Showing papers on "Combustion published in 1988"

Fundamentals of Air Pollution Engineering

Abstract: Analysis and abatement of air pollution involve a variety of technical disciplines. Formation of the most prevalent pollutants occurs during the combustion process, a tightly coupled system involving fluid flow, mass and energy transport, and chemical kinetics. Its complexity is exemplified by the fact that, in many respects, the simplest hydrocarbon combustion, the methane-oxygen flame, has been quantitatively modeled only within the last several years. Nonetheless, the development of combustion modifications aimed at minimizing the formation of the unwanted by-products of burning fuels requires an understanding of the combustion process. Fuel may be available in solid, liquid, or gaseous form; it may be mixed with the air ahead of time or only within the combustion chamber; the chamber itself may vary from the piston and cylinder arrangement in an automobile engine to a 10-story-high boiler in the largest power plant; the unwanted byproducts may remain as gases, or they may, upon cooling, form small particles. The only effective way to control air pollution is to prevent the release of pollutants at the source. Where pollutants are generated in combustion, modifications to the combustion process itself, for example in the manner in which the fuel and air are mixed, can be quite effective in reducing their formation. Most situations, whether a combustion or an industrial process, however, require some degree of treatment of the exhaust gases before they are released to the atmosphere. Such treatment can involve intimately contacting the effluent gases with liquids or solids capable of selectively removing gaseous pollutants or, in the case of particulate pollutants, directing the effluent flow through a device in which the particles are captured on surfaces. The study of the generation and control of air pollutants can be termed air pollution engineering and is the subject of this book. Our goal here is to present a rigorous and fundamental analysis of the production of air pollutants and their control. The book is intended for use at the senior or first-year graduate level in chemical, civil, environmental, and mechanical engineering curricula. We assume that the student has had basic first courses in thermodynamics, fluid mechanics, and heat transfer. The material treated in the book can serve as the subject of either a full-year or a one-term course, depending on the choice of topics covered. In the first chapter we introduce the concept of air pollution engineering and summarize those species classified as air pollutants. Chapter 1 also contains four appendices that present certain basic material that will be called upon later in the book. This material includes chemical kinetics, the basic equations of heat and mass transfer, and some elementary ideas from probability and turbulence. Chapter 2 is a basic treatment of combustion, including its chemistry and the role of mixing processes and flame structure. Building on the foundation laid in Chapter 2, we present in Chapter 3 a comprehensive analysis of the formation of gaseous pollutants in combustion. Continuing in this vein, Chapter 4 contains a thorough treatment of the internal combustion engine, including its principles of operation and the mechanisms of formation of pollutants therein. Control methods based on combustion modification are discussed in both Chapters 3 and 4. Particulate matter (aerosols) constitutes the second major category of air pollutants when classified on the basis of physical state. Chapter 5 is devoted to an introduction to aerosols and principles of aerosol behavior, including the mechanics of particles in flowing fluids, the migration of particles in external force fields, Brownian motion of small particles, size distributions, coagulation, and formation of new particles from the vapor by homogeneous nucleation. Chapter 6 then treats the formation of particles in combustion processes. Chapters 7 and 8 present the basic theories of the removal of particulate and gaseous pollutants, respectively, from effluent streams. We cover all the major air pollution control operations, such as gravitational and centrifugal deposition, electrostatic precipitation, filtration, wet scrubbing, gas absorption and adsorption, and chemical reaction methods. Our goal in these two chapters, above all, is to carefully derive the basic equations governing the design of the control methods. Limited attention is given to actual equipment specification, although with the material in Chapters 7 and 8 serving as a basis, one will be able to proceed to design handbooks for such specifications. Chapters 2 through 8 treat air pollution engineering from a process-by-process point of view. Chapter 9 views the air pollution control problem for an entire region or airshed. To comply with national ambient air quality standards that prescribe, on the basis of health effects, the maximum atmospheric concentration level to be attained in a region, it is necessary for the relevant governmental authority to specify the degree to which the emissions from each of the sources in the region must be controlled. Thus it is generally necessary to choose among many alternatives that may lead to the same total quantity of emission over the region. Chapter 9 establishes a framework by which an optimal air pollution control plan for an airshed may be determined. In short, we seek the least-cost combination of abatement measures that meets the necessary constraint that the total emissions not exceed those required to meet an ambient air quality standard. Once pollutants are released into the atmosphere, they are acted on by a variety of chemical and physical phenomena. The atmospheric chemistry and physics of air pollution is indeed a rich arena, encompassing the disciplines of chemistry, meteorology, fluid mechanics, and aerosol science. As noted above, the subject matter of the present book ends at the stack (or the tailpipe); those readers desiring a treatment of the atmospheric behavior of air pollutants are referred to J. H. Seinfeld, Atmospheric Chemistry and Physics of Air Pollution (Wiley-Interscience, New York, 1986). We wish to gratefully acknowledge David Huang, Carol Jones, Sonya Kreidenweis, Ranajit Sahu, and Ken Wolfenbarger for their assistance with calculations in the book. Finally, to Christina Conti, our secretary and copy editor, who, more than anyone else, kept safe the beauty and precision of language as an effective means of communication, we owe an enormous debt of gratitude. She nurtured this book as her own; through those times when the task seemed unending, she was always there to make the road a little smoother. R. C. Flagan J. H. Seinfeld

Chemical Kinetic Data Base for Combustion Chemistry. Part 3: Propane

Abstract: This publication contains evaluated and estimated data on the kinetics of reactions involving propane, isopropyl radical, n‐propyl radical, and various small inorganic and organic species which are of importance for proper small inorganic and organic species which are of importance for proper understanding of propane pyrolysis and combustion. It is meant to be used in conjunction with the kinetic data given in earlier publications which are of direct pertinence to the understanding of methane pyrolysis and combustion, but which also contain a large volume of data that are applicable to the propane system. The temperature range covered is 300–2500 K and the density range 1×1016 to 1×1021 molecules cm−3.

Droplet vaporization model for spray combustion calculations

Abstract: The re-examination of the classical droplet vaporization model is made in order to develop the simple but sufficiently accurate calculation algorithm which can be used in spray combustion calculations. The new model includes the effects of variable thermophysical properties, non-unitary Lewis number in the gas film, the effect of the Stefan flow on heat and mass transfer between the droplet and the gas, and the effect of internal circulation and transient liquid heating. To evaluate the competing simplified models of the droplet heating, the more-refined, extended model of heat transfer within a moving circulating droplet is considered. A simplified, one-dimensional ‘effective conductivity’ model is formulated for the transient liquid heating with internal circulation. As an illustration, the dynamic and vaporization histories of the droplets injected into the steady and fluctuating hot air streams are analyzed.

On the Theory of Slow Combustion

Abstract: Publisher Summary Physical theories of slow combustion are usually based on the conception that the transfer of heat to the unburned gaseous mixture from the products of combustion—heated owing to the reaction—is a result of simple thermal conduction. The thickness of the combustion layer separating the region of the initial mixture from that of the products of combustion is then determined completely by thermal conduction in the gas and by purely chemical properties of the given reaction. It is essential that this thickness is independent of the characteristic dimensions of the problem. The characteristic dimensions of the problem to be large in comparison with the thickness of the combustion layer are assumed in the chapter. Then, in determining the hydrodynamical movement of the gas accompanying the combustion process, the whole transition layer is considered as a surface separating the burned and unburned gas. In the considered thermal conduction regime of slow combustion, the rate of propagation of the combustion is certainly small in comparison with the velocity of sound.

An analytical study of the hydrogen-air reaction mechanism with application to scramjet combustion

Abstract: A chemical kinetic mechanism for the combustion of hydrogen has been assembled and optimized by comparing the observed behavior as determined in shock tube and flame studies with that predicted by the mechanism. The reactions contained in the mechanism reflect the current state of knowledge of the chemistry of the hydrogen/air system, and the assigned rate coefficients are consistent with accepted values. It was determined that the mechanism is capable of satisfactorily reproducing the experimental results for a range of conditions relevant to scramjet combustion. Calculations made with the reaction mechanism for representative scramjet combustor conditions at Mach 8, 16, and 25 showed that chemical kinetic effects can be important and that combustor models which use nonequilibrium chemistry should be used in preference to models that assume equilibrium chemistry. For the conditions examined the results also showed the importance of including the HO2 chemistry in the mechanism. For Mach numbers less than 16, the studies suggest that an ignition source will most likely be required to overcome slow ignition chemistry. At Mach 25, the initial temperature and pressure was high enough that ignition was rapid and the presence of an ignition source did not significantly affect reaction rates.

High Combustion Temperature for the Reduction of Particulate in Diesel Engines

Abstract: Experiments on the effects of temperature T and equivalence ratio Φ on soot formation at high pressures up to 5 MPa were conducted. Discussion of the trajectory in relation to both soot and NO formation region gives suggestion of a possibility of high temperature ― rich mixture combustion to reduce particulate formation in diesel engines

Method and apparatus for shale gas recovery

Abstract: A process for the in situ gasification of shale avoids the necessity of initially fracturing the shale bed and includes the placement of a gas-fired heater assembly within a bore hole followed by the application, from above ground, of fuel gas and combustion air, both of which are regulated to maintain an initial start-up temperature of over 1000 degrees F. and thereafter a constant temperature of below 1500 degrees F. throughout a reaction zone formed in the surrounding shale bed. Specifically, a production temperature of 1200 degrees F. has been found most desirable. By maintenance of this temperature, voids created in the reaction zone as kerogen is retorted to evolve natural gas, become black body radiators assisting to insure a sustained, constant high volume extraction of natural gas having a BTU value of over 800 and devoid of any liuqids. The apparatus includes the provision of fuel gas and combustion air supply lines leading from above ground to the interior of the heater assembly, together with a product gas line having a gas extraction opening through the side wall of the heater assembly adjacent its top.

Reheat buzz: an acoustically coupled combustion instability. Part 2. Theory

Abstract: Reheat buzz is a low-frequency instability of afterburners. It is caused by the interaction of longitudinal acoustic waves and unsteady combustion. Similar combustion instabilities occur in laboratory rigs. A theory is developed to determine the frequency and mode shape of the instability and is tested by comparison with the experimental results described in Part1. The predicted and measured frequencies are found to be within 6 Hz (7%) of each other. The theory is able to predict the observed variation of frequency with equivalence ratio, inlet Mach number and geometry.

Fuel injection system for internal combustion engines

Abstract: A fuel injection system for an internal combustion engine and a method of controlling fuel injection according to which a predetermined fuel quantity is delivered from a high-pressure pump to the internal combustion engine, first and second return flow quantity are returned through first and second relief ducts, the second relief duct including a control throttle having a constant cross-section, and an electronic control unit controls flow delivery in accordance with characteristic values including those of the internal combustion engine, the pump, and a quantity measuring device for measuring the second return flow, and in accordance with the predetermined fuel delivery quantity also used as a characteristic value.

Tin dioxide gas sensors. Part 2.—The role of surface additives

Abstract: It has been shown earlier (J. F. McAleer, P. T. Moseley, J. O. W. Norris and D. E. Williams, J. Chem. Soc., Faraday Trans. 1, 1987, 83, 1323) that the gas response of porous pellets of tin dioxide depends crucially on electronic surface states involving adsorbed oxygen, and on the rates of combustion reactions involving the gases to be detected. It is expected, therefore, that the use of surface additives capable of either pinning the Fermi level of the tin dioxide or altering the rate of combustion (depending on choice of material and temperature) would profoundly affect the gas sensor response of the material. This is found to be the case. Studies of the influence of surface additions of precious metals and of metal oxide particles on the gas response behaviour of tin dioxide are described. The use of precious metals at temperatures near to ambient imposes an oxygen-independent Schottky barrier on the tin dioxide surface and results in a distinct low-temperature response to carbon monoxide, probably by adsorption on the precious metal modifying the surface potential (and hence the Schottky barrier). This particular effect is expected only when the precious metal particles distributed over the oxide surface are extremely small (1–10 nm): the effect disappears if the catalyst particles are aggregated by heating. The distribution of particles of a foreign oxide (here Ag2O or ZnO) on the surface of the tin dioxide also appears to pin the surface-energy levels to those of the additives, and tin dioxide treated in this way exhibits gas-sensing properties that are modified to resemble those of the additive oxide in bulk. At higher temperatures, especially in the presence of a precious-metal catalyst, the gas is completely oxidised within a thin outer shell of the specimen and consequently the response to the gas of the measured resistance of the pellet disappears. Indeed, a response to the reaction products (H2O and CO2) is obtained.

