摘要:

For a furnace burning solid wastes, one of the key areas in design is the sizing of the furnace which is often determined on the basis of empirically selected furnace heat release rate and grate burning rate. An independent estimation of these factors would require the knowledge of physical processes of refuse combustion such as drying and heating of the refuse bed, chemical reactions of waste combustion, supply and distribution of combustion air, and mixing of combustion air with the burning refuse bed.

ISSN:0010-2202    

DOI:10.1080/00102209808952043

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

New results were obtained on pollutants evolution during the combustion of four oxygenated fuels, whichwere compared withn-tetradecane andn-octane combustion. Three different techniques were adopted on a single cylinder direct injection diesel engine, equipped with optical accesses: two-colour pyrometry for the measurement of in-cylinder soot loading, high speed cinematography for the visualization and analysis of spray and combustion, fast sampling valve for the measurements of in-cylinder combustion products. In particular, the sampling line downstream of the fast sampling valve was adapted for the in-cylinder aldheydes measurements. Heat release analysis and fast sampling valve have shown that CO2formation rate and heat release rate during the diffusion phase of combustion increase with the fuel oxygen content. Acetylene concentrations are influenced by fuel cetane number and oxygen content but, at the same fuel cetane number, they decrease when oxygen content increases. In-cylinder aldheydes concentrations are connected with premixed phase fraction of combustion and then influenced by fuel cetane number. In comparison withn-tetradecane fuel combustion, high burning rate and low visible flame distribution were observed through high speed cinematography tests, when oxygenated fuels were burned. Investigation on in-cylinder soot loading showed a great difference between the combustion behavior of ethers and glycolethers. The glycolethers show lower soot loading at the same fuel oxygen content.

ISSN:0010-2202    

DOI:10.1080/00102209808952044

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The axisymmetric Navier-Stokes model together with detailed chemical kinetics and variable transport properties has been applied to analyze the effects of the multidimensional flow on the flame characteristics in the nitrogen-diluted hydrogen counterflow nonpremixed flame. Computations are carried out for the laminar counterflow hydrogen-air flames with two fuel dilutions. In order to investigate the effects of the jet exit velocity profiles on the hydrogen-air diffusion flame structure, computations are made for two boundary conditions simulating the plug-flow and parabolic-flow velocity profiles at nozzle exit. In case of the highly diluted hydrogen flames, the near-extinction flame structure and extinction flame process are numerically studied for two nozzle exit area-averaged velocities based on the plug-flow profile. Numerical results indicate that the jet exit profiles significantly influence the flame structure in terms of strain rate, flame thickness, peak temperature, overlap of fuel and air, and differential diffusion. Effects of multidimensional flow and strain rate on the near-extinction structure of the highly diluted hydrogen flames are also discussed in detail.

ISSN:0010-2202    

DOI:10.1080/00102209808952045

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We perform a numerical study of the effect of including a small amount of hydrogen in lean methane-air premixed flames at high pressure and high temperature conditions. It has been shown recently (Bell and Gupta (1997)) that hydrogen addition extends the lean operating limit of natural gas engines, leading to a potential decrease in pollutant formation. We suggest here that the origin of this effect is that, at constant global equivalence ratio, the stretch resistance of these flames is considerably increased by hydrogen blending, while other flame properties, such as ignition time and burnt gas temperature, are comparatively little modified.

ISSN:0010-2202    

DOI:10.1080/00102209808952046

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The critical rate of catalytic surface reactions leading to gas-phase ignition in non-premixed stagnation-point flows over a porous plate is investigated theoretically. The relationships between the critical rate of catalytic surface reactions at ignition and the temperature of fuel mixture supplied from the lower side of the porous plate exhibit a C-shaped ignition curve and a near-linear ignition profile for small and great injected mass fluxes, respectively. Physically, the upper and the lower branches of C-shaped ignition curves are governed by the diffusionally and the kinetically controlled ignition, respectively. The entire near-linear ignition profiles are diffusionally controlled. The diffusionally controlled ignition mechanisms for the upper branch of C-shaped ignition curves and the near-linear ignition profiles are caused by rapid catalytic reactions and great injected mass fluxes, respectively. Two characteristic ignition temperatures, i.e., the critical ignition temperature and the minimum ignition temperature, as functions of various system parameters are identified and analyzed. The transition between the kinetically and the diffusionally controlled ignition is investigated. In addition, influences of the injected mass flux, the strain rate of flow, the Prandtl number and the Schmidt number on the C-shaped ignition curve and the near-linear ignition profile are systematically discussed.

ISSN:0010-2202    

DOI:10.1080/00102209808952047

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This investigation aimed at examining the combustion behavior of polymer particles in groups and at comparing it to that of single particles. Combustion observations were subsequently related to measurements on emissions of organic pollutants, such as PAHs and soot, which were previously measured in this laboratory under similar conditions. The following plastics (polymers), commonly found in municipal waste streams, were burned in powder form: poly(styrene) (PS), poly(ethylene) (PE), polyvinyl chloride) PVC, and poly(methyl methacry-late) (PMMA). Particles, 125-212um, were introduced to a drop-tube furnace, at steady-flow conditions, and burned in cylindrical streams (clouds), in 1250 K air. The particle mass loading in the furnace was varied to achieve either dilute clouds, where isolated (single) particle combustion occurred, or dense clouds where interactive particle combustion look place. Information on the combustion characteristics and flame temperatures of the particles was obtained by cinematography and three-color pyrometry. Results revealed striking differences in the combustion behavior of the four polymers burning in particle clouds. PVC particles burned with bright individual flames, resisting the formation of group flames, even at high particle number densities. In dense clouds, envelope flame diameters were generally smaller and their durations were shorter than in single particle combustion. Poly(ethylene) particles in very dilute clouds burned individually, surrounded by low-sooting, faint envelope flames. When particles burned in close proximity to each other, they abruptly exhibited localized flash-vaporization and formed highly-luminous, large, group flames, “puffs”. At high particle number densities the entire stream was engulfed in a cooler flame containing finely-dispersed soot. Poly(styrene) particles burned mostly as discrete entities at relatively low flowrates, and the progression to partial group flames was gradual as the particle mass loading increased. PS particles consistently formed flames with long wakes which, upon extinction formed strings of highly-agglomerated soot. Flame temperatures were lower in group combustion than in individual particle combustion. While single particle envelope flames were previously recorded to be in the neighborhood of 2000 K, those of group flames were found to be only a few hundred degrees above the gas temperature, at globally fuel-rich conditions.

ISSN:0010-2202    

DOI:10.1080/00102209808952048

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents a direct Reynolds stress, stretched flamelet model for the premixed swirling turbulent reacting flows. The model adopts a statistical presumed joint pdf of turbulent flame stretching and flame wrinkling, together with an established laminar flame data library for fuel oil. The main virtue of the model is that the application of the model is not restricted to a single combustion regime. It is capable of realizably extending to both the fully chemically controlled combustion condition (the laminar flame model) and the fully mixing controlled combustion condition (the eddy break-up model).

ISSN:0010-2202    

DOI:10.1080/00102209808952049

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A multi-dimensional code has been developed to study the effects of injection pressure and nozzle hole inlet conditions on diesel engine performance and emissions. The code includes a new liquid core and spray breakup model. The models were validated using spray visualization images obtained from a single-cylinder version of the Caterpillar 3406 heavy-duty truck engine instrumented with an endoscope system. The computational results were also compared with experimental emissions data. The results show that combustion and emissions predictions are controlled by the details of the spray model. With modifications to the spray model to account for Rayleigh-Taylor and Kelvin-Helmholtz drop breakup mechanisms, the predicted liquid and vapor-fuel penetration agrees well with that measured. The models were applied over a wide range of engine operating conditions and were found to provide good prediction accuracy. The simulations also showed that sharp edged-inlet nozzles give significantly lower particulate emissions than rounded-inlet nozzles with the same rate-of-injection profile as has been seen experimentally.

ISSN:0010-2202    

DOI:10.1080/00102209808952050

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An experimental study of flame-spreading process over thin aluminum (99 % Al and 1 % Mn( sheets was investigated in oxygen-enriched environments. The objective of this study was to determine the dependency of flame-spreading rate over aluminum sheets as a function of initial chamber pressure, sample thickness, oxygen purity, oxygen flow condition, and sample orientation. The reaction mechanism of aluminum in oxygen was also studied by examining the recovered partially-burned sample using a scanning electron microscope (SEM( coupled with an energy dispersive spectrometer (EDS(. The flame-spreading rate over aluminum sheets was measured by an array of fast-response lead-selenide (Pb-Se( IR photodetectors. The initial chamber pressure was varied from 0.1 to 6.3MPa. Two grades of oxygen gas were used with purities of 99.996 % and 99.75 %. In terms of the effect of pressure on the flame-spreading rate, as the initial chamber pressure was increased, the flame-spreading rate was found to increase to a maximum, decrease to a minimum, and then increase again. Based upon the comparison of flame-spreading rates in horizontal, upward, and downward orientation, the flame-spreading process over aluminum sheets was found to be dominated by the solid-phase heat conduction mechanism. The continuous oxygen flow showed a strong influence on the flame-spreading behavior, and it was demonstrated that the flame can be blown off when the counter-current flow velocity exceeds a critical value. The flame-spreading rates under high-purity (∼ 99.996 %( oxygen environments were found to be significantly greater than those in commercial grade (∼ 99.75%( oxygen. In addition, the oxygen content in the while ceramic-type nodules formed on the burned edge of the recovered partially-burned sample is much higher than that on the unbumed surface. These imply that there exist heterogeneous reactions between aluminum and either oxygen or gaseous aluminum sub-oxides on the burning surface.

ISSN:0010-2202    

DOI:10.1080/00102209808952051

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of microexploding fuel droplets injected into the shear layer in an axisymmelric dump combustor are studied numerically. The fuel droplets considered are multicomponent consisting of a solid high-energy fuel core surrounded by a liquid carrier. When droplets microexplode, pressure waves are generated that reverberate through the system and in some cases couple with the characteristic frequencies of the system. In a particular case, the low frequency quarter wave acoustic mode of the inlet is amplified, resulting in the formation of a large vortex structure near the combustor step. Periodic energy release associated with this large vortex structure sustains the low frequency oscillations even though droplets are injected continuously at a constant rate. By phase-coupling droplet injection to an external acoustic forcing frequency, it is demonstrated that pressure fluctuations at the forced frequency may be amplified or attenuated by the microexplosion of the fuel droplets.

ISSN:0010-2202    

DOI:10.1080/00102209808952052

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor