Showing papers on "Combustion published in 1985"

The Mathematical Theory of Combustion and Explosions

Abstract: Various topics in the area of combustion and explosives are discussed. The general subjects considered include: basic physical concepts of the science of combustion, the time-independent theory of thermal explosions, time-dependent statement of the problem of the initiation of chemical reaction waves in fuel mixtures, laminar flames, complex and chain reactions in flames, the gas dynamics of combustion, and diffusional combustion of gases. 561 references.

The derivation and numerical solution of the equations for zero mach number combustion

Abstract: We present a limiting system of equations to describe combustion processes at low Mach number in either confined or unbounded regions and numerically solve these equations for the case of a flame propagating in a closed vessel. This system allows for large heat release, substantial temperature and density variations, and substantial interaction with the hydrodynamic flow field, including the effects of turbulence. This limiting system is much simpler than the complete system of equations of compressible reacting gas flow since the detailed effects of acoustic waves have been removed. Using a combination of random vortex techniques and flame propagation algorithms specially designed for turbulent combustion, we describe a numerical method to solve these zero Mach number equations. We use this method to analyze the competing effects of viscosity, exothermicity, boundary conditions and pressure on the rate of combustion for a flame propagating in a swirling flow inside a square.

On the determination of laminar flame speeds from stretched flames

Abstract: The effects of stretch on the determination of the laminar flame speed are experimentally studied by using the positively-stretched stagnation flame and negatively-stretched bunsen flame, and by using lean and rich mixtures of methane, propane, butane, and hydrogen with air whose effective Lewis numbers are either greater or less than unity. Results demonstrate that flame speed determination can be influenced by stretch through two factors: (1) Preferential diffusion which tends to increase or decrease the flame temperature and burning rate depending on the effective Lewis number, and (2) Flow divergence which causes the flame speed to assume higher values when evaluated at the upstream boundary of the preheat zone instead of the reaction zone. Recent data on flame speed including the present ones are then examined from the unified viewpoint of flame stretch, leading to satisfactory resolution of the discrepancies between them. The present study also proposes a methodology of determining the laminar flame speeds by using the stagnation flame and linearly extrapolating the data to zero stretch rate.

The Structure of Hexane Soot I: Spectroscopic Studies:

Abstract: Soot produced from the combustion of fossil fuels, widely distributed in the atmosphere, is significantly different from most carbons for which the surface structure and/or reactivity have been studied The composition and surface structure of soot derived from the combustion of n-hexane have been examined by FT-IR, Raman, 13C CP/MAS NMR, and EPR spectroscopies as well as through desorption measurements Carbon-oxygen functionalities on the fresh carbon surface include acid anhydride, a carbonyl conjugated with an aromatic segment, an alkylketone, and aryl ether linkages Also present, confirmed by isotopic substitution, is a quantity of unsaturated C-H, dependent upon the combustion conditions The degree of aromaticity and the graphitic nature of this soot have been determined

Method of controlling pyrolysis temperature

Abstract: A method of controlling temperature during a pyrolysis reaction wherein the predominant pyrolysis reactions are endothermic. A fuel and oxidizer are combusted in a combustion zone to produce a hot gas stream at a superatmospheric pressure. The hot gas stream is then passed through a converging-diverging nozzle to accelerate the hot gas stream to a velocity of at least about mach 2. The reactant to be pyrolyzed is injected into the supersonic hot gas stream to produce a reaction mixture flowing at supersonic velocity and initiate the endothermic pyrolysis reactions. Substantially immediately thereafter the velocity of the reaction mixture is reduced over a predetermined reaction time to convert the kinetic energy of the reaction mixture to thermal energy in an amount sufficient to substantially offset the endothermic reactions taking place while maintaining supersonic flow. At the end of the predertermined reaction time the velocity of the reaction mixture is reduced to subsonic flow and the reaction quenched. The present invention is particularly adapted to the pyrolysis of methane to produce acetylene and ethylene by contacting the methane with hot gases resulting from the reaction of hydrogen with oxygen.

Mathematics of combustion

Abstract: The applications of numerical techniques to the study of combustion processes is considered. The basic equations governing combustion processes are introduced, and some novel approaches to combustion reaction modelling are described. Among the specific applications discussed are: the Burger and Korteweg-de Vries equations of detonation processes; turbulent combustion modelling; and analysis of finite amplitude waves in combustible gases.

The mathematics of combustion

Abstract: An introduction to combustion theory Sensitivity analysis of combustion systems Turbulent combustion Detonation in miniature Finite amplitude waves in combustible gases.

Laminar burning speed measurements of indolene-air-diluent mixtures at high pressures and temperatures

Abstract: The laminar burning speeds of two practical multi-component hydrocarbon fuels similar to automotive gasoline were measured using a spherical combustion bomb with central ignition. Mixtures with equivalence ratios between 0.7 and 1.6, and volume fractions of simulated residual gas between 0 and 0.3 were tested at pressures from 0.4 atm to 12 atm and unburned gas temperatures from 350 K to 550 K. The laminar burning speeds were fitted to a power function expression involving the unburned gas pressure and temperature, and the diluent fraction. The pressure and temperature dependences of the laminar burning speed for undiluted mixtures agreed well with values reported by other investigators for various fuels, indicating that these dependences are independent of fuel type. The percentage reduction in laminar burning speed due to the addition of simulated residual gas was found to be a function only of the amount added, independent of the properties of the mixture.

Chemical kinetics of soot particle growth

Abstract: The light given off by a candle flame and the black smoke from wood­ burning fireplaces, diesel engines, and industrial furnaces have a common origin: tiny carbonaceous soot particles. The light of a candle comes from incandescent soot particles that ultimately burn up in the air at the top of the flame. (But a cold object placed in the flame will quickly become covered with black soot.) In the other cases, however, the soot may be emitted into the atmosphere as a pollutant. In spite of generations of effort, soot emission from many practical combustion systems remains a serious problem, and the viability of the fuel-efficient passenger car diesel engine may rest on our ability to make significant reductions in soot emissions. The morphology of soot particles can be best observed with electron micrographs such as that shown in Figure 1. We see 10 to 30 nm spherical units attached in necklace-like chains, with each sphere containing the order of 105 carbon atoms and 104-105 hydrogen atoms, putting the spheres somewhat above molecular in size. The structure in Figure 1 is nearly the same for soot generated on a bunsen burner and in a diesel engine. A great deal of work has been reported that correlates soot formation with fuel type, flame temperature, or flow fields (1), yielding an extensive and very useful body of engineering data, but these data have provided little insight into the detailed chemistry of soot formation. Soot formation involves some interesting and unusual chemistry. First, soot formation represents growth from species the size of fuel molecules, with perhaps 1 to 10 carbon atoms, to particles with hundreds of thousands of carbon atoms. Such growth takes place at flame temperatures, generally between 1000 K

Combustion instability sustained by unsteady vortex combustion

Abstract: The determination of an internal feedback mechanism which leads to combustion instability inside a small scale laboratory combustor is presented in this paper. During combustion instability, the experimental findings show that a large vortical structure is formed at an acoustic resonant mode of the system. The subsequent unsteady burning, within the vortex as it is convected downstream, feeds energy into the acoustic field and sustains the large resonant oscillations. These vortices are formed when the acoustic velocity fluctuation at the flameholder is a large fraction of the mean flow velocity. The propagation of these vortices is not a strong function of the mean flow speed and appears to be dependent upon the frequency of the instability. Continued existence of large vortical structures which characterize unstable operation depends upon the fuel-air ratio, system acoustics, and fuel type.

Description and Analysis of Diesel Engine Rate of Combustion and Performance Using Wiebe's Functions

Abstract: Two laboratory engines, one direct injection and one indirect injection, were operated for a range of speeds, loads, injection timings, fuels, and steady and transient conditions. Rate of combustion data were derived and analyzed using a double Wiebe's function approximation. It is shown that three of the six function parameters are constant for a wide range of conditions and that the other three can be expressed as linear functions of the amount of fuel injected during ignition lag. Engine noise, smoke, and thermal efficiency correlate with the parameters describing the amount of premixed combustion and diffusive combustion duration. These characteristics may be optimized by reducing the quantity of premixed combustion while maintaining the duration of diffusive combustion to less than 60 /sup 0/CA.

Fuel Effects on Gas Turbine Combustion—Ignition, Stability, and Combustion Efficiency

Abstract: An analytical study is made of the substantial body of experimental data acquired during recent Wright-Patterson Aero Propulsion Laboratory sponsored programs on the effects of fuel properties on the performance and reliability of several gas turbine combustors, including J79-17A, J79-17C (Smokeless), F101, TF41, TF39, J85, TF33, and F100. Quantitative relationships are derived between certain key aspects of combustion, notably combustion efficiency, lean blowout limits and lean light-off limits, and the relevant fuel properties, combustor design features, and combustor operating conditions. It is concluded that combustion efficiency, lean blowout limits, and lean lightoff limits are only slightly dependent on fuel chemistry, but are strongly influenced by the physical fuel properties that govern atomization quality and spray evaporation rates.

Method and apparatus for monitoring and adjusting λ-probe-controlled catalytic exhaust gas emission control systems of internal combustion engines

Abstract: A method for testing and adjusting catalytic exhaust gas emission control systems of internal combustion engines, in which the fuel-air-ratio is regulated by means of a λ-probe (control-probe) arranged in the exhaust gas stream upstream of the catalyst, whereby the exhaust gas stream is measured downstream of the catalyst by means of a further λ-probe (test-probe). The voltage average value and amplitude magnitude of the signal produced by the test-probe are determined and serve for adjusting the operating point of the control system and for the recognition of the catalyst efficiency.

Fuel cell power plant

Abstract: This invention relates to a fuel cell power plant. The power plant comprises a fuel cell (10) employing a molten carbonate as an electrolyte, a reformer (24) for reforming fuel into a reactive gas to be.supplied into the anode (14) of the cell (10), an expansion turbine (84) connected to a compressor (36), a combustor (62) for burning a gas exhausted from the anode (14) and introducing the combustion gas into the cathode (16) of the fuel cell (10) along with a gas compressed by the compressor (36), and a waste heat recovery system (92). The power plant is characterized by the provision of another combustor (110) on the passage through which cathode exhaust gas (76) is sent from the cathode to the turbine and a passage for leading a part (112) of the anode exhaust gas to the another combustor, whereby unburnt gas included in the anode exhaust gas is burnt with the cathode exhaust gas supplied as oxygen source so that the temperature of the turbine driving gas is raised, as a result, the overall thermal efficiency of the power plant increases (Fig. 1).

Chemistry of hydrocarbon combustion

Abstract: 1 Historical background.- 1.1 Early hypotheses.- 1.2 Studies of hydrocarbon combustion, 1930s to mid-1950s.- 1.3 Summary and conclusions.- 1.4 References.- 2 Analytical-phenomenological studies of overall hydrocarbon combustion.- 2.1 Introduction.- 2.2 Alkanes.- 2.3 Alkenes.- 2.4 Cycloalkanes and aromatic compounds.- 2.5 References.- 3 Study of elementary reactions involved in hydrocarbon combustion.- 3.1 Conventional indirect methods.- 3.2 Specialized indirect techniques.- 3.3 Direct methods involving production and monitoring of specific atoms or radicals.- 3.4 References.- 4 Some elementary species (other than those containing carbon) involved in combustion.- 4.1 Introduction.- 4.2 Hydroxyl (OH) radicals.- 4.3 Hydroperoxy (HO2) radicals.- 4.4 Oxygen (O) atoms.- 4.5 Hydrogen (H) atoms.- 4.6 References.- 5 Elementary carbon-containing species in combustion.- 5.1 Alkyl radicals.- 5.2 Alkylperoxy radicals.- 5.3 Alkoxy radicals.- 5.4 Acyl and acylperoxy radicals.- 5.5 Other hydrocarbon radicals.- 5.6 References.- 6 Pyrolytic reactions of hydrocarbons.- 6.1 Introduction.- 6.2 Pyrolysis of alkanes.- 6.3 Pyrolysis of alkenes and dialkenes.- 6.4 Pyrolysis of alkynes.- 6.5 Pyrolysis of cycloalkanes and aromatic compounds.- 6.6 Coke and carbon formation.- 6.7 References.- 7 Prediction of the behaviour of combustion systems: modelling.- 7.1 Introduction.- 7.2 Stoichiometric/semikinetic models.- 7.3 Models based on detailed mechanisms.- 7.4 References.

Low nox premix burner

Abstract: The invention relates to an improved premix burner and a method of its operation for combustion with a minimum of NO x emissions. The improvement is achieved by combining staged combustion with a premix burner in a manner such that mixing of the secondary air with the flame is delayed.

Flamelet and distributed combustion in premixed turbulent flames

Abstract: Calculations are reported that compare the properties of idealized premixed flames in which either flamelet or distributed combustion occurs. The calculations are based on the Monte Carlo solution of a modelled transport equation for the joint probability density function (pdf) of the velocities and the reaction progress variable. In the joint pdf equation, it is the molecular diffusion term that is fundamentally different for the two types of combustion, and consequently different models for the term are employed. For flamelet combustion, at moderate at high Damkohler numbers, the progress variable pdf is a double-delta-function distribution, and the turbulent flame speed is more than twice the turbulence intensity (independent of the Damkohler number). For distributed combustion, on the other hand, even at high Damkohler number, the progress variable pdf shows significant probability of partially reacted fluid. The flame speed is less than in flamelet combustion and incraases with Damkohler number.

A Discussion of Turbulent Flame Structure in Premixed Charges

Abstract: Propagation of turbulent flames in spark-ignition engines is considered from the viewpoint of the different possible regimes of premixed turbulent combustion. Nondimensional parameters defining known combustion regimes are reviewed, and numerical values of these parameters are estimated for both research and production engines. The reaction-sheet regime is inferred to apply at least for some operating conditions, and therefore literature on turbulent flame propagation in the reaction-sheet regime is reviewed. Implications of these results on interpretations of existing experimental observations of combustion in engine cylinders and on modeling of turbulent flame propagation in engines are discussed.

Dynamic features of combustion

Abstract: The dynamic features of combustion are discussed for four important cases: ignition, inflammation, explosion, and detonation. Ignition, the initiation of a self-sustained exothermic process, is considered in the simplest case of a closed thermodynamic system and its stochastic distribution. Inflammation, the initiation and propagation of self-sustained flames, is presented for turbulent flow. Explosion, the dynamic effects caused by the deposition of exothermic energy in a compressible medium, is illustrated by self-similar blast waves with energy deposition at the front and the adiabatic non-self-similar wave. Detonation, the most comprehensive illustration of all the dynamic effects of combustion, is discussed with a phenomenological account of the development and structure of the wave.

Non-catalytic porous-phase combustor

Abstract: A non-catalytic porous-phase combustor and process for generating radiant energy wherein the gas phase reaction and combustion take place within the pores of a multilayer porous plate to provide higher combustion intensity and to provide a greater proportion of heat released by radiation. The combustor comprises a porous plate having at least two discrete and contiguous layers, a first preheat layer comprising a material having a low inherent thermal conductivity and a second combustion layer comprising a material having a high inherent thermal conductivity and providing a radiating surface. Combustion intensities of about 400,000 to about 750,000 Btu/hr-ft 2 may be achieved in the combustion layer of the porous phase combustor.

Turbocharger for internal combustion engines

Abstract: A turbocharger for an internal combustion engine is disclosed, including a turbine drivable by the exhaust energy of the internal combustion engine, and an air compressor coupled by a shaft to an impeller of the turbine for charging air into engine cylinders in response to rotation of the shaft. A rotor is mounted on the shaft and stator cores and coils are disposed around the rotor. The rotor and the stator cores and coils jointly constitute a motor-generator which operates as a motor or a generator dependent on operating conditions of the internal combustion engine.

Experimental investigation on the stabilization mechanism of jet diffusion flames

Abstract: Two contrary concepts have been suggested in order to explain the mechanism of flame stabilization based on premixed and diffusion flamelet combustion respectively. To contribute to the understanding of which model represents the true stabilization mechanism, two different natural gas jet diffusion flames, at exit velocities between flame detachment and blow-off, were investigated. The measured profiles of gas composition and velocity around the stabilization zone were used to derive the rate of mixing and fuel burnout. The results show that, for the flames investigated, about forty to fifty percent of the total fuel flow is already mixed at a molecular level upstream of the flame stabilization zone. This mixture then reacts over a very short distance, supporting the concept of premixed combustion in lifted jet diffusion flames.