Showing papers on "Combustion published in 1992"

Evaluated Kinetic Data for Combustion Modelling

Abstract: This compilation contains critically evaluated kinetic data on elementary homogeneous gas phase chemical reactions for use in modelling combustion processes Data sheets are presented for some 196 reactions Each data sheet sets out relevant thermodynamic data, rate coefficient measurements, an assessment of the reliability of the data, references, and recommended rate parameters Tables summarizing the preferred rate data are also given The reactions considered are limited largely to those involved in the combustion of methane and ethane in air but a few reactions relevant to the chemistry of exhaust gases and to the combustion of aromatic compounds are also included

Steam: its generation and use

Abstract: This book contains 57 chapters divided into the following sections: steam fundamentals; steam generation from chemical energy; application of steam; environmental protection; specification, manufacturing and construction; operations; maintenance and life extension; steam generation from nuclear energy; and balance of plant Chapters related to coal include: coal pulverization; burners and combustion systems for pulverized coal; cyclones; stokers; atmospheric fluidized-bed boilers; pressurized fluidized-bed combustion; coal gasification; and fuel ash effects on boiler design and operation

Control of combustion-generated nitrogen oxide emissions: Technology driven by regulation

Abstract: Nitrogen oxides in the atmosphere contribute to photochemical smog, to the formation of acid rain precursors, to the destruction of ozone in the stratosphere and to global warming. Over the past 150 years, global emissions of nitrogen oxides into the atmosphere have been increasing steadily. A significant amount of the nitrogen oxide emissions is attributed to combustion of biomass and fossil fuels. Increasingly stringent NOx emissions regulations are being implemented in a number of industrialized countries. These regulations have driven and continue to drive the development of NOx emissions control techniques. This paper reviews existing and some emerging technologies for reduction of NOx emissions from combustion sources and examines the prospects of these technologies for meeting stricter emissions regulations. Both combustion modification and post-combustion methods for NOx reduction are considered. The important role of research on the chemistry of nitrogen oxides in combustion gases in development and optimization of emissions control techniques is described.

Solid‐State Gas Sensors: A Review

Abstract: During the past three decades, gas sensors based either on the surface characteristics or the bulk electrolytic properties of ceramics, have been the subject of extensive research and development. The application of these sensors range from air-to-fuel ratio control in combustion processes such as in automotive engines and industrial furnaces to the detection of leakage of inflammable and toxic gases in domestic and industrial environments. While the solid-state physical sensors, measuring pressure, temperature, and other physical parameters have been commercially successful, less success has been achieved by their chemical analogs, to measure moderate to very low concentrations of gases of importance. These gases include: 02, H2, CO, CO2, NOx, SO=, propane, methane, ethanol, and so on. The semiconductor-based chemical sensors owe their popularity to their small size, simple operation, high sensitivity, and relatively simple associated electronics. However, most of them still suffer from nonselectivity. They also have poor shelf-life and are relatively less stable at higher temperatures. The sensing characteristics and performance of some of the solid-state gas sensors are reviewed in this paper, together with their sensing mechanism, which still is a gray area and has not been fully understood. The recent emergence of concern over environmental pollution and effleieney in a variety of combustion processes and of increased awareness over a need to monitor potentially hazardous gases has stimulated substantial research and development in the field of gas sensors. These gases include, CO, CO2, NOx (x = 0.5, 1, and 2), SOx (x = 2 and 3), a fraction of unburned hydrocarbons [ineluding liquefied petroleum gas (LPG) also known as cooking or town gas] and hydrogen. Requirements to detect and monitor these gases has already led to the development of a wide variety of devices and methods, as evideneed by a large number of instruments now available commercially. The majority of these detection and/or metering devices involve the application of surface or bulk chemical and physical properties of materials and can, therefore, be called solidstate chemical sensors. 1-5 However, before addressing the topic of these gas sensors, it is appropriate to briefly outline some of the environmental concerns. LP gas can form explosive mixture with ambient air and ean lead to personal injury upon continuous exposure, even in small concentrations. A number of industrially important eatalytie processes require either producer gas (CO + H2) in various compositions or H2 and CO separately as feed stocks. The producer gas is synthesized by the steam reforming of natural gases and other hydrocarbons under conditions of high temperatures and pressures. The accidental eseape or leak of either CO or H2 from sueh a high temperature and pressure system can be a source of explosion and health hazard. The combustion of hydrocarbon fuels is a widely used method of obtaining useful energy in various industries. Burning of fossil fuel in the "lean-burn combustion" manner is regarded as the most fuel and energy efficient mode of fuel utilization, since under these eonditions, the hydrocarbons in the fuel are fully eonverted into CO2 and H20. However, the compositional analysis of the flue gases in most of the combustion furnaces, indicates the presence of CHJCO/CO2/H2 in the final reaction product, in accordance with the thermodynamic predictions under the conditions of these processes. This could be attributed to the occurrence of the following reaetions side-by-side

Heat injection process

Abstract: A method for heat injection into a subterranean formation is provided. The method utilizes flameless combustion. The absence of a flame eliminates the flame as a radiant heat source and results in a more even temperature distribution throughout the length of the burner. Flameless combustion is accomplished by preheating the fuel and the combustion air to a temperature above the autoignition temperature of the mixture. Preheating hydrocarbon fuel requires the inclusion of a carbon formation suppressant such as carbon dioxide or steam to prevent carbon formation.

Recovery and upgrading of hydrocarbon utilizing in situ combustion and horizontal wells

Abstract: Disclosed are a method and apparatus for recovering and/or upgrading hydrocarbons utilizing in situ combustion and horizontal wells. Vertical injection wells are utilized to inject an oxidant into a reservoir for in situ combustion, with the combustion gases vented through vertical wells offset from the injection wells, thus causing the combustion front to travel toward the vertical offset wells. Production of hydrocarbons is through horizontal wells positioned beneath the vertical offset wells. Upgrading occurs when the horizontal wells are shut in and hot fluids injected through the offset wells into hydrocarbons that have accumulated at the bottom of the offset wells.

Method for enhanced oil recovery through a horizontal production well in a subsurface formation by in-situ combustion

Abstract: A horizontal production well is located in the lower portion of a heavy viscous oil-bearing reservoir. A vertical injection well is located in the upper portion of the reservoir. Oxygen-enriched gas is injected down the injector well and ignited in the upper portion of the reservoir to create a combustion zone that reduces viscosity of oil in the reservoir as the combustion zone advances downwardly toward the horizontal production well, the reduced-viscosity oil draining into the horizontal production well under force of gravity.

Smoke and fire characteristics for cerrado and deforestation burns in Brazil: BASE-B experiment

Abstract: Five test fires were performed during August and September 1990 in the cerrado (savannalike region) in central Brazil (three fires) and tropical moist forest (two fires) in the eastern Amazon. This paper details the gases released, the ratios of the gases to each other and to particulate matter, fuel loads, and the fraction consumed (combustion factors), and the fire behavior associated with biomass consumption. Models are presented for evaluating emission factors for CH4, CO2, CO, H2, and particles less than 2.5 micron diam (PM2.5) as a function of combustion efficiency. The ratio of carbon released as CO2 (combustion efficiency) for the cerrado fires averaged 0.94 and for the deforestation fires it decreased from 0.88 for the flaming phase to less than 0.80 during the smoldering phase of combustion. For tropical ecosystems, emissions of most products of incomplete combustion are projected to be lower than previous estimates for savanna ecosystems and somewhat higher for fires used for deforestation purposes.

Numerical simulations of Lewis number effects in turbulent premixed flames

Abstract: The structure of a premixed flame front propagating in a region of two-dimensional turbulence is investigated using full numerical simulation including heat release, variable properties, and one-step Arrhenius chemistry. The influence of reactant Lewis number (Le = ratio of thermal to species diffusivity) is reported for Le = 0.8, Le = 1.0, and Le = 1.2 flames. Local flame behaviour is described by comparing the local instantaneous turbulent flame structure (local consumption rate of reactants) to the steady one-dimensional laminar flame structure for the same thermochemical parameters. Statistics of flame front strain rates and curvature are calculated and global quantities of interest in modelling (flame surface area, mean reactant consumption rate per unit area of flame, and turbulent flame speed) are reported. Principal findings are: that probability density functions (p.d.f.s) of flame curvature are nearly symmetric about a near-zero mean; that the flame tends to align preferentially with extensive tangential strain rates; that the local flame structure of the non-unity Lewis number flames correlates more strongly with local flame curvature than with tangential strain rate; that the mean consumption rate per unit area is relatively insensitive to curvature and is controlled by the mean tangential strain rate; and, that more flame area is generated for Le 1. Implications of the results for flamelet models of turbulent premixed combustion are discussed.

How fast can we burn

Abstract: The roots of our present understanding of tubulence, flame chemistry and their interaction are traced. Attention is then focused on premixed turbulent combustion and the different analyses of stretch—free theories of turbulent burning velocity, u t , are reviewed and new work presented. The various expressions for u t are very different and this becomes more important when allowance must be made for flame stretch. On the basis of previous asymptotic analyses the appropriate dimensionless groups emerge for the correlation of experimental values of u t and a correlation based on these is presented save that,‘pro tem’, the Lewis rather than the Markstein number is employed. The presented correlations are used as a test bed for a stretched flame, Reynolds stress, laminar flamelet model of turbulent combustion. Computed laminar flame data on flame quenching by stretch are generalised and used in the model. The problems of appropriate probability density functions of both stretch and temperature are discussed. There is good agreement between model predictions and experiment over a wider range than would be distance scale should be greater than the laminar flame thickness. The reasons for this wider applicability are discussed, particularly in relation to recent direct numerical simulations. Some of the concepts discussed are applied to spherical explosions and continuous swirling combustion. There is wide diversity in burning rates because of widely different circumstances, but our knowledge is becoming adequate enough to develop reasonably accurate mathematical models for the wide range of engineering applications.

A spectral closure for premixed turbulent combustion in the flamelet regime

Abstract: Premixed turbulent combustion in the flamelet regime is analysed on the basis of a field equation. This equation describes the instantaneous flame contour as an isoscalar surface of the scalar field G(x,t). The field equation contains the laminar burning velocity sL as velocity scale and its extension includes the effect of flame stretch involving the Markstein length [Lscr ] as a characteristic lengthscale of the order of the flame thickness. The scalar G(x,t) plays a similar role for premixed flamelet combustion as the mixture fraction Z(x,t) in the theory of non-premixed flamelet combustion.Equations for the mean . For the case of plane normal and oblique turbulent flames the turbulent burning velocity sT and the flame shape is calculated. In the absence of flame stretch the linear relation sT ∼ u′ is recovered. The flame brush thickness is of the order of the integral lengthscale. In the case of a V-shaped flame its increase with downstream position is calculated.

Thermal radiation heat transfer - Third edition

Abstract: The authors have revised this text to incorporate new general information, advances in analytical and computational techniques, and new reference material. Wide coverage focuses on thres subject areas: radiation from opaque surfaces, radiation interchange between various types of surfaces enclosing a vacuum or transparent medium, and radiation including the effects of partially transmitting media, such as combustion gases, soot, or windows.

Methods and apparatus for burning fuel with low NOx formation

Abstract: Improved methods and burner apparatus are provided for discharging mixtures of fuel and air into furnace spaces wherein said mixtures are burned and flue gases having low NO x content are formed therefrom. The methods basically comprise discharging a first fuel mixture containing a portion of the fuel and flue gases from the furnace space into the furnace space whereby the mixture is burned in a primary reaction zone therein and flue gases having low NO x content are formed therefrom, and then discharging the remaining portion of the fuel into a secondary reaction zone wherein the remaining portion of fuel mixes with air and flue gases to form a second fuel mixture which is burned in the secondary reaction zone and additional flue gases having low NO x content are formed therefrom.

Combustion of diesel fuel from a toxicological perspective. I. Origin of incomplete combustion products.

Abstract: Since the use of diesel engines is still increasing, the contribution of their incomplete combustion products to air pollution is becoming ever more important. The presence of irritating and genotoxic substances in both the gas phase and the particulate phase constituents is considered to have significant health implications. The quantity of soot particles and the particle-associated organics emitted from the tail pipe of a diesel-powered vehicle depend primarily on the engine type and combustion conditions but also on fuel properties. The quantity of soot particles in the emissions is determined by the balance between the rate of formation and subsequent oxidation. Organics are adsorbed onto carbon cores in the cylinder, in the exhaust system, in the atmosphere and even on the filter during sample collection. Diesel fuel contains polycyclic aromatic hydrocarbons (PAHs) and some alkyl derivatives. Both groups of compounds may survive the combustion process. PAHs are formed by the combustion of crankcase oil or may be resuspended from engine and/or exhaust deposits. The conversion of parent PAHs to oxygenated and nitrated PAHs in the combustion chamber or in the exhaust system is related to the vast amount of excess combustion air that is supplied to the engine and the high combustion temperature. Whether the occurrence of these derivatives is characteristic for the composition of diesel engine exhaust remains to be ascertained. After the emission of the particles, their properties may change because of atmospheric processes such as aging and resuspension. The particle-associated organics may also be subject to (photo)chemical conversions or the components may change during sampling and analysis. Measurement of emissions of incomplete combustion products as determined on a chassis dynamometer provides knowledge of the chemical composition of the particle-associated organics. This knowledge is useful as a basis for a toxicological evaluation of the health hazards of diesel engine emissions.

Resolution of gas phase and surface combustion chemistry into elementary reactions

Abstract: It is well known for many decades, that combustion chemistry is a complex phenomenon, and realistic reaction mechanisms for simple hydrocarbons have been published in the last decade. Nevertheless, for 2D-or 3D-applications in combustion science and technology nearly exclusively one-step approaches are used at the present to make solutions possible within realistic computing times or to avoid principal physical problems (e.g. closure problems in modeling turbulent combustion). However, this is paid with a huge disadvantage: No extrapolation is possible to other experimental or operational conditions, and even interpolation is dangerous. This review describes (1) how detailed reaction mechanisms can be developed for simple hydrocarbons and be verified using literature data on flame structure, flame propagation, and ignition from the literature; (2) how these mechanisms can be extended to the treatment of very large hydrocarbons by use of additivity rules and processing of these rules by computer programs generating reaction mechanisms; (3) how these large reaction mechanisms can be simplified, for use in multi-dimensional codes, e.g. by use of lumping techniques or by equilibration of fast reactions in a systematic way; (4) how treatment in terms of sets of elementary reactions can be transferred to the handling of surface reactions, e.g. for the description of catalytic combustion. Examples are given for each of these developments. The special role of sensitivity analysis is emphasized in the understanding of detailed reaction mechanisms and the identification of rate-limiting steps which should be objects of further research efforts.

Dry low NOx single stage dual mode combustor construction for a gas turbine

Abstract: In a gas turbine (10), a plurality of combustors (14), each having a plurality of fuel nozzles (32) arranged about a longitudinal axis of the combustor, and a single combustion zone (70), each fuel nozzle having a diffusion passage (74) and a premix passage (60), the premix passage communicating with a plurality of premix fuel distribution tubes (66) located within a dedicated premix tube (46) adapted to mix the premix fuel and combustion air prior to entry into the single combustion zone (70) located downstream of the premix tube (46).

Hydrocarbon ignition: Automatic generation of reaction mechanisms and applications to modeling of engine knock

Abstract: A computational technique is described which automatically develops detailed chemical kinetic reaction mechanisms for large aliphatic hydrocarbon fuel molecules. This formulation uses the LISP language to apply general rules which identify the chemical species produced, the reactions between these species, and the elementary reaction rates for each reaction step. Reaction mechanisms for cetane (n-hexadecane) and most alkane fuels C{sub 7} and smaller are developed using this automatic technique, and detailed sensitivity analyses for n-heptane and cetane are described. These reaction mechanisms are then applied to calculation of knock tendencies in internal combustion engines. The model is used to study the influence of fuel molecule size and structure on knock tendency, to examine knocking properties of fuel mixtures, and to determine the mechanisms by which pro-knock and anti-knock additives change knock properties.

Low NOx burner assemblies

Abstract: A burner assembly (10) for process heaters or the like comprising a burner block (14), primary gas jets (20), secondary gas jets (22), a flame holder (26), and an air register for installation in a furnace wall or furnace floor is described. The burners are characterized in that primary fuel is introduced into the primary combustion zone (24) of the burner at an angle horizontal to the flame holder whereby the fuel induces furnace gases from the furnace into the primary combustion zone. Similarly, the secondary fuel jets introduce a secondary fuel through the burner block for consumption in a combustion zone at the surface of the burner block. The secondary fuel also draws furnace gases into the combustion zone for consumption. The design provides for intense mixing of combustion air with the fuel and furnace gases, resulting in low NOx levels.

Turbine engine control system

Abstract: Fuel flow is scheduled to a plurality of combustion stages by putting a plurality of engine fuel flow governors in parallel with each other and letting the governor which outputs the lowest fuel demand signal be the one which schedules the total fuel flow to the engine. Fuel flows to the plurality of combustion stages are then individually scheduled to achieve the lowest fuel flows consistent with predefined temperature limits for the corresponding stages of combustion.

Effect of support material on the catalytic combustion of diesel soot particulates

Abstract: Several potential support materials were mixed with soot and subsequently the combustion temperature of the soot in 15% O2 was determined. Al2O3 and SiO2 showed no catalytic effect, TiO2 and ZrO2 lowered the soot combustion temperature with 80–90 K, whereas CeO2, La2O2CO3 and V2O5 (reference catalyst) showed a substantial activity for soot combustion. After poisoning with sulfur dioxide, the catalytic effect of CeO2 was strongly inhibited, whereas La2O2CO3 and V2O5 retained their high activity.

Method for apparatus for combusting fuel in a combustion chamber

Abstract: To avoid high NOx emissions, the fuel is oxidized with an extremely high exhaust gas recirculation ration substantially without flames and without pulsations.