Showing papers on "Combustion published in 1982"

The combustion rates of coal chars: A review

Abstract: A brief description is given of devolatilization of raw coal and combustion of the residualchar. Major achievements in the study of devolatilization and important areas for further experimentation are noted; however, attention is focussed on the rate processes involved in char combustion. Means of calculating reaction rates are shown which account for temperatures of particles, mass transfer and diffusion of oxygen into the particle's pore structure, and reaction on the pore walls. Theoretical consideration is then given to the changes in the size, density, and pore structure of chars as they burn. Experimental data are shown for observed reactivities of coal chars corrected for external mass transfer effects, and intrinsic reactivities are reported for various coal chars and other carbons corrected for pore diffusion effects. Measured data on mass-transfer rates and changes in particle structure during combustion are given. Recommendations are made for further research on char reactivity and the manner in which pore structure develops during combustion. The need for combustion-oriented kinetics studies of coal develatilization is outlined.

The thermodynamics and gas dynamics of internal-combustion engines

Abstract: This volume gathers together papers by leading authorities on internal combustion engines, completing the work begun in the first volume by R.S. Benson. These state-of-the-art essays examine various methods of evaluating the performance of engines, including considerations of scavenging, in-cylinder flows, turbocharger matching, heat transfer, and a section on the modelling of pressure exchangers. This is the most comprehensive analytical text available on the subject, containing detailed analyses of internal combustion engines previously found only in technical papers.

Development of the cone calorimeter, a bench scale heat release rate apparatus based on oxygen consumption

Abstract: A new bench-scale rate of heat release calorimeter utilizing the oxygen consumption principle has been developed for use in fire testing and research. Specimens may be of uniform or composite construction and may be tested in a horizontal, face-up orientation, or, for those which do not melt, in a vertical orientation. An external irradiance of zero to over 100 kW m−2 may be imposed by means of a temperature-controlled radiant heater. The rate of heat release is determined by measuring combustion product gas flow and oxygen depletion, while the mass loss is also recorded simultaneously. The instrument has been designed to be capable of higher accuracy than existing instruments and yet to be simple to operate and moderate in construction cost. The instrument is thermed a ‘cone calorimeter’ because of the geometric arrangement of the electric heater.

Development of the cone calorimeter—A bench-scale heat release rate apparatus based on oxygen consumption†

Abstract: A new bench-scale rate of heat release calorimeter utilizing the oxygen consumption principle has been developed for use in fire testing and research. Specimens may be of uniform or composite construction and may be tested in a horizontal, face-up orientation, or, for those which do not melt, in a vertical orientation. An external irradiance of zero to over 100 kW m−2 may be imposed by means of a temperature-controlled radiant heater. The rate of heat release is determined by measuring combustion product gas flow and oxygen depletion, while the mass loss is also recorded simultaneously. The instrument has been designed to be capable of higher accuracy than existing instruments and yet to be simple to operate and moderate in construction cost. The instrument is thermed a ‘cone calorimeter’ because of the geometric arrangement of the electric heater.

Size Distribution of Fine Particles from Coal Combustion

Abstract: Measurements of the particle size distribution at the outlets of six coal-fired utility boilers showed a peak at a particle diameter near 0.1 micrometer. This submicrometer mode appears to be a general feature of coal combustion that results from a volatilization-condensation process in the boiler. At the boilers tested, the submicrometer mode contained 0.2 to 2.2 percent of the total fly ash mass. The importance of this mode is greater than its small quantity suggests because particles in the submicrometer size range are often much more difficult to collect with conventional particulate control devices than larger particles. Thus, the submicrometer mode may significantly influence the design and selection of future power plant emission controls. The particle mass in the submicrometer mode was correlated with the nitric oxide concentration in the flue gas. This correlation suggests that control of nitric oxide by modification of the combustion conditions may reduce the generation and emission of submicrometer particles.

Vaporization of refractory oxides during pulverized coal combustion

Abstract: A laboratory coal combustor was used to study the vaporization behavior of ash duringpulverized coal combustion. The variation in the amount and composition of the ash vaporized with coal type was investigated. The effect of coal size and combustion temperature on the vaporization rate of Si, Mg and Ca was also investigated. At a moderate combustion temperature of 2000° K, the amount of ash vaporized was onthe order of a few percent of the total ash content of the coals tested. The ash vaporized from combustion of subbituminous coals and lignites is composed primarily of MgO or of Na2O if the coal contains high concentrations of sodium. The ash vaporized from combustion or bituminous coals is composed primarily of SiO2 and iron oxide. This effect of rank is a result of the appreciable vaporization of the organically bound magnesium present in the low rank coals. The vaporization rates of Si and Mg are dependent on the coal size and vary by over four orders of magnitude in the combustion temperature range of 1600–3000° K. A model presented to interpret the experimental results considers the degree of dispersion of mineral matter in coal, chemical reduction of refractory oxides (SiO2, MgO, CaO) to the corresponding volatile suboxide or metal vapor, and the internal and boundary layer transport processes. The model adequately describes the vaporization rate of both metals associated with mineral inclusions and those organically bound in the parent coal, and the changes in vaporization rates with changes in temperature and in coal particle size.

Carbon dioxide power cycle

Abstract: An improved direct fired power system generating and employing a combustion gas which includes carbon dioxide or a working fluid including a combustion chamber (20) for burning a mixture which includes oxygen, carbonaceous fuel and recycled carbon dioxide working fluid at a first pressure of above 1100 PSI thereby providing a combustion gas which includes carbon dioxide and water at substantially the first pressure and above 31° C. A first turbine (16) allows the gas to expand therethrough to generate power and reduce the combustion gas pressure to a second pressure below 1100 PSI while maintaining gas temperature above 31° C. A second burner (20) heats the combustion gas to a higher temperature and a second turbine (21) allows the gas to expand therethrough to generate power and reduce the pressure to a third pressure while maintaining gas temperature above 31° C. A heat exchanger (26) includes ducts (28), (30) in heat exchange relationship. Duct (30) conducts recycled carbon dioxide working fluid at substantially the first pressure therethrough and to the combustion chamber. Duct (28) conducts combustion gas from turbine (21) therethrough to transfer heat to the recycled carbon dioxide working fluid to condense at least a portion of the water in the combustion gas but maintain the carbon dioxide thereof in a gaseous phase. Condensed water is separated from the gas. A condensor (33) cools the gas to a first temperature above 31° C. and a compressor (42) compresses the gas to a fourth pressure of at least 1100 psi but below the first pressure. A second condensor (44) cools the gas to a second temperature below the first temperature but above 31° C. and a second compressor (24) compresses the gas to substantially the first pressure to provide recycled carbon dioxide working fluid which is delivered to heat exchanger (26).

Ignition and Combustion of Boron Particles and Clouds

Abstract: PE Nomenclature = heat capacity of the gases = boron heat capacity = oxide heat capacity = heat absorbed by reaction of B2O3 with H2O = heat absorption associated with surface reaction(s) (per unit mass of boron) = heat of vaporization of B2O3 = particle burning mass flux = heat release associated with gas-phase reaction(s) (per unit mass of oxygen) = heat release of B + B2O3 reaction = particle radius = molar rate of boron consumption = molar evaporation rate of boric oxide = molar rate of removal of B2O3 by water reaction = time = particle temperature = effective surroundings radiation temperature = particle surface temperature — ambient temperature = oxide layer thickness = ambient oxygen mass fraction = surroundings absorptivity = particle emissivity = boron density = boric oxide density = density-diffusivity product = Stef an-Boltzmann constant

Internal group combustion of liquid droplets

Abstract: A quasi-steady internal group combustion model of a spherical droplet cloud has been developed to assess the effects of the collective behavior of fuel droplets on combustion characteristics and cloud structures. Analytical solutions are obtained for the predictions of the distributions of the temperature, concentrations of fuel vapor, and oxidizer in strongly and weakly interacting zones. Overall burning rate under internal group combustion mode at various flame penetration is also obtained. Numerical analysis is carried out to determine the combustion behavior of droplet clouds at some selected group combustion numbers. It was found that for a cloud of n-butylbenzene droplets, the group envelope flame is stabilized on the boundary of the droplet cloud for a group combustion number of 1.36. As the group combustion number decreases, the envelope flame penetrates into the droplet cloud and divides the cloud into two zones; a strongly interacting zone located inside the group envelope flame and a weakly interacting zone established between the envelope flame and the boundary of the cloud. In the strongly interacting zone, the droplet vaporizes and the vapor produced is consumed at the group envelope flame. The droplets in a weakly interacting zone burn with an envelope flame surrounding eachmore » droplet. When the group combustion number decreases to 0.1, the group envelope flame degenerates into a point flame at the center of the droplet cloud.« less

Analysis of Organic and Elemental Carbon in Ambient Aerosols by a Thermal-Optical Method

Abstract: A thermal-optical method has been developed for the analysis of organic and elemental carbonaceous aerosol on glass or quartz fiber filters. Organic carbon is volatilized in two steps: at 350°C in an O2 (2%)-He mixture and at 600°C in He. The volatilized organic carbon is oxidized to CO2, reduced to CH4, and measured by a flame ionization detector. Elemental carbon is combusted to CO2 in O2 (2%)-He at 400, 500, and 600°C, and the CO2 is measured as above. The reflectance of the filter segment, which is continuously monitored with a He-Ne laser system, decreases during the organic analysis because of pyrolytic conversion of organic to elemental carbon and increases during the combustion of elemental carbon. Correction for pyrolytic production of elemental carbon is accomplished by measuring the amount of elemental carbon oxidation necessary to return the filter reflectance to the value it had before pyrolysis occurred. This is facilitated by the slow, three step elemental carbon combustion process. All switching of gas flows, timing, temperature control, pyrolysis correction, analog to digital conversion electronics, electrometer functions, signal integration, data storage, and data outputs are controlled by a microcomputer system built around a Motorola 6802 microprocessor. The instrument has been used to measure organic and elemental carbon concentrations at 42 urban sites in the United States.

Numerical modelling of turbulent flow in a combustion tunnel

Abstract: A numerical technique is presented for the analysis of turbulent flow associated with combustion. The technique uses Chorin's random vortex method (rvm), an algorithm capable of tracing the action of elementary turbulent eddies and their cumulative effects without imposing any restriction upon their motion. In the past, the rvm has been used with success to treat nonreacting turbulent flows, revealing in particular the mechanics of large-scale flow patterns, the so-called coherent structures. Introduced here is a flame propagation algorithm, also developed by Chorin, in conjunction with volume sources modelling the mechanical effects of the exothermic process of combustion. As an illustration of its use, the technique is applied to flow in a combustion tunnel where the flame is stabilized by a back-facing step. Solutions for both nonreacting and reacting flow fields are obtained which satisfactorily describe the essential features of turbulent combustion in a lean propane-air mixture that were observed in the laboratory by means of high speed Schlieren photography.

Laminar burning velocities of methanol, ethanol and isooctane-air mixtures

Abstract: Variation of the laminar burning velocities of methanol, ethanol and isooctane with equivalenceratio, pressure and temperature were determined using a constant volume bomb. Measurements were conducted during the prepressure period of combustion and a density correction scheme was employed for calculation of burning velocities from measured data. The maximum burning velocities of methanol, ethanol and isooctane occur at an equivalence ratio of 1.075, as 0.50, 0.47, and 0.455 m/s, respectively. Laminar burning velocity for the three fuels showed a pressure and temperature dependence in the following form, in the range of 0.1–0.8 MPa, and 300–500 K, Ul=Ulr (P/Pr)m(T/Tr)n where m is −0.2, −0.17 and −0.22 for methanol, ethanol and isooctane, respectively, for stoichiometric mixtures. The exponent n was found to be 1.75 for methanol and ethanol and 1.56 for isooctane. Obtained results agree, to a certain extent, with the limited experimental results of previous investigators.

Method for oil recovery by in situ exfoliation drive

Abstract: A method for recovering oil from a bed of tight reservoir rock in which a chamber is formed at the base of the bed followed by alternately combusting rubble in the chamber while recovering oil liberated by pyrolysis and spalling the walls of the chamber by injection of a coolant when oil production decreases. The method is practiced from a single well by extending a casing into the chamber and extending a tubing through the casing so that oxidant and coolant can be introduced into the chamber through the annulus between the casing and tubing while oil is recovered by a pump disposed in the tubing. Multiple well operation is practiced by forming a pancake fracture between the chamber and a laterally displaced well from which the oil can be pumped after seepage through the fracture. Oxidant and coolant are injected into the chamber in multiple well operation via a well at the bottom of which the chamber is formed.

Pyrolysis of carbonaceous materials

Abstract: A process for the pyrolysis of carbonaceous materials at an elevated temperature or an elevated temperature and an elevated pressure in which a fuel is burned in the presence of a combustion supporting material, in an amount sufficient to supply at least the stoichiometric amount of oxygen for combustion of all of the fuel, to produce an effluent containing significant amounts of nitrogen and carbon dioxide and having an elected temperature, passing the effluent to a pyrolysis zone, wihtout removal of components therefrom, to thereby create an elevated temperature within the pyrolysis zone and pyrolyzing the carbonaceous material in the pyrolysis zone in the presence of the effluent from the burning step and at an elevated temperature. The burning step may additionally be carried out at a high flame velocity to produce an effluent having an elevated pressure and the carbonaceous material may thus additionally be pyrolyzed at an elevated pressure.

Mineral matter and trace-element vaporization in a laboratory-pulverized coal combustion system

Abstract: The composition and size distribution of fly ash produced by burning a Montana lignite at two temperatures, 2050 and 2450, were determined. The ash showed a bimodal size distribution with a submicron fraction that was significantly enriched in the volatile trace species. The amount of submicron aerosol increased markedly with combustion temperature, from 4% of the ASTM ash value of the coal at 2050 K to 20% at 2450 K, supporting the hypothesis that the enrichment in more volatile species of the smaller ash particles is due to a process of vaporisation and recondensation of mineral constituents.

Froude modeling of pool fires

Abstract: We present an algorithm for the burning of moderate-scale (0.1–0.7 m dia.) pool fires in terms of the pool scale and fuel properties. Previously one could not solve the energy balance at the fuel surface due to lack of information on the feedback radiation. In general this feedback radiation depends on the flame radiation temperature and absorption-emission coefficient, as well as the flame size and shape. through the use of scanning radiometer measurements on gaseous burner fires it is shown that the flame size and shape are independent of fuel chemistry for a given overall rate of combustion heat release, as suggested by Froude modeling. The average absorption-emission coefficient at an assumed global flame temperature is related to the radiant fraction of combustion heat release. An analytic flame shape expression is developed which provides the mean beam length required for predicting the radiative feedback. The remaining terms of the energy balance are solved using established procedures.

Combustion engine system

Abstract: A flow through catalytic reactor (10) which selectively catalytically decomposes methanol into a soot-free hydrogen-rich product gas utilizing engine exhaust at temperatures of 200° to 650° C. to provide the heat for vaporizing and decomposing the methanol. The reactor (10) is combined with either a spark ignited (28) or compression ignited (54) internal combustion engine or a gas turbine (202) to provide a combustion engine system. The system may be fueled entirely by the hydrogen-rich gas produced in the methanol decomposition reactor or the system may be operated on mixed fuels for transient power gain and for cold start of the engine system. The reactor (10) includes a decomposition zone formed by a plurality of elongated cylinders (12) which contain a body (114) of vapor-permeable, methanol decomposition catalyst preferably a shift catalyst such as copper-zinc. A vaporizer (14) is provided for vaporizing liquid methanol prior to introduction into the elongated cylinders (12). Exhaust gas from the internal combustion engine is passed in contact with the elongated cylinders (12) to supply the heat needed for methanol decomposition. The partially cooled exhaust gases are then passed to the vaporizer (14) where residual heat in the exhaust is utilized in vaporization of liquid methanol.

Rapid starting methanol reactor system

Abstract: The invention relates to a methanol-to-hydrogen cracking reactor for use with a fuel cell vehicular power plant. The system is particularly designed for rapid start-up of the catalytic methanol cracking reactor after an extended shut-down period, i.e., after the vehicular fuel cell power plant has been inoperative overnight. Rapid system start-up is accomplished by a combination of direct and indirect heating of the cracking catalyst. Initially, liquid methanol is burned with a stoichiometric or slightly lean air mixture in the combustion chamber of the reactor assembly. The hot combustion gas travels down a flue gas chamber in heat exchange relationship with the catalytic cracking chamber transferring heat across the catalyst chamber wall to heat the catalyst indirectly. The combustion gas is then diverted back through the catalyst bed to heat the catalyst pellets directly. When the cracking reactor temperature reaches operating temperature, methanol combustion is stopped and a hot gas valve is switched to route the flue gas overboard, with methanol being fed directly to the catalytic cracking reactor. Thereafter, the burner operates on excess hydrogen from the fuel cells.

Internal combustion engine with an exhaust gas turbocharger

Abstract: In the operation of supercharged internal combustion engines, certain operating conditions exist during which the exhaust gas turbochargers cannot supply adequate supercharging air for the internal combustion engine due to a low production of exhaust gas by the engine To eliminate this problem, an auxiliary compressor with a flywheel is proposed, which is constantly driven by an auxiliary drive mechanism and whose power input can be considerably reduced by closing its air conduit In case of lacking charging air, the auxiliary compressor is used in a simple way, by opening the closure devices on its air side, in order to enable a supply of supercharging air to the internal combustion engine The power required for driving the auxiliary compressor is derived primarily from energy stored in the revolving flywheel mass as well as from the power of the auxiliary drive mechanism

A kinetic model of nitric oxide formation during pulverized coal combustion

Abstract: A mathematical model of NO formation during pulverised coal combustion was developed from a proposed kinetic mechanism involving 12 overall chemical reactions. Most significantly, the model describes the complex conversion of coal bound nitrogen compounds to NO during combustion. The predictions of the model compare favourably with literature data and are in qualitative agreement with trends observed in practical coal combustion.

Characterization of the thermal properties of forest fuels by combustible gas analysis

Abstract: The thermal decompositions of forty-three typical forest fuels have been characterized up to 500 degrees C. The fuels studied include foliage, wood, small stems, and bark. Evolved gas analysis gave quantitative measurements of the oxygen stoichiometry for combustion of volatile pyrolysis products. Oxygen consumption by the volatiles is highly correlated to their calculated heats of combustion. Char heats of combustion were also determined and found to be very similar for the fuels studied. These data were used to partition total heat of combustion into flaming and glowing components. Addition of combustible gas analysis to other thermal analysis techniques provides a more complete comparison of thermal behavior over a wide temperature. (Refs. 30).

Characteristics of single particle coal combustion

Abstract: A two-color optical pyrometer has been developed to measure the burning history of singlecoal particles. From the intensity traces at two wavelengths information on burning times, burning temperatures, the duration of a volatile flame, and projected areas were obtained for two lignite and three bituminous coals. The coals were pulverized, classified in 38–45 and 90–105 micron size ranges, and burned at furnace temperatures of 1250 and 1700 K in atmospheres containing from 15% to 100% oxygen. The intensity traces at short times showed the influence of either attenuation by volatiles or, in some cases, an intense peak attributed to luminous radiation by soot. A model was developed to simulate the combustion of a coal particle. Model predictions of the duration of volatile flames were in agreement with the values inferred from the intensity traces. Burning times predicted by the model were in partial agreement with measured values. At 1700 K the bituminous coal burned close to the predicted diffusion-limited times while the lignite coal took longer. At 1250 K the experimental burn-out times for all coals were longer than predicted. Possible reasons for the low predictions may be differences in volatile yields and retardation of the reaction by finely distributed ash particles.

Structure and extinction of near-limit flames in a stagnation flow

Abstract: Experimental studies of the structure and extinction of near-limit premixed flames in astagnation flow were made using counterflow twin flames established in the forward stagnation region of a porous cylinder. The stagnation surface between the two flames can be expected to be adiabatic and noncatalytic wall surface. Near-limit rich- and lean-methane/air and propane/air flames were used in the experiment. The structure of the twin flames, the flame temperature, the distance between the two flame zones, and the concentrations of reactants on the stagnation surface were measured, and the extinction mechanism is discussed. Two distinct modes of flame extinction exist in the stagnation flow field: one is flameextinction which occurs close to the stagnation surface due to incomplete combustion and the other is flame extinction which occurs at a finite distance from the stagnation surface due to flame stretch. The Lewis number of the deficient reactant in the premixed combustible gases (fuel in the lean mixture and oxygen in the rich mixture) is responsible for the existence of these two distinct modes of flame extinction. These results strongly support the theoretical predictions by Sivashinsky and by Sato and Tsuji. The extinction of a flame in which the diffusion coefficient of the excess reactant is muchlarger than that of the deficient reactant is also affected by dilution of the reaction zone by the excess reactant with the larger diffusion coefficient.

An experimental study on stability and combustion characteristics of an excess enthalpy flame

Abstract: A further experimental study was conducted on the excess enthalpy flame system proposedby Takeno and Sato to burn mixtures of low heat content. In the light of previous experimental findings an entirely new burner was designed to reduce the heat loss as much as possible. A bundle of ceramic tubes was used as a combustion tube and four perforated ceramic plates were placed upstream and downstream of the tube to reduce the radiative heat loss from the heated tube. The stability and combustion characteristics of the burner were studied to explore to what extent the range of flame stability was extended below the normal lean limit. It was found that the flame stabilized ahead of, in, or behind, the combustion tube, depending on flow rate and equivalence ratio. The stability limits for the respective flames extended below the normal limit. The observed temperature distributions revealed that the heat recirculation through the perforated plates, as well as the combustion tube, played an important role in the flame stabilization. General characteristics of the proposed flame system are discussed on the basis of the experimental findings obtained so far.