A Theory of Thermal Propagation of Flame

Abstract: Publisher Summary There has been a conception of the thermal propagation of flame as the most usual mechanism of combustion connected with the successive ignition of the explosive mixture by the heat liberated during the reaction. The existing theories, however, are unsatisfactory and therefore, a rational theory must find an expression for the velocity of flame propagation in a mixture for which the kinetics of chemical reaction is given as a function of temperature and concentration of the reacting substances. The chapter presents an equation of heat conduction that allows for the heat liberated owing to chemical reaction together with the diffusion equation governing the concentrations of the reacting substances and reaction products—also allowing for the change of these concentrations due to chemical reaction. The equation leads to conclusions that are very essential for the subsequent study.

Characterization of combustion aerosols for haze and cloud formation: Final report

Abstract: Aerosols resulting from the combustion of acetylene, wood, and JP-4 aviation fuels have been characterized in both the laboratory and the larger field scales by activity as cloud condensation nuclei (CCN), the total particle or condensation nuclei (CN) count, ion chromatography (IC) on filter samples, and morphology by scanning electron microscopy. The CCN/CN ratio for a given aerosol sample is a quantitative indicator of the ability of a combustion aerosol to become involved in atmospheric removal by nucleation scavenging. On both the laboratory and the field scales, this ratio was in the range 0.2 to 1.0 for the wood combustion aerosol, 0.2 to 0.5 for the acetylene case, and only 0.01 to 0.03 for JP-4. The CCN/CN ratios are identical for both the field and laboratory studies, implying that laboratory studies of CCN activities can be justifiably extrapolated to field studies. Aging and size-classified nucleation studies are also reported. 20 refs., 9 figs., 3 tabs.

An artifact in the measurement of N2O from combustion sources

Abstract: An artifact in the use of sampling containers for the measurement of nitrous oxide emissions from fossil fuel combustion has been identified. The storage of moist combustion products containing SO2 and NO for periods as short as 2 hours can lead to the formation of several hundreds of parts-per-million of N2O in the sample containers where none originally existed. The drying of the gas in a 0°C trap before introduction into the container reduces, but does not eliminate N2O formation. Removing SO2 prior to the sample container appears to eliminate the artifact. This finding may have important consequences with respect to the validity of the existing data base on N2O emissions from combustion sources and the role of combustion generated N2O in the atmospheric N2O balance.

Heat transfer in steam boiler furnaces

Abstract: This is a useful reference book focusing on state-of-the-art concepts explaining the mechanisms of the process as well as basic engineering methodologies for calculating heat transfer in furnaces firing pulverized coal, gas, and fuel oil. Solving these problems is especially relevant to high reliability and efficiency in furnace chambers. One of the most complex problems in heat transfer analysis is the calculation of heat transfer. That is why this book provides such extensive material on the conditions of combustion, motion of gases and mass transfer when burning different fuels. The accuracy of such data as thermophysical properties of a layer of impurities on waterwall tubes as well as the radiative properties of flame, especially of its solid particles is imperative and therefore studied in this book.

Model for Heat Transfer and Combustion In Spark Ignited Engines and its Comparison with Experiments

Abstract: A detailed model of in-cylinder heat transfer in spark ignited engines has been developed. The model is based on a well established boundary layer representation which is driven by a flow model which describes all of the major in-cylinder fluid motions: swirl, squish, axial piston-driven motion and turbulence. The flow model allows for bowl-in-piston and recessed head geometries, divided into four flow regions

Method and apparatus for generating highly luminous flame

Abstract: A burner (10) and method is disclosed in which a first oxidizing gas (14) containing a high oxygen concentration is injected as a stream into the central zone of a combustion tunnel (12), and part of the fuel (18) is injected (19) into said central pyrolysis zone to mix with said first oxidizing gas to create a highly luminous, high temperature flame core containing microparticles of carbon of the proper size for maximum luminosity and high temperature, and a relatively small amount of hydrocarbon radicals. In addition, the remaining part of the fuel is injected (20) in a plurallity of streams about said flame core to mix with a second oxidizing gas (15) containing a lower oxygen concentration than the first oxidizing gas and injecting said second oxidizing mixture about said flame core and said remaining fuel flow to mix with said remaining fuel flow. This creates a plurality of fuel lean flames which are directed toward said luminous flame core to form a final flame pattern having high temperature, high luminosity and low NOx content.

Optimizing the oxidation of carbon monoxide

Abstract: A method for reducing the amount of carbon monoxide produced in the combustion of carbonaceous fuels. The fuel is coated on at least a portion of its exterior surface with a microporous layer of solid particulate matter which is non-combustible at temperatures in which the carbonaceous fuel combusts. This invention is particularly applicable in the reduction of carbon monoxide in the burning of carbonaceous fuel elements found in currently available "smokeless" cigarettes.

Three-dimensional furnace computer modelling

Abstract: A fully three-dimensional computer model of a pulverized fuel, tangentially fired furnace is presented. The model predicts gas flows, species concentrations and temperatures, particle trajectories and combustion and radiation heat fluxes. The gas phase conservation equations of momentum, enthalpy and mixture fraction are solved utilizing the k-e turbulence model. A Lagrangian approach is used to predict particle trajectories. Particle dispersion in the turbulent flow is modelled by a stochastic method. Coal devolatilization and char burnout are modelled and radiative heat transfer is handled by a discrete transfer method. The predictions are compared with data obtained in an operating 500 MW(e) furnace. Input conditions for the computations are the actual coal feed rate, particle size distribution, specific energy and chemical analysis. The predictions are compared with furnace measurements of temperatures, O2 concentrations, wall heat fluxes and carbon burnout. Agreement between the predictions and data is very satisfactory.

Gas turbine combustor and combustion method therefor

Abstract: A gas turbine combustor comprising a head combustion chamber and a rear combustion chamber connected to a downstream side of the head combustion chamber, a first stage burner for premixing first stage fuel and air and supplying the resultant fuel and air premixture into the head combustion chamber to effect first stage premix combution, a second stage burner for premixing second stage fuel and air and the resultant fuel and air premixture into the rear combustion chamber to effect premix combustion in addition to the first stage premix combustion, and a device for regulating flow rates of combustion air to be premixed with first and second stage fuel. The combustor is further provided with a pilot burner in the head combustion chamber to form pilot flame and stabilize the first stage premix combustion.

Apparatus and process for producing high density thermal spray coatings

Abstract: An attachment for supersonic thermal spray equipment by which inert shield gas is directed radially outwardly about the central core of a supersonic, particle-carrying flame to isolate the same from ambient atmosphere. The shield gas is injected tangentially against the inner surface of a constraining tube attached to and extending from the discharge end of the thermal spray gun nozzle, causing the shield gas to assume a helical flow path which persists until after it exits the tube and impacts the work piece. A process using the shielding apparatus with a high-velocity, thermal spray gun and employing oxygen and hydrogen as gases of combustion and inert gas to introduce metal powder, having a narrow particle size distribution and low oxygen content, into the high-velocity combustion gases, produces significantly improved, high-density, low-oxide metal coatings on a substrate.

Combustion and Diffusion Flames at High Pressures to 2000 bar

Abstract: The combustion of methane with oxygen in supercritical homogeneous aqueous fluids has been investigated and stationary diffusion flames generated to pressures of 2000 bar. A reaction autoclave with sapphire windows contains high pressure homogeneous mixtures of water and methane to 500°C. A typical mixture composition is 70 to 30 mole percent of H2O and CH4. A quasi-circular fluid flow permits the steady injection of oxygen through a 0.5 mm nozzle at rates of 1 — 10 mm3 s−1 at constant pressures. — Above 400°C spontaneous ignition of flames occurred. The flames were observed and recorded with microscope and video camera. Emission spectra in the UV-region were obtained and samples could be taken for analysis. Below about 400°C flame-less oxidation is detected. The stationary diffusion flames are cone-shaped and typically about 3 mm high. Flame examples for pressures between 300 and 2000 bar are shown. Preliminary temperatures derived from OH-spectra are close to 3200 K. — Water can be replaced by argon.

Single-particle biomass pyrolysis: correlations of reaction products with process conditions

Abstract: Single, thermally thick particles of lodgepole pinewood were pyrolyzed under well-defined conditions of industrial importance. Particle thickness, heating level, moisture content, density, and grain axis relative to one-dimensional heating were varied using a Box-Behnken experimental design. Gross product fractions, as well as components therein, were measured and the batch yields were correlated with second-order polynomials. The empirical equations correlating the batch yields, together with their prediction uncertainties, are presented and are suitable for use in simulations of wood combustion and thermal conversion. Comparison of large particle pyrolysis product distributions to other studies of small-particle pyrolysis yields shows the trends with particle size to be consistent. Tar yield minima depend on both particle size and heating rate. Gas yield is dependent on both particle size and heating intensity. Because some process controllables were found to alter product yields from large particles in a multiplicative way, rather than an additive way, suggestions for future experiments are made.