摘要:

The investigation reported here concerns with an attempt to generalize the existing observations of the propagating gasless SHS process. A Damkohler number is realized to embody such main factors affecting the steady propagation speed as the thermal properties, stoichiometry of the reaction, carbon particle size, compression effect and the reactant diffusion. The governing equations in their nondimensional form are solved numerically to obtain steady propagation speeds and preheat lengths. These computed speeds and lengths are examined in the light of the existing knowledge of laminar flame propagation in gaseous reactant systems to discover a useful analogy.

ISSN:0010-2202    

DOI:10.1080/00102209408935467

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Acetylene oxidation in a jet-stirred reactor has been investigated at high temperature (800-1100 K) in the pressure range 1 to l0atm. Molecular species concentration profiles of H2, CO, CO2, CH4, C2H2, C2H4, C2H6were obtained by probe sampling and GC analysis. Acetylene oxidation was modeled using a comprehensive kinetic reaction mechanism including the most recent findings concerning the kinetics of the reactions involved in the oxidation of C1,—C6hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet-stirred reactor, ignition delay times measured in shock tube, atmospheric pressure C2H2/Air flame speeds, and C2H2/O2/Ar premixed flame structures obtained at low pressure on flat flame burners. The mechanism has also been used successfully to represent the kinetics of the oxidation of CH4, C2H4, C2H6, C3H6, C3H3, mixtures of CH4with C2H6and/or C3,H8in the same conditions

ISSN:0010-2202    

DOI:10.1080/00102209408935468

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Predictions of a mathematical model are compared with NO data for pulverised -coal flames. The mathematical model comprises a two-dimensional parent code for the aerodynamics and combustion to which a fuel-NO post processor is appended. The data, which include local concentrations of NO, HCN and NH3, were obtained in a large scale laboratory cylindrical combustor for a conventional burner and for a low NO burner. Four models for the Volatiles-derived NO and two models for the char-derived NO have been tested.

ISSN:0010-2202    

DOI:10.1080/00102209408935469

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The premixed flame propagating through a vertical channel and subject to buoyancy effects is analyzed. In the limit of strong thermal expansion of the burned gas and small normal flame speed, assuming the channel to be wide enough, the problem transpires to be closely related to the classical Rayleigh-Taylor problem for a long bubble rising through a vertical tube. The important distinction between the two systems occurs near the channel walls where the flame interface acquires a long skirt. The skirt length is found to be inversely proportional to the normal flame speed. Similar to the Rayleigh-Taylor problem there is a one-parameter family of propagation modes. The multiplicity is resolved by a natural selection principle

ISSN:0010-2202    

DOI:10.1080/00102209408935470

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper discusses results obtained in a study of the transition to turbulence of gas jet diffusion flames in microgravity. The experiments were conducted at the 2.2-second Drop Tower of the NASA Lewis Research Center. Propane flames burning in quiescent air at atmospheric pressure were investigated. Significant differences have been observed between the transition processes of gas jet diffusion flames in microgravity and normal gravity These include the appearance of large scale structures in microgravity which are manifested at the flame base and are convected downstream. These structures appear intermittently at first, and, then, as Reynolds number is increased, a continuous train of structures is observed along the flame front. The experimental observations are explained in terms of flow transition and instability of the shear layer associated with the injection of the jet flow into quiescent surroundings

ISSN:0010-2202    

DOI:10.1080/00102209408935471

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The flame and vaporization characteristics of an n-octane droplet burning in reactive flows are investigated through numerical analyses of a convective, reactive flow over a wetted porous sphere under various flow temperatures, Reynolds numbers, and ambient equivalence ratios. The liquid fuel is assumed to come through the porous sphere and vaporize at the sphere's surface. The gas flow field is predicted by solving the quasi-steady conservation equations of mass, momentum, and energy, in which gas-phase combustion is modeled by a one-step global finite-rate chemical reaction. Numerical results reveal that multiple solutions for flame configurations and vaporization rates exist under certain flow conditions for both rarely oxidizing and reactive flows. Reactive flows increase the vaporization rate slightly at low ambient temperatures, while significantly at high ambient temperatures. Double flames occur in both the upper and lower branch solutions. In the upper branch situation, both the premised and nonpremixed flames merge at relatively low ambient temperatures, low ambient equivalence ratios, or high Reynolds numbers. In the lower branch solution, however, double flames do not exist at suffficiently low ambient temperatures or high Reynolds numbers where the envelope flame does not appear.

ISSN:0010-2202    

DOI:10.1080/00102209408935472

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A two zone turbulent flow laboratory reactor has been constructed and validated for use in staged combustion studies. A premixed fuel/air feed enters the toroidal backmixed primary zone. The effluent mixes with additional injected oxidant and/or steam, and then enters the linear flow secondary zone. This sequence emulates many large scale combustors. Extracted gas samples from cooled probes located in each zone are subjected to several dedicated on-line gas analyzers, and separation/analyses by on-line/batch gas chromatography. Modeling of the combustor is performed with detailed reaction mechanisms and an idealized perfectly stirred reactor + plug flow reactor sequence. The experimental feed rates and measured temperatures are input to the model. Staged combustion for NO minimization has been demonstrated for an ethylene/monomethyl amine feed

ISSN:0010-2202    

DOI:10.1080/00102209408935473

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The interaction between burning char/carbon particles of different sizes is analyzed using a quasi-steady approximation. The method of solution is based on the expansion into irreducible multipoles developed in the earlier paper. It is assumed that the chemical reaction which occurs at the surface of particles is of first order. The method is applied for the analysis of the burning rate of spherical and cylindrical clouds of particles. The results are presented in terms of correction factor which is defined as a ratio of a burning rate of a particle located inside a cloud to an isolated particle burning rate. It is shown that the burning rate of a cloud of particles is determined by a combustion rate of a primary (central) particle with the radius which is equal to the average radius of particles in a cluster. The results obtained with the developed model are validated by comparison with the available experimental data

ISSN:0010-2202    

DOI:10.1080/00102209408935474

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The method of self-propagating high-temperature synthesis (SHS) can be utilized to produce a variety of advanced materials. After ignition, due to high exothermicity of the reactions involved, the process is characterized by a combustion wave which propagates through the reacting mixture in a self-sustained manner without requiring additional heat. By assuming that the reaction rate is proportional to the instantaneous surface area of the nonmelting component and to the instantaneous concentration of the melting reactant in the formed outlying melt, a new analytical expression for the velocity of the combustion front is developed. This expression accounts for the influence of temperature, particle size, reactant proportions and inert dilution. Experimental data for front propagation velocity for the titanium-carbon reaction available in the literature are described with good accuracy by the expression developed in this work.

ISSN:0010-2202    

DOI:10.1080/00102209408935475

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A laboratory study was conducted to assess the effectiveness of the chemicals calcium magnesium acetate (CMA), calcium acetate (CA), and calcium benzoate (CB) in reducing NOxemission from coal-fired furnaces. CMA, which is currently being used as a non-corrosive road deicing salt, has demonstrated exceptional effectiveness in our laboratory as an in-boiler S02 removal agent (Levendis et al., 1993). This is due to the affinity of the calcium and magnesium components of CM A for sulfur; the reaction results in solid sulfate salts. The current investigation explored the role of the organic component of CMA, as well as that in CA and CB, in removing NOxemissions that are typically found in post-flame regions of furnaces burning pulverized coal or residual oil. Bench-scale experiments were conducted at gas temperatures ranging from 450 to 1450°C and oxygen concentrations between 0 to 5%. The residence time was in the order of 4 s, Injection of the CMA reagent at a mass ratio of CMA/NO of 41 (or an equivalent acetate/NO molar ratio of 18) reduced NO, by more than 90% (at 0% O2and temperatures above 850°C) to 50% (at 5% O2and 650 to 850°C). At an oxygen concentration of 2%, NOxreduction seemed to be most effective between 1000 and 1350°C with NOxreductions of 70 to 80%. The efficacy of calcium acetate (CA) and calcium benzoate (CB) as NO, reducers was also explored, with CA (CA/NO mass ratio of 41 and acetate/NO molar ratio of 15) being less efficient than CMA at a similar φ with oxygen present but as efficient in 0% oxygen. CB (CB/NO mass ratio of 41 with benzoic acid/NO molar ratio of 9) was as efficient as CMA, regardless of O2concentration, but at temperatures higher by 200°C

ISSN:0010-2202    

DOI:10.1080/00102209408935476

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor