摘要:

We describe the results of 357 experimental fires conducted in an environmentally controlled large wind tunnel. The fires were burned over a range of particle sizes, fuel bed depths, packing ratios, moisture contents and windspeeds. We find that spread rate decreases with moisture content in a way which depends on the fuel type and diameter. It decreases as the square root of the packing ratio. Fuel bed depth has little effect on spread rate, and fuel diameter has significant effect only for diameters above 1 mm. The relationship between rale or spread and windspeed is virtually linear

ISSN:0010-2202    

DOI:10.1080/00102209808935753

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The laminar flamelet concept is based on the premise that scalar properties in laminar diffusion flames are nearly universal functions of mixture fraction. It has been well-tested and proven for temperature and the major species, however, few studies have addressed its applicability for minor species especially the radical species. In this study, we present a direct numerical simulation of an axisymmetric, laminar, methane-air diffusion flame to examine these universal relationships, including the major and minor chemical species, and the radical species. The numerical model solves the axisymmetric, time-dependent, reactive-flow Navier-Stokes equations coupled with sub-models for soot formation and radiation transport, and includes a detailed reaction mechanism for methane-air combustion. Quantitative comparisons with existing experimental data show a slightly wider computed flame compared to the experimental flame, however, the peak values and radial locations of temperature and soot volume fraction line up well with the experimental measurements. To study the universal relationships, scatter plots are made for temperature and the major and minor species throughout the entire flame and compared with existing experimental measurements. Excellent agreement is obtained between the computations and experiments for temperature and mole fractions of CH4, O2, OH, H2O, O, H, CO2and N2, as a function of mixture fraction in the fuel lean, stoichiometric and fuel rich regions of the flame. The computations underpredict the concentration of H2and CO in the fuel rich region, however, excellent agreement is obtained in the fuel lean and stoichiometric regions. The computations also overpredict the concentration of CH3in the stoichiometric and fuel rich regions, however, the peak concentration occurs at the same mixture fraction for both the experiments and computations. The scatter plots indicate that many of the species studied, including the minor species and radical species, can be considered universal functions of mixture fraction, however some of the species show more scatter than others. The species which showed the least scatter were those whose production rates were fastest in the stoichiometric and fuel lean regions of the flame. Those species whose production rates were highest in the very fuel rich region showed less universality with mixture fraction.

ISSN:0010-2202    

DOI:10.1080/00102209808935754

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To understand the effect of deposit in combustion chamber on engine-out hydrocarbon emissions, a two-zone model which predicts the hydrocarbon emissions contributed from combustion chamber deposits is presented and test one cylinder spark ignition engine is used to accumulate the combustion chamber deposit. The experiments are conducted on hydrocarbon emissions under various operating conditions in the presence of combustion chamber deposits. The model can successfully predict the hydrocarbons contributed from combustion chamber deposits on various engine operating conditions. The experimental results show that there exists an equilibrium thickness of deposits in combustion chamber if engine operates for a certain period of time. The combustion chamber deposits will contribute 20 ∼ 30 percent of the engine-out hydrocarbon emissions by the investigation.

ISSN:0010-2202    

DOI:10.1080/00102209808935755

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The results of infrared absorption experiments, performed on a steady, nonreacting flow of methane and argon to test a new inversion method for tomographic reconstruction of spatially nonuniform distributions, are presented. The absorption coefficient distributions to be reconstructed are expressed as a weighted sum of Karhunen-Loève eigenfunctions, formed by applying the Karhunen-Loève procedure to a training set containing aprioriinformation regarding the distributions to be reconstructed. Reconstruction of asymmetric absorption coefficient distributions is accomplished by utilizing a set of laser absorption measurements obtained using an infrared helium neon laser. Issues pertinent to the practical application of the new inversion method, such as the construction of a training set using probe sampling, the effect of experimental error, and the precise modeling of laser absoroption paths, are discussed. Reconstruction of absorption coefficient distributions from only 42 laser absorption measurements typically achieve normalized errors of 10% or less over 80% of the domain.

ISSN:0010-2202    

DOI:10.1080/00102209808935756

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We study the structure and propagation of combustion waves in thermite systems in which the heterogeneous mixture of solid reactants initially forms a solid matrix. This solid matrix is destroyed by the combustion wave as one of the reactants melts, producing a bath of one reactant in which particles or droplets of the other reactant are suspended. Gravity can lead to relative motion and hence separation of the reactants. We formulate a simplified mathematical model of this process in order to gain insight into how relative motion and separation affect the characteristics of the combustion wave. We analytically determine the structure of one dimensional uniformly propagating combustion waves and show that depending on the characteristics of the system, such solutions may fail to exist or may be nonunique. We also investigate the dependence of the combustion velocity on gravity.

ISSN:0010-2202    

DOI:10.1080/00102209808935757

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A Zone Model has been developed for the prediction of NO reduction by “reburning” in turbulent diffusion flames. The computations of fluid dynamics are decoupled from those of detailed combustion chemistry including those of the nitrogen species. The calculations begin with the computations of the stream function, heat release, temperature, and major species concentration distributions using a commercial CFD code and simple, one or two step chemistry. The modeled space is then subdivided into volume elements (zones) bounded by streamlines and some axial coordinate. The sizes of these zones are much larger than those of a computational grid so that it is practicable to use detailed chemistry for the calculation of progress of reaction within such a zone. In the experimental investigation natural gas with and without additive NH3was used as “reburn” fuel. It was injected axially into the NO bearing combustion products of a 335 kW natural gas-air flame to obtain a parabolic flow which can be modeled more easily. Detailed in-flame measurements permitted critical tests of the prediction method by the comparison of experimental and calculated data.

ISSN:0010-2202    

DOI:10.1080/00102209808935758

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This work examined the combustion behavior (flame characteristics and temperatures) and the emissions (SO2, NO, NO2, CO, CO2, polynuclear aromatic hydrocarbons (PAH), soot and ash) from blends of a pulverized bituminous coal and ground waste automobile tires. The following fuel feed compositions were examined: 100% coal, 75–25% and 50–50% coal and tire blends, as well as 100% tire. Coal and tire particles were in the size ranges of 63–75 and 180–212 μm, respectively. Combustion of cylindrical streams of particles look place under steady flow conditions, in an electrically-heated drop-tube furnace in air, at a gas temperature of 1150°C and a particle heating rate of ≈105°C/s, The bulk equivalence ratio, φ, in the furnace was varied in the range of 0.5 to 2, by varying the particle mass loading. Combustion observations on burning clouds of particles were conducted with simultaneous pyrometry and cinematography. Interparticle flame interactions were visually observed mostly in the near-stoichiometric and fuel-rich regions. Volatile flame interactions were apparent at a lower φ for tire crumb particles than for coal particles and became progressively more intense with increasing φ until, at sufficiently high φs large group flames formed for tire particles. As particle flame interactions increased, average maximum temperatures in the flame decreased. Coal particles resisted the formation of group flames, even at high φs. Such observations correlated with the trends observed for the PAH emissions of the two fuels, those of tire crumb being much higher than those of coal and commencing at a lower φ. A certain degree of stratification in the combustion of blends of particles of the two fuels was observed. This kept the PAH emissions at levels much lower than those expected based on the weighted average emissions of the two fuels. NOxemissions from tires were much lower than those of coal, while those of the blends were close to the weighted average emissions. Combustion or fuel blends in the two aforementioned particle size cuts, generated the lowest NOxemissions when the small coal particles were combined with either the small or the large tire particles. SO2emissions from the blends were found to be close to the weighted average emissions of the two fuels. Blending coal with tire reduced the CO2emissions of coal but increasedtheCO emissions. CO emissions were significant only in the fuelrich region. Tire ash was of similar size and shape as the parent tire particles themselves. To the contrary, the ash of coal was polydisperse, including large cenospheres and tiny particle fragments. Particulate emissions (soot and ash), measured in the range of 0.4 to Sum, increased with φ. Generally, tire produced more mass of submicron particulates than coal. Particulate emissions of blends of the two fuels were close to those expected based on weighted average of the two.fuels,

ISSN:0010-2202    

DOI:10.1080/00102209808935759

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To estimate the inhibition effect of some polyfluorocarbons containing N, O, or S atoms such as (CF3)3N, (CF3)2NCF2H, (C2F5)2O, CF3SF5, and C2F5SF5on flame propagation, the laminar burning velocity was measured for mixtures of 9.50 vol% methane, 90.00 vol% air, and 0.50vol% inhibitor and of 1.87 vol%n-heptane, 97.63 vol% air, and 0.50vol% inhibitor. The five compounds have higher ability as fire suppressants than CF3CHFCF3and CF3H, which have already been put to practical use.

ISSN:0010-2202    

DOI:10.1080/00102209808935760

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In pulverised coal flames, the most important volatile nitrogen component forming NOx, is HCN. To be able to model the nitrogen chemistry in coal flames it is necessary to have an adequate model for HCN oxidation. The present work was concerned with developing a model for HCN/NH3/NO conversion based on systematic reduction of a detailed chemical kinetic model. Models of different complexity were developed and tested under conditions similar to those in a pulverised coal flame. Comparisons of the models were made for ideal chemical reactors simulations (plug flow reactor and well-stirred reactor). Provided that the CO/H2chemistry was described adequately, the reduced HCN/NH3/NO model compared very well with the detailed model over a wide range of stoichiometries. Decoupling of the HCN chemistry from the CO/H2chemistry resulted in over-prediction of the HCN oxidation rate under fuel rich conditions, but had negligible effect on the CO/H2chemistry. Comparison with simplified HCN models from the literature revealed significant differences, indicating that these models should be used cautiously in modelling volatile nitrogen conversion.

ISSN:0010-2202    

DOI:10.1080/00102209808935761

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A systematically derived model is presented for the turbulent combustion of CO/H2-air mixtures in diffusion flames with high mixing rates. The mixing of fuel and air is expressed by a mixing variable. The conversion of CO to CO2, of H2to H2O and of the non-equilibrium intermediate species concentrations are determined by two reaction progress variables. The thermal NO production is calculated in a postprocessing step. In the paper the turbulent source terms in the transport equations for the scalar variables are discussed. A case of a turbulent CO/H2diffusion flame with chemical super-equilibrium of intermediate species is presented. The influence of the intermediate species HO2an H2O2on the simulated characteristics of the flame is investigated.

ISSN:0010-2202    

DOI:10.1080/00102209808935762

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor