摘要:

In this work, the luminescent species present in flame front at combustions of ethanol and acetylene, in a long tube and without the air influence, were mapped. The flame emission was analyzed from 300 to 600nm, with steps of 50nm, and at 306.4, 431.3 and 516.5nm, corresponding to the emission maxima of OH, CH and C2excited radicals. Three gaseous mixtures with partial pressures of 2.00 kPa acetylene with 7.20 kPa oxygen, 4.53 kPa acetylene with 4.67 kPa oxygen, and 3.33 kPa ethanol with 6.67 kPa oxygen were studied. The results show that the fuel enrichment in the combustion of acetylene/O2enhanced the concentration of the C2excited radical relative to the concentrations of OH and CH excited radicals in the flame front. For the combustion of fuel-rich mixtures of ethanol/O2the main species in the flame front was the CH excited radical.

ISSN:0010-2202    

DOI:10.1080/00102209808952078

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The cascade hypothesis, which was introduced in application for premixed combustion by Yakhot (1988) and Sivashinsky (1988), is examined against the correlations of the turbulent burning velocity data by Bradley, Lau and Lawes (1992) (BLL data). A new, less restrictive formulation of the cascade hypothesis is suggested. The formulation is shown to be consistent with the BLL data. Various flame characteristics - fractal dimensions, inner cutoffs, main asymptotic regimes - are determined form the BLL data on the basis of the cascade hypothesis.

ISSN:0010-2202    

DOI:10.1080/00102209808952079

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A need exists to develop and demonstrate a low pollutant emission gas turbine combustor design that uses liquid fuel for propulsion applications. The present work addresses this need by developing and demonstrating design guidelines for a liquid fueled, lean burn, gas turbine combustor injector. This injector is designed to accommodate all the combustion air, and includes a fuel and air mixing section with an internal venturi contour that contains an aerodynamic swirler, and an atomizer. The atomizer is a plain jet, airblast type with eight ports that spray radially into a high-velocity cross-stream of combustion air. Reacting test results show that the fuel and air are sufficiently well mixed to create a uniform distributed reaction which is (1) of finite length, and (2) free from pulsation or other combustion-induced instabilities. Emissions data at elevated pressure and temperature establish that this injector has low pollution emissions, and high combustion efficiency.

ISSN:0010-2202    

DOI:10.1080/00102209808952080

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Immersion of energetic materials into molten-salt baths is being considered as a method for their safe destruction. In the present research, a solid energetic material, 2,6-dinitrotoluene (DNT), and a solid nonenergetic material, solidifiedn-dodecane, were studied. Cylindrical samples initially about 1 cm in diameter were injected into salt baths, and data were taken photographically. As salt temperatures increased, surface regression rates increased. Thin gas films were observed to exist around the samples. In addition, DNT bubbles displayed sudden rapid size increases with strong increases in opacity suggesting that chemical reactions were taking place in the bubbles; these behaviors were not observed with bubbles from the dodecane samples. Temperature profiles inside the samples were measured using thermocouples; data indicate that thin thermal boundary layers existed near the sample surfaces. Estimates suggest that sample lifetimes and surface regression rates were controlled by convective heat transfer through the gas films, even for the energetic material, with radiant heat transfer being subdominant. Sample lifetimes were in the range 1-2.5 s. In addition to advancing fundamental knowledge, these results are of use for aiding in the design of molten-salt reactors.

ISSN:0010-2202    

DOI:10.1080/00102209808952081

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The thermal stability of jet fuels results from a complex set of chemical reactions, and the deposition process is further complicated by physical mechanisms such as agglomeration and solvation. Although a vast amount of experimental data has been obtained by several researchers, the specific mechanisms responsible for thermal degradation of fuels and the consequent deposit-formation process are still largely unknown. This is primarily due to the fact that the fluid flow and the heat transfer which influence the deposition process vary significantly from experiment to experiment. It is thought that Computational Fluid Dynamics with Chemistry (CFDC) models can be used to correlate the data obtained from a number of experiments and, thereby, explore this large data base to aid the understanding of the deposition phenomenon. The success of this approach depends on the accuracy of the global-chemistry models used in the CFDC codes. Recent experiments on blended fuel prepared by mixing a hydrotreated fuel with a non-hydrotreated one suggest that the thermal stability of the blend cannot be linearly extrapolated from the thermal-stability characteristics of the neat fuels. The global-chemistry models developed previously are found to be insufficient for the simultaneous prediction of deposition and oxidation rates associated with the blended fuel; however, a nine-step model developed most recently appears to yield qualitatively correct results. To improve the predictive capabilities of this model, the rate expressions for the bulk-fuel reactions are modified by taking the antioxidant behavior in jet fuels into account. The resulting modified nine-step global-chemistry model yielded the experimentally observed thermal stability characteristics for the blended fuels. Predictions made for higher flow-rate and temperature conditions also matched well with the experimental data. Overall, the modified nine-step global-chemistry model is found not only to improve the accuracy in predicting quantities such as oxygen consumption and surface deposits but also to provide additional capabilities for predicting quantities such as hydroperoxides and bulk insolubles.

ISSN:0010-2202    

DOI:10.1080/00102209808952082

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Multi-wavelength absorption/emission measurements of extinction coefficient, temperature, and soot volume fraction in a large (6 m by 6 m) JP8 pool fire using anin situwater-cooled fiberoptic probe are reported. These measurements provide the firstin situinformation on radiative properties, temperature, soot, and the associated time scales in large pool tires. Soot extinction coefficients on the order of 5 to 30m-1were measured in the visible regime, indicating paths lengths for radiative transport in the infrared of approximately 0.1 to 0.3 m. Temperature measurements follow an approximately normal distribution with a mean of 1400 K. and a standard deviation of approximately 67 K. Integral length scales of approximately 0.25 m were deduced from the temperature data. This length scale corresponds to the size of the smaller combusting eddies visually observed in large fires. Soot concentration integral length scales of 1.4 m were determined from the absorption measurements. Soot volume fractions ranging from 0 to 6.0 ppm were measured. In comparison to laboratory-scale flames, excellent agreement was observed between the volume fractions determined by extinction and emission measurements, indicating a uniform temperature distribution (and hence uniform flame coverage) within the 2.0 cm long by 1.0 cm diameter cylindrical sampling volume. Soot volume fractions determined by emission show a strong peak in the PDF just above 1.0 ppm. The same peak is observed on the soot volume fraction determined by absorption, but an additional maxima in the PDF is observed near 3.0 ppm, indicating the occasional presence of thick, cold soot. The primary uncertainty in the results is due to uncertainty in the soot indices of refraction. Fortunately, the uniform flame volume observed in the results show that the environment is promising for the study of these refractive indices.

ISSN:0010-2202    

DOI:10.1080/00102209808952083

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The plasma-chemical technique for intensification of combustion is based on the interaction of a jet of low-temperature air plasma and the fuel. In order to determine the principal characteristics of a combustor operation process having a plasma-chemical element, an appropriate mathematical model has been used. Interphase interaction is taken into account by considering the drops of liquid as the sources of mass, impulse and heat for the gaseous phase. Simulation of plasma-chemical intensification processes is carried out through solving the equation of fuel concentration conservation in which the rate of its variation is expressed through the value of the resulting reaction of activation energy. Plasma-chemical action raises the efficiency of fuel combustion under idle running and partial loads conditions up to 3-9% as shown by experimental data obtained during the tests of a marine gas turbine combustor operating on distillate liquid fuel. The emission of carbon oxide during plasma-chemical reactor operation drops by a factor of 1.2- 1.6 depending on the amount of plasma-chemical products added.

ISSN:0010-2202    

DOI:10.1080/00102209808952084

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Superequilibrium concentrations of oxygen atoms which enhance the production of prompt NO in laminar premixed methane-air flames are usually computed using elaborate flame codes. This paper presents a simple method to compute superequilibrium O atom concentrations and simplifies the prompt NO mechanism using steady state relationships such that the flamefront NO production depends solely on the rates of just 3 reactions. The results show that the contribution of the N2O mechanism to the total NO increases dramatically with pressure and that the Fenimore mechanism is more important than the Zeldovich and N2O pathways in the cooler regions of the flame.

ISSN:0010-2202    

DOI:10.1080/00102209808952085

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This analysis discusses the effects of acoustic perturbations and chemical reactions on droplet combustion when the ambient temperatue is larger than the adiabatic flame temperature. The acoustic field is simulated by sinusoidal perturbations. The chemical reaction occurs as a small rate, a consequence of the condition of the ambient temperature being larger than the adiabatic flame temperature. The results show that the vaporization rate increases due to the presence of the acoustic field and increases with increasing Damkohler number.

ISSN:0010-2202    

DOI:10.1080/00102209808952086

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Calorific values of solid sludge obtained from paper recycling mill rejects were estimated by first drying the sludge in a pilot scale rotary dryer and then determining the heal of combustion of these sludge samples. Sludge samples with varying moisture and inorganic contents were studied. Study revealed that a net thermal energy saving was possible by optimizing final moisture content of sludge before combustion. Sludge containing high amount of inorganic components needs to be dried to a final moisture content sufficient enough to ensure a net energy saving after drying and combustion. Thus, high inorganic containing sludge samples from a fine paper recycling mill generated significantly less energy compared to that of a deinking mill sludge which was more rich in fiber content. Although the presence of inorganic components, decomposable fillers in particular, and moisture in sludge negatively influenced the energy recovery, a net gain in the thermal energy was obtainable from all the three studied sludge compositions by optimizing the residual moisture content during drying of the wet sludge.

ISSN:0010-2202    

DOI:10.1080/00102209808952087

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor