Showing papers on "Combustion published in 1981"

Substoichiometric combustion of low heating value gases

Abstract: The combustible component of a gas stream of low heating value is combusted using less than a stoichiometric amount of oxygen with minor production of carbon monoxide due to the use of an oxygenation catalyst comprising at least three metals in a perovskite-type crystal structure. This combusted gas can be directly vented to the atmosphere after energy has been extracted from it for a useful purpose.

Multiple-site underground magnetic heating of hydrocarbons

Abstract: A first underground deposit of lignite or coal is heated by magnetic induction to recover hydrocarbon liquids and gases. The carbon remaining is combusted with air and steam to produce a gas which is combusted to generate electrical energy. The electrical energy is transmitted to second underground deposits of oil shale, tar sand or heavy oil, and is used to heat the second deposits in order to recover hydrocarbon liquids and gases.

Substoichiometric combustion of low heating value gases using different platinum catalysts

Abstract: Low heating value gases are combusted substoichiometrically in two combustion zones in series in contact with two different supported platinum catalysts in which the concentration of platinum in the catalyst in the first zone is higher than the concentration of platinum in the second catalyst The combusted gas of reduced carbon monoxide can be directly vented to the atmosphere after energy has been extruded from it for a useful purpose

Turbulence Production in Premixed Turbulent Flames

Abstract: —A second order closure theory developed earlier is used to study the processes influencing the turbulent velocity field in a premixed turbulent flame with degrees of heat release of practical interest. The flow field is chosen so that the time-averaged flame structure is one-dimensional and statistically stationary. Earlier work suggests that in the absence of turbulence production due to Reynolds stresses as is the case in a flame orthogonal to the oncoming reactants, the case we consider, dilatation resulting from heat release reduces the level of turbulence. In contrast it is shown here that with sufficient heat release turbulence increases on passage through the flame because of a buoyancy production mechanism arising from the self-induced, mean pressure gradient. This mechanism overwhelms the effects of dilatation at temperature ratios characteristic of combustion. The same buoyancy mechanism also causes counter-gradient diffusion as predicted in an earlier paper and as observed in recent e...

The structure of laminar alkane-, alkene-, and acetylene flames

Abstract: The detailed knowledge of combustion mechanisms is important for example for the control of (kinetically determined) pollutant formation (e.g., NO, hydrocarbons, soot), or for the extrapolation to technologically important but experimentally inaccessible conditions. By suitable separation and elimination of unimportant reactions, a mechanism is developed with the aid of the present kinetic data for the elementary reactions involved. This mechanism explains, without fitting, the currently available experimental results for laminar premixed flames of alkanes, alkenes, and acetylene (flame velocity and structure of free flames, concentration and temperature profiles in burner-stabilized flames). These experimental results are simulated by the solution of the corresponding conservation equations with suitable models describing diffusion and heat conduction in the multicomponent mixture considered. In lean and moderately rich flames the hydrocarbon is attacked by O, H, and OH, in the first step. These radicals are produced by the chain-branching steps of the oxyhydrogen reaction. The alkyl radicals formed in this way always decompose to smaller alkyl radicals by fast thermal elimination of alkenes. Only the relatively slow thermal decomposition of the smallest alkyl radicals (CH 3 and C 2 H 5 ) competes with recombination and with oxidation reactions by O atoms and O 2 . This part of the mechanism is rate-controlling in the combustion of alkanes and alkenes, and is therefore the reason for the similarity of all alkane and alkene flames.

In-situ combustion method for recovery of heavy oil utilizing oxygen and carbon dioxide as initial oxidant

Abstract: An in-situ combustion method for recovering viscous oil from a subterranean, viscous oil-containing formation comprising injecting a mixture of essentially pure oxygen and carbon dioxide into the formation to initiate an in-situ combustion operation followed by injecting essentially pure oxygen.

Downhole steam generator with improved preheating, combustion and protection features

Abstract: An apparatus for generation of steam in a borehole for penetration into an earth formation wherein feedback preheater means are provided for the fuel and water before entering the combustor assembly. First, combustion gases are conducted from the combustion chamber to locations in proximity to the water and fuel supplies. Secondly, both hot combustion gases and steam are conducted from the borehole back to the water and fuel supply. The water used for conversion to steam is passed in a countercurrent manner through a plurality of annular water flow channels surrounding the combustion chamber. In this manner, the water is preheated, and the combustion chamber is cooled simultaneously, thereby minimizing thermal stresses and deterioration of the walls of the combustion chamber. The water is injected through slotted inlets along the combustion chamber wall to provide an unstable boundary layer and stripping of the water from the wall for efficient steam generation. Pressure responsive doors are provided at the steam outlet of the combustor assembly. The outlet doors and fluid flow functions may be controlled by a diagnostic/control module. The module is positioned in the water flow channel to maintain a relatively constant, controlled temperature.

Retorting and Combustion Processes in Surface Oil-Shale Retorts

Abstract: Lawrence Livermore's mathematical model for a batch oil-shale retorting process has proved useful in understanding in situ retorting in a bed of oil-shale rubble. This model is based on an improved understanding of the physical and chemical processes involved in retorting. It has since been modified to calculate the retorting of shale moving through a retort, as required for a continuous process in surface equipment. Calculations were made in which the retorting process that releases oil from raw shale is physically separated from the combustion process that recovers energy from spent shale by burning the residual carbon. Calculations were also made with the retorting and combustion processes combined in one unit. Results of the calculations illustrate the advantages and disadvantages of inert-gas and combustion retorts. Temperature control and the efficient use of energy from the nonliquid products of pyrolysis are key problems in surface retorting processes. The amount of gas produced by the combustion of char with air is insufficient to retort shale without steep temperature gradients which, in turn, may make the temperature difficult to control and result in the loss of oil yield. 13 figures, 3 tables.

Chemical kinetics and modeling of combustion processes

Abstract: 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.

Vaporization and condensation of mineral matter during pulverized coal combustion

Abstract: The factors governing the amount and properties of the submicron aerosol (fume) produced on combustion of coal have been studied by burning size-graded Montana lignite particles in a laminar drop-tube furnace at 1750 K. The coal particle temperatures achieved vary from 1800 K to 2800 K as the oxygen concentration in which the particles burn is increased from 5% to 100%. Size fractionation of the ash yields a bimodal size distribution. The average size of the fine particles varies from less than 50diameter to greater than 300 , depending on the combustion conditions. These fine particles are produced by vaporization of the mineral matter species during combustion and their subsequent recondensation. The amount of fume produced as metal oxides increases from 0.1% of the total ash at particle temperatures around 1800 K to 20% at 2800 K. The chemical composition of the Montana lignite fume is dominated by the refractory oxides MgO and CaO at all but the lowest temperatures (T The oxidation of the vaporized reduced-state species away from the particle surface results in a supersaturation of the refractory oxides, leading to their nucleation. A simple model in which growth of these particles then occurs by coalescent collisions and by heterogeneous condensation of new material released from the burning particles provides a good representation of the observed particle sizes as a function of residence time and degree of ash vaporization.

A theoretical study on an excess enthalpy flame

Abstract: A further theoretical study was performed on the excess enthalpy flame system proposed by Takeno and Sato to burn mixtures of low heat content. The previous analyses were extended to include effects of the finite length of the porous solid inserted for internal heat recirculation, so as to predict the flammability limit. In the analysis the temperature of the solid is an eigenvalue of the system, while mass flow rate remains a controllable parameter. Numerical calculations have revealed the existence of a critical mass flow rate above which combustion cannot be sustained. The critical flow rate is more than ten times the burning velocity for a thin porous disk of the order of the flame thickness. Below the critical flow rate, the system has two combustion states with the distinct solid temperatures. As the flow rate is decreased asymptotically to the burning velocity, the inserted disk comes to play the role of a downstream flame holder for the state with the higher solid temperature, whereas it plays the role of an upstream flame holder for the state with the lower solid temperature.

The influence of oxygen concentration on fuel parameters for fire modeling

Abstract: The influence of oxygen concentration on fuel parameters in pool fires with areas of about 0.007 m 2 and 0.07 m 2 is described for methanol, polyoxymethylene (POM), polymethyl-methacrylate (PMMA), heptane, polypropylene (PP) and polystyrene (PS). Fuel parameters include mass loss rate, combustion efficiency, convective and radiative fractions of heat of complete combustion, and yields of CO 2 , CO, and soot and low-vapor-pressure liquid products. For combustion in excess air, the combustion efficiency and the yield of CO 2 are not very sensitive to changes in m 02 and fuel areas. The fuel mass loss rate, yield of unburnt soot, flame radiative heat flux, and radiative fraction of heat of complete combustion increase and flame convective heat flux and convective fraction of heat of complete combustion decrease as m 02 is increased; for m 02 values much higher than 0.233, all the parameters approach their respective asymptotic values. There appears to be an attenuation of flame radiation by cold vapors near the surface as well as a change in the flame shape as m 02 is varied.

Direct Observations of Devolatilizing Pulverized Coal Particles in a Combustion Environment

Abstract: Direct observations of the early stages of combustion of size-graded (≈100μm) pulverized coal particles are reported. The particles are introduced on the centerline, of a high temperature, transparent, laminar flow reactor fed by a gas fueled, premixed flat flame. Photographs of particle emission, high magnification shadowgraphs of burning particles, and micrographs of partially burnt captured material have been obtained. The ignition of both bituminous coal and lignite subjected to rapid heating (≈105K/sec) by hot combustion products is characterized by, bright diffuse emission attributed to burning of ejected volatile matter. After approximately 5 msec this emission ceases, and incandescence attributed to heterogeneous char oxidation is observed. Shadowgraphs and micrographs of burning bituminous coal indicate that, coincident with ignition, ejected volatile matter forms a condensed phase surrounding the particle. The condensed phase is evidently a soot-like material resulting from pyrolytic cracking of hydrocarbons in the volatile matter. Viscous drag forces cause the condensed material to be swept into laminar wake structures which eventually separate from the particles. Under oxidizing conditions this condensed volatile matter is oxidized during the early stages of char burning, while under reducing conditions it persists throughout the flow reactor. Although burning lignite appears similar to bituminous coal in emission, shadowgraphic and micrographic observations, indicate that a condensed phase is not formed during devolatilization. Nor are, changes in particle size or shape observed during the earliest stages of combustion. These observations are consistent with previous results which showed that bituminous coal volatiles contain large fractions of soot producing heavy hydrocarbons, while lignite volatiles are largely composed of CO, CO2, H2, H2O and light hydrocarbons. The observations are also consistent with differences in the pore structure and swelling properties of the two coasl.

An improved method for the determination of carbon in soils and soil extracts by dry combustion

Abstract: A method for the determination of carbon in soils and soil extracts is described. It involves the dry combustion of samples in a standard tube furnace and the direct titrimetric determination of the evolved carbon dioxide as carbonic acid in a sodium hydroxide trap. Liquid samples are dried onto a siliceous earth bed prior to combustion. The method has a range of about 0.5 to 10 mg C.

On Spinning Propagation of Combustion Waves

Abstract: We consider a system of reaction-diffusion equations describing the propagation of combustion waves along a thermally insulated cylindrical sample of solid fuel. Uniform propagation of a plane combustion wave is subjected to a linear stability analysis. It is shown that, if the activation energy is sufficiently high and the diameter of the sample sufficiently large, then the experimentally observed spinning propagation of combustion waves appears as a Hopf-type bifurcation of the solution corresponding to a plane wave.The possibility of similar phenomena in gas combustion is discussed.

Coal Combustion Aerosol Formation Mechanisms: A Review

Abstract: The composition and size distribution of particles emitted by coal combustion sources depend upon various mechanisms leading to their formation. A review of current ideas about possible mechanisms for formation of combustion aerosols is presented. Available data regarding fly ash size distribution and elemental concentrations in various size fractions were analyzed. These data were qualitatively compared with theoretical model predictions to indicate the relative contributions of various mechanisms in the formation of aerosols.

Electrolysis fuel supplementation apparatus for combustion engines

Abstract: A combustion engine is provided with a fuel supplementation system in which water is broken down by electrolysis into hydrogen and oxygen which are then added to the fuel delivery system. The electrolysis takes place in a chamber in which a pusher gas rises through perforated horizontal electrode plates to sweep the hydrogen and oxygen from the plates as it is generated, thereby preventing the accumulation of these gases in the chamber. In addition, the electrolyte can be circulated, passing it through a filter, to increase the turbulence and agitation within the chamber. The rate at which the water is electrolyzed is varied, as by modulating the voltage applied to the plates, in accordance with the throttle position of the engine. Since gases do not accumulate in the chamber, variations in the rate at which these gases are yielded are affected substantially instantaneously. Lignite activited water can be added to the electrolyte to inhibit the formation of sludge.

A model for solid propellant combustion

Abstract: A model has been developed to describe the combustion characteristics of composite solid propellants. The model is based on several new concepts. First, the oxidizer and binder have different surface temperatures rather than a single averaged temperature that has previously been assumed. Second, the overall burn rate is calculated from a time averaged approach rather than the conventional space averaging used in most propellant combustion models. A key contribution in the time averaging approach is use of an ignition delay time for the oxidizer. Third, a generalized flame standoff distance has been developed based on a modified Burke-Schumann diffusion flame analysis. The analysis accounts for variable oxidizer/fuel (O/F) ratio that differing oxidizer size fractions can experience. The analysis shows that the primary diffusion flame can extend over either the oxidizer or the fuel depending on the local O/F ratio. Calculated results for a series of HMX composite propellants show several key trends and excellent agreement when compared to experimental data. The propellants vary in oxidizer particle size and concentration over a range of pressures and temperatures. The model indicates that the fuel binder has a more significant influence than previously thought.

Phenomenological combustion model for a quiescent chamber diesel engine

Abstract: A phenomenological model is presented for prediction of the combustion characteristics of a quiescent chamber diesel engine. Predictions with the model have shown acceptable agreement with a range of experimental data. The major physical processes controlling combustion have been characterized, and the dominant role of air entrainment and turbulent mixing confirmed quantitatively. 45 refs.