Modeling Of Combustion Processes Research Articles

Venting Of Defiagrations: Dynamics Of The Process In Systems With A Duct And Receiver

This paper describes the application of a proposed model to vented gaseous explosions in a small and large-scale equipment with venting of deflagration through exhaust duct to receiver or atmosphere. It was shown that introduction of a duct and vacuumed receiver into explosion protection system can have strong influence on dynamics of vented deflagration and increase of maximum explosion pressure. The physics of this phenomenon was studied. Coincidence between values of the main unknown parameter of the vented combustion process model turbulization factor x from this work and results following from K.I. Shchelkin and B. Karlovits theories was obtained and c o n f i e d by cinegrams. The 3.7-4 times growth of burnout rate in the vessel due to high level turbulence combustion in the duct was determined by inverse problem method. The discovered effect of combustion intensification can be removed by increase of vent relief pressure or sprinkling of cooling agent into gas mixture flow at the beginning of a duct.

Asymptotic behaviour of some reaction-diffusion systems modelling complex combustion on bounded domains

SynopsisWe consider three models of multiple-step combustion processes on bounded spatial domains. Previously, steady-state convergence results have been established for these models with zero Neumann boundary conditions imposed on the temperature as well as the mass fractions. We retain here throughout the same boundary conditions on the mass fractions, but in our first set of results we establish steady-state convergence results with fixed Dirichlet boundary conditions on the temperature. Next, under certain physically reasonable assumptions, we develop, for two of the models, estimates on the decay rates of both mass fractions to zero, while for the remaining model we develop estimates on the decay rate of one concentration to zero and establish a positive lower bound on the other mass fraction. These results hold under either set of boundary conditions, but when the Dirichlet conditions are imposed on the temperature, we are able to obtain estimates on the rate of convergence of the temperature to its (generally nonconstant) steady-state. Finally, we improve the results of a previous paper by adding a temperature convergence result.

Weakly nonlinear asymptotic models and analogs of detonation processes

Two simplified, qualitative models of combustion and detonation processes have been developed and studied in recent years. One is an analog, posed independently by Fickett and Majda, and one is an asymptotic model, derived by Rosales and Majda, that is valid near a Mach 1 regime where the reaction front is moving close to the sound speed in the material ahead and the particle velocity is small in comparison. In this paper, after reviewing the recent literature on these two models, we analyze the scalings required to obtain the asymptotic equations, thereby revealing the range of parameter values for which the asymptotic model is valid. Along with the analysis we give a simple one-dimensional derivation of the asymptotic equations, and it is indicated how the formulation of the model changes when the chemical kinetics is reversible.

Combustion: a study in theory, fact and application

Part 1 Combustion of gases: fundamentals of chemical kinetics - reaction rates, chemical equilibrium, chemical kinetic rate equations flame propagation in laminar flows - aerodynamics, dynamic stability, flammability limits flame propagation in turbulent flows - vortex stretching, combustion models, wrinkled laminar flame and local reaction models ignition and flame stabilization explosion and detonation diffusion flames. Part 2 Combustion of liquids and solids: combustion of droplets and sprays combustion of coal, combustion of char, transformations of ash, fixed-bed and fluidized-bed combustion free-burning fires - cellulosic materials, fire suppression combustion of condensed systems - the SHS process, combustion of solid propellants environmental aspects of combustion - major pollutants, clean systems. Part 3 Combustion design and research fundamentals: application of chemical reactor theory to combustor design physical modeling of combustion processes - similarity theory basic diagnostic techniques in combustion - measurements, visualization, diagnostics combustion in practical systems - gas-turbibes, boilers, LCVG. Appendices: The earliest scientific definition of combustion and flame data for thermochemical calculations.

Modeling of the Combustion Process in a Dual Fuel Direct Injection Engine

Analytical methods to provide a guideline for predicting the limit for acceptable power output of dual fuel engines due to the onset of autoignition and knock are described. This is achieved primarily through improved modeling of the chemical reaction rates of the charge during compression and subsequently following pilot ignition. Some performance results with methane as a fuel are presented.

Laser‐doppler velocimeter measurements in simulated entrained gasifier flows

AbstractA laser‐Doppler velocimeter (LDV) was used in a cold‐flow study of a simulated entrained‐flow coal gasifier. The study was designed to provide fundamental information about the flows in such a gasifier and to provide data for the validation of a turbulence submodel used in modeling combustion processes. Measurements in 20 swirling and nonswirling flow cases were made with several levels of replication. This study emphasized the effects of inlet conditions on flow properties within the simulated reactor.Unsteady flow phenomena with time scales on the order of seconds to minutes were sometimes observed. The unsteadiness was apparently associated with relaminarization‐type flow transitions.Comparisons were made with model predictions from PCGC‐2, a model for combustion processes based on the k, — ϵ turbulence model. Several areas of weakness in the model results were observed, but the unusual flow regimes measured in this study may be beyond the abilities of practical computer models.

揺動火格子式ごみ焼却炉のごみの燃焼過程モデル

揺動火格子式ごみ焼却炉のごみの燃焼過程モデル

Internal combustion engine fundamentals

1 Engine Types and Their Operations 2 Engine Design and Operating Parameters 3 Thermochemistry of Fuel-Air Mixtures 4 Properties of Working Fluids 5 Ideal Models of Engine Cycles 6 Gas Exchange Processes 7 SI Engine Fuel Metering and Manifold Phenomena 8 Charge Motion within the Cylinder 9 Combustion in Ignition Engines 10 Combustion in Compression Ignition Engines 11 Pollutant Formation and Control 12 Engine Heat Transfer 13 Engine Friction and Lubrication 14 Modeling Real Engine Flow and Combustion Processes 15 Engine Operating Characteristics Appendixes

Combustion in supersonic flow

Examples of numeric modeling of complex combustion processes in supersonic flows are presented which illustrate the possibility of obtaining useful information which may reveal their basic regularities determined by the parameters of the entrance streams, mode of injection, type of fuel, and the interaction of various factors pertaining to combustion. Hydrogen combustion was used in the analysis. Peculiar results are presented on numerical modeling in situations where the kinetics of the exothermal reactions were subject to limitations imposed by the hydrodynamic conditions, and where the development of the motion of a continuous medium was part of the combustion process. The discovery of small supersonic velocities in the reverse flow in the recirculation zone, confirmed by the presence of static pressure distributions, was noted and studied.

Initiation of detonation combustion for coal dust in a methane-air mixture

This paper studies the combustion of coal dust behind the leading shock wave in a mixture of oxygen with acetylene and in air with different contents of methane. The model of combustion processes for coal dust is presented. The possibility of initiation of heterogeneous detonation in air with a low methane content is considered. It is shown that the distance at which heterogeneous detonation forms decreases by 3% with a mass concentration of coal dust of 0.14 g/m/sup 3/. The effect of radiation weakens the process of carbon sublimation, thus limiting the increase in particle temperature.

Temperature coefficients for reactions of OH radicals with alkanes between 300 and 1000 K

AbstractRecently, Atkinson et al. have developed a more sophisticated approach than simple additivity to determine group rate constants at room temperature for reactions of OH radicals with alkanes. In this article, use is made of reliable experimental data at room temperature and at 753 K to determine temperature coefficients for these reactions. Evidence based on experiment is cited in support of the expression k = AT1e−E/RT as a suitable quantitative expression for the variation of k with temperature between 300 and 1000 K for OH attack at any particular specific group in an alkane. Values are given for A and E for a number of groups found in both linear and branched alkanes. With highly branched alkanes, steric effects may limit the use of even the more sophisticated additivity approach used here. Use of the group values permits the calculation of both the overall rate constant for OH + alkane, the agreement with the limited amount of experimental data available being very good, and the proportions of each species of alkyl radical formed in the overall attack. Such information is vital to quantitative modeling of combustion processes currently being carried out extensively. The values given in the article are recommended for use over the temperature range 300–1000 K.

Pulverized-coal combustion research at Brigham Young University

This review paper presents a comprehensive summary and analysis of research work conducted principally at the Brigham Young University Combustion Laboratory over the past decade. An attempt is made to set forth the philosophy and foundations for the laboratory research, which include commitments to both measurement and modeling of complex combustion processes. Recent work has emphasized pulverized-coal processes. The review paper reports past results, together with some recent, previously unpublished results, and provides an integration and summary of key findings. Information from independent investigators is also included or referenced where comparisons are made or where similar work provided clarification. Among the most significant results include the following: (1) measurement of local properties (e.g. velocity, concentration, temperature, mixing rate) from reacting and nonreacting gaseous and particle-laden flows for a variety of test conditions. These data provide a basis for determining controlling processes and for evaluating comprehensive coal reaction models; (2) development and application of comprehensive pulverized-coal combustion models for premixed and diffusion flames; (3) evaluation of combustion models by extensive comparisons with detailed profile data from this and other laboratories. Research needs and concerns in each area of activity are also identified, and future possible laboratory directions are considered.

Modelling of combustion process in a spark ignited hydrogen engine

This paper reports the relative merits of the Eddy Entrainment model over the Reynolds Parameter model in describing the combustion process in a spark ignition engine using hydrogen as fuel. The relative performance of each model is analysed with reference to the experimental data obtained from a single-cylinder engine. From the present investigation and in comparison of the performance of these models with other fuels it is found that both the models are capable of satisfactorily predicting the performance of hydrogen fuel engines due to (a) higher laminar flame speeds and (b) small quench distance.

Chemical kinetics and modeling of combustion processes

Chemical kinetic modeling is an important tool in the analysis of many combustion systems. The use of detailed kinetic models in the interpretation of fundamental kinetics experiments in shock tubes and plug flow reactors is widespread. Recently these models, coupled with fluid mechanical models, have become valuable in helping to understand complex phenomena in practical combustion devices. This paper reviews the mechanisms used for the combustion of hydrocarbon fuels and some of the practical problems to which they have been applied. Chemical kinetic reaction mechanisms are strongly hierarchical in that mechanisms for the combustion of more complex fuels contain within them submechanisms for simpler fuel molecules. With this basic structure in mind, mechanisms for H2−O2, CO, CH4, and CH3OH are discussed, followed by C2 species including ethane, ethylene, and acetylene, and finally by a single C3 species, propane. Validation of the elementary reactions and rates in a reaction mechanism is strongly influenced by the combustion environment being studied. For this reason, we emphasize comprehensive reaction mechanisms developed using data from a variety of experimental systems. We review some of the principles and techniques involved in the development and application of these kinetics models for hydrocarbon fuels. Applications of reaction mechanisms to combustion systems include purely kinetic problems and others requiring a treatment of transport effect. The former class includes shock tubes, plug flow reactors, and stirred reactors, while the latter includes laminar flame propagation, flame quenching, and flame inhibition. Each of these combustion systems is discussed, emphasizing the role of chemical kinetics.

Measurements of Mixing and Species Concentrations Within a Gas Turbine Type Combustor

Abstract —Results are presented of detailed gas analysis traverses carried out within a gas turbine type research combustor. The combustor was run at approximately atmospheric pressure, and fuelled by propane vapour. Two sets of results are described; these were obtained by using two alternative fuel injector nozzles in an attempt to modify the degree of fuel-air mixing within the combustor. Detailed measurements on axial and radial planes within the combustor of quantities of interest in gas turbine combustion at idle (equivalence ratio, temperature, carbon monoxide and unburned hydrocarbon) are presented and discussed. Some molecular hydrogen measurements are also given. With this combustor, the primary air addition method is shown to have a dominant influence on combustion and hence the pollutant levels at the combustor exit. The implications of the results of the gas analysis surveys for the computer modelling of gas turbine combustion processes are discussed.

Current status of droplet and liquid combustion

The present understanding of spray combustion in rocket engine, gas turbine, Diesel engine and industrial furnace applications is reviewed. In some cases, spray combustion can be modeled by ignoring the details of spray evaporation and treating the system as a gaseous diffusion flame; however, in many circumstances, this simplification is not adequate and turbulent two-phase flow must be considered. The behavior of individual droplets is a necessary component of two-phase models and recent work on transient droplet evaporation, ignition and combustion is considered, along with a discussion of important simplifying assumptions involved with modeling these processes. Methods of modeling spray evaporation and combustion processes are also discussed including: one-dimensional models for rocket engine and prevaporized combustion systems, lumped zone models (utilizing well-stirred reactor and plug flow regions) for gas turbine and furnace systems, locally homogeneous turbulent models, and two-phase models. The review highlights the need for improved injector characterization methods, more information of droplet transport characteristics in turbulent flow and continued development of more complete two-phase turbulent models.

A Linear Model And a Related Very Stable Numerical Method For Thermal Secondary Oil Recovery

Abstract This paper describes a linear mathematical model of the underground combustion process. The principal features of the model are:a large number of component in the system (oxygen, inert gas, two different ail components, combustion gas, the vapours of the liquids and the solutions of the combustion gas in the liquids), all together twelve components;the inclusion of complex physical-chemical processes (combustion of the oil components and they vapours, evaporation of the liquid, solution of the combustion gas in the liquids and their effects on the viscosities, heat conduction):a new approach to obtain a highly stable numerical method, based on:the use of more equations than the number of unknowns, exploiting the stability features of each equation,a new numerical treatment of the reaction term, for obtaining increased stability andthe use of a new, unconditionally stable, finite difference scheme for degenerating parabolic differential equations (including, first-order equations) [see ref. (4)]. The complexity of the system is also characterized by the fact that it involves 163 physical-chemical parameters, not counting the input data related to the numerical work itself. The results of some "numerical tests" designed to check the consistency of the model are presented. The calculations show the following features to be in agreement, with laboratory experiments:because the wall of the reactor tube is supposed to be insulated against heat losses, it is difficult to find conditions which assure a heat front of constant temperature;if the ignition is successful and a heat front is obtained, it moves with constant velocity under constant injection conditions;water injection has a stabilizing effect on the heat front and increases its velocity. INTRODUCTION THE PRACTICAL AND THEORETICAL problems of secondary oil recovery by in-situ combustion are well known. Because the actual three-dimensional underground combustion process is extremely complicated, much effort has been concentrated on experimental and theoretical studies of linear laboratory models. The main difficulty in the theoretical work is mathematical, namely to find a sufficiently stable numerical method which permits the use of a large time step in the computation, so that the computer time needed for the computation will be practically feasible. The order of magnitude of this time step is the only limit which restricts the possible complexity of the mathematical model, because otherwise it is not difficult to "write down as general and complicated differential equations as one likes. The main purpose of this paper is to present a numerical method which is stable enough to allow the consideration of a very general mathematical model possessing qualitatively new features. No attempt has been made to compare laboratory data with the results obtained by computation. We are convinced that the 163 physical-chemical input data involved are sufficient to fit the model to any laboratory experiment. Nevertheless, some results of a qualitative nature, showing important features of the combustion process, are included in the conclusions.

The art of partial modeling

The strict requirements of similarity theory are shown to be so numerous and restrictive that complete modeling of combustion processes is practically impossible; all successful modeling so far has involved deliberately ignoring many of the similarity rules. The paper reviews some of the more notable examples of this partial modeling, and mentions the physical facts which underlie their success. It is emphasized that every combustion-modeling technique represents a compromise between the requirements of cheapness and reliability.