摘要:

Detailed measurements have been performed for heavy fuel oil (HFO) sprays, generated by a twin-fluid atomiser, in a large-scale laboratory cylindrical furnace. Data are reported for mean gas temperature, major species concentrations (02, C02, CO and unburnt hydrocarbons), incident wall radiation flux, flue-gas NOxand solid particulates, Together they allow for an assessment of the effect of the secondary air swirl and excess air levels on the combustion characteristics. The main conclusions drawn are: (i) an increase in secondary air swirl (0.9 to 1.3) leads to improvements in mixing, droplet vaporisation and chemical reaction in the near burner region (NBR). The implications of the changes are manifest in the pollutant emissions wherein the higher swirled flame presents lower exit NOx, level due to less “fuel NOx, ” formation but higher solids emissions due to lower cenospheres residence times in the NBR; (ii) an increase in combustion excess air (15% to 25%) leads to more combustion in the NBR due to extra 02and thus more droplet heating and faster vaporisation rates there. The consequences of this increase, apart from reducing the thermal efficiency, are an increase in the exit NOx, level due to increased “fuel NOx, ” formation while the solids emissions are unchanged due to similar cenospheres residence limes in the NBR; (iii) N02emissions are negligible and solid emissions are essentially cenospheres. There has been scant validation of mathematical models for HFO in the NBR due to the lack of data. Since the NBR plays the dominant role in pollution formation little success in forecasting pollutant emissions can be expected unless the combustion/aerodynamics of it are reasonably well predicted. The data presented herein will help redress this problem.

ISSN:0010-2202    

DOI:10.1080/00102209108951717

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The majority of experimental data on which current vent design practice is based, has been obtained in compact vessels of length lo diameter ratio (L/D) less than 3. This leads to great uncertainty when designing vents for larger L/D vessels. The need for more information on explosions in long enclosures has been noted in recent critical reviews and official guides. In this work methane/air explosions were investigated in closed vessels of large L/D with the aim of providing experimental data relevant to the explosion protection of such vessels. A 76mm diameter tube of an L/D of 21.6 and a 162 mm diameter tube of variable L/D (6.2-18.4) were employed. High rates of pressure rise, associated with fast flame speeds and significant overpressures, characterized the very early stages of these explosions, indicating the need for fast and effective pressure relief within the initial 10% of the total explosion time, Lower flame speeds and lower rates of pressure rise succeeded the fast initial phase. Small changes in the spark position were found to have a significant effect on the initial flame speeds and rates of pressure rise. The rates of pressure rise measured in this work did not scale in accordance with the ‘cube root’ law and therefore, the Ka concept cannot be used for large L/D vessels. Different scaling trends were determined on a tentative basis, and the need for more data was pointed out. Recent literature on this type of explosion has concentrated on phenomena occurring in the later stages, such as the tulip flames, pressure wave effects, acoustic instabilities and transition to turbulence. These later stages or the explosion arc irrelevant, from a safety point of view, unless the vessel can withstand overpressures of 1.5 to 2 times the initial pressure, generated in the earlier stages. Thus, the present work has shown that the very early phases are the most important, and should dominate vent design considerations because of the high rates of pressure rise and high overpressures measured in this period.

ISSN:0010-2202    

DOI:10.1080/00102209108951718

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A novel method to analyze the vorticity generation or destruction in jet diffusion Flames is presented. The analysis employs a generic flame structure and a single conserved scalar to examine the vorticity generation or destruction in jet diffusion flames. The analysis shows that the volumetric expansion and baroclinicity can result in vorticity destruction or generation depending on the flame structure, or the stoichiometry. Three regimes concerning vorticity generation or destruction are identified for jet diffusion flames. The analysis also defines a non-dimensional parameter, describing the relative importance of baroclinicity to volumetric expansion. The parameter is the ratio of Reynolds number to Froude number and multiplied by the square root of the Schmidt number.

ISSN:0010-2202    

DOI:10.1080/00102209108951719

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A novel vortex combustor (VC) burning various solid, liquid, and gaseous fuels was recently developed and tested for commercial heating applications. The combustor is characterized by the strong swirl and low temperature combustion environment. This paper presents the computer simulation of this VC firing dry ultrafine coal at 0.6 MW thermal input and 26% excess air. The overall model of gas-particle flow and combustion in the VC is briefly described along with typical numerical results of combustor performance in gas flow, particle flow, gaseous combustion, and particle combustion.

ISSN:0010-2202    

DOI:10.1080/00102209108951720

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The methodological aspects and the potentials of a quantitative imaging technique, suitable for the analysis of the condensed phases fields of diesel sprays in isothermal and burning conditions are described. The technique is based on the simultaneous detection of two polarized components of light scattered by the liquid fuel and/or the carbonaceous material present in a pulsed laser sheet, which crosses a diesel spray injected into a high pressure, high temperature environment. A couple of digital images are recorded: the first one is the pattern of the vertically polarized scattered light and it is used as descriptor of the scatterers concentration; the second one is the pattern of the ratio between two polarized components and it is used as descriptor or the scatterers characteristics

ISSN:0010-2202    

DOI:10.1080/00102209108951721

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The oxidation of propane in air at elevated pressure was investigated in a chemical flow reactor and modelled with a comprehensive chemical kinetic model. Results are presented for pressures of 3.6. and 10 atmospheres, temperatures near 850 and 900 K, and equivalence ratio of 0.3. Gas samples were analyzed using gas chromatography with aldehydes additionally sampled using a dinitrophenylhydrazine/acetoni-trile(DNPH/ACN) procedure. Major product species observed include C3H6, C2H5. and CO: trace amounts of CH4and C02were detected, as well as H2and oxygenated species including CH2O, CH3CHO, C3H60, and C2H5CHO, Fuel conversion was increased with increased pressure and temperature, and the product distribution was significantly shifted in favor of C3H6over C2H4with increased pressure and decreased temperature. Comparison between modelling and measured results for ethylene concentrations supported the use of Tsang's recent values for the rate of propyl radical decomposition. The model compared well to fuel and major intermediates at 6 and l0atm; however, at 3atm, the model deviated significantly from the experimental results. Also, a comparison to oxygenated intermediates and H6indicates a need for additional model development. Major production paths are obtained from the model and discussed.

ISSN:0010-2202    

DOI:10.1080/00102209108951722

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Methane oxidation in jet-stirred reactor has been investigated at high temperature (900–1300 K) in the pressure range 1–10 atm. Molecular species (H2, CO, C02, CH4. C2,H2, C2H4, C2,H6) concentration profiles were obtained by probe sampling and GC analysis. Methane oxidation was modeled using a detailed kinetic reaction mechanism including the most recent kinetic findings concerning the reactions involved in the oxidation of C1,-C4hydrocarbons. The proposed mechanism is able to reproduce experimental data obtained in our high-pressure jet stirred reactor and ignition delay times measured in shock tube in the pressure range 1–13 atm, for temperatures extending from 900 to 2000 K and equivalence ratios of 0.1 to 2. It is able to correctly reproduce H and O atoms concentrations measured in shock tube at ≈ 2 atm at 1850–2500 K. The same kinetic mechanism can also be used to model the oxidation of ethylene, ethane, propyne and allene in various conditions.

ISSN:0010-2202    

DOI:10.1080/00102209108951723

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An apparatus employing an Argon-Ion laser with light polarized perpendicularly to the scattering plane was constructed to measure the size histories of boron particles in the ignition and combustion zones. Three powder samples, having initial radius around 0.05 μm, 3.5μm, and 5.0 μm, were studied. Two kinds of measurement of relative light scattering intensities were performed: one is the relative scattered intensity at two different angles (backward and forward) to determine the size histories of particles with initial radius around 0.05 μm, and another is the relative backward scattered intensity to determine the size histories of particles with initial radius around 3.5μm and 5.0μm. The measured light scattering intensities were interpreted by Mie theory. It was found that the particle-size change is negligible during ignition, and particle radius decreases linearly with time in the combustion zone. Further considerations showed that the combustion of these kinds of boron particles is controlled by surface chemical kinetics. From analysis of the data, we have found that the chemical reaction rate,ω˙ on the boron particle surface during full-fledged combustion can be expressed as toω˙ = kpXo, in which k = 0.0625 ± 0.0125 (mole/cm2sec-atm), corresponding to a reaction probability 0.4 = 0.08 at T = 2500 K, and faring smoothly with earlier data at low temperature. These data provide a basis for calculation of clean-surface boron particle combustion.

ISSN:0010-2202    

DOI:10.1080/00102209108951724

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209108951725

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor