摘要:

Motivated by the importance of soot to the emission of particulates and other pollutants from combustion processes, current understanding of soot morphology and optical properties is reviewed, emphasizing nonpremixed flame environments. The understanding of soot morphology in flames has grown rapidly in recent years due to the development of methods of thermophoretic sampling and analysis by transmission electron microscopy (TEM). The results show that soot consists of nearly spherical primary particles, having diameters generally less than 60 nm, which collect into open structured aggregates that are mass fractal objects. Aggregates grow by cluster/cluster aggregation to yield broad aggregate size distributions with the largest aggregates containing thousands of primary particles and reaching dimensions of several urn. The optical properties of soot aggregates generally are not suited for the Rayleigh and Mie scattering approximations which has led to the development of approximate Rayleigh-Debye-Gans (RDG) scattering models for polydisperse fractal aggregate populations of soot Evaluation of RDG models for conditions where both soot structure and scattering properties are known indicates encouraging agreement between predictions and measurements at both visible and infrared wavelengths, as well as reasonable accuracy for Rayleigh scattering theories in the infrared. Thus, there is potential for nonintrusive measurements of both soot concentrations and structure in flame environments, which should be helpful for diagnosing problems of particulate and pollution emissions from combustion processes. However, additional work is needed to realize this potential, including: reliable solutions of the inverse problem, to yield soot properties from scattering and extinction measurements, must be developed; existing uncertainties about soot refractive indices, including effects of fuel type and flame conditions, must be resolved; and more definitive assessment of the limitations of existing approximate theories for soot optical properties must be obtained.

ISSN:0010-2202    

DOI:10.1080/00102209508960399

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A comprehensive study of ammonia oxidation in laminar flames and Sow reactors using detailed chemical kinetic modelling is reported. A flat premixed NH3/NO flame and counterflow CO/O2/N2and CH4/O2/N2diffusion flames doped with ammonia have been studied along with NH3/NO/O2and NH3/NO/O2/C2H6flow reactors. Available kinetic data has been reviewed and a detailed reaction mechanism for the C/N system is proposed and results from computations are compared with experimental data. The destruction and formation of NO is found to be dominated by NH2, NH and N radicals in most of the cases studied. It is shown that the relative significance of the different NH, radicals in the various NO formation channels depends entirely on the flame conditions and that the role of the amidogen is crucial in nitric oxide reduction.

ISSN:0010-2202    

DOI:10.1080/00102209508960400

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The accuracy and precision of a sizing anemometer, based on diffraction of light from a laser beam of 240 μm diameter and 514.5 nm wavelength at a collection angle of 3.82° with a central “pointer volume” formed by a laser Doppler test volume of 41 μm diameter and 488 nm wavelength and using non-spherical coal particles, have been evaluated experimentally. The required independent measurement of the coal particle size was based on an aerodynamically determined diameter which was related to the measured exit velocity of the coal particles at the exit of a rapidly converging nozzle. The accuracy and precision were found to be +2, +7, −20 μm and ±2, ±7, ±10 μm, respectively, for mean values of 15,30, 60 μm at a coal feeding of 0.0133(g/min), corresponding to a number density of 7.1-10−10(m−3. The poor accuracy for the largest si2e is due to saturation of the sizing photodetector. The accuracy and precision became worse by 10% and 50%, respectively, when the feeding rate increased by a factor of 35 and thus when the number density also increased from 7.1-10−10to 2.5 · 10−8. The application of the instrument is illustrated by simultaneous measurements of size and velocity in a small scale, 11.3 kW, burner operated at a swirl number of 0.5 and piloted by a gas pilot flame supporting a 0.24 g/min coal Same. The mean velocities showed that particle size classes characterised by mean diameters of 12 and 36 μm recirculated while those of 64 μm penetrated the recirculation zone. The arithmetic and Sauter mean diameters decreased with axial and radial distance, primarily due to the centrifuging effects of the swirl air.

ISSN:0010-2202    

DOI:10.1080/00102209508960401

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Control of the unreacted fuel would reduce total hydrocarbons from engines, therefore it is necessary to understand the mechanism of exhaust hydrocarbons from spark ignition engines. The authors of this paper would like to pay close attention to the effects of a ring crevice. The fuel-air mixture supplied to a spark ignition engine is compressed into the ring crevice in the compression stroke. The unreacted fuel within the crevice is exhausted in the expansion stroke, if the flame cannot enter the inside of the crevice. The purpose of this work is to separate the effects of the ring crevice on hydrocarbon emission from the other effects, so that the authors have proposed an element model for estimating the in-cylinder oxidation of the hydrocarbon from the crevice. To verify propriety of the theoretical model, the authors have also carried out the experiment with the linear crevices, different from a normal ring crevice, mounted on the piston top, and have obtained the agreement of values between the experimental and the theoretical results.

ISSN:0010-2202    

DOI:10.1080/00102209508960402

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

During the first week of April, 1991 the Wisconsin Department of Natural Resources (WDNR) conducted a series of air emissions tests of a small industrial wood-fired boiler in northern Wisconsin. The boiler was firing a virgin hogged wood/wood waste fuel with a moisture content of about 35 percent The pollutants measured were particulates, nitrogen oxides (NOx), carbon monoxide (CO), total hydrocarbons (THC), benzene, formaldehyde (CHOH), polycydic organic matter (POM, eg. benzo (a) pyrene), aldehydes, and trace metals (As, Ba, Cu, Pb, Mn, Ni, K. Se, Na, and Zn)

ISSN:0010-2202    

DOI:10.1080/00102209508960403

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The use of pure oxygen in the combustion of fossil-fuels is fuelled by the Urge potential for NOxreduction. This paper describes experiments conducted on a semi-industrial scale test furnace using a single oxy-natural gas burner. The burner was operated in two modes: the oxygen acting as the high velocity fluid, entraining the fuel gas into the flame, and vice versa. A steam-cooled gas-sampling probe was employed allowing gas samples to be taken from inside the furnace. Temperature and species concentration, including NOxwere measured and were corroborated by numerical predictions. This study investigated two main areas, (a) the influence of mixing on the flame characteristics and the formation of nitric oxide in semi-industrial scale burners at high temperature combustion and (b) verification of the model used for high temperature combustion processes. The numerical analysis indicates that reasonable agreement can be obtained for the gas temperature and species concentration, using a 4-step reaction mechanism for the combustion process. The temperature predictions appear to be accurate within ± 50 K and computed NOx, emissions differ at most by 20% from measured NOx, levels. This study shows that NOx, emissions are influenced by the mixing of oxygen and fuel and injection angles. Also fast combustion produced a higher flame temperature and complete combustion but resulted in lower NOx, emissions.

ISSN:0010-2202    

DOI:10.1080/00102209508960404

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The salient fundamental factors that influence the design of low NOxburners and of NOxabatement schemes are reviewed. They have been examined through laboratory combustor studies, which simulate some of the salient features of practical systems, while still preserving flexibility and the ability to extract mechanisms. These studies have shown that coal ignition properties and flame attachment to the burner have great influence on coal nitrogen convention to NOxin axial turbulent diffusion flames. They have also shown that distributed air addition is more effective at reducing NOxformation than simple air staging, and these results conform to field data from full scale applications

ISSN:0010-2202    

DOI:10.1080/00102209508960405

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper deals with the numerical modelling of heavy residual fuel oil combustion. Some results of combustion-generated nitric oxide and coke are presented. The emissions of both species are greatly affected by a gas temperature and thus the modelling of soot concentration, which affects radiation heat transfer is of vital importance. The calculated results of three combustion cases, the thermal inputs of which are 1.8,3.5 and 36 MW, respectively, are compared with the measured ones

ISSN:0010-2202    

DOI:10.1080/00102209508960406

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper reports the application of a full three-dimensional mathematical model to a fuel-oil fired power station boiler of the Portuguese Electricity Utility. Special emphasis is placed on the formation of nitric oxide. Models for thermal and fuel-NO formation are included and several variants of the models are employed. The predicted results are compared with measurements. Concentrations of O2, CO2and CO are in good agreement with the data whereas the temperature, although in qualitative agreement, is underestimated along the profile crossing the flame region. It is shown that fuel NO is an important source of the total NO formed. Nevertheless, the NO mole fraction is underestimated. Several hypotheses were checked to identify the source of discrepancy and the most probable ones are the temperature underestimation in the flame region and the experimental uncertainties.

ISSN:0010-2202    

DOI:10.1080/00102209508960407

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Mathematical modelling and simulation can be used to assess the effect of modifications of the combustion process and pollutant formation. In this paper two pulverized coal combustion plants are considered. The first plant is a bituminous coal-fired furnace with eight swirl burners and a thermal power of 490 M W. In order to reduce NOx-formation, the furnace system was modified using a different burner design and a modified burnout air arrangement for realizing the staging of combustion air. Both cases were investigated. The second plant is a brown coal-fired furnace with an electric power of 150 MW. The goal was to reduce CO-emissions and to improve the burnout of the coal. For a more flexible discretization of the domain a method was developed which allows that each burner can be discretized by an independent grid system. Using this method, details of the burner geometry can be considered and the governing processes of pollutant formation in the near-burner zone may be described in more detail.

ISSN:0010-2202    

DOI:10.1080/00102209508960408

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor