Showing papers on "Combustion published in 1980"

Estimation of rate of heat release by means of oxygen consumption measurements

Abstract: Measurement of the rate of oxygen consumption provides a simple, versatile and powerful tool for estimating the rate of heat release in fire experiments and fire tests. The method is based on the generalization that the heats of combustion per unit of oxygen consumed are approximately the same for most fuels commonly encountered in fires. A measurement of the rate of oxygen consumption can then be converted to a measure of rate of heat release. Data on heats of combustion are presented to support this generalization. The applicability of the technique to combustion under fire conditions is examined, possible sources of error in the measurements are discussed, and applications of the method are reviewed. It is concluded that the accuracy of oxygen consumption based rate of heat release measurements should compare favorably with those derived from conventional calorimetric measurements.

In situ combustion process for the recovery of liquid carbonaceous fuels from subterranean formations

Abstract: An integrated in situ combustion process for producing subterranean carbonaceous deposits in which the resulting flue gas of low heating value is combusted over an oxidation catalyst at substoichiometric conditions and is expanded in a gas turbine which drives the air compressor for injecting the combustion air into the underground carbonaceous deposit. An oxidation catalyst is provided for reducing carbon monoxide in the combusted flue gas comprising platinum and palladium.

Influence of Chemical Kinetics and Unmixedness on Burning in Supersonic Hydrogen Flames

Abstract: Good agreement has been obtained between published profiles of composition and pitot pressure with the calculated results from a computer program in which finite rate chemistry was used. Significant differences are noted between results calculated using 7 species and 8 reactions and those calculated using 12 species and 25 reactions. Differences are also found between results in which the effect of unmixedness on reaction in turbulent flow is applied or is not applied. ULTI-REACTION finite-rate chemistry has been used for many years in computer simulation of complex flowfields, and results have been good in laminar flows. Mixing of fuel and air is faster in turbulent flows than in laminar flows, but in turbulent flows the folding together of large volumes of fluid alternately rich in either fuel or oxygen produces the phenomenon of "unmixedness" in which the time-averaged temperature and composition at a point do not represent correctly the degree to which fuel and air are mixed on a molecular scale. Thus, the use of time-averaged values of temperatures and concentrations in the finite-rate chemistry equations is incorrect and can lead to serious errors in calculated results. This by no means rules out the use of time- averaged values, since the effects of unmixedness may be small for many turbulent, reacting flows. One purpose of this paper is to demonstrate that this is so by calculating some results with and without the effects of unmixedness. Another purpose of the paper is to report improvement in the ability of a computer program to simulate burning of H 2 in a super- sonic air stream when an eddy breakup chemistry model is replaced with one in which finite reaction rates, corrected for unmixedness, are used. In a prior investigation,1 the usefulness of a parabolic marching computer program was evaluated by comparing computed results with data from five experimental test cases. Mixing of fuel and oxidant was computed for parallel in- jection of H2 using a two-equation turbulence model, and the extent of chemical reaction was deduced by comparing the data with results obtained from three different assumptions: 1) no reaction, corresponding to zero combustion efficiency; 2) complete burning of all fuel mixed with oxygen, corresponding to combustion efficiency = 1; and 3) finite-rate burning based on the rate of decay of large turbulent eddies into small ones. The last of these assumptions, the eddy- breakup (EBU) model,2 provided a means for obtaining combustion efficiency values intermediate between 0 and 1 and is believed to be useful as a tool to account for the effects of unmixedness on chemical reaction in turbulent flows if chemical reaction rates are large enough so that the production of combustion products is limited by the mixing rate. In this paper three of the experimental test cases used in the previous computer program evaluation are reanalyzed using the same program but with a finite-rate chemistry system reported by Spiegler. 3 In this chemistry system the effect of unmixedness on individual reactions is modeled by decreasing any rate for which one or more of the species involved goes negative during fluctuation of its concentration about the average value. (Temperature fluctuations are not considered.) In addition to calculations using Spiegler's system of 7 species and 8 reactions, calculations were also made using 12 species and 25 reactions. The latter system required the solution of twice as many differential equations for chemical species, but this was judged to be necessary in order to examine the effect of the added equations on the generation rates of radicals such as H, O, and OH. The elemental reactions by means of which H2 and O2 are transformed into H2O provide multiple paths between the reactants and the product, most of which depend on the presence of high concentrations of radicals. The relative importance of the paths changes as conditions in the flow change, and it is important not to neglect any path which might be a large source or sink for one or more of the radicals, since such a path might be critical for prediction of ignition.

Turbulent flows with premixed reactants

Abstract: This chapter considers turbulent flows in which the reactants have been fully mixed prior to reaction. Application to combustion is emphasized both because many practical combustion systems require the fuel and oxidizer to be premixed, and also because the premixed flame provides a convenient test for contemporary ideas about turbulent reacting flows. Only gaseous species are considered. The rates of the chemical kinetic processes leading to combustion are strongly dependent on temperature. Consequently, the propagation of a premixed laminar flame requires thermal conduction and diffusion from the hot products to preheat the reactive mixture. In a turbulent flame, these molecular processes are augmented both indirectly, by distortion of flame surfaces, leading to an increase in their area, and directly, by turbulent mixing. The result is that the mean rate of heat release is generally more strongly influenced by the turbulence than by chemical kinetic factors so that premixed turbulent combustion is primarily a complex fluid mechanical problem. However, ignition and flame quenching provide examples of situations in which both chemical kinetics and fluid mechanics are likely to be important. Premixing leads to a significant simplification in the analysis as the composition of the flow is essentially uniform, in terms of the elements involved, i.e., the Z[s of (1.19) are constants. It also causes complications; the scalar thermodynamic variables of temperature, density, and composition often fluctuate strongly within this type of flame, between values characteristic of the unburned and fully burned mixtures. These intense scalar fluctuations pose theoretical and experimental difficulties, some of which have not yet been solved. Following a review of knowledge concerning premixed turbulent combustion, this chapter concentrates on theoretical models which are based on prior specification of a probability density function for the fluctuating thermodynamic state of the mixture. It is argued that such models provide the best available compromise between complexity and generality of application.

Method of in-situ retorting of carbonaceous material for recovery of organic liquids and gases

Abstract: The method of the present invention involves a two-phase process for in-situ retorting and recovery of carbonaceous material contained within typical subterranean tar sand formations, and includes formation of conventional arrays of in-seam ducts, and positioning heating devices to heat a section of the formation over a large extent thereof. The operation of the heating devices in the first phase is controlled to provide heat into the formation without burning of the carbonaceous material therein, resulting in development of a quasi-stable zone of pyrolysis about the heating duct, to thermally crack the carbonaceous material producing various organic liquid oil fractions and derived condensible vapors and non-condensible gases. The products produced thereby are then withdrawn through a suitable array of collection wells. In the second phase of the process a residual coke layer that will have formed as a result of the pyrolysis of the carbonaceous material is burned by introducing a combustion-supporting gas, such as air or oxygen, into the hot sand-coke blanket preferrably via the line source heating ducts spontaneously igniting the coke to produce a temperature elevation in the zone of pyrolysis to both crack the proximate carbonaceous material and to burn away the coke layer from around the shut-in collection wells freeing them to continue withdrawal of the products of the cracking process. After combustion of the basal sand-coke blanket air flow to the tar sand formation will be terminated and the heater operation restored, repeating the process.

Process for recovering products from oil shale

Abstract: A process for recovering hydrocarbon products from a body of fragmented or rubblized oil shale. The process includes initiating a combustion zone adjacent the lower end of a body of oil shale and using the thermal energy therefrom for volatilizing the shale oil from the oil shale above the combustion front. Improved recovery of hydrocarbon products is realized by refluxing the heavier fractions in the volatilized shale oil. The heavier fractions are refluxed by condensing the heavier fractions and allowing the resulting condensate to flow downwardly toward the combustion front. Thermal energy from the combustion zone cracks the condensate producing additional lower molecular weight fractions and a carbonaceous residue. The carbonaceous residue is burned in the combustion front to supply the thermal energy. The temperature of the combustion front is maintained by regulating input of oxygen to the combustion zone. The process also includes sweeping the volatilized products from the rubblized oil shale with a noncombustible gas. The flow rate of sweep gas is also controlled to regulate the temperature of the combustion front. The recovered products can be enriched with hydrogen by using water vapor as part of the noncombustible sweep gas and cracking the water vapor with the hot carbon in the combustion front to produce hydrogen and an oxide of carbon.

Underground gasification of bituminous coal

Abstract: In the underground gasification of a swelling coal the high gas-flow link between the injection and the production wells is produced by introducing hot air into the injection well at a pressure sufficient to fracture the coal. The bulk permeability of the coal proximate to the link is increased and the plugging of the link during the subsequent in situ combustion and gasification procedure is suppressed by continuing the injection of the hot air, heated to a temperature below the softening point of the coal, into the injection well, through the link to the production well without combustion of the coal.

Environmental Impact of Residential Wood Combustion Emissions and its Implications

Abstract: Currently available information suggests a substantial environmental impact from residential wood combustion emissions. Air pollution from this source is widespread and increasing. Current ambient measurements, surveys, and model predictions indicate winter respirable (<2 μm) emissions from residential wood combustion can easily exceed all other sources. Both the chemical potency and deliverability of the emissions from this source are of concern. The emissions are almost entirely in the inhalable size range and contain toxic and priority pollutants, carcinogens, co-carcinogens, cilia toxic, mucus coagulating agents, and other respiratory irritants such as phenols, aldehydes, etc. This source is contributing substantially to the nonattainment of current particulate, carbon monoxide, and hydrocarbon ambient air quality standards and will almost certainly have a significant impact on potential future standards such as inhalable particulates, visibility, and other chemically specific standards. Emission from...

Low NOX burner

Abstract: An improved burner for both liquid and gaseous fuels in which the combustion air is divided into at least two parts, comprising primary and secondary air. The primary air, which is insufficient to completely burn the fuel, creates a flame zone in which there is a deficiency of air, which produces quantities of carbon monoxide and hydrogen. The combustion products are recirculated, cooled and re-entered into the combustion zone in the region of the fuel and primary air entry, resulting in a reduction in the oxides of nitrogen. The secondary air, in quantities greater than the primary air, is introduced into a second combustion zone downstream of the first combustion zone. In the second combustion zone the deficiency in air is made up by the secondary air so that complete combustion can be carried out. If desired, a third quantity of air can be introduced still farther downstream in the flame zone.

Fossil charcoal as evidence of past atmospheric composition

Abstract: The presence of charcoal in the geological record offers a new approach to assessing oxygen levels in palaeoatmospheres. Charcoal is formed by the incomplete combustion of woody tissues. The combustion of wood is supported by the generation of the combustible gases carbon monoxide and methane during the pyrolysis process. As the combustion ranges of these gases are restricted with decreasing oxygen availability to a level below which no combustion will occur, the production of charcoal and its appearance in the geological column constitute a record of changing oxygen availability through time. We show here that the occurrence of charcoal in rocks from the Lower Carboniferous onwards suggests that atmospheric oxygen never fell below 0.3 of present atmospheric level (PAL) during this time. Detrital charcoal formed by forest fire must have contributed an appreciable fraction to inert carbonaceous matter in sediments (kerogen) during post-Devonian time.

A comprehensive model for fluidized bed coal combustors

Abstract: A comprehensive model for the simulation of fluidized bed coal combustors (FBC) is developed, capable of predicting the combustion efficiency, char and limestone elutriation and the corresponding particle size distribution in the bed and in the entrained materials, solids withdrawal rate from the bed, bed temperature profile, sulfur dioxide retention, sulfur dioxide and NOx emissions, concentrations of oxygen, carbon monoxide, carbon dioxide, volatiles, sulfur dioxide and NOx along the combustor height. The model can also simulate combustors with varying cross section along the bed height. The performance of the model is compared with the data obtained from four different combustors. Agreement between the computed results and the data is good. The salient features in the model which need further investigation are pointed out.

Dual stage-dual mode low nox combuster

Abstract: An improved dual stage-dual mode combustor capable of reduced emissions of nitrogen oxide from a combustion turbine is disclosed. The combustor includes two combustion chambers separated by a throat region. Fuel is initially introduced and ignited in the first chamber. Thereafter, fuel is introduced near the downstream end of the first chamber for ignition and burning in the second chamber. Burning in the first chamber is extinguished by shifting the fuel flow to burning in the second chamber and after termination of the flame in the first chamber, fuel is reintroduced into the first chamber for premixing only with burning in the second chamber. By selectively controlling the percentage of fuel introduced into the first stage, low emissions of nitrogen oxide are realized.

Piston for internal-combustion engines

Abstract: In a cooled composite piston having a cooling passage adjacent to the interface and a method of making same, the upper part consists of forged steel and is formed on its underside with ribs bearing on mating surfaces of the lower part. To improve the resistance to thermal and mechanical stresses, the upper part has been welded by means of charge carrier rays to the lower part, which consists of cast ferrous material.

Computational kinetics and sensitivity analysis of hydrogen–oxygen combustion

Abstract: Kinetic modeling calculations on the H2–O2 system have been carried out with an extensive reaction set to probe the vicinity of the three explosion limits. Sensitivity analysis is used throughout this investigation to study system behavior, in particular, to elucidate mechanistic details. The concentrations and sensitivity profiles are discussed in light of the appropriate experimental results and existing theories of hydrogen combustion. The results indicate the present model to be useful over a wide pressure–temperature range. The reaction set is also used to probe the sensitivities for an experimental study designed to measure the rate constant of an important elementary reaction, H+O2+M→HO2+M, involved in this system. The versatility of the reaction set is also demonstrated by a study of a related chemical reaction, the decomposition of hydrogen peroxide. Finally, prospects for utilizing the methods and results of this study to examine other complex kinetic schemes are discussed.

Combustion chamber of a gas turbine with pre-mixing and pre-evaporation elements

Abstract: A combustion chamber for a gas turbine which is equipped with a number of tubular-shaped elements, within which there occurs between the fuel and the compressed air a pre-mixing/pre-evaporation process. Each tubular element is closed at its end at the side of its combustion space by a flame baffle provided with one or a number of openings, so that the combustion first can occur downstream of the flame baffle, whereby there is appreciably reduced the emissivity of noxious substances from the combustion process.

Liquid fuel combustion device

Abstract: PURPOSE:To provide an instantenous blue flame vapourized combustion without using any electric heater by a method wherein an evaporation cylinder and air blowing port are arranged at the top end of the outer cylinder in a fuel injection combustion device composed of an inner and outer cylinders CONSTITUTION:Inner cylinder 2 is arranged in the outer cylinder 1 having a bottom therein and air feeding pipe 3 is connected to the side surface 11 at the top end of the outer cylinder 1 being directed upward of the inner cylinder 2 At the bottom portion 12 of the outer cylinder 1 is arranged a fuel injection nozzle 4 and at the upper end of the outer cylinder 1 are arranged an evaporation cylinder 5 and an air blow-out port 6 for blowing out the combustion air Thereby, the fuel from the nozzle 4 is descended down between the outer cylinder 1 and the inner cylinder 2 under an action of air flowed from the air feeding pipe 3, then circulated from lower end of the inner cylinder 2 into the inner cylinder 2, evaporated by the combustion heat and combustioned, so that an instanteneous blue flame evaporated combustion may be produced near the upper end of the inner cylinder 2 without using any electric heaters