摘要:

The reactions of organically-bound nitrogen in coal char during combustion have been studied in a laboratory furnace using size-graded char particles prepared by the pyrolysis of a Montana lignite. The time-resolved variations of nitrogen-to-carbon ratio during char oxidation have reveated that there is no selectivity between nitrogen and carbon loss due to oxidation but that the char-nitrogen can undergo devolatilization in parallel with the oxidation. The paper illustrates that the rates of devolatilization of fuel nitrogen can be obtained from oxidation experimentations under conditions where: (1) carbon devolatilization is unimportant, as in the case for char, and (2) the oxidation of nitrogen and carbon is nonselective. The oxidation rate of char-nitrogen can be given by the product of the char oxidation rate and the mole ratio of nitrogen to carbon in the char. The devolatilization rate of char-nitrogen is correlated by a first-order kinetics, showing good agreement with those of previous investigators.

ISSN:0010-2202    

DOI:10.1080/00102208208952554

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Comparisons were made of computed and measured flame fronts, flame tip propagation rates, and pressures for eight configurations of a divided-chamber, stratified-charge engine differing in speed, equivalence ratio, and throat area. In the model, conversion from reactants to products was assumed to be mixing limited so that the controlling processes were turbulence and wall effects. Turbulence was represented by a k — e model and wall effects by the “law of the wall” and Reynolds analogy. The results were also compared with those from earlier models that attempted to account for finite rate kinetics too, through one overall irreversible reaction.

ISSN:0010-2202    

DOI:10.1080/00102208208952555

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The chemical and thermal structure and the emission performance of an aerodynamic flameholder are presented and examined. Recirculation is established by injecting a premixed jet into an opposing mainstream of premixed reactants. The injection of the jet directly into the recirculation zone provides a control of the stabilization zone mixture ratio, temperature, and size not found in bluffbody flameholding. The size and stoichiometry of the recirculation zone is dictated by the jet velocity and mixture ratio respectively. A parametric study of the controlling variables (main and jet stream velocities, main and jet stream equivalence ratios) reveals the partitioning between the recirculation zone and wake in both the heat release and pollutant production. An examination of the emission indexes and flowfield profiles of temperature and species concentration establishes the influence and control of jet and mainstream conditions on pollutant production. A reduction in jet velocity and/or an enrichment of the jet, for example, effects a substantial change in NOxemission. Further, jet enrichment extends the lean blow-off limit of the mainstream. There exists a point, however, beyond which the reaction is not supported in the wake and further leaning of ihe mainstream results in a substantial emission of unspent fuel.

ISSN:0010-2202    

DOI:10.1080/00102208208952556

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The concentration of lhe OH radical in a stoichiometric methane-air flat flame at atmospheric pressure was measured with both laser-absorption spectroscopy and molecular-beam mass spectrometry (MBMS). The nonequilibrium peak OH concentrations and the OH decay rate measured from the two techniques were in good agreement. The OH profile from the MBMS measurements, however, was shifted downstream from the absorption measurements by the MBMS sampling process. A comparison of temperature profiles from thermocouple measurements and from a molecular-beam time-of-flight technique exhibited a similar downstream shift. The MBMS measurements effectively sampled the gas properties approximately five orifice diameters ahead of the sampling-probe tip. Perturbation of the OH concentration profile using various sampling probes indicate the importance of minimizing the length of the sampling-orifice channel to reduce composition relaxation during sampling.

ISSN:0010-2202    

DOI:10.1080/00102208208952557

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The orientation of the burner to the wind direction has been found to have a marked effect on the ability of the flame to resist being blown out by the wind. By using an effective wind speed (V+Ueff) instead of the actual wind speed V, it is shown thai for a given gas the data for different burner inclinations can be collapsed on to a single stability curve, which is the same as that for the case where wind direction is normal to the burner axis.

ISSN:0010-2202    

DOI:10.1080/00102208208952558

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Flame inhibition by dry-chemical powders was studied by adding various powders to a diffusion flame and measuring the composition and temperature profiles using a molecular-beam mass-spectrometer sampling system. The diffusion flame was a methane/oxygen flame held near the stagnation plane of an opposed-jet burner. The downward-flowing jet contained a mixture of air and powder, the upward-flowing jet a mixture of methane and nitrogen. Powders of Al2O3, NaHCO3K.HCO3, NH4H2PO4and KCI were used. Particle diameters were in the range from 38 to 43 μm. In order to obtain significant inhibition without extinguishing the flame, powder feeding rates of 3 mg/litergas were used for NaHCO3, KHCO3and NH4H2PO4; 2 mg/litre gas for KCI. Arbitrarily, a feeding rate of 2 mg/litergas was used also for Al2O3. Concentrations of the major species (CH4, O2, N2, H2O, and CO2) were measured using the mass spectrometer; the temperature was measured using the time-of-flight technique.

ISSN:0010-2202    

DOI:10.1080/00102208208952559

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Results of qualitative and quantitative chemical analyses of stable combustion products found in smoke particulates of chlorinated pofymers are described. Chemical composition profiles have been established in both nonflaming and flaming modes, comparing pofyvinylchloride (PVC) samples with nonchlorinated polypropylene (PP). The nonflaming combustion analysis indicates similarity between the PVC and PP samples, suggesting similar degradation processes. In the flaming combustion of these polymers mainly aromatic compounds were identified, supporting a stepwise ring growth mechanism leading to the formation of the multi-ring structure of soot nuclei. The main influence of the chlorine atom appears in the higher production of the substituted polycycloaromatic hydrocarbons (PAH), which in turn may account for the observation that a higher quantity of soot is released during the combustion of PVC than during the combustion of non-chlorinated polymers. Finally, the presence of additives upon PVC soot formation seems to affect the physical rather than the chemical processes that influence smoke particulate formation.

ISSN:0010-2202    

DOI:10.1080/00102208208952560

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The subsonic isobaric forced-convective flow of air past a pyrolyzing, char-forming body outgassing combustible fuel vapor is examined; the goal is to seek a generalized approach toward establishing approximate criteria for extinction of burning. A Shvab-Zeldovich formulation (incorporating, inter alia, a one-step irreversible exothermic finite-rate chemical reaction) is adopted to describe the gas-phase burning of initially unmixed reactants. For specificity, a sublimation model is adopted to describe the endothermic gasification at the surface of the (isothermal) pristine body; a nonisothermal porous char layer (through which combustible vapor, from pyrolysis of the pristine-body surface, can diffuse to the surrounding air) envelops the pristine body. Important features of the steadily burning configuration can be obtained for any simple bluff body, and sequentially the question of flame stability can be addressed via exploitation of the well-studied counterflow-diffusion-flame two-point-boundary-value problem for describing extinction of unpremixed burning. Thus, known results for the minimum Damk6hler number (ratio of forced-convective-fiow time to chemical-reaction time) compatible with vigorous burning of large-activation-energy, large-heat-of-combustion, counterflow diffusion flames are applicable. The uncoupling of the analysis for the heat transfer-flow problem from the analysis of the gas-phase flame-extinction problem depends on the fact (associated with all analyses known to the authors, for parameter values of practical interest) that always, during vigorous burning, the oxygen concentration at the gas-solid interface is extremely small. This observation permits a formulation of the composite problem which defers the detailed flame analysis until after the kinematic field, the temperature field of the char, and the usual Shvab-Zeldovich passive scalar variables in the region outside of the char, have been deduced. One can then use the rather extensive results which are already available in the literature to dispose, in most cases, of the extinction part of the problem. Aside from its role in the foregoing balance, the importance of the presence of the char lies in its capacity to store heat, if combustion is absent temporarily due, for example, to an enhanced external flow velocity, the heat stored in the char can supply the energy for continued pyrolyzation. Then, upon the resumption of a flow condition which permits a steady vigorously burning configuration, spontaneous reignilion can occur, provided that the time interval of enhanced velocity has been short enough so that pyrolyzation has not yet ceased and provided that the surface of the char is not yet below the ignition criterion of the pyrolyzate-air combination.

ISSN:0010-2202    

DOI:10.1080/00102208208952561

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

A theoretical study is presented of the combustion of a spherical fuel particle in a forced convective oxidizing gas flow. The analysis makes use of the boundary layer and flame-sheet approximations to describe the reacting flow. The governing boundary layer equations are solved by expanding the velocity, temperature and species distributions into a series of the azimuthal angle. Profiles of these variables at several angular positions along the particle surface and the local mass burning rates are presented. An explicit expression for the particle regression rate is developed in terms of the Reynolds and mass transfer numbers. The predicted dependence of the regression rate on these parameters agrees qualitatively with already existing experimental observations for droplets vaporizing and burning in convective environments.

ISSN:0010-2202    

DOI:10.1080/00102208208952562

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208208952563

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor