摘要:

—It is known that, for nozzle diameters greater than some critical value, free jet flames remain stable at all driving pressures. For releases from orifices smaller than this limiting diameter, subsonic jet flames become unstable when the exit velocity is increased above some blow-out stability limit. In these unstable jet flames, it has been postulated that flow conditions suitable for stable flame formation may be obtained by increasing the driving pressure to produce a supercritical (choked and underexpanded) jet. This paper presents an experimental study of the flame blow-out stability limits in high pressure natural gas jets. The critical diameter for unconditionally stable flames is determined and the postulate of high pressure restabilisation confirmed. Also, previous work on the probabilities of subsonic jet light-up resulting from a localised ignition has been extended to supercritical jets. It is shown that anyignition at or beyond that axial location associated with the lower flammable limit cannot result in the establishment of a stable flame.

ISSN:0010-2202    

DOI:10.1080/00102208808923967

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

—Soot inception in pyrolysis and combustion occurs via high temperature molecular growth processes. While the subsequent steps of soot surface growth, agglomeration, aggregation and oxidation have been extensively investigated, relatively little knowledge of the soot inception chemistry exists. This kind of molecular level understanding is needed to provide a basis for intervening to mitigate the soot formation process. The present study focused on the molecular precursors of soot in a variety of hydrocarbon/oxygen/nitrogen flames. A Wolfhard-Parker type two-slot burner was used to establish stable vertical laminar diffusion flames. Methane, ethane, ethylene, acetylene and 1,3-butadiene were used as fuels, alone or in mixtures. Quenched probe sampling of the pyrolysis zone on the fuel side of these flames for gas chromatographic analysis shows that the principal stable products are ethane, ethylene, acetylene, methylacetylene, diacetylene, vinylacetylene, butadiene and benzene. The relative amounts of these species vary with the type of fuel molecule used. For example, ethane is a significant intermediate in methane diffusion flames, because of the recombination of methyl radicals present in high concentration. The methyl radicals are also responsible for the relatively high concentrations of methylacetylene observed in methane flames, but not with other fuels. With diffusion flames containing unsaturated molecules in the fuel, sharp increases in the concentration of. acetylenes was observed relative to methane flames. Probing normal to the vertical flame front across steep concentration and temperature gradients, the first visually observed onset of soot formation is at the location of sharp increases in the concentration of molecular intermediates. Methane flames doped with acetylene, 1,3-butadiene and mixtures or these unsaturates show that both are essential for the formation of benzene, the first aromatic soot precursor. These studies, combined with detailed flame structure studies of soot and soot precursor formation should lead to an improved understanding of the chemistry of soot inception.

ISSN:0010-2202    

DOI:10.1080/00102208808923968

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The details of a numerical simulation of particle size distribution evolution during ash-free char oxidation are presented. This work represents the first application of the population balance modeling approach to char combustion, and includes the effects of both oxidation and fragmentation. The simulation consists essentially of a transfer function 'hat determines the evolution of the entire char particle size distribution with lime. Determination of the input parameters to the model, and the sensitivity of the results to variations in these parameters are discussed.

ISSN:0010-2202    

DOI:10.1080/00102208808923969

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A numerical model of a pulse combustor has been developed to simulate the nonlinear wave motion resulting from the periodic combustion process. The wave pattern is followed in time by integrating the unsteady, one-dimensional equations of continuity, momentum and energy for vairable-are geometry, including losses due to friction and heat transfer. The resulting periodic wave pattern is governed by the pulse combustor geometry, the fuel mixture, and the combustion and injection processes. The simplified pulse combustor used in in this paper coasists of a combustion chamber and tail pipe joined by a short transition section. The resulting periodic wave patern is governed by the pulse combustor geometry, the fuel mixture, and the combustion and injection processes. The simplified pulse combustor used in in this paper coasists of a combustion chamber and tail pipe joined by a short transition section. The model for the combustion process is guided by experimentally obtained chemiluminescence measurements taken in an operating pulse combustor of similar design. The injection of fuel and an is also prespecified by experimentally measured rates.

ISSN:0010-2202    

DOI:10.1080/00102208808923970

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A novel way of dynamically stabilising an upwards propagating curved flame in a tube is presented. The method is optical and non-perturbntinp. Shape and velocity field measurements are reported and hriefly discussed in the light of existing theories. Extinction of the centre of the flamc through stretch effects has also been observed.

ISSN:0010-2202    

DOI:10.1080/00102208808923971

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor