Showing papers on "Combustion published in 1969"

Spread of a laminar diffusion flame

Abstract: A theoretical description is presented for a laminar diffusion flame spreading against an air stream over a solid- or liquid-fuel bed. Both a thin sheet and a semi-infinite fuel bed are considered. The burning process is described as follows: The hot flame heats the unburned fuel bed, which subsequently vaporizes. The resulting fuel vapor reacts with the oxygen supplied by the incoming air, thereby producing the heat that maintains the flame-spread process. The formulated model treats the combustion as a diffusion flame, for which the details of the reaction kinetics can be ignored by assuming infinite reaction rates. The model includes the chemical stoichiometry, heat of combustion, gas-phase conductive heat transfer, radiation, mass transfer, fuel vaporization, and fuel-bed thermal properties. The radiation is mathematically treated as a heat loss at the flame sheet and a heat gain at the fuel-bed surface. The calculated flame-spread formulas are not inconsistent with available experimental data. These results reveal much of the physics involved in a spreading, flame. For instance, the flame-spread rate is strongly influenced by (1) the adiabatic stoichiometric flame temperature, and (2) the fuel-bed thermal properties, except for the fuel-bed conductivity parallel to the propagation direction.

Fuel cells : their electrochemistry

Abstract: Book on fuel cells electrochemistry covering direct energy conversion methods, electrode kinetics, electrocatalysis, organic substances, electrochemical combustion, research techniques, etc

Method of recovering hydrocarbons by in situ combustion

Abstract: The invention provides a method for recovering hydrocarbons from a geological formation having combustible organic material. A passageway is established from a point in the formation, through same, and to the surface of the ground. The combustible organic material is ignited. Oxygen-containing gas is passed into the resulting combustion zone by establishing at lower than normal formation pressure, a pressure drop from the combustion zone to a point outside the formation through the passageway. The temperature of combustion is controlled to only partially volatilize the organic material. The gases resulting from the partial combustion are passed to the surface of the ground. The method is preferred to recover hydrocarbons and other chemicals from a coal stratum and/or from an oil sand. In the preferred specific embodiment, the method is applied to recovering hydrocarbons from a coal stratum and a separate oil sand stratum, separated by a stratum of kerogen. In the latter heat of combustion is by conduction passed from the coal stratum to the oil sand stratum.

Combustion of Boron Particles at Atmospheric Pressure

Abstract: Single particles of pure crystalline boron were injected into streams of hot oxidizing gases, generated by a gas-burner, at atmospheric pressure. Two powder samples, having average diameters of 34.5 and 44.2 μ respectively, were studied. Gas temperatures were varied from 1800 to 2900 °K, mole fractions of oxygen from 0.08 to 0.37, and mole fractions of water from 0 to 0.21. Qualitative photographic and spectroscopic observations of the panicle combustion process are described. Ignition temperatures of boron particles, 1850 to 2000 °K, were found to be independent of particle size and of gas temperature, but affected by the composition of ambient gases. Burning times, ranging from 10 to 40 msec, were found to be inversely proportional to the mole fraction of oxygen in the gas, to decrease slightly with increasing gas temperature, and to decrease substantially with addition of water vapor. Experimentally determined burning rates are correlated with diffusion rates of gaseous oxidants to the surface...

The structure of counterflow diffusion flames in the forward stagnation region of a porous cylinder

Abstract: An experimental study has been made of the structure and the blow-off mechanism of the laminar counterflow diffusion flame established in the forward stagnation region of a porous cylinder. Concentration profiles of the stable species were determined using a microprobe sampling technique and gas-chromatographic analysis for hydrocarbon flames at atmospheric pressure. The over-all structure of the flame was examined by optical interferometry. Experimental results show that there are always various intermediate hydrocarbons and some oxygen on the fuel side of the flame. Hydrogen and carbon monoxide, which are the intermediate products, exist on both the fuel and air sides of the flame. The maximum concentrations of hydrogen and various intermediate hydrocarbons are found near the stagnation point of the counterflow. Although the flame approaches the cylinder surface when the fuel-ejection rate is decreased or the stagnation velocity gradient is increased, the differences in the concentration profiles for the case of a low fuel-ejection rate and for the case of a large stagnation velocity gradient are remarkable. It has been confirmed that critical blow-off of the flame is due to chemical limitations on the combustion rate in the flame zone and is clearly distinguished from blow-off caused by thermal quenching of the flame.

Optical studies of the generation of noise in turbulent flames

Abstract: A study of the mechanism of noise generation in turbulent premixed flames, turbulent diffusion flames and in liquid-spray combustion of hydrocarbon fuels is described. It is shown that all these flames may be represented acoustically as an assembly of monopole sound sources in their combustion zones. The radiated sound pressure is dependent upon the rate of change of the rate of increase of volume of the fuel and oxidant during combustion. The rate of volume increase is proportional to the rate of consumption of the fuel and oxidant in the flame. To measure this quantity, an optical technique has been employed that relies on observations of changes in the intensity of emission from the free radicals C2 generated in the reaction zones of these flames. For the premixed flames, good quantitative agreement is obtained between the radiated sound pressure calculated from these intensity measurements, using simple acoustic theory, and the values recorded simultaneously with a microphone. Similar agreement is obtained for diffusion flames, with the assumption made that the fuel and oxidant burn in stoichiometric proportions. Qualitative agreement is obtained for the liquid-fuel flames. The mean intensities of emission from premixed flames, burning under varied conditions of turbulence, were found to depend linearly upon the total flow rate of the combustible mixture and to be independent of the conditions of turbulence. This observation is compatible with the wrinkled laminar flame model of turbulent flame propagation.

Kinetics of engine-generated nitrogen oxides and carbon monoxide

Abstract: For temperatures characteristic of combustion in the spark-ignition automotive engine chemical equilibrium calculation of combustion product composition yields significant quantities of carbon monoxide and nitric oxide as well as atomic hydrogen, atomic oxygen and the hydroxyl radical. For continuous, equilibrium of combustion products during the engine expansion process, atomic species and free radicals must recombine, nitric oxide must decompose and carbon monoxide should to a considerable extent be oxidized. However, measurements indicate that carbon monoxide and nitric oxide concentrations appearing in engine exhaust correspond more closely to combustion temperature equilibrium values than to exhaust temperature values. It is therefore apparent that certain of the chemical reactions pertinent to carbon monoxide oxidation and nitric oxide decomposition may be kinetically limited during the expansion process. A theoretical analysis of the chemical kinetics of the internal combustion engine expansion process has been undertaken as the objective of the present work. Fourteen coupled non-linear differential equations based on thirty-two elementary chemical reactions were integrated numerically through use of a Runge-Kutta procedure. The integration was performed in a step-wise manner beginning at the initial point of expansion. Initial conditions included a chemical equilibrium distribution of species corresponding to average conditions of real engine combustion products just prior to expansion. Results were obtained in the form of concentration-time histories throughout expansion for each of the thirteen chemical species considered. It was found that the atomic species and the hydroxyl radical fail to recombine at a rate sufficient to maintain a continuous chemical equilibrium. Consequently these species persist in excess quantities throughout the process. Further, it was found that the persistence of excess concentrations of these species severely inhibits the oxidation of carbon monoxide during expansion. It was found that of the five elementary reactions directly involving nitric oxide, none was sufficiently rapid to effect an appreciable decomposition of nitric oxide.

Glass melting furnace and method of operating it

Abstract: THIS INVENTION RELATES TO A METHOD AND APLPARATUS FOR INCREASING THE MELTING RATE IN A GLASS TANK UTILIZING OXYFUEL COMBUSTION TECHNIQUES. MORE PARTICULARLY, AN OXYFUEL FLAME IS DIRECTED TOWARD THE FEED END OF A GLASS TANK SO AS TO CONTROL THE LOCATION AND MELTING OF THE RAW GLASS BATCH MATERIALS THAT ARE ADDED TO THE MELTING ZONE.

Research on combustion instability in liquid propellant rockets

Abstract: Nonlinear combustion instabilities in liquid propellant rockets, considering various combustion models and experimental techniques

Vortex mixing for supersonic combustion

Abstract: Fundamental concepts of mixing and combustion theory are examined in order to define an optimum system. By analogy with the familiar parameter “combustion intensity,” a “mixing intensity” is defined as the total mass of fuel and air mixed per unit time, volume, and density. Mixing intensity is related to the mean kinetic energy of turbulence generated in a mixing system. The efficiency of generation of turbulence is defined by the ratio of the kinetic energy of turbulenee generated to the kinetic energy loss from the mean flow. Bluff body mixers are compared with turbulent jet mixers, and turbulent intensities are determined as a function of fuel/air ratio and jet-to-stream-velocity ratio. For turbulence generated by a baffle system or by jets, the mixing intensity is shown to be proportitional to the rms velocity and the square root of the number of sources. Substantial increases in mixing rates can be obtained by applying a swirling motion to the central fuel jet. Radial and axial pressure gradients are set up which, in the case of strong swirl, result in reverse flow along the axis. Empirical equations for velocity decay, mass entrainment, and angle of jet expansion are given as functions of the degree of swirl. However, further work is needed on the behavior of these parameters in an external flow field. For the combustion chamber of a scramjet, the degree of swirl imparted to the fuel can be altered readily by varying the proportion of fuel introduced axially and tangentially into the swirl chamber. The rate of mixing, angle of jet expansion, and the size of the internal reverse-flow zone can all be controlled by variation of the swirl number. With the ability to initiate and remove the reverse-flow region, an optimized combustion system could operate efficiently from low-subsonic to high-supersonic Mach numbers.

Combustion of vertical cellulosic cylinders in air

Abstract: Theoretical and experimental studies are reported on the combustion of vertically oriented cylinders of α-cellulose and birchwood in air. Cylinder diameters from 1/8 to 1 in. and lengths from 1 to 6 in. were investigated. A similarity theory for the natural-convection boundary layer adjacent to a vertical flat plate is developed for conditions of large temperature variations, of wall mass transfer and of boundary-layer combustion. The theory is used to calculate the standoff distance of the envelope flame that surrounds burning α-cellulose cylinders. Experimental measurements of the flame standoff distance are reported which support the similarity hypothesis used in the theory and which agree resonably well with the theoretical calculation. Experimental measurements of flame-plume heights for birchwood and α-cellulose cylinders are correlated with the experimental mass-loss rates by use of Froude number. These last results can best be fitted by means of a formula which differs from that of Thomas and from that of Putnam and Speich.

Comparison of combustion instabilities found in various types of combustion chambers

Abstract: Combustion instabilities in motors and furnaces are contrasted under three separate headings: System instabilities involve, in an essential way, interactions between processes occuring in the combustion chamber and processes occurring in at least one other component of the system. Combustion chamber instabilities consist of unsteady phenomena that are localized within the combustion chamber. Intrinsic instabilities are inherent in the reactants themselves and would be observed if combustion were to occur in the absence of any external influences. The second category, combustion-chamber instabilities, is again divided into three subcategories: Acoustic instabilities involve, in an essential way, the propagation of acoustic waves in the combustion chamber. Shock instabilities are characterized by the presence of steep-fronted finite-amplitude shock or detonation waves in the combustion chamber. Fluid-dynamic instabilities are associated with the establisment of special kinds of flow patterns, such as vortices, in the chamber. Experimental and theoretical aspects of each of these types of instabilities are discussed separately. Characteristics of each type of instability are described, and the kinds of chambers in which each has been observed are indicated. Attention is given to surface-burning systems, such as solid-propellant rockets and hybrid rocket motors, and also to volume-burning systems, such as liquid-propellant rocket engines and both gas-fired and oil-fired industrial burners. Experimental procedures for investigating each type of instability are reviewed along with selected experimental results, and the character and state of development of the theoretical methods that have been used for describing each type of instability are compared. The review is an attempt to bring about discussions between specialists who study combustion instabilities in different systems. Classification according to the type of instability rather than the type of system can emphasize the similarities and differences that exist among combustion instability problems encountered in different systems. One resulting observation is that examples of system instabilities and of acoustic instabilities are common to all kinds of combustion systems.

Location of action of burning-rate catalysts in composite propellantcombustion.

Abstract: H + 62 + M -> HO2 + M Reaction in Lean Hydrogen-Oxygen Mixtures," Journal of Chemical Physics, Vol 43, No 9, Nov 1965, pp 3237-3247 7 Getzinger, R W, "A Shock Wave Study of Recombination in Near Stoichiometric Hydrogen-Oxygen Mixtures," Eleventh Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, Pa, 1967, pp 117-124 s Stull, D R, JANAF Thermochemical Tables, Dow Chemical Co, Midland, Mich; may be purchased as Rept PB-168370 ($1000) and addenda PB-168370-1 and PB-168370-2 ($300 each), National Bureau of Standards, CFSTI, US Dept of Commerce, Springfield, Va 9 Bird, P F, Duff, R E, and Schott, G L, "HUG, a Fortran-Fap Code for Computing Normal Shock and Detonation Parameters in Gases," Rept LA-2980, Feb 1964, Los Alamos Scientific Lab, The Univ of California, Los Alamos, N Mex 10 White, D R and Millikan, R C, "Oxygen Vibrational Relaxation in O2-H2 Mixtures," Journal of Chemical Physics, Vol 39, No 8, Oct 1963, pp 2107-2108 11 White, D R and Millikan, R C, "Vibrational Relaxation of Oxygen," Journal of Chemical Physics, Vol 39, No 7 Oct 1963, pp1803-1806 12 White, D R and Millikan, R C, "Oxygen Vibrational Relaxation in O2-He and O2-Ar Mixtures," Journal of Chemical Physics, Vol 39, No 7, Oct 1963, pp 1807-1808 13 Gilbert, R B and Strehlow, R A, "Theory of Detonation Initiation Behind Reflected Shock Waves," AIAA Journal, Vol 4, No 10, Oct 1966, pp 1777-1783 14 Getzinger, R W and Blair, L S, "A Shock Tube Study of the Effects of Nitrogen and Water Vapor on Recombination in the Hydrogen-Oxygen System," 6th International Shock Tube Symposium, Freiberg, Germany, April 12-14, 1967; also The Physics of Fluids, to be published 15 Shchelkin, K I and Troshin, Ya K, Gas Dynamics of Combustion, Mono Book Corp, Baltimore, Md, 1965, pp 1-53 16 Voitsekhovskii, B V, Mitrofanov, V V, and Topchian, M E, Struktura Fronta Detonatsii v Gaza, Akademiya Nauk SSSR Novosibirsk, 1963, pp 81-96; transl as The Structure of a Detonation Front in Gases, Rept FTD-MT-64-527 (AD 633821), Feb 1966, Foreign Technology Div, Wright-Patterson Air Force Base, Ohio, pp 81-97 17 Strehlow, R A and Engels, C D, "Transverse Waves in Detonations II Structure and Spacing in H2—O-2, C2H2—O2, C2H4—O2 and CEU—O2 Systems," AIAA Journal, to be published

Exhaust gas purification

Abstract: This invention is concerned with a process for the effective removal of carbon monoxide hydrocarbons and the oxides of nitrogen from the exhaust stream of mobile internal combustion engines. This purification is accomplished by passing the exhaust gas from an engine operating at near the stoichiometric fuel-air ratio through a high-temperature catalyst. This catalyst is normally a noble metal catalyst. The exhaust gas is then cooled to a temperature in the vicinity of 700* F., ammonia is added and the ammoniated stream is passed over a second catalyst which can be either a base metal catalyst or a noble metal catalyst.

Supercritical bipropellant droplet combustion

Abstract: Fuel droplets burning at pressures sufficient to reach critical temperature under zero gravity conditions in free fall apparatus

Formation and decomposition of surface oxide in carbon combustion

Abstract: The formation of surface oxide on graphitized carbon black by reaction with oxygen at 500°C and the subsequent desorption of the oxide as CO at 600–750°C have been studied gravimetrically. The surface oxide is formed exclusively during the initial transient period of fast combustion observed by previous workers, and for each O atom chemisorbed one labile C atom is removed from the surface. The kinetics of desorption follow the relation: –dθ/dt=Dθ exp {–[E1+β(1 –θ)]/RT}, where log10Dθ= log10D1+α(1 –θ), and θ is the fraction of O on the surface at time t related to that present during steady combustion. D1, E1, α and β are constants. Values of 70 and 57 kcal mole–1 were found for E1 with two specimens at lower and higher burn-off respectively; the corresponding values of β were 43 and 47 kcal mole–1. Apart from the effect of catalytic impurities, two distinct processes are required to account for the kinetics of combustion. Only one of these produces stable oxide. A hypothesis is proposed which identifies this with reaction at “arm-chair”{112l} edges of the carbon lattice.

Process fo melting glass

Abstract: MELTING OF GLASS BATCH WHEREIN THE PRODUCTS OF COMBUSTION OF A GASEOUS FUEL ARE INTRODUCED INTO THE MOLTEN GLASS BATH AT A SUBMERGED LEVEL THEREIN, WITH THE GASEOUS FUEL BEING COMBUSTED IN AN OXIDIZING MEDIUM LOW IN NITROGEN.

Nonlinear Longitudinal Instability in Rocket Motors with Concentrated Combustion

Abstract: Liquid rocket motors with concentrated combustion, studying nonlinear longitudinal instabilities with shock waves in combustion chambers

Fuel injection systems for internal combustion engines

Abstract: This invention relates to fuel injection systems for internal combustion engines of the kind in which fuel is fed to an engine through one or more electrically operated fuel injection valves or injectors which are opened intermittently. The invention provides means for controlling the injection valve or valves under engine overrun conditions, and also means for controlling the fuel pressure to the injection valves in accordance with the engine induction passage pressure.

The mechanism of flame spreading over the surface of igniting condensed-phase materials

Abstract: This paper describes an experimental and theoretical investigation of the fundamental mechanism by which a flame spreads over the surface of a condensed-phase materials in a quiescent gaseous environment containing a component with which it can react chemically. It is postulated that the advancing flame vaporizes the surface material lying before it. As these vapors diffuse away from the surface, they undergo an exothermic reaction with the chemically active component in the gaseous environment, and ignite; thus, flame spreading is viewed as continuous diffusive, gas-phase ignition. Flame-spreading velocities have been measured for a variety of solid materials in O2/inert environments between 4 and 415 psia. Well-defined experimental, conditions yielded reproducible results, and thus suggest that flame-spreading, velocity is an intrinsic combustion quantity. All data can be correlated by a power-law relationship between the flame-spreading velocity (V) and two gas-phase parameters-pressure (P) and reactive component mole fraction (Yox)—in the form V ∞ ( P Y m ) Φ . It is concluded that V is controlled by a gas-phase physical process—probably either heat or mass transfer—which supports the mechanism proposed. Temperature distributions ahead of the propagating flame were obtained from surface-mounted, fine-wire thermocouples. The temperature level as the flame passes over the thermo-couple bead is independent of P, Yox, and inert diluent, and about 120°C below that measured previously during steady-state vaporization. Thus, it is concluded that direct surface attack by oxygen is unimportant during flame spreading and that the transient vaporization phenomenon is probably quite different than that of steady pyrolysis. The mathematical statement of the postulated flame-spreading mechanism is sufficiently complex that a complete analytical solution is currently impossible. Postponing numerical solutions, simplistic analyses were conducted that resulted in predicted flame-spreading characteristics that were well supported by the data obtained over the entire range of experimentation. Based on the evidence presented, the authors conclude that the postulated theory is probably valid, and engineering design of systems involving flame-spread control now can be put on a rational basis.

A quasi-global chemical kinetic model for the finite rate combustion of hydrocarbon fuels with application to turbulent burning and mixing in hypersonic engines and nozzles.

Abstract: Chemical kinetic model for hydrocarbon fuels combustion and application to multidimensional finite difference mixing analyses in hypersonic engines and nozzles