摘要:

Abstract—We study the efficiency of a novel flow-type combustion system designed to bum toxic and inflammable effluent gases from a low pressure Metal-Organic Vapor Phase Epitaxy (MOVPE) reactor. The combustion reaction of the toxic and flammable gases has been optimized. We report on the kinetics of phosphine pyrolysisand oxidation, finding that for the total gas flows introduced into the combustion chamber (10-25 SLM) the transit time (≥1s) does not limit the conversion efficieney. The measured reaction's activation energy is 38 (+\· 7) kcal/mole, which is higher than values which have appeared in the literature for the combustion of phosphine and comparable to the value published for the heterogeneous decomposition of this gas.

ISSN:0010-2202    

DOI:10.1080/00102209408935365

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The inhibitory effects of CH3CI on an atmospheric pressure fuel-lean CH4/air premixed laminar flat flame are investigated through stable species (water-cooled quartz microprobe and gas chromatography) concentration measurements and detailed chemical modeling. Varying degrees of CH3CI in the feed (at a fixed π) result in consistently higher observed CO/CO2molar concentration ratios at all heights-above-burner.Modeling of these flames with detailed elementary reaction mechanisms yields predicted stable species concentration profiles which are consistent with the experimental observations. Rate-of-production analyses derived from the modeling indicates that the CI atom is a dominant radical in the CH3CI/CH4flames. Forfuel-lean conditions, the inhibitory effect results primarily from the slowdown of CO burnout by OH due to depletion of OH by HCI, which is generated primarily from fast H abstractions by CI.

ISSN:0010-2202    

DOI:10.1080/00102209408935366

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A series of measurements designed to investigate the heat feedback in pool fires burning liquid fuels are reported. Such measurements are essential for the development and validation of detailed models which predict the burning rate of liquid hydrocarbons and solid polymers. The radial variation of the local radiative and local net heat flux incident on the surface of 0.30 m diameter pool fires were measured. A water-cooled, nitrogen purged, narrow view-angle gauge was developed to measure the radiative flux incident on the fuel surface. Measurements of the mass burning rate in a burner composed of annular rings was used to estimate the local heat feedback. A number of different fuels were studied, yielding flames with a wide range of heat release rates and luminosities. Consideration of the heat balance for a control volume enclosing the liquid PPOI indicated that radiation was an important component of the heat feedback for non-luminous fires and a dominant component in luminous fires.

ISSN:0010-2202    

DOI:10.1080/00102209408935367

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A theoretical analysis is developed to study the effect of radiative heat transfer on downward flame spread over a thin fuel in low gravity. The combustion model, which is an extension of that in Duh and Chen (1991). approximates gas—phase radiation using a two—flux method applied in the cross—stream direction. Numerical results show that there is a quenching limit in the low—gravity region which is inaccessible if radiation is neglected. The main controlling factor in low gravity (g < 0.05) is the conduction to radiation parameter (N∞) where the flame spread rate increases with an increase in Nee. Also, the Darnkohler number alone is found to be insufficient to characterize the flame spread behavior. On the other hand, in higher gravity the Damkohler number becomes dominant. Parametric studies are carried out by changing the gravity level and the ambient oxygen concentration subject to gas—phase radiation. Finally, a flammability map is constructed that combines the two effects.

ISSN:0010-2202    

DOI:10.1080/00102209408935368

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An enhanced diffusion model is proposed for scalar mixing in turbulence. Using a Lagrangian frame analysis and a model simplification the enhancement in the diffusivity due to the velocity field is estimated. The model explains many of the characteristics of turbulent scalar mixing observed in direct numerical simulations.

ISSN:0010-2202    

DOI:10.1080/00102209408935369

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper presents a steady state mathematical model of a direct-fired continuous reheating furnace. The model was developed to identify the design and operating parameters that significantly affect furnace performance. The actual furnace, which requires a full three-dimensional mathematical description, is approximated two-dimensionally. The fuel and air streams enter the furnace in such a way that the load is heated by direct impingement of a turbulent diffusion flame jet. The details of the combustion space model, which includes a turbulence model and a discrete-ordinates representation of the radiation field, are provided. In addition, the results of parametric studies, in which the fuel firing rate and the load and refractory emissivities were varied, are provided.

ISSN:0010-2202    

DOI:10.1080/00102209408935370

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A textile made up of an organic-inorganic hybrid fibre containing 70% cellulose and 30% silicic acid was used as a raw material for the preparation of the thermostable support for combustion catalysts. The hybrid textile was burnt to obtain a pure knitted silica fibre. The surface area and crystallinity of this fibre was measured as a function of burning temperature. The knitted silica fibre obtained by burning the hybrid textile at 950°C was found to have sufficient strength and a high BET specific surface area (≈ 140m2/g) to be used as a support for the catalysts for catalytic combustion.

ISSN:0010-2202    

DOI:10.1080/00102209408935371

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An extensive set of flame blowout limit curves has been measured for the case of a hydrogen jet flame surrounded by a heated, supersonic, coflowing air stream and some ideas are proposed to explain the observed trends. The stagnation temperature of the Mach 2.2 air stream was varied from 294 K up to the autoignition temperature of 900 K; hydrogen injection velocities were varied up to 1191 m/s. It was found that the flame blowout curves display two distinct stable regions which are bounded by the: (a) far-field blowout limit and (b) near-field blowout limit. Far-field blowout occurs after a flame first lifts off and is associated with a sufficiently large fuel velocity; the shape of the far-field blowout curve can be explained by previous subsonic lifted flame analyses. Near-field blowout is a sudden blowout for which no liftoff occurs; it results from a sufficiently large air velocity. In all cases the flame attachment point is in the shear layer at a distance of about 1 em from the fuel tube lip.

ISSN:0010-2202    

DOI:10.1080/00102209408935372

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Kerosene-fueled flames with the spray emanating from a commercial atomizer positioned on the axis of stabilizing disks with blockage ratios of 0.74, 0.56 and 0.39 without and with a quarl diffuser are characterised in terms of flammability limits, droplet velocities according to their size, mean droplet sizes,liquid fluxes and local temperatures. Detailed measurements were obtained with a disk blockage ratio of 0.74, for an overall equivalence ratio of 0.26 and a Reynolds number of 53700 based on the area averaged velocity of the air in the annulus upstream of the bluff body and the outer diameter of the pipe. The velocities and liquid fluxes are presented for three 5 µm size classes, namely 10-15, 30-35 and 50-55 µlm, to emphasize the behaviour of small, medium and large droplet sizes in the region of flame stabilization and isothermal-flow results are presented in the absence of the quarl to allow comparison of the near disk flow with and without combustion.

ISSN:0010-2202    

DOI:10.1080/00102209408935373

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The asymptotic structure of counterflow nonpremixed methanol flames is analyzed using a reduced four-step mechanism, deduced from a starting mechanism containing twenty-seven elementary reactions. The four overall steps represent I) fuel-consumption reaction, where the fuel reacts with radicals to form H2and CO, II) water-gas shift reaction where CO reacts with radicals to form CO2, III) radical-recombination reaction, and IV) chain-branching reaction. The outer structure of the flame is the classic Burke-Schumann structure governed by the overall one-step reaction CH30H + 1.502– CO2+2H2O. The inner structure is presumed to consist of two layers, an inner layer of thickness of orderδ6, and an oxidation layer of thickness of order E. The asymptotic analysis is performed forδ ≪E ≪ 1. The structure of the inner layer is presumed to be influenced primarily by the fuel-consumption reaction and the radical-recombination reaction, and the equations governing the structure of the inner layer are similar to those for premixed, methanol flames analyzed previously using the same reduced chemical-kinetic mechanism. Therefore, results of this previous analysis modified for diffusion flames are used here. In the oxidation layer all radicals are presumed to be in steady-state, In the analysis of the structure of the oxidation layer, a parameter D appears, which is roughly proportional to the square of the ratio of the thickness of the region where the global recombination reaction occurs, to the thickness of theregion where the water-gas shift reaction is not in equilibrium. The structure of the oxidation layer is resolved by treating the quantity D to be of order unity (referred here as the full asymptotic model), and in the limit for large values of D. Results are obtained for the quantity Xq, which is proportional to the strain rate at extinction, Qq, for values of pressure p between 1 atm. and 10 atms, and for various levels of dilution of the oxidizer stream The predictions of the asymptotic models of the critical conditions of flame extinction were found to agree reasonably well with the predictions of previous detailed numerical calculations at p = 1 atm., and for various levels of dilution of the oxidizer stream. However, the deviations between the predictions of the asymptotic models and the results of the detailed numerical calculations increased with the increasing values of p. These differences are attributed to the inaccuracies associated with the asymptotic description of the inner layer.

ISSN:0010-2202    

DOI:10.1080/00102209408935374

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor