Showing papers on "Combustion published in 2000"

An Introduction to Combustion: Concepts and Applications

Abstract: Preface Preface to the Second Edition Preface to the First Edition 1: Introduction 2: Combustion and Thermochemistry 3: Introduction to Mass Transfer 4: Chemical Kinetics 5: Some Important Chemical Mechanisms 6: Coupling Chemical and Thermal Analyses of Reacting Systems 7: Simplifed Conversation Equations for Reacting Flows 8: Laminar Premixed Flames 9: Laminar Diffusion Flames 10: Droplet Evaporation and Burning 11: Introduction to Turbulent Flows 12: Turbulent Premixed Flames 13: Turbulent Nonpremixed Flames 14: Burning of Solids 15: Pollutant Emissions 16: Detonations Appendix A: Selected Thermodynamic Propertiesof Gases Comprising C-H-O-N System Appendix B: Fuel Properties Appendix C: Selected Properties of Air, Nitrogen, and Oxygen Appendix D: Diffusion Coefficients and Methodology for their Estimation Appendix E: Generalized Newton's Method for the Solution of Nonlinear Equations Appendix F: Computer Codes for Equilibrium Products of Hydrocarbon-Air Combustion

Combustion aerosols: factors governing their size and composition and implications to human health.

Abstract: Particulate matter (PM) emissions from stationary combustion sources burning coal, fuel oil, biomass, and waste, and PM from internal combustion (IC) engines burning gasoline and diesel, are a significant source of primary particles smaller than 2.5 μm (PM2.5) in urban areas. Combustion-generated particles are generally smaller than geologically produced dust and have unique chemical composition and morphology. The fundamental processes affecting formation of combustion PM and the emission characteristics of important applications are reviewed. Particles containing transition metals, ultrafine particles, and soot are emphasized because these types of particles have been studied extensively, and their emissions are controlled by the fuel composition and the oxidant-tem-perature-mixing history from the flame to the stack. There is a need for better integration of the combustion, air pollution control, atmospheric chemistry, and inhalation health research communities. Epidemiology has demonstrated t...

Internal combustion powered tool

Abstract: An internal combustion powered tool, such as a nail or fastener driver, and a control system, spark source, and rotary valve for use in an internal combustion powered tool are disclosed. The tool may include, for example, a cylinder and a piston reciprocally moveable within the cylinder. A combustion chamber is defined at one end of the cylinder, with the piston comprising a portion of one end of the combustion chamber. The tool may have a fastener driver associated with the piston, and a magazine for feeding fasteners into registration with the driver. A fuel flow passageway extends between a fuel source and the combustion chamber, and a metering valve controls the flow of fuel to the combustion chamber. A spark source within the combustion chamber is provided for igniting the fuel, and an intake and exhaust valve that includes a pair of diametrically opposed apertures is provided. At least one fan external to the combustion chamber induces an intake of fresh air into the combustion chamber through one of the apertures and an exhaust of combustion products from the combustion chamber through the other aperture. Additional and alternative details and features are described in the disclosure.

Chemical kinetics of hydrocarbon ignition in practical combustion systems

Abstract: Chemical kinetic factors of hydrocarbon oxidation are examined in a variety of ignition problems. Ignition is related to the presence of a dominant chain-branching reaction mechanism that can drive a chemical system to completion in a very short period of time. Ignition in laboratory environments is studied for problems including shock tubes and rapid compression machines. Modeling of the laboratory systems is used to develop kinetic models that can be used to analyze ignition in practical systems. Two major chain-branching regimes are identified, one consisting of high temperature ignition with a chain branching reaction mechanism based on the reaction between atomic hydrogen with molecular oxygen, and the second based on an intermediate temperature thermal decomposition of hydrogen peroxide. Kinetic models are then used to describe ignition in practical combustion environments, including detonations and pulse combustors for high temperature ignition and engine knock and diesel ignition for intermediate temperature ignition. The final example of ignition in a practical environment is homogeneous charge, compression ignition (HCCI), which is shown to be a problem dominated by the kinetics of intermediate temperature hydrocarbon ignition. Model results show why high hydrocarbon and CO emissions are inevitable in HCCI combustion. The conclusion of this study is that the kinetics of hydrocarbon ignition are actually quite simple, since only one or two elementary reactions are dominant. However, many combustion factors can influence these two major reactions, and these are the features that vary from one practical system to another.

A Review on Polycyclic Aromatic Hydrocarbon (PAH) Emissions from Energy Generation

Abstract: Polycyclic aromatic hydrocarbons (PAH) emitted from fluidized bed combustion have been reviewed. Firstly, the PAH origin is undertaken. Secondly, the state of the art on their sampling and analytical procedures are commented. Finally, the influence of the fuel, fossil and nonfossil fuels, the combustor type and the combustion variables are analyzed concerning PAH formation and emission in solid/gaseous phase.

Fine Particle and Gaseous Emission Rates from Residential Wood Combustion

Abstract: Residential wood combustion emissions were analyzed to determine emission rates and to develop chemical emissions profiles that represent the appliances and woods typically used in wood-burning communities. Over 350 elements, inorganic compounds, and organic compounds were quantified. A range of 4−9 g/kg dry fuel of particulate matter (<2.5 μm) and 5−22 g/kg volatile organic compounds were observed. Samples were collected using a dilution stack sampler equipped with a 2.5-μm particle selective cyclone. Emissions were diluted 20−70 times, cooled to ambient temperature, and allowed 80 s for condensation prior to collection. Wood type, wood moisture, burn rate, and fuel load were varied for different experiments. Fine particle and semivolatile organic compounds were collected on filter/PUF/XAD/PUF cartridges. Inorganic samples and mass were collected on Teflon and quartz filters. Volatile organic carbon compounds were trapped with Tenax (C8−C20), canister (C2−C12), and 2,4-dinitrophenylhydrazine impregnated ...

Source Apportionment of Wintertime Gas-Phase and Particle-Phase Air Pollutants Using Organic Compounds as Tracers

Abstract: Two chemical mass balance receptor models are developed which can determine the source contributions to atmospheric pollutant concentrations using organic compounds as tracers. The first model uses particle-phase organic compounds to apportion the primary source contributions to atmospheric fine particulate organic carbon concentrations and fine particle mass concentrations. The second receptor model simultaneously uses both volatile gas-phase hydrocarbons and particle-phase organic compounds as tracers to determine source contributions to non-methane organic gases in the atmosphere. Both models are applied to data collected in California's San Joaquin Valley during two severe wintertime air pollution episodes. Source contributions to fine particle air quality are calculated for two urban sites, Fresno and Bakersfield, and one background site, Kern Wildlife Refuge. Primary particle emissions from hardwood combustion, softwood combustion, diesel engines, meat cooking, and gasoline-powered motor vehicles contribute on average 79% of the airborne fine particle organic compound mass at the urban sites during both episodes with smaller but still measurable contributions from fine particle road dust and natural gas combustion aerosol. Anthropogenic primary particle sources contribute less than 10% of the fine particle mass concentration at the background site. The combined gas-phase and particle-phase organic compound receptor model shows that gasoline-powered motor vehicle exhaust and gasoline vapors are the largest contributors to non-methane organic gases concentrations followed by natural gas leakage. Smaller but statistically significant contributions to organic vapors from wood combustion, meat cooking, and diesel exhaust also are quantified.

Reverse microemulsion synthesis of nanostructured complex oxides for catalytic combustion

Abstract: Catalysts play an important role in many industrial processes, but their use in high-temperature applications-such as energy generation through natural gas combustion, steam reforming and the partial oxidation of hydrocarbons to produce feedstock chemicals--is problematic. The need for catalytic materials that remain stable and active over long periods at high operation temperatures, often in the presence of deactivating or even poisoning compounds, presents a challenge. For example, catalytic methane combustion, which generates power with reduced greenhouse-gas and nitrogen-oxide emissions, is limited by the availability of catalysts that are sufficiently active at low temperatures for start-up and are then able to sustain activity and mechanical integrity at flame temperatures as high as 1,300 degrees C. Here we use sol-gel processing in reverse microemulsions to produce discrete barium hexa-aluminate nanoparticles that display excellent methane combustion activity, owing to their high surface area, high thermal stability and the ultrahigh dispersion of cerium oxide on the their surfaces. Our synthesis method provides a general route to the production of a wide range of thermally stable nanostructured composite materials with large surface-to-volume ratios and an ultrahigh component dispersion that gives rise to synergistic chemical and electronic effects, thus paving the way to the development of catalysts suitable for high-temperature industrial applications.

Large-eddy simulation of a turbulent piloted methane/air diffusion flame (Sandia flame D)

Abstract: The Lagrangian Flamelet Model is formulated as a combustion model for large-eddy simulations of turbulent jet diffusion flames. The model is applied in a large-eddy simulation of a piloted partially premixed methane/air diffusion flame (Sandia flame D). The results of the simulation are compared to experimental data of the mean and RMS of the axial velocity and the mixture fraction and the unconditional and conditional averages of temperature and various species mass fractions, including CO and NO. All quantities are in good agreement with the experiments. The results indicate in accordance with experimental findings that regions of high strain appear in layer like structures, which are directed inwards and tend to align with the reaction zone, where the turbulence is fully developed. The analysis of the conditional temperature and mass fractions reveals a strong influence of the partial premixing of the fuel.

Detailed chemical kinetic mechanisms for combustion of oxygenated fuels

Abstract: Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate, a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available in the literature, which was obtained at low temperature, subatmospheric conditions in closed vessels, using pressure measurements as the main diagnostic. Some qualitative agreement was obtained, but the experimental data consistently indicated lower overall reactivities than the model, differing by factors of 10 to 50. This discrepancy, which occurs for species with wellestablished kinetic mechanisms as well as for methyl esters, is tentatively ascribed to the presence of wall reactions in the experiments. The model predicts a region of weak or negative dependence of overall reaction rate on temperature for each methyl ester. Examination of the reaction fluxes provides an explanation of this behavior, involving a temperature-dependent competition between chain-propagating unimolecular decomposition processes and chain-branching processes, similar to that accepted for hydrocarbons. There is an urgent need to obtain more complete experimental data under well-characterized conditions for thorough testing of the model.

Morphology and burning rates of expanding spherical flames in H2/O2/inert mixtures up to 60 atmospheres

Abstract: Recognizing that previous experimental studies on constant-pressure, outwardly propagating, Spherical flames with imaging capability were limited to pressures less than about 5 atm, and that pressures within internal combustion engines are substantially higher, a novel experimental apparatus was designed, to extend the environmental pressure to 60 atm. Results substantiate previous observations of the propensity of cell formation over the flame surface due to hydrodynamic and diffusive-thermal instabilities and provide convincing evidence that wrinkled flame is the preferred mode of propagation in hydrogen/air mixtures in environments with pressures above only a few atmospheres. It is further shown that, by using helium as the diluent, and by reducing the oxygen concentration of the combustible, diffusional-thermal instability can be mostly suppressed and the hydrodynamic instability delayed. Stretch-free laminar flame speeds were subsequently determined for such smooth flames up to 20 atm and were compared with the calculated values, allowing for detailed chemistry and transport.

Combustion chemistry of propane: A case study of detailed reaction mechanism optimization

Abstract: Detailed chemical reaction mechanisms describing hydrocarbon combustion chemistry are conceptually structured in a hierarchical manner with H2 and CO chemistry at the base, supplemented as needed by elementary reactions of larger chemical species. While this structure gives a logical organization to combustion chemistry, the degree to which this organization reflects actual reactive fluxes in flames is not known. Moreover, it has not been tested whether sets of rate parameters derived by optimizing fits to small-hydrocarbon combustion data are secure foundations upon which to optimize the rate parameters needed for modeling the combustion of larger hydrocarbons. In this work, a computer modeling study was undertaken to discover whether optimizing the rate parameters of a 258-reaction C3 combustion chemistry mechanism that was added to a previously optimized 205-reaction C3 mechanism would provide satisfactory accounting for C3 flame speed and ignition data. The optimization was done with 21 optimization targets, 9 of which were ignition delays and 12 of which were atmospheric pressure laminar flame speeds; 2 of the ignition delays and 2 of the flame speeds, all for methane fuel, had served as optimization targets for the C3 rate parameters. It was found in sensitivity studies that the coupling between the C3 and the C3 chemistry was much stronger than anticipated. No set of C3 rate parameters could account for the C3 combustion data as long as the previously optimized (against C3 optimization targets only) C3 rate parameters remained fixed. A reasonable match to the C3 targets could be obtained, without degrading the match between experiment and calculation for the C3 optimization targets, by reoptimizing six of the previously optimized and three additional C3 rate parameters.

Overview of dust explosibility characteristics

Abstract: This paper is an overview of and introduction to the subject of dust explosions. The purpose is to provide information on the explosibility and ignitability properties of dust clouds that can be used to improve safety in industries that generate, process, use, or transport combustible dusts. The requirements for a dust explosion are: a combustible dust, dispersed in air, a concentration above the flammable limit, the presence of a sufficiently energetic ignition source, and some confinement. An explosion of a fuel in air involves the rapid oxidation of combustible material, leading to a rapid increase in temperature and pressure. The violence of an explosion is related to the rate of energy release due to chemical reactions relative to the degree of confinement and heat losses. The combustion properties of a dust depend on its chemical and physical characteristics, especially its particle size distribution. In this paper, the explosion characteristics of combustible dusts will be compared and contrasted with those of flammable gases, using methane as an example. These characteristics include minimum explosible concentration, maximum explosion pressure, maximum rate of pressure rise, limiting oxygen concentration, ignition temperature, and amount of inert dust necessary to prevent flame propagation. The parameters considered include the effects of dust volatility, dust particle size, turbulence, initial pressure, initial temperature, and oxygen concentration. Both carbonaceous and metal dusts will be used as examples. The goal of this research is to better understand the fundamental aspects of dust explosions.

Measurements of excess O3, CO2, CO, CH4, C2H4, C2H2, HCN, NO, NH3, HCOOH, CH3COOH, HCHO, and CH3OH in 1997 Alaskan biomass burning plumes by airborne Fourier transform infrared spectroscopy (AFTIR)

Abstract: We used an airborne Fourier transform infrared spectrometer (AFTIR), coupled to a flow-through, air-sampling cell, on a King Air B-90 to make in situ trace gas measurements in isolated smoke plumes from four, large, boreal zone wildfires in interior Alaska during June 1997. AFTIR spectra acquired near the source of the smoke plumes yielded excess mixing ratios for 13 of the most common trace gases: water, carbon dioxide, carbon monoxide, methane, nitric oxide, formaldehyde, acetic acid, formic acid, methanol, ethylene, acetylene, ammonia and hydrogen cyanide. Emission ratios to carbon monoxide for formaldehyde, acetic acid, and methanol were 2.2±0.4%, 1.3±0.4%, and 1.4±0.1%, respectively. For each oxygenated organic compound, a single linear equation fits our emission factors from Alaska, North Carolina, and laboratory fires as a function of modified combustion efficiency (MCE). A linear equation for predicting the NH3/NOx emission ratio as a function of MCE fits our Alaskan AFTIR results and those from many other studies. AFTIR spectra collected in downwind smoke that had aged 2.2±1 hours in the upper, early plume yielded ΔO3/ΔCO ratios of 7.9±2.4% resulting from O3 production rates of ∼50 ppbv h−1. The ΔNH3/ΔCO ratio in another plume decreased to 1/e of its initial value in ∼2.5 hours. A set of average emission ratios and emission factors for fires in Alaskan boreal forests is derived. We estimate that the 1997 Alaskan fires emitted 46±11 Tg of CO2.

Combustion Chemistry of Nitrogen

Abstract: The purpose of this chapter is to examine reactions of nitrogen-containing species that are important in high-temperature gas-phase systems so as to provide the best set of rate coefficients presently available for use in combustion chemistry modeling. Since the 1984 review of N/H/O rate coefficients by Hanson and Salimian 1984 there has been a major review of nitrogen chemistry under combustion conditions by Miller and Bowman (1989). Several compilations of evaluated rate coefficients have also appeared. We update these discussions where appropriate and then analyze a number of chemically activated reactions that are relevant to understanding nitrogen chemistry.

A six-wafer combustion system for a silicon micro gas turbine engine

Abstract: As part of a program to develop a micro gas turbine engine capable of producing 10-50 W of electrical power in a package less than one cubic centimeter in volume, we present the design, fabrication, packaging, and experimental test results for the 6-wafer combustion system for a silicon microengine. Comprising the main nonrotating functional components of the engine, the device described measures 2.1 cm/spl times/2.1 cm/spl times/0.38 cm and is largely fabricated by deep reactive ion etching through a total thickness of 3800 /spl mu/m. Complete with a set of fuel plenums, pressure ports, fuel injectors, igniters, fluidic interconnects, and compressor and turbine static airfoils, this structure is the first demonstration of the complete hot flow path of a multilevel micro gas turbine engine. The 0.195 cm/sup 3/ combustion chamber is shown to sustain a stable hydrogen flame over a range of operating mass flows and fuel-air mixture ratios and to produce exit gas temperatures in excess of 1600 K. It also serves as the first experimental demonstration of stable hydrocarbon microcombustion within the structural constraints of silicon. Combined with longevity tests at elevated temperatures for tens of hours, these results demonstrate the viability of a silicon-based combustion system for micro heat engine applications.

A flame surface density approach to large-eddy simulation of premixed turbulent combustion

Abstract: The flame surface density approach to the modeling of premixed turbulent combustion is well established in the context of Reynolds-averaged simulations. For the future, it is necessary to consider large-eddy simulation (LES), which is likely to offer major advantages in terms of physical accuracy, particularly for unsteady combustion problems. LES relies on spatial filtering for the removal of unresolved phenomena whose characteristic length scales are smaller than the computational grid scale. Thus, there is a need for soundly based physical modeling at the subgrid scales. The aim of this paper is to explore the usefulness of the flame surface density concept as a basis for LES modeling of premixed turbulent combustion. A transport equation for the filtered flame surface density is presented, and models are proposed for unclosed terms. Comparison with Reynolds-averaged modeling is shown to reveal some interesting similarities and differences. These were exploited together with known physics and statistical results from experiment and from direct numerical stimulation in order to gain insight and refine the modeling. The model has been implemented in a combustion LES code together with standard models for scalar and momentum transport. Computational results were obtained for a simple three-dimensional flame propagation test problem, and the relative importance of contributing terms in the modeled equation for flame surface density was assessed. Straining and curvature are shown to have a major influence at both the resolved and subgrid levels.