摘要:

The flammability limits of methane have been reinvestigated by using the AC discharge ignition method. This work has partly been motivated by the necessity of evaluating the flammability characteristics of CFC alternatives. In the study, the effects of spark duration time and spark gap on the flammability limits of methane have extensively been explored. The resulting flammable range tends to become wide if the spark duration time is too long and/or the spark gap is too large. The effects of inadequate spark duration time and spark gap are exaggerated if the height of the experimental vessel is too small. As a result, the spark duration time of 0·1–0·2 sec combined with the spark gap of 6–8  mm has been found to make an optimum condition for the correct measurement of the flammability limits by the AC discharge ignition method.

ISSN:0010-2202    

DOI:10.1080/00102209908924200

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study aims to investigate surface catalytic reaction and flame combustion of lean premixed mixture in CST (catalytically stabilized thermal) combustor that consists of a catalyst bed and a thermal combustor. Two types of CST combustor, Pd catalyst (one stage) and Pd/Pt catalyst (two stages), were tested. After surface ignition, two systems showed different behaviors in the temperatures of the catalyst bed. The temperature of Pd catalyst system remained at almost the constant temperature, 78O–790°C, insensitive to the preheat temperature. However, the temperature of Pd/Pt catalyst increased steadily with the preheat temperature. Pd/Pt catalyst system had a lower preheat temperature for flame ignition in the thermal combustor than the Pd catalyst system. The lean flammability limit of CST combustor was also investigated. The lean combustion supported by surface catalytic reaction was more stable than flame combustion alone.

ISSN:0010-2202    

DOI:10.1080/00102209908924201

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Laser-desorption time-of-flight mass spectrometry (LDMS) was used to analyze soot collected from seven different hydrocarbon fuels (methane, n-hexane, n-heptane, n-octane, n-decane, benzene and toluene) burning with air under normal atmospheric pressure. To evaluate the technique, samples of two different types of furnace blacks, two types of graphite, a synthetic diamond and a C70fullerene also were analyzed. With proper experimental design, the C70produced a single peak of mass 840 Da, thereby showing the ability of LDMS to remove and singly ionize large intact molecular species from the sample for the purpose of chemical analysis. The LDMS soot analysis showed that each mature soot has a unique chemical fingerprint. A family of fuels (e.g., normal alkanes) produces soot that is similar in appearance when mature and that therefore might be expected to yield similar mass spectra, but it is found instead that each spectrum has unique features that are different for each parent fuel. These initially surprising results point to the need for further study of fuel pyrolysis in flames.

ISSN:0010-2202    

DOI:10.1080/00102209908924202

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper gives a detail investigation about the trace elements (TEs) in typical Chinese coals, TEs partitioning during combustion and their different environment impacts. Firstly, it is determined that the contents of 9 TEs (As, Be, Cd, Co, Cr, Cu, Ge, Ni, Pb) and 3 sulfur species (sulfate SO4, sulfide S2−and Organic S0) in 7 density fractions of Qingshan bituminous coal, and the TEs occurrence mode is studied with Solari (1989) model. Moreover, the contents of 12 TEs (including above-mentioned 9 TEs and Mn, V, Zn) in 7 Chinese typical coals are determined and che-momelric methods (factor and cluster analysis) are used to investigate the TEs combination in these coals. Secondly, 8 fly ashes with 4 sizes are sampled during Qingshan bituminous coal combustion in a thermal power plant. Higher temperature and reducing atmosphere are found to enhance greatly the metals enrichment in the submicron and micrometer panicles. An enrichment coefficient is used to describe the TEs partitioning in the fly ash size-fractions and the results are discussed according to three factors: TEs combination in coals, combustion condition in a combustor. and fly ashes size. Finally it is also studied, by the sequential extraction analysis, that the TEs speciation in ashes (dregs and fly ashes) from Qingshan bituminous coal combustion, in order to assess reasonably the TEs environmental impacts.

ISSN:0010-2202    

DOI:10.1080/00102209908924203

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

For a more extensive investigation of polymers, a better understanding of its gasification process is extremely essential. Especially compared with the extensive studies in the gas phase, the solid phase received rather little attention. Thus, the purpose of this paper is in its comparison of several modeling approaches for thermal degradation and systematic demonstration of the effects of basic assumptions on the model results, while taking account of in-depth radiation. For this object, this study has examined in more detail the degradation for a horizontally positioned polymer which is exposed to external radiation. After a preliminary study, three different solid degradation models were chosen from the literature, and their corresponding mass and energy conservation equations and boundary conditions were assembled. The in-depth non-gray as well as gray radiation was taken into account by solving relevant radiative transfer equation. In order to concentrate on the fundamental mechanisms of polymer degradation, gas phase reactions and subsequent heat feedback from the gas were neglected. This corresponds to a nitrogen environment. Various other parameters such as the polymer refractive index, polymer absorption coefficient, convective heat loss, solid fuel thickness and external radiative heat flux were changed to discuss their effects on the quantitative as well as qualitative change in the mass loss rate. While the effect of the solid fuel thickness on the mass loss rate was negligible for a thick sample, each parameter among the polymer refractive index, polymer absorption coefficient, convective heat loss, and external radiative heat flux incurred a non-negligible change in the results. Furthermore, the convection term in the energy equation, which is usually neglected in the in-depth pyrolysis by many other works, was shown to account for 29% decrease in the mass loss rate. Finally, depending on the solid degradation model used, the addition of gray radiation to the energy equation was shown to augment or diminish the mass loss rate. It was further enhanced by taking account of the non-gray radiation. This results from the fact that the inner solid is more quickly heated due to the far-reaching effects of radiation from the surface.

ISSN:0010-2202    

DOI:10.1080/00102209908924204

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor