摘要:

Measurements of soot concentrations in diffusion flames of ethylene and ethane are presented over a wider range of length and time scale than previous experiments. In the past, this type of data has been examined in terms of fuel to soot conversion fractions as functions of local flame variables such as equivalence ratio and temperature. Here, instead, we examine the total soot mass produced from flames of lengths 4-95cms and find that the growth region is described by a continuous function of time independent of flame size and local stoichiometry for the particular fuel. Soot mass flow varies as time to a power of 2-3 for the fuels tested. This result is considered in terms of gas-particle collision rates as the soot growth rate determining process.

ISSN:0010-2202    

DOI:10.1080/00102209108924086

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A non-intrusive technique for measuring the concentration of gaseous species in reacting and non-reacting sprays is presented. Infrared absorption is the basis for the measurement. In a two-phase situation. the light scattered by particles can be deduced by measuring extinction of wavelengths at which no absorption occurs. As a result. combined infrared extinction and scattering (IRES) is employed for two-phase flows. The technique. although based on line-of-sight absorption. has the potential to be spatially-resolved for either symmetric or asymmetric fields depending upon the deconvolution technique applied. The technique is demonstrated using a single phase methanol vapor/air free jet and non-reacting and reacting methanol sprays. To complement these results. measurements of droplet size and velocity as well as gas velocity can be achieved using other non-intrusive approaches such as phase Doppler interferometry. These complementary measurements may be combined with the concentration measurements to quantify vaporization. The results illustrate the applicability of this relatively inexpensive and simple technique which adds valuable information to the study of sprays.

ISSN:0010-2202    

DOI:10.1080/00102209108924087

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper describes a U.S. Bureau of Mines investigation of large-scale coal dust explosions in an experimental mine using a high speed clectropneumatic mechanism for the rapid grab-sampling of gases and dusts. This technique enables themonitoring of pyrolysis and charring in fuel dust particles, and the collection of gaseous combustion products, in both large and small-scale explosions. Data obtained from full-scale dust explosion tests at the Bureau of Mines Lake Lynn Test facility show the following: Rapid sampling appears to “freeze” the burned gas compositions at the flame temperature values.Gas samples taken entirely in the flame zone consist of pyrolysis and combustion products with very low residual oxygen.The particles collected in the flame zone show signs of extensive pyrolysis and charring. Measurements of gas concentrations and particle flame temperatures suggest that char burning may have occurred in the flame zone.

ISSN:0010-2202    

DOI:10.1080/00102209108924088

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Detailed measurements of soot volume fraction, mixture fraction and temperature arereported in a laminar diffusion flame, fuelled by pre-vaporised kerosine and supported ona pressurised WolfhardParker burner. The distributions of these properties in the flameflowfield are simulated computationally and the key parameters in a simplified model of soot formation determined. The model formulation, incorporating the processes of nucleation,surface growth and coagulation, is tailored for subsequent application to turbulent flameprediction.

ISSN:0010-2202    

DOI:10.1080/00102209108924089

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The flow fields were measured for the stretched cylindrical premixed flame and the counterflowtwin flames with stoichiometric methane-air mixtures using LOV. A quantitative comparison of the flowstructure was made based on the actual velocity gradients and flame stretch rates. The similarity betweenthe flow structures for both flame types was clarified over a wide range of velocity gradients. The extinctioncharacteristics were compared with each other and it was shown that the cylindrical flame was extinguishedat a lower velocity gradient and a lower stretch rate than the twin flames. The flame diameter of thecylindrical flame at the state of flame extinction was larger than the flame distance for the twin flames. Themechanism behind these characteristics was discussed from the view point of investigating the effects ofhigh curvature on the extinction for highly stretched flames.

ISSN:0010-2202    

DOI:10.1080/00102209108924090

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The experimental and numerical studies of the boundary layer diffusion flame over a porous plate have been conducted for two different flows in the presence and absence of flow separation. The present study investigates the local acceleration induced by flame and the interaction between separation of flow and diffusion flame. The main conclusions are summarized as follows: In the flow without flow separation, positive local acceleration makes the distortion and the overshoot of velocity in the boundary layer with diffusion flame. In the flow affected by flow separation, the effect of chemical reaction suppresses the tendency for flow separation. In the case of a lower fuel mass flux, a less active chemical reaction does not overcome the influence of flow separation, therefore separation bubble still exists and velocity overshoot could not be observed. On the other hand, a more active chemical reaction in the case of a higher fuel mass flux changes the pressure distribution as the favorable gradient so that the positive local acceleration makes the velocity overshoot downstream.

ISSN:0010-2202    

DOI:10.1080/00102209108924091

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Nitric oxide formation in laminar, adiabatic, stoichiometric. premixed CH4-air flames wascalculated over a range of pressures from 0.1 to 20 atmospheres. The detailed kinetics model (46 speciesand 212 reversible reactions) included four chemical pathways to NO formation, and the relative importanceof these pathways was found to vary with pressure and with position in the flame. In the flamefront,the rates of the Zeldovich mechanism and the N20 intermediate mechanism were increased substantiallyby the presence of superequilibrium °atoms. The Fenimore mechanism also contributed substantialamounts of NO. In the postflame gases, the calculations suggested that most of the NO was formed fromthe Zeldovich mechanism, but the N20 intermediate mechanism became important at high pressures whereit contributed as much as 10% of the postflame NO. Experimental measurements of superequilibriumradical concentrations and ffamefront NO formation are clearly essential to confirm the suggested importanceof superequilibrium (0) concentrations and the N20 mechanism for NO formation in high pressureflames.

ISSN:0010-2202    

DOI:10.1080/00102209108924092

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The theory of large activation energy asymptotics is used to model the interaction of pressure disturbances characterised by different length scales with conventional flames. Byconventional flames it is understood that the deflagration Mach number is low and of the order of where 0 is the non dimensional activation energy and s is a positive power arising from the detail of a (global) kinetic scheme.

ISSN:0010-2202    

DOI:10.1080/00102209108924093

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Two ignition criteria. Scmenov-Frank-Kamenetski (SFK) and van't Hoff. are examined for homogeneous-heterogeneous reactions using the parameter continuation technique and bifurcation analysis. The model and parameters are based on the propane oxidation in air with simplified kinetics for stagnation-point flow.

ISSN:0010-2202    

DOI:10.1080/00102209108924094

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Flames in narrow clearances are studied by using a spectral infrared imaging method and some of the results are reported herein. The spectral band employed in the method is a 2–2.5 micrometer band, which is to capture the spatial and temporal distributions of radiation emission from water vapor present over the flame fronts. The infrared radiation image was obtained using our new high-speed imaging system which enables us to achieve a framing rate of over 1,800 frames/sec with exposure period of as short as 20 microseconds that employs a 64 × 128 PtSi Schottky barrier imager. The infrared images of water vapor emission from flames in narrow clearances offer some new findings not attainable in the previous schlieren cinematographic imaging.

ISSN:0010-2202    

DOI:10.1080/00102209108924095

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor