Showing papers on "Combustion published in 1968"

Sound emission from open turbulent premixed flames

Abstract: A study of the noise produced by turbulent premixed flames stabilized on open burners is described. It is shown that such flames may be represented acoustically as a collection of monopole sound sources in the combustion zone. The radiated sound pressure is dependent on the rate of change of the rate of increase of volume of the gas during combustion, which varies owing to the turbulence in the flow. The rate of volume increase is proportional to the rate of consumption of combustible gas mixture in the flame. To measure this quantity, an optical technique has been developed which relies on observations of changes in the intensity of emission from the free radicals C 2 or CH generated in the reaction zone. Good quantitative agreement is obtained between the radiated sound pressures calculated from these intensity measurements and the values recorded simultaneously with a microphone. A correlation observed between the mean emission intensities of C 2 and CH radicals and the total flow rate of combustible gas mixture both in the laminar and turbulent flames, and in their transition region, supports the wrinkled laminar flame concept of turbulent flame propagation.

Pyrolysis and Combustion of Cellulosic Materials

Abstract: Publisher Summary This chapter discusses pyrolysis and combustion of cellulosic materials. Cellulosic materials form the bulk of the readily available natural fuels. Modern technology has caused a sharp decline in the value of wood and other cellulosic substances as fuel, but it has produced a significant increase in their application as industrial and constructional materials and has created a concerted emphasis on the problems of pyrolysis and combustion. The threat and magnitude of disastrous fires have been further enhanced with the development of modern incendiary and nuclear warfare. In comparison with the potential catastrophe of urban fires, the hazards of fire in the wildlands cannot be ignored or underestimated. Fire may be defined as the interaction among fuel, energy, and environment. The type and magnitude of any fire that either develops into a destructive force or into a useful tool depend on the supply of fuel. The paper and textile industries have been concerned about the aging, deterioration, and degradation of cellulosic materials at elevated temperatures for practical reasons.

Oxidation of Crude Oil in Porous Media

Abstract: Experimental results on the oxidation reaction kinetics in the forward combustion oil recovery process are presented. A total of 48 runs were made wherein a stationary thin layer of coked unconsolidated sand was burned isothermally in a combustion cell. Individual runs were made at various temperature levels to permit determination of the effect of temperature upon the reaction. An expression was obtained for the burning rate of carbon as a function of carbon concentration, combustion temperature, and oxygen partial pressure. The carbon burning rate for two types of crude oil indicated a first order reaction with respect to both carbon concentration and oxygen partial pressure. The effect of combustion temperature on the reaction rate constant matched the Arrhenius equation. The activation energy was similar for the 2 crude oils examined. The activation energy decreased for a porous media containing clay. The rate of oxidation of crude oil at reservoir temperature was found to be significant. Other significant findings included information on hydrogen-carbon content of fuel residues, fuel reactivity and the products of combustion. (17 refs.)

Investigation of the detonation of aluminum powder-oxygen mixtures.

Abstract: It is shown that mixtures containing 48 to 64% (by mass) fine aluminum powder in oxygen are detonable. In 26.4-mm-diam tubes the detonation induction distances of these mix- tures are less than 1.6 m; they decrease with increasing aluminum concentration. The det- onation wave speeds for the lean mixtures are approximately 1550 m/sec and decrease slightly with increasing amounts of aluminum in the mixture. The pressures behind the detonation waves were found to be approximately 31 atm for the mixtures examined. The measured detonation speeds and pressures are approximately 9 and 14%, respectively, below the theo- retical values. This deviation is probably caused by incomplete combustion of the alumi- num particles. The detonation waves of these mixtures show the typical characteristics of spin. LTHOUGH the existence of detonation waves in solid fuel-gaseous oxidizer mixtures has been questioned by some researchers, there appears to be evidence that detonation waves can exist in heterogeneous mixtures. When high- energy shock waves were passed through mixtures .of kerosene droplets and gaseous oxidizer (Kling and Maman1), detona- tion waves were obtained with a stoichiometric mixture only after reflection of the incident shock. The measured speeds agreed with the calculated ones. Cramer2 observed "detona- tion-like" waves propagating through DECH (diethylcyclo- hexane, CioH20) fuel spray-oxygen mixtures. Eraser3 was able to detonate both octane-oxygen and benzene-oxygen mixtures (also initiated with high-energy shock waves). Nicholls et al. 4 also reported "detonation-like" waves in heterogeneous DECH-oxygen mixtures. Although these observations support the theory that liquid-gas mixtures detonate, they do not permit us to predict the behavior of solid-fuel systems. The combustion of metal powders with gaseous oxidizers was studied by Hartmann and Greenwald.5 They reported that aluminum dust can be ignited easily in air, oxygen, carbon dioxide, and under certain conditions it can react even with nitrogen. Cassel et al. 6 measured the burning velocities of powdered aluminum in various oxygen-nitrogen atmo- spheres. For a 70% oxygen, 30% nitrogen atmosphere, they reported "tube" burning speeds of approximately 40 cm/sec. Bunsen-burner flame speeds of aluminum powder-oxygen mixtures have been measured previously (not reported) at this laboratory and were found to be approximately 25 cm/sec. Mixtures having low burning speeds are somewhat difficult to detonate.

An experimental description of destructive liquid rocket resonant combustion.

Abstract: Rotating detonation-like wave concept explains phenomenon during destructive liquid rocket resonant combustion mode

The Cool Flames of Hydrocarbons

Abstract: This review describes the properties of the cool-flame and two-stage ignition processes that characterize the gaseous oxidation of hydrocarbons and discusses the chemical reactions that are responsible for these phenomena. Cool flames result from a chainthermal acceleration of reaction rate. It is probable that the free-radical chain involved is propagated by the reaction of an alkyl radical with oxygen to give an alkyperoxy radical which isomerizes to a hydroperoxyalkyl radical. The decomposition of this radical produces a hydroxyl radical, which attacks the hydrocarbon rapidly and unselectively to regenerate an alkyl radical. Branching probably results from the pyrolysis of mono- and dihydroperoxides, from the oxidation of aldehydes, and from radical-molecule reactions. This reaction scheme explains the existence of a low-temperature ignition peninsula and the relation of the extent and shape of this peninsula to the molecular structure of the hydrocarbon. The chemical relevance of cool flames to abnormal combustion phenomena, such as knock, in gasoline engines is discussed.

Transition from Branching‐Chain Kinetics to Partial Equilibrium in the Combustion of Lean Hydrogen‐Oxygen Mixtures in Shock Waves

Abstract: Concentration profiles of the OH radical in the shock‐initiated combustion of lean hydrogen‐oxygen‐argon mixtures at low pressures (∼0.3 atm) and temperatures (∼1400°K) are found to exhibit pronounced spikes prior to attainment of partial equilibrium. It is shown that this effect is not encompassed within the accepted mechanism for the H2–O2 reaction. Possible reconciliations are presented and discussed.

Electrical Control of Gas Flows in Combustion Processes

Abstract: The theory of the ionic wind is developed for flame ions travelling towards electrodes of various configurations so that entrainment as well as main stream gas velocities can be predicted. It is shown that, by confining entrainment to specified regions, large flow velocities can be induced at the flame itself, where they can be used to modify a variety of combustion processes. Theoretical maximum values of the flow parameters are calculated for several configurations likely to be of practical use and these are compared with results of experiment. The experiments are designed to test the general theory and to determine to what extent the theoretically deduced maxima are altered by inevitable practical complications such as entrainment of hot gas, deposition of soot and other specks on the electrodes and convergence of lines of force on to individual strands of gauze-electrodes. The potentialities of varying parameters such as geometry, temperature, pressure and composition as well as super­-imposing magnetic fields are also examined. A variety of practical examples is considered in the light of this theory. Experiments confirm that confined entrainment can be used to aerate diffusion flames in an accurately controllable manner without risking flash-back or requiring an air supply, metering and mixing systems. Similarly, it is demonstrated that combustion intensity can be increased by field-induced recirculation of hot products, thereby minimizing random turbulence and heat losses to the large obstacles usually employed for this purpose.

Solid waste disposal method and apparatus

Abstract: A solid waste disposal system is described with a storage and receiving carousel, a shredder, a dryer, a compressor-turbine assembly for compressing air for combustion of waste and for receiving hot gasses produced in the combustion process. Two combustion systems, a fluid bed reactor and a gasifying pyrolyzer, are described. Particulate matter harmful to the turbine and also causing air pollution is removed from the hot high pressure gas upstream of the turbine. The malodorous air from the waste storage, shredding and drying is compressed and used for combustion and the part of the hot exhaust gases from the turbine are used in the dryer.

Examination of Effective Rates of Combustion Heat Release in a Dual-Fuel Engine:

Abstract: The combustion processes in a dual-fuel engine are examined through the computation and analysis of effective rates of heat release. Methane was adopted as the primary fuel and the effect of deliberately introducing carbon dioxide along with the methane was also examined to simulate operation on methane sources containing carbon dioxide as a major contaminant. An examination of the various heat release records suggests that dual-fuel combustion generally appears to undergo two distinct phases. The first phase is associated mainly with the consumption of the pilot and some associated gaseous fuel, while the second phase is dependent on the concentrations and the quality of the gaseous fuel employed. Under light audible knock, the first phase gets prolonged and persists over a much longer period than under knock-free combustion. The rates of burning are excessively high and project well over the second phase. This is indirectly indicative of the auto-ignition nature of knock and the simultaneous rapid burni...

Combustion microwave diagnostic system

Abstract: Systems to resonate the combustion chamber of internal combustion engines at radio frequencies, at all available engine r.p.m. are disclosed. Methods, to employ radio frequency resonances for mechanical and electrical measurements within and near the combustion chamber, at all available engine r.p.m., are also disclosed. The system comprises a tunable source of coherent radio frequency energy and a hybrid transmission line to convey the radio frequency energy into the combustion chamber and also to detect the energy reflected from the combustion chamber. The methods, to perform mechanical and electrical measurements within the combustion chamber are ones that correlate the change in the number and properties of the resonances with the continuously changing properties of the combustion chamber.

A theoretical study of nonlinear combustion instability in liquid-propellant rocket engines.

Abstract: Nonlinear combustion instability in liquid propellant rocket engines, describing nonsteady combustion process with aid of Crocco time lag hypothesis

Variable Property Effects on Liquid Droplet Combustion

Abstract: The combustion characteristics of a liquid fuel droplet burning in an oxidizing atmosphere are considered. Formulas for fuel burning rates, flame temperature, and position, as well as fuel and oxidizer concentration and temperature profiles, are given which include the effects of very general transport property variation. The relative importance of diffusion of species and heat conduction in the system is discussed. Specific calculations are shown for 1) power law temperature variation of thermal conductivity and binary diffusion coefficient, and 2) benzene droplets burning in air.

The Application of Separated Flames in Analytical Flame Spectroscopy

Abstract: Premixed hydrocarbon-air flames invariably show two separate reaction zones. In the primary zone, the combustible gas mixture burns principally to carbon monoxide, hydrogen, and water, and in the outer mantle, or secondary diffusion flame, the hot gases burn with atmospheric oxygen to carbon dioxide and water. Teclu [J. Prakt. Chem. 44, 246 (1891)] and Smithells and Ingle [Trans. Chem. Soc. 61, 204 (1892)] independently demonstrated the existence of these two zones in various premixed hydrocarbon-air flames, using the flame separator. This device consists of a wide glass or silica tube fitted over the bunsen type burner to form an extension above the inner burner port. The primary combustion then occurs at the inner burner port, while the pale blue secondary diffusion flame is maintained at the top of the outer glass tube. An alternative method of separation of premixed hydrocarbon-air flames consists of sheathing the flame with an inert gas to lift off or separate the secondary diffusonzone. The interconal zone of flames separated by these methods are extended in length and exhibit very low radiative background. The interconal zone also contains the hottest part of the flame, and can be viewed without interference from radiation produced in a secondary diffusion zone that would normally surround it in separated flames. It is the hot interconal zone of premixed flames that is most frequently employed in analytical flame photometry, because it is in this region that the greatest population of atoms occurs when elements are introduced into the flame by nebulization of solutions of their salts. Thus, separated flames may be employed with advantage in thermal emission, atomic absorption, and atomic fluorescence spectroscopy. This paper describes the separation of the air-acetylene and nitrous oxide-acetylene flames, and some applications of these flames in analytical flame spectroscopy.

Smooth top gas range

Abstract: A smooth top gas range which includes a hood that draws cooking vapors and fumes and air into a regenerative type heat exchanger for preheating prior to combustion with gas at the burner surface unit. Each burner unit is enclosed in a separate combustion compartment with heat being transmitted to a cooking vessel through an air impervious compartment wall or plate by means of radiation. The combustion products exhaust from the combustion compartment, are cooled to a safe temperature by the heat exchanger and are finally vented to the room.

Gas turbine engine with combustion chamber bypass for fuel-air ratio control and turbine cooling

Abstract: A gas turbine engine which may otherwise be of conventional configuration, single or plural shaft, regenerative or nonregenerative, is provided with a controlled bypass from the compressor to the turbine bypassing the combustion apparatus. Flow through this bypass is controlled so as to maintain the fuel-air ratio in the combustion chamber substantially constant notwithstanding variations in fuel flow and airflow with the load carried by the engine. Control of flow through the bypass may respond to setting of the fuel control device, to compressor discharge pressure, or to burner outlet temperature.

Wet and Partially Quenched Combustion

Abstract: In the conventional underground combustion process (dry combustion) much heat is left behind in the swept formation and goes to waste. If in underground combustion so much water is injected together with the air that the water enters the combustion zone, the fire - although locally quenched - will be chased downstream at a velocity imposed by the water-flow rate. Oil will be displaced by the leading edge of a heat slug ahead of the combustion front. Per unit formation swept the air requirement is much less than in dry or normal wet combustion. The heat losses from a short heat slug only have to be made up for and this determines the minimum air supply required to maintain a partially quenched combustion drive. Partially quenched combustion is expected to be less destructive to producing wells than other combustion processes. The quality of the water for normal wet and partially quenched combustion processes need only fulfill injection requirements.

Effects of Chemical Kinetics on Near Equilibrium Combustion in Nonpremixed Systems

Abstract: The method of matched asymptotic expansions is employed for a systematic analysis of some chemical kinetic effects on near equilibrium combustion of nonpremixed systems. The model problem of a spherically symmetrical liquid fuel droplet in an oxidizing enviroment is chosen as a vehicle of study because it leads to relatively concise analytical solutions. As a consequence of the choice of a one‐step irreversible finite‐rate Arrhenius reaction, it is shown that perturbations from the equilibrium (infinite‐rate reaction) mass burning rate and perturbations from the equilibrium temperature and composition profiles are affected functionally by the choice of reaction orders with respect to oxidizer and fuel. Pressure dependences of burning‐rate perturbations are derived.

Gas turbine assembly having low-pressure groups and high-pressure groups adapted to be selectively connected either in series or in parallel

Abstract: A gas turbine installation which includes a combustion chamber, a compressor unit supplying the combustion chamber and having a low-pressure compressor and a high-pressure compressor, a drive turbine unit driven by the combustion gases and driving the compressor unit, and an output engine driven by the combustion gases, in particular an output turbine, whereby the low-pressure compressor and high-pressure compressor are adapted to be connected either in series or in parallel.

Method and apparatus for high temperature waste disposal

Abstract: 1,198,603. Burning refuse. K.W. STOOKEY. 28 Jan., 1969 [25 March, 1968], No. 4551/69. Heading F4B. Apparatus for use in the disposal of waste material having both an organic and metallic content, comprises a vertical combustion chamber 12 into which is continuously supplied a hot air blast via a line 31 to the hearth (40, Fig. 2) of the chamber 12, the said hot air blast passing vertically upwards through the waste product which is introduced through the inlet 47, and a secondary combustion chamber 54 for collecting and combusting the outflow of gaseous and entrained material from a line 52 connected to a collection ring 50 around the chamber 12, the pressure condition maintained in the chamber 12 being such that there is a slight sub-atmospheric pressure within the line 52 so that the combustion product flow does not exit through the opening 47. The conditions in the chamber 54 are continuously monitored to effect the complete combustion of the gaseous material, the solid particulate material being continuously removed without varying the said conditions by means of a butterfly-valvecontrolled separator 80. As shown, the hot air blast fed into the hearth (40) through tuyeres 33, originates from a combination of a combustion device 20 and a heat-exchanger 22, the line 28 exiting from the heat-exchanger and which which includes a control valve 29 and a steam line 35 controlled by a valve 35a, becoming the said hot air blast line 31. Should there be a substantial increase in the inorganic content of the waste product, the temperature in the hearth can be increased by either opening a combustion product by-pass line 69 or by providing auxiliary fuel from a line (73) which injects fuel in proximity to the tuyeres 33.