摘要:

Tests were conducted with a naturally staged, axial jet burner firing pulverized coal to evaluate near burner combustion modification alternatives for controlling NOxemissions to ultra low levels in a combustor operating with hot, running slag walls. The study focused on the use of small amounts of natural gas rather than swirl air to aid the stabilization of the axial pulverized coal flames. The relative importance of primary jet velocity and primary air stoichiometyr were determined for these gas stabilized flames. Decreases in primary jet velocity had a dramatic effect on near burner NO production while primary air stoichiometry appeared to have a negligible effect. Another near Burner modification, the use of a vitiated secondary air stream, did not significcantly affect NO levels. Ultra low No levels (below 90 ppmv) were achieved in theis hot-walled combuster by optimizing the performance of the gas stabilized burner in conjunction with staged combustion and reburning.

ISSN:0010-2202    

DOI:10.1080/00102209708935666

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Flame acceleration experiments were performed in hydrogen-air and hydrogen-air-steam mixtures in a 1.5m-diameter, 5.7m-high cylindrical vessel, fitted with repeated obstales, to investigate the effects of obstacles on combustion behavior. The obstacles were made of 16.5cm-outer-diameter aluminum pipes. The study included a hydrogen concentration range of 10 to 20%, steam concentrations of up to 40%, obstacle spacing of0.55m to 1.1m, and flow area blockages of 10% and 28%. The experiments were performed at an initial temperature of 128°C and an initial pressure of 100kpa.

ISSN:0010-2202    

DOI:10.1080/00102209708935667

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In this work, we model the transient pyrolysis of a slab of polymer of finite thickness subjected to irradiation in which heat is supplied uniformly to the surface of the polymer. The sample of polymer is located on a substrate. The temperature of the polymer rises and it undergoes pyrolysis when the material reaches a critical temperature. A pyrolysis front then develops as a moving boundary. We investigate the effect of the sample thickness on the regression rate of the moving boundary in the case where no char is formed. The result was presented in terms of the pyrolysis of polyethylene on an aluminium substrate. Further investigation was done on the effect of the formation of a char layer on the regression rate of the moving boundary.

ISSN:0010-2202    

DOI:10.1080/00102209708935668

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Visual observations, high speed movie sequences and image processing techniques have been used to examine unconfined vertical lifted turbulent diffusion flames issuing from precessing jeta (PJ) nozzles. These techniques provide qualitative information about the dynamic motions in the flame and quantitative data on the size and number of flame structures, the celerity of those structures, flame dimensions, residence times and characteristic strain rates. The information is used to provide new insight into the flame stabilisation mechanism of, and combustion processes occurring in, a PJ flame and to enable a comparison with similar studies in free turbulent jet diffusion flames and pool fires. Large-scale structures are seen to form near to the base of the PJ flame and move downstream with a slow, nearly constant speed in a manner reminiscent of the puffing motions in a pool fire. The entrainment and mixing of these structures is such that the flame tip oscillates as the residual unburned mixture in each structure, becomes combustible and burns out rapidly as a single entity. It is proposed that the puffing motions in these unconfined flames are the result of a buoyant instability, which is analogous to that in a pool fire. However the buoyant puff structures are the result, not the cause, of the stabilisation process. The high stability of the PJ flame, previously reported, is deduced to be related to the rapid decay in jet velocity and to the increase in entrainment which occurs in and upstream from the stabilisation region. The frequency of puffing is found to be uncorrelatetagging.bd with the frequency of precession. Global residence times and characteristic rates of shear are also measured and found to be reduced relative to those in a simple jet flame. The implications of the reduced shear on models of NOxgeneration in jet flames is discussed.

ISSN:0010-2202    

DOI:10.1080/00102209708935669

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The pyrolysis of general biomass materials is modeled via a superposition of cellulose, hemi-cellulose and lignin kinetics. All three of the primary biomass components are modeled with multi-step kinetics involving both competetive primary pyrolysis and secondary tar decomposition reactions. Only “typical” (untreated) feedstocks are considered at atmospheric pyrolysis pressures. The kinetics scheme is then coupled to the porous particle model of Miller and Bellan (1996) along with appropriate properties and heats of reaction to provide a complete model for the pyrolysis of arbitrary biomass feedstocks and sample sizes. Comparisons with past isothermal and thermogravimetry experiments for a variety of biomass materials under both kinetically controlled and diffusion limited conditions show favorable agreement with the model predictions. In addition, discussions are provided which support the use of competetive char production kinetics over single and successive reaction schems which cannot currently be reconciled with observed pyrolysis behavior.

ISSN:0010-2202    

DOI:10.1080/00102209708935670

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Soot formation during isothermal pyrolysis of naphthalene, anthracene and pyrene was investigated. The particle number density of soot aerosol formed was demonstrated to depend linearly on hydrocarbon concentration. The equations to calculate the particle number density and the soot surface area were obtained. Particle number densities of the soot formed during pyrolysis of polycyclic aromatic hydrocarbons were demonstrated to be an order of magnitude higher and the apparent activation energy of soot aerosol formation is two times less than the parameters obtained during pyrolysis of benzene or acetylene. Sooting tendency of the hydrocarbons investigated as relative to methane can be arranged at 1623 K as follows: methane: ethylene: acetylene: diacetylene: benzene: toluene: p-xylene: naphthalene: anthracene: pyrene: 1: 4: 7.6: 50: 7.4: 5.5: 4: 112:91: 74.

ISSN:0010-2202    

DOI:10.1080/00102209708935671

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The characteristics of thermally stabilized flames of premised propane and air flowing inside an adiabatic refractory tube were investigated numerically. The effect of various parameters such as the mass rate of flow W, the thermal conductivity of the tube wall kw, the equivalence ratio Φ and the tube length / on the flame front was studied for the stable states of combustion at multiple locations. The results are quite different from those for conventional combustion.

ISSN:0010-2202    

DOI:10.1080/00102209708935672

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The Successful utilization of premixed oxygen/acetylene flames in the chemical vapor deposition of diamond has led to an interest in scaleable configurations, realized in this work using a stagnation-flow reactor. through a computational model that incorporates detailed gas-phase kinetics, molecular transport, and surface chemistry, the roles of process varibles such as flame stoichiometry, rate of strain, and the use of flow diluents are explored. For parameterization, we have characterized diamond deposition using the surface fluxes of atmoic hydrogen and methyl radical, and have correlated the modeling results with experimental data from a scaled-up stagnation-flow reactor. Flame temperature, stoichimetry, and diluent addition were found tohave a strong effect on diamond film quality. Modeling results are presented, and the utility of the flame model in conjuction with an experimental diamond deposition study is demonstrated.

ISSN:0010-2202    

DOI:10.1080/00102209708935673

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A formation of pockets, explained by a passive front model, is controlled by breaking a vibrating air/methane flame at its top. Three types of pockets were observed droplet-shaped, spade-shaped ' and string-shaped. Using a near stoichiometric mixture, droplet-shaped pockets were quantified at 0.355 atrti. From either their hydraulic diameter, or their axisymmetrical volume and area, global quantities such as stretch K, burning velocity Sd and curvature Co are obtained. Sd, at least twice the laminar burning speed SL, reaches a maximum ranging from 3.5 SL, to 6.4 SL. K is correctly expressed by the product - Sd Co; from Poinsot el al. correlation connecting burning velocity to high curvature and strain, global relations written between Sd and K, and Sd and Co on the other hand, concur with data. A minimum experimental diameter at the final stage of combustion is found; its value is consistent with that of minimum diameter given by Poinsot et al.

ISSN:0010-2202    

DOI:10.1080/00102209708935674

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

An apparatus has been designed, built, and extensively tested for making short-duration autoignition temperature measurements of hydrocarbon fuels under atmospheric pressure conditions where the fuel/air stoichiometry, the nature of the hot metal surface, and the contact time between the fuel/air mixture and the heated surface are well controlled. This approach provides a much more reliable database to establish the importance of fuel structure and surface effects on measured autoignition temperatures than the current ASTM E659 procedure, which involves variable ignition delay times and unspecified stoichiometries for ignition in a heated glass flask. Two series of tests have been conducted: (1) over 1100 individual autoignition temperature determinations for the ignition of 15 hydrocarbon fuels containing 1 to 8 carbon atoms on heated nickel, stainless steel, and titanium surfaces for three different stoichiometries (φ = 0.7, 1.0 and 1.3); and (2)∽ 190 determinations for 10 linear and branched alkanes on heated nickel for stoichiometric conditions. Excellent repeatability has been achieved within a given series of measurements, and good replicate values have been obtained for data collected on separate days.

ISSN:0010-2202    

DOI:10.1080/00102209708935675

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor