, biodiesel, dimethyl ether, ethyl alcohol, etc. In order to pre-calculate the effectiveness of any of the methods for reducing harmful emissions, a simulation of combustion processes in a marine diesel engine when running on diesel fuel with and without the addition of dimethyl ether is carried out. In this study, the AVL Fire program, which is included in the AVL software package and allows you to get visual results on the formation of combustion products in the diesel cylinder, the distribution of temperature flows, soot formation, etc., is used. The 3NVD24 marine diesel engine, which is equipped with the necessary measuring complex for conducting practical research with the possibility of experimental confirmation of the computer modeling results, is used as a prototype for the analysis. Based on the model calculations, various factors of the harmful compounds formation during combustion are analyzed.

Simulation of combustion process in diesel/butanol dual fuel engine

ABSTRACT To investigate the feasibility of diesel engines with high butanol substitution rate (BSR), the performance and emissions of diesel–butanol dual fuel engines are studied numerically. It i based on a four-cylinder diesel engine, which is modified into a diesel–butanol dual fuel engine with port-injected butanol fuel and direct-injected diesel fuel. The simulation is performed using GT-Power software, and simulation results are validated with the experimental data. The engine speeds are set at 1600, 2300, and 3600 rpm, respectively. The engine load is set at 25%, 50%, and 75% engine load, respectively. The BSR varies from 0% to 80% with an interval of 10%. The results show that, with the increase of BSR, the peak cylinder pressure (PCP), and the maximum pressure rise rate (MPRR) decrease, while the brake mean effective pressure (BMEP) and the indicated thermal efficiency (ITE) increase under various working conditions. Among them, the MPRR increases by 9%–12%, while the ITE increases by 6%–7%. In terms of emissions, the nitrogen oxide (NOX) decreases obviously (decrease by 32%–54%), while the carbon monoxide (CO) and the hydrocarbons (HC) decrease slightly (CO: decrease by 4%–10%, HC decrease by 3%–4%).

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.

Особенности расчета нестационарного теплообмена в стенах вращающихся печей

A refined calculation of the non-stationary temperature of the walls of a rotary kiln is proposed, taking into account the non-stationary thermal conductivity in the enclosing walls and the accumulation of heat in them, intended for use in numerical simulation of combustion and heat transfer processes. The influence on heat transfer of the alternating contact of the inner surface of the walls of a rotary kiln with a gaseous medium and a layer of technological material is considered. The adequacy of the method was verified by numerical solution of the differential equation of non-stationary thermal conductivity of walls in the conditions of a computational experiment.

Вопросы численного моделирования горения в диффузионном факеле

The study is devoted to mathematical models of mass transfer during diffusion combustion of gaseous fuel. A numerical approach is presented that makes it possible to estimate the effect of combustion conditions on the length of a direct-flow diffusion flame. A simplified method for calculating the heat release in a diffusion flame is applied, taking into account the fact that the chemical reactions of combustion are concentrated in it at the flame front. Some results of numerical simulation of diffusion combustion processes and complex radiative-convective heat transfer in industrial furnaces in the production of cement clinker are presented.

Special Issue on Modelling, Simulation and Control in Combustion Processes of Renewable Fuels

The modeling and simulation of combustion processes is still a challenging field [...]

The molecular dynamics simulation of lignite combustion process in O2/CO2 atmosphere with ReaxFF force field

Pressurized oxy-fuel combustion is a complex process consisting of free radical collisions and reactions. ReaxFF reactive Molecular Dynamics (MD) simulation method is a useful tool to investigate the chemical events in coal combustion at atomistic level. In this work, the impact of operating conditions on the distribution of main fragments and the reaction mechanisms were examined using a lignite coal model with ReaxFF force field to simulate the process of oxy-fuel combustion under pressures. The ReaxFF MD simulations found that the decomposition of coal molecular structure would be enhanced by increasing the pressure/density, oxygen concentration and temperature. The variety of initial reactions increased with temperature. Increasing pressure promoted the effective collision of molecules and the coal structure was more likely to be attacked by oxidants, so the chemical bonds in coal molecule broke earlier and the consumption of O2 increased at higher pressure. The dehydrogenation reaction on the macromolecular structure of coal and small fragments was also promoted after increasing pressure/density. However, the number of fragments decreased as the pressure/density continued to grow, because large fragments further decomposed or some small molecular benzene ring structures with less than 6C atoms were re-polymerized. The dehydrogenation reaction of coal molecule and small fragments was promoted after increasing the pressure. O2 attacked the benzene ring structure, the C atom on the outer side of the coal, and the carbon-containing fragments in the system, indicating that the increase of O2 concentration promoted the ring opening and oxidation reactions, thereby promoting the decomposition and combustion of coal. The work in this paper has confirmed the findings obtained by other oxy-fuel experimental work from the microscopic point of view.

The energy equation for modeling reacting flows on RANS, LES and DES approaches

Computational Fluid Dynamics (CFD), through high-performance computing and robust codes, has proven to be an invaluable tool for the simulation of combustion processes, ranging from low speeddiffusive flames up to detonations. This work intends to provide a review of details needed in modeling asReynolds-averaged Navier–Stokes (RANS), large eddy simulation (LES) or Detached eddy simulation (DES)energy equation in CFD codes used for solving chemically reacting turbulent flows. When the density is variable, traditional Reynolds averages introduce many open correlations between any quantity f and density fluctuations which are difficult to close. Therefore, Favre’s mass-weighted average technique must be preferred.