摘要:

The detailed structure of counter-flow, ethylene diffusion flame has been studied under atmospheric conditions. The temperature and mole fraction profiles of major, minor, aromatic and polycyclic aromatic hydrocarbon (PAH) species have been determined under the strain rate of 56.6 s−1. Flame sampling was achieved by using a heated quartz microprobe connected to a silica-coated stainless steel sampling line which transferred the sample to an on-line Gas Chromatograph/Mass Spectrometer (GC/MS). Rapid insertion method was used to obtain the temperature profiles with a silica coated Pt/Pt+139% Rh thermocouple. Visually, the flame showed 3 different color zones: Blue, yellow and orange. The blue zone with a maximum flame temperature of 1577°C was located in the oxidizer side of the flame. The most abundant hydrocarbon pyrolysis product was C2H2, which was located in the yellow zone. Benzene was measured as the most abundant aromatic species with 220 ppm maximum level, located in the yellow zone. Naphthalene (50 ppm) and pyrene (5 ppm) were the most abundant PAH formed. Increasing strain rate resulted in decreasing residence times and cooler flame temperature thereby leading to die observation of fewer number and lower peak levels of aromatics and PAH when compared to the lower strain rate ethylene flame studied before (Olten and Senkan, 1999).

ISSN:0010-2202    

DOI:10.1080/00102200008935774

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Pulsed detonation thermal spray applicators are used to deposit particulate-based coatings on metal components. The coatings usually consist of a unique class of thermal spray materials that are widely employed in numerous industries to enhance the surface of metal components. This paper presents an analysis and numerical simulation of an open tube pulsed detonation thermal spray applicator. Calculations are made to determine the theoretical detonation states attainable for typical operating conditions and to track the particle trajectories as they traverse the barrel, eventually impacting the target workpiece. The present investigation focuses on the combustion of acetylene in oxygen, diluted with nitrogen. Key parameters studied are: nitrogen dilution percentage, oxygen-carbon ratio, barrel location of solid-particle axial injection, and size of the injected particles. Results are presented on the effect of these design parameters on several important quantities including: detonation speed, velocity of the detonation product gases, detonation pressure, detonation temperature, temperature and velocity profiles of the solid particle as it travels through the pulsed detonation thermal spray applicator, percentage melt history of the solid particles, and temperature, velocity, and percentage melt of the solid as it impacts the workpiece.

ISSN:0010-2202    

DOI:10.1080/00102200008935775

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A theoretical model for the rate of entropy generation has been developed for an axi-symmetric laminar diffusion flame in which a cylindrical fuel stream is surrounded by a co-flowing oxidizer jet in a confined environment. The solution for the diffusion flame is generated by solving the mass, momentum, energy and species conservation equations, simultaneously, using a finite difference method with the appropriate boundary conditions. A single step global reaction kinetics between fuel and oxygen is considered for the solution. The effects of varying the inlet air temperature and the air-fuel ratio on the total rate of entropy generation as well as the contribution of the individual subprocesses towards entropy generation are investigated.

ISSN:0010-2202    

DOI:10.1080/00102200008935776

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Results of experiments concerning the combustion and desulfurization of ebonite in bubbling fluidized bed are presented in the paper. Two experimental facilities of different scale, the first one operated batchwise, the second one under steady state conditions, were used. Experiments carried out at bench scale were aimed at determining the mechanism of sulfur release during combustion and to evaluate the extent of the contact between released sulfur and sorbent. They demonstrated that a significant amount of sulfur is released during devolatilization stage. Therefore, desulfurization efficiency was limited by occurrence of poor contact between sulfur and calcium. The desulfurization efficiency was very sensitive to the size of sorbent panicles and bed solids. Results of steady state combustion, carried out at pre-pilot scale, were elaborated in terms of bed carbon loading and efficiencies of combustion and desulfurization. The comparison with an already tested reference fuel, South African coal, demonstrated similar combustion behavior. Combustion performances were strongly dependent on the excess air ratio. The combustion efficiency was always larger than 90%. Desulfurization efficiency was not satisfactory, approaching a maximum value of 80% at Ca/S molar ratio equal to 10. A theoretical assessment of results, based on a mathematical model, was proposed in both cases. It allowed the determination of the contact efficiency between gaseous sulfur and available sorbent, which was equal to 85% and 65% for the smaller and bigger facilities, respectively.

ISSN:0010-2202    

DOI:10.1080/00102200008935777

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A numerical study on the premixed wrinkled flame front has been conducted in order to examine the motion of the wrinkled flame front and flame/flow interaction in an oscillating flow field. The conventionalG-equation is solved to determine the time dependent behavior of the flame front by using a model in which the flame front is regarded as a source of volume and vorticity. To confirm the numerical simulation, the response of the wrinkled premixed flame under the oscillating flow field is experimentally observed. The experimental results, where flame/flow interaction is clearly observed, can be depicted by the numerical analysis. The wrinkled region of the flame front hardly responds to the upstream flow oscillation even if this oscillation is as large as the mean velocity of the flow field. The behavior of the wrinkled flame front is found to result from flame/flow interaction due to volume expansion and vorticity production at the flame front. Especially in a time varying flow field, vorticity production plays a decisive role in the motion of the wrinkled region of the flame front by counteracting the oscillating flow field.

ISSN:0010-2202    

DOI:10.1080/00102200008935778

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The formation of crystallinity in combustion generated soots is explored by three traditional methods that are based on their sensitivity to the Bragg diffraction produced by multilayer atomic structures. These techniques are high resolution electron microscopy (HRTEM), X-Ray diffraction (XRD), and dark field transmission electron microscopy )DFTEM). These methods provide complementary information on the nature of the crystallinity in combustion generated soots. The lattice parameters of both flame generated soots and diesel soots are consistent with the structure of disordered carbons with graphitic basal planes. The initial evidence of crystallinity in flame generated particles is detected by XRD in