Modeling Of Combustion Processes Research Articles

Numerical Modelling of Coal Combustion Processes in the Vortex Furnace with Dual-Port Loading

The work is devoted to numerical simulation of pulverized-coal combustion processes in the vortex furnace which is a prospective design of a boiler unit for thermal power plants. New modification of this design characterized by additional tangential-injection nozzle located at the bottom of combustion chamber has been studied. Numerical results for the case of Siberian brown coal combustion in this vortex furnace with dual-port loading are presented, including 3-D aerodynamic structure, the fields of temperatures, radiated heat fluxes, species and dispersed phase concentrations, and NOx emissions.

Three Dimensional Modeling of Combustion Process and Emissions Formationin Pre and Main Chambers of an Idirect Injection Diesel Enginge

The combustion processes and emission formation in pre and main chambers of a Lister 8.1 IDI diesel are simulated with the Computational Fluid Dynamics (CFD) code. The model includes spray atomization, mixture formation and distribution and subsequently the combustion processes and emissions formation modeling are carried out with considering of flow configurations in two chambers. A part load (50% load) and a full load simulation of engine are carried out. Also, the amount of mass burning rate of fuel, temperature, heat losses and emissions formation in pre and main chamber are presented with more details. The simulation results, such as the mean in-cylinder pressure and exhaust emissions are compared with the measured values and show good agreement .This work demonstrates that multidimensional modeling can be used at complex chamber geometry to gain more insight into the flow field, combustion process and emissions formation. The simulation results show that the CFD combustion simulation tool works quite correctly for the predicting combustion process and emission formation in Lister 8.1 IDI diesel engine.

Multi-Zone Models of Combustion and Heat Transfer Processes in SI Engines

Shrnutí Tato práce představuje sadu nově vyvinutých nástrojů implementovatelných do komplexních kódů pro simulaci spalovacích motorů pro zajištění výpočtů týkajících se vysokotlaké části termodynamického cyklu čtyřdobého zážehového motoru. Tento více-zónový simulační nástroj pracuje na základě jednoduché kvazi-dimenzionální metody reflektující reálnou geometrii spalovacího prostoru a používá specifický přístup k popisu chemické transformace složek. V případech abnormálně rychlých chemických reakcí je klasické kinetické schéma adaptivně kombinováno s flexibilní metodou chemické rovnováhy pro zlepšení numerických vlastností soustavy rovnic. Reálná 3-D geometrie spalovacího prostoru je zohledňována pomocí předem vytvořených geometrických charakteristik. Je zde prezentován nový univerzální nástroj zajišťující tato data. Nový kód má schopnost pracovat v prediktivním stejně jako inverzním módu. Vybrané výsledky týkající se obou těchto režimů jsou prezentovány v závěru příspěvku.

A Readily Accessible Platform for Detailed Combustion Emissions Calculations

This paper explores the modeling and simulation of combustion processes in a gas turbine combustor both with and without water injection for NO x control. The combustor can be modeled as a series and/or parallel combinations of perfectly stirred reactors (PSRs) and plug flow reactors (PFRs). Kinetics models require solution of non-linear and stiff ordinary differential equations (ODEs). The CVODE code from Lawrence Livermore National Laboratory can be used for the solution of these ODEs. Here we show that a reduced kinetics set coupled with an Excel callable version of CVODE (as a dynamic link library (dll)) can be used to predict emission trends in combustors. Student use is promoted by using Excel as the pre- and post-processor.

A biomass pyrolysis model for CFD application

The CFD modeling of biomass combustion or gasification systems needs a description of the volatiles composition that is formed during devolatilization and char oxidation processes. The present model can be used as a submodel in the CFD modeling of combustion or gasification process. This study is a combination of relevant models and data available in the literature to formulate a model that predicts the volatiles in terms of a few simple species. The volatile species considered by this model are CO, CO2, H2O, H2, light hydrocarbons, and heavy hydrocarbons. The model predicts the volatiles as a function of temperature for different biomasses. The model was applied for pyrolysis of briquettes made from agricultural residues. The results are in good agreement with data from literature.

Modeling and Application of Combustion Process in Gasoline Engines under Transient Conditions

In this paper，a model for working process simulation of gasoline engines was developed under transient conditions. Therefore，the working process of gasoline engines could be described on theoretical basis. The computer program was edited. The results of simulation are agreed perfectly with that of test，and can provide support for design and study of transient emissions.

Simulation of flow behavior of particles by cluster structure-dependent drag coefficient model for chemical looping combustion process: Air reactor modeling

A computational fluid dynamic (CFD) model for the air reactor of chemical looping combustion (CLC) technology has been developed, with special focus on flow of clusters. To model effects of clusters on flow behavior of gas and particles in a riser of air reactor, the model of cluster structure-dependent (CSD) drag coefficient is proposed on the basis of the minimization of energy dissipation by heterogeneous drag (MEDHD). The momentum balances that characterize the clusters in the dense phase and dispersed particles in the dilute phase are proposed. The CSD drag coefficient model is incorporated into the two-fluid model. The distributions of concentration and velocity of particles are predicted in a riser of air reactor. The Ergun/Wen and Yu drag model underestimates the distribution of concentration of particles in the riser. Dynamic evolution of clusters is reproduced and the profile of concentration and solid fluxes is analyzed. Predictions using the CSD drag coefficient model are in agreement with experimental data published in the literature. The distributions of O2 concentration and temperatures of gas phase and particles are predicted with CuO as oxygen carrier in the AR.

Controlling Gasoline Low Temperature Combustion by Diesel Micro Pilot Injection

The simultaneous reduction of fuel consumption and pollutant emissions, namely NOx and soot, is the predominant goal in modern engine development. In this context, low temperature combustion concepts are believed to be the most promising approaches to resolve the above mentioned conflict of goals. Disadvantageously these combustion concepts show high peak pressures or high rates of pressure rise due to early ignition and high reaction rates especially at high loads. Furthermore, there are still challenges in controlling combustion phasing. In this context using a small amount of pilot diesel injected directly into the combustion chamber to ignite a highly diluted gasoline air mixture can overcome the aforementioned difficulties. As the gasoline does not ignite without the diesel, the pilot injection timing can be used to control combustion phasing. By increasing dilution even high loads with low rates of pressure rise and without knocking are possible. This paper shows the results of experimental investigations carried out on a heavy duty boosted single cylinder diesel engine. Based on the indicated cylinder pressure, the combustion process is characterized by performing knock analyses as well as thermodynamic analyses. Furthermore, an optically accessible engine has been set up to investigate both the diesel injection and the combustion process by means of digital high speed imaging. Together with the thermodynamic analyses the results of these optical investigations make up the base for the presented theoretical model of this combined diesel-gasoline combustion process. To show the load potential of this Dual-Fuel-CAI concept, the engine was operated at 2100 1/min with an IMEP of 19 bar. NOx emissions did not exceed 0.027 g/kWh.

Numerical Simulation and Backfilling Materials Research on Coal Spontaneous Combustion of Thick Seam Large-Scale Top-Caving Region in Resources Conformity Coal Mine

This paper aimed at fire control in thick seam large-scale top-carving region. On the basis of coal and oxygen compounding theory, theoretical analysis, numerical simulation and experiment are combined, and a coal spontaneous combustion process model is built according to fluid mechanics and control theory. By studying and testing on top-carving coal spontaneous combustion process, conclusion is drawn that spontaneous combustion area is the largest in partly-closed region, followed by unclosed region. A totally closed baffle leads to the smallest spontaneous combustion area and the smallest possibility of fire. With local materials in a certain condition, new, cheap backfilling materials are developed. Thus provide theoretical basis for study on the forecasting and prevention of thick seam large-scale top-carving coal spontaneous combustion.

Modeling of Auto-Ignition and Combustion Processes for Dual-Component Fuel Spray

Modeling of Auto-Ignition and Combustion Processes for Dual-Component Fuel Spray

Influence of particle shape and internal thermal gradients of biomass particles on pulverised coal/biomass co-fired flames

The practice of employing pulverised coal/biomass co-firing in power plants is gradually increasing. This is mainly because of the benefits associated in reducing the coal based CO 2 and biomass based SO x and NO x emissions. However, biomass is difficult to mill due to its fibrous texture and this results in the presence of large particles of different shapes which influence the combustion characteristics. Existing computational fluid dynamics (CFD) models often ignore thermal gradients within the particles and this leads to inaccuracy in the combustion process modelling. In this paper, a CFD sub-model for the heat transfer within large particles is developed. The model is validated for the heating up, moisture release and devolatilisation of single wood particle measurements that are available in the literature. The impact of fuel particle sizes on the combustion characteristics has been investigated in terms of ignition, devolatilisation and char combustion in a co-firing case of an industrial combustion test facility. The predictions, while considering the internal thermal gradients with particle size and shape distribution, were identified to be in excellent agreement with measured data. The code was worked well when coupled with ANSYS FLUENT and with a negligible amount of extra time for the computations.

Oxy-fuel coal combustion—A review of the current state-of-the-art

Carbon dioxide emissions will continue being a major environmental concern due to the fact that coal will remain a major fossil-fuel energy resource for the next few decades. To meet future targets for the reduction of greenhouse gas (GHG) emissions, capture and storage of CO 2 is required. Carbon capture and storage technologies that are currently the focus of research centres and industry include: pre-combustion capture, post-combustion capture, and oxy-fuel combustion. This review deals with the oxy-fuel coal combustion process, primarily focusing on pulverised coal (PC) combustion, and its related research and development topics. In addition, research results related to oxy-fuel combustion in a circulating fluidised bed (CFB) will be briefly dealt with. During oxy-fuel combustion, a combination of oxygen, with a purity of more than 95 vol.%, and recycled flue gas (RFG) referred to as oxidant is used for combusting the fuel producing a gas consisting of mainly CO 2 and water vapour, which after purification and compression, is ready for storage. The high oxygen demand is supplied by a cryogenic air separation process, which is the only commercially available mature technology. The separation of oxygen from air as well as the purification and liquefaction of the CO 2-enriched flue gas consumes significant auxiliary power. Therefore, the overall net efficiency is expected to be decreased by 8–12% points, corresponding to a 21–35% increase in fuel consumption. Alternatively, ion transport membranes (ITMs) are proposed for oxygen separation, which might be more energy efficient. However, since ITMs are far away from becoming a mature technology, it is widely expected that cryogenic air separation will be the selected technology in the near future. Oxygen combustion is associated with higher temperatures compared with conventional air combustion. Both fuel properties as well as limitations of steam and metal temperatures of the various heat exchanger sections of the boiler require a moderation of the temperatures in the combustion zone and in the heat-transfer sections. This moderation in temperature is accomplished by means of recycled flue gas. The interdependencies between the fuel properties, the amount and temperature of the recycled flue gas, and the resulting oxygen concentration in the combustion atmosphere are reviewed. The different gas atmosphere resulting from oxy-fuel combustion gives rise to various questions related to firing, in particular, with respect to the combustion mechanism, pollutant reduction, the risk of corrosion, and the properties of the fly ash or its resulting deposits. In this review, detailed nitrogen and sulphur chemistry was investigated in a laboratory-scale facility under oxy-fuel combustion conditions. Oxidant staging succeeded in reducing NO formation with effectiveness comparable to that typically observed in conventional air combustion. With regard to sulphur, a considerable increase in the SO 2 concentration was measured, as expected. However, the H 2S concentration in the combustion atmosphere in the near-flame zone increased as well. Further results were obtained in a pilot-scale test facility, whereby acid dew points were measured and deposition probes were exposed to the combustion environment. Slagging, fouling and corrosion issues have so far been addressed via short-term exposure and require further investigation. Modelling of PC combustion processes by computational fluid dynamics (CFD) has become state-of-the-art for conventional air combustion. Nevertheless, the application of these models for oxy-fuel combustion conditions needs adaptation since the combustion chemistry and radiative heat transfer is altered due to the different combustion gas atmosphere. CFB technology can be considered mature for conventional air combustion. In addition to its inherent advantages like good environmental performance and fuel flexibility, it offers the possibility of additional heat exchanger arrangements in the solid recirculation system, i.e. the ability to control combustion temperatures despite relatively low flue gas recycle ratios even when combusting in the presence of high oxygen concentrations.

Existence and uniqueness of the traveling front in premixed combustion of porous media

We study a mathematical model of combustion processes in an inert porous media filled with a combustible gaseous mixture. We focus on the phenomenon of a combustion wave driven by a local pressure elevation. In this article, we are concerned with subsonic pressure-driven flames and with the case of a quadratic dependence of the friction force on the velocity of the gaseous mixture. After a suitable non-dimensionalization, the resulting mathematical model includes three nonlinear ordinary differential equations (ODEs). The system contains an unknown parameter V that represents the traveling wave speed. The existence of the traveling wave is proven in this study. It means that the parameter V can be chosen so that the corresponding phase trajectory satisfies the boundary conditions. Moreover, under reasonable assumptions about the monotonicity of the flame front, we prove the uniqueness of the pressure-driven wave.

Numerical modeling of fires on gas pipelines

When natural gas is released through a hole on a high-pressure pipeline, it disperses in the atmosphere as a jet. A jet fire will occur when the leaked gas meets an ignition source. To estimate the dangerous area, the shape and size of the fire must be known. The evolution of the jet fire in air is predicted by using a finite-volume procedure to solve the flow equations. The model is three-dimensional, elliptic and calculated by using a compressibility corrected version of the k - ξ turbulence model, and also includes a probability density function/laminar flamelet model of turbulent non-premixed combustion process. Radiation heat transfer is described using an adaptive version of the discrete transfer method. The model is compared with the experiments about a horizontal jet fire in a wind tunnel in the literature with success. The influence of wind and jet velocity on the fire shape has been investigated. And a correlation based on numerical results for predicting the stoichiometric flame length is proposed.

Modelling of biomass combustion process

Abstract The paper presents a different approach on biomass combustion process modelling based on Bond Graph methodology. The main thermal-chemical processes used for biomass to energy conversion are oxidative. This study focused on oxidation process with heat generation using solid fuels. The important number of biomass categories and different conversion technologies influence the model input parameters in terms of temperatures, mass flows, heat exchange, requiring different models for combustion processes. The large range of biomass based products can be represented by carbon, hydrogen, oxygen, chlorine, sulphur, and nitrogen composition. In order to highlight the modelling method advantages, the research focused on wood biomass combustion. The product was represented by carbon, hydrogen, and oxygen composition given through their molar fraction. The paper presents the results on combustion process kinetics with respect to reactant and reactor input data, especially for the transitory regimes like ignition. The model provides information on time variation of the heat of reaction, reaction products concentration, and reactants concentration / accumulation, based on global mass and energy balance of the process.

Computationally intelligent modeling and control of fluidized bed combustion process

In this paper modelling and control approaches for fluidized bed combustion process have been considered, that are based on the use of computational intelligence. Proposed adaptive neuro-fuzzy-genetic modeling and intelligent control strategies provide for efficient combining of available expert knowledge with experimental data. Firstly, based on the qualitative information on the desulphurization process, models of the SO2 emission in fluidized bed combustion have been developed, which provides for economical and efficient reduction of SO2 in FBC by estimation of optimal process parameters and by design of intelligent control systems based on defined emission models. Also, efficient fuzzy nonlinear FBC process modelling strategy by combining several linearized combustion models has been presented. Finally, fuzzy and conventional process control systems for fuel flow and primary air flow regulation based on developed models and optimized by genetic algorithms have also been developed. Obtained results indicate that computationally intelligent approach can be successfully applied for modelling and control of complex fluidized bed combustion process.

Modeling of the fluidized bed combustion process and NO x emissions using self-organizing maps: An application to the diagnosis of process states

Efforts to reduce harmful emissions and the increasing demands for combustion efficiency have generated a number of challenges for power plants. Changes in the operation of a combustion process, for example, can induce fluctuations that have unexpected consequences such as an increased level of emissions. Despite the importance of these changes, their impact and relevance are often ignored in analyses of industrial process data due to the complexity of these phenomena. It seems that the behavioral evolution of a process could be understood more easily by monitoring the transition of the process from one characteristic state to another. We demonstrate here that the self-organizing map (SOM) provides an efficient method for revealing the most characteristic features of input data, making it a powerful tool for discovering general phenomena and visualizing the behavior and evolution of a combustion process. In this approach the process data are analyzed using a SOM and K-means clustering to create subsets representing the separate process states in the boiler. A trajectory analysis is then performed to indicate fluctuations in the process and their implications. The results show that process fluctuations can significantly affect the levels of nitrogen oxides released. The method enables efficient diagnosis, and provides a clear illustration of the evolution of the process and an applicable means of defining the best path for achieving a more efficient process that produces less emissions.

Adequacy of Experimental and Theoretical Models of Combustion Processes

Adequacy of experimental and mathematical models of combustion processes is analyzed. A four-level classification of adequacy of various models is proposed. Examples are given to characterize the degrees of adequacy of mathematical models and experimental concepts available in combustion science.

Thermodynamic analysis of combustion processes and pollutants emission using nonlinear optimization approach

AbstractMathematical formulation and modeling of combustion processes is an important tool in the understanding of this phenomenon. Determination of equilibrium temperature and composition is often the first stage in calculation of combustion characteristics. There are number of different techniques for simulation of combustion process. In this study a basic model has been developed based on the minimization of Gibb's free energy to simulate the combustion processes. A nonlinear mathematical optimization has been developed based on Lagrange multipliers and solved using Quasi‐Newton method written in MathCAD environment. The effect of various parameters such as initial temperature, pressure, and equivalence ratio on the equilibrium temperature and composition has been investigated. In contrast with the equilibrium constant method, obtained results out of this work show that the maximum flame temperature for normal paraffins occurs around the equivalence ratio of 1.05. In addition, from environmental point of view, effects of different conditions on the emission of pollutants in a combustion process have been studied. The simulation results showed that the NO and NO2 emission rates pass through a maximum point and there is an optimum point where the NOCO emission could be minimized. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Simplified model of combustion process in a diesel engine for real-time operation

In a diesel engine, three combustion parameters, which describe the crank angle at the start of ignition, the total amount of heat release and the combustion duration can be used to control the speed, efficiency, noise and exhaust emission. Pressure analysis of a diesel engine cylinder can be used for identifying these parameters. The combustion parameters can be determined using the pressure signal and the pressure derived from a mathematical model of the combustion process. One such mathematical model of the combustion process called the Wiebe function is widely used in application. In this work, we investigated the Wiebe function and the analysis shows that the computational time to determine the combustion parameters is too high to be used in the real-time operation. Therefore, several alternative models were formulated, which are cheap in computation. Thus, these models are more suitable for real-time operation.