Showing papers on "Combustion published in 1995"

Evaluated kinetic data for combustion modelling supplement I

Abstract: This compilation updates and expands a previous evaluation of kinetic data on elementary, homogeneous, gas phase reactions of neutral species involved in combustion systems [J. Phys. Chem. Ref. Data 21, 411 (1992)]. The work has been carried out under the auspices of the European Community Energy Research and Development Program. Data sheets are presented for some 78 reactions and two tables in which preferred rate parameters are presented for reactions of ethyl, i‐propyl, t‐butyl, and allyl radicals are given. Each data sheet sets our relevant thermodynamic data, experimental kinetic data, references, and recommended rate parameters with their error limits. A table summarizing the recommended rate data is also given. The new reactions fall into two categories: first, to expand the previous compilation relating largely to the combustion in air of methane, ethane and aromatic compounds; and second, provide data for some of the key radicals involved in the combustion of higher alkanes.

Liquid rocket engine combustion instability

Abstract: Since the invention of the V-2 rocket during World War II, combustion instabilities have been recognized as one of the most difficult problems in the development of liquid propellant rocket engines. This book is the first published in the United States on the subject since NASA's Liquid Rocket Combustion Instability (NASA SP-194) in 1972. In this book, experts cover four major subject areas: engine phenomenology and case studies, fundamental mechanisms of combustion instability, combustion instability analysis, and engine and component testing. Especially noteworthy is the inclusion of technical information from Russia and China--a first.

Toward a global estimate of black carbon in residues of vegetation fires representing a sink of atmospheric CO2 and a source of O2

Abstract: This study was performed to quantify the black carbon content of vegetation fire residues for use in assessing the impact of vegetation fires on atmospheric carbon dioxide levels. Samples of laboratory fire residues from different vegetation types were analyzed for black carbon and corresponding hydrogen. Two pretreatment steps removed all inorganic and organic carbon. An elemental analysis was then conducted to quantify black carbon and its hydrogen/carbon (H/C) ratio. Results of 22 experimental fires are presented which demonstrate that black carbon is definable as the fire produced carbon fraction with molar H/C ratio of {le} 0.2 which is resistant to heating to 340 C in pure oxygen. Correlation studies of black carbon formation to the carbon monoxide/carbon dioxide ratio of emissions showed that the major source of black carbon is flaming combustion. More than 80% of the black carbon produced by vegetation fires was found to remain in the fire residues. Based on the ratios determined of black carbon to emitted carbon dioxide and to the fire exposed carbon, the annual global black carbon formation was estimated to be from 50 to 270 teragrams per year. The fire-induced sequestration of carbon from the short-term biospheric cycle to the long-term geologicalmore » cycle may be a significant sink of atmospheric carbon dioxide and source of oxygen, and should be considered in atmospheric analyses. 54 refs., 3 figs., 4 tabs.« less

Thermoacoustic oscillations in combustion chambers of gas turbines

Abstract: This paper presents an overview of thermoacoustic oscillations in modern gas turbine combustors with premixed combustion. In conventional combustors a substantial percentage of air enters downstream of the primary zone of combustion. As a consequence, the liners of conventional combustors are very powerful sound attenuators. In a modern premixing combustor effectively all of the air enters through the burners, and there is almost no sound attenuation downstream of the primary zone of combustion. The combination of this problem with the difficulties to stabilize premixed flames has led to a situation where thermoacoustic stability has become the key issue of modern combustion technology. The relative importance of a variety of self-excited oscillations and oscillations that are forced by aerodynamic instabilities is investigated. It is found that the two leading excitation mechanisms are associated with periodic (lean) extinction and with vortex rollup in the primary zone of combustion. For the latter case a simple combustor model is used to study the amplification effects due to resonant wave motion and coincidence of mechanical eigenfrequencies of combustor walls with excitation frequencies.

Urban Leakage of Liquefied Petroleum Gas and Its Impact on Mexico City Air Quality

Abstract: Alkane hydrocarbons (propane, isobutane, and n-butane) from liquefied petroleum gas (LPG) are present in major quantities throughout Mexico City air because of leakage of the unburned gas from numerous urban sources. These hydrocarbons, together with olefinic minor LPG components, furnish substantial amounts of hydroxyl radical reactivity, a major precursor to formation of the ozone component of urban smog. The combined processes of unburned leakage and incomplete combustion of LPG play a significant role in causing the excessive ozone characteristic of Mexico City. Reductions in ozone levels should be possible through changes in LPG composition and lowered rates of leakage.

Methane combustion over palladium catalysts: The effect of carbon dioxide and water on activity

Abstract: The influence of water and carbon dioxide on the activity of a series of palladium catalysts for the combustion of methane has been studied. It has been found that both compounds have an inhibitory effect but the extent of this depends on the experimental conditions. When both are present in the feedstream, the effect of carbon dioxide is negligible, the total decrease in activity only being equal to that of water alone. It is concluded that both water and carbon dioxide poison the same active sites on the palladium oxide with water able to displace carbon dioxide to form an inactive surface hydroxide. The magnitude of the effect due to both additives decreases with increasing reaction temperature and conversion. This is due both to the increased amount of water producted in the reaction reducing the effect of added water or carbon dioxide, and to the decreasing stability of the surface hydroxide at higher temperatures. In relation to practical applications, it is concluded that carbon dioxide will have no effect on catalytic activity under normal working conditions but water present in the feedstream may reduce the activity of the catalysts very significantly at lower temperatures. However, above about 450°C the effect of water is also expected to be very small.

Modes of occurrence of environmentally· sensitive trace elements in coal

Abstract: Coal utilisation, especially coal combustion, causes the release of many inorganic elements into the environment. Various pollution control procedures and devices are used by the coal industry to minimise the release of these elements. Selective mining and coal cleaning procedures reduce the amount of the inorganic constituents in coal prior to combustion. Electrostatic precipitators, chemical additives, baghouses, and flue-gas scrubbers reduce particulate and element emissions after combustion.

Apparatus and method for internal combustion engine control

Abstract: In a control apparatus and control method for an internal combustion engine having an exhaust purifying catalytic device for adsorbing nitrogen oxide contained in exhaust gases from the engine, the adsorption state of nitrogen oxide adsorbed by the catalytic device is estimated by an electronic control unit during the lean-combustion driving of the engine. If the catalytic device is saturated with nitrogen oxide, the ignition timing is delayed and the exhaust gas is recirculated to the intake side of the engine with the lean air-fuel ratio kept unchanged. This starts the nitrogen oxide reduced driving mode for deteriorating the combustion state in the engine. At this time, the engine output will not change by a great amount. Further, a reducing atmosphere is created around the catalytic device by unburnt gases, generated due to the deterioration of the combustion state, to deoxidize the adsorbed nitrogen oxide. As a result, the purifying ability of the catalytic device can be recovered to suppress the discharge amount of nitrogen oxide without deteriorating the smoothness of engine driving and fuel economy.

Internal combustion engines

Abstract: Review of basic principles air-standard cycles and their analysis fuel-air cycles and their analysis actual cycles and their analysis fuels carburetion injection ignition combustion and combustion chambers engine friction and lubrication heat rejection and cooling measurements and testing performance parameters and characteristics two-stroke engines.

Direct Observation of Alkali Vapor Release during Biomass Combustion and Gasification. 1. Application of Molecular Beam/Mass Spectrometry to Switchgrass Combustion

Abstract: Electricity from biomass and biomass-derived fuels has become an attractive and viable alternative energy source. Alkali metal release during biomass combustion can cause significant problems in terms of severe fouling and slagging of heat transfer surfaces in boilers thus reducing efficiency, and in the worst case, leading to unscheduled plant shutdown. Future biomass to electricity facilities will benefit from increased efficiencies by incorporating integrated gasification combined cycle systems that use biomass combustion gases to directly drive an aeroderivative turbine. These systems will have even lower tolerances for alkali vapor release because accelerated erosion and corrosion of turbine blades results in shorter turbine lifetimes. One solution to the fouling and slagging problem is to develop methods of hot gas cleanup to reduce the amount of alkali vapor to acceptable levels. A detailed understanding of the mechanisms of alkali metal release during biomass combustion as well as identifying alkali metal containing vapors and how the vapors lead to fouling and slagging could greatly benefit the development of hot gas cleanup technology. This paper demonstrates the application of molecular beam/mass spectrometry to the study of alkali metal speciation and release during switchgrass combustion. We have successfully used this experimental technique to identify alkali metal containing species released during the combustion of switchgrass at four different conditions : 1100 °C in He/O 2 -(20%), 800 °C in He/O 2 (20%), 1100 °C in He/O 2 (5%), and 1100 °C in He/O 2 (10%)/steam(20%). These conditions were chosen to study the effect of temperature, oxygen concentration, and excess steam on alkali metal release and speciation. Initial feedstock composition is the most significant factor which affects the amount and species of alkali metal released during biomass combustion. The switchgrass sample screened in the present study is high in both alkali metal (potassium) and chlorine. As a result, the predominant alkali metal containing species released during switchgrass combustion is potassium chloride. Varying the combustion condition affects the amount of alkali metal released by a factor of 2 or less. Adding excess steam to the combustion environment tends to shift the form of alkali metal release from the alkali chloride to the hydroxide.

Thin-film gas sensors based on semiconducting metal oxides

Abstract: In recent years, there has been a gradual realization that an intact environment and properly functioning ecosystems are essential to the continuance of human life; this has led to the tightening up of environmental legislation. As far as air pollution is concerned, gases like sulfur dioxide, the oxides of nitrogen (NO x ), carbon monoxide and carbon dioxide are considered to be the main culprits. Most sulfur dioxide is produced by the combustion of fossil fuels that contain sulfur (coal, oil and natural gas), the sulfur being oxidized to produce sulfur dioxide. This is why SO 2 emissions can only be prevented by chemical binding. Oxides of nitrogen are also produced when fossil fuels are burnt. These oxides are largely the result of reactions between oxygen and nitrogen from the air. The main source of NO 2 emissions is automobiles. In 1986 alone, more than half (2 million tonnes in the former FRG) of all NO x emissions could be directly attributed to this source. In the same year, somewhat less NO x (1 million tonnes in the former FRG) was produced by power stations, distant heating plants and other conversion areas. Air pollution by CO emissions from automobiles is an even more clear-cut case. As CO is produced by the incomplete combustion of fossil fuels, it is not surprising that automobiles alone produced 6.5 million tonnes of this gas in 1986 (former FRG), while the three other user groups (industry/households, trade and business/power stations and distance heating plant, other conversion areas) are only responsible for approximately 2.5 million tonnes (former FRG). The presence of hydrocarbons (CH x ) in exhaust gases is also due to incomplete combustion. Hydrocarbons along with carbon dioxide and water vapour are also considered to be the main causes of the greenhouse effect. With hydrocarbons too, the main source of emissions is the automobile. The emission of CO and CH x from automobiles is particularly abundant when there is an excess of fuel (rich mixture, air coefficient λ<1). The introduction of catalytic converters only provides sufficient recombustion of these components in a very narrow range around λ = 1. Therefore, to obtain the most efficient combustion and the least emission of pollutants, it would seem necessary to monitor the combustion process in each cylinder of a vehicle and to control it so that the exhaust gas expelled from each cylinder has a λ value corresponding to the maximum degree of conversion for the catalytic converter. Fast λ measurements are, therefore, of crucial importance, as they make regulation possible during non-stationary phases of engine operations (starting, braking, acceleration) that account for 80% of the total operating time. Attempts are also being made to introduce combustion regulation in incinerators by means of coefficients. This type of emission would also require sensors that are capable of continuously monitoring the concentration of pollutant components. Sensor elements based on semiconducting metal oxides seem to be promising both for individual cylinder control in automobiles and for monitoring pollutant components

Dynamics of aluminum combustion

Abstract: A study has been performed modeling both steady and unsteady combustion of aluminum. Law's steadystate aluminum combustion model has been expanded to include the effects of multiple oxidizers and their products, oxide accumulation on the surface of the burning aluminum particle, and convection. Both transport and thermodynamic properties are calculated internally for varying temperatures, relaxing the normal assumption of unity Lewis number. The aluminum combustion model has been compared to experimental data from burners, laser-ignited particles, and propellant under a variety of conditions, showing a reasonable degree of agreement. Calculations with the model show that O2 is a stronger oxidizer than H2O, which in turn is stronger than CO2. The aluminum combustion model was incorporated into a computer model for predicting acoustic effects in a Rijke burner. Calculations have shown that a significant part of the increase in acousticgrowth due to the addition of aluminum is due strictly to the change in the gas temperature profile. The change in temperature profile apparently causes the location of the velocity antinode to shift relative to the Rijke burner flame and thereby cause an increase in the flame response. The acoustic model agrees reasonably well with available acoustic growth rates for data where aluminum particles have been added to a propane Rijke burner. Nomenclature ak = sum of the mole fractions of the oxidizers in Eq. (1) Cp = heat capacity, J/kg D = diffusivity, irr/s d = particle diameter, m F = ratio of total mass flux to mass flux aluminum H = total flux of energy in aluminum combustion model, W/m2; heat of reaction, J/mol j = mass flux due to diffusion, kg/m2/s k =. arbitrary constant in Eq. (1) M = nondimensional mass flux used in Law's aluminum combustion model /?2 = mass flux, kg/m2/s Nu = Nusselt number p = pressure, N/m2 Qr = heat production due to a reaction, W/m3; heat caused by radiation, W/m2 <92 = enthalpy in the region from the flame to infinity q = heat flux, W/m2 Re = Reynolds number r = radial distance, m; reaction rate, kg/mVs T = temperature, K t = time, s v — velocity, m/s; volume, m3 \v = transport property weighting factor A- = mole fraction 77 = fraction of vaporized oxide that moves toward the particle surface 0 = fraction of metal oxide that vaporizes at the flame A = fraction of metal that reacts with the particular oxidizing species v = stoichiometric mass ratio of oxide or oxidizer to metal f = fraction of condensed products with move inward or outward p = density, kg/m3 T = characteristic time lag, s

Monolith perovskite catalysts of honeycomb structure for fuel combustion

Abstract: New method of dispersed perovskites synthesis based upon mechanochemical activation of the solid starting compounds is elaborated. The influence of defect structure of these compounds as well as surface segregation on their catalytic properties is discussed. Basic stages of the monolith perovskite catalysts preparation are optimized. The experimental samples of monolith catalysts of various shapes are obtained, possessing high activity, thermal stability and resistance to catalytic poisons.

Dynamic and control of fluidized catalytic crackers. 1: Modeling of the current generation of FCC`s

Abstract: An improved and updated model for modern fluidized bed catalytic crackers (FCC) is presented. It is based on a more detailed kinetic description of the kinetics in both the reactor and the regenerator using the full range of published data both on FCC performance and kinetic rates. It includes a complete description of CO to CO{sub 2} combustion kinetics including the effect of catalytic combustion promoters. The model describes FCC operation in both full and partial CO combustion as well as the transition from one to the other. The reactor kinetics are based on a ten-lump model which allows feed and catalyst characterization based on laboratory experiments. The model overcomes some of the deficiencies and inadequacies of present models and is in good agreement with observed trends in industrial units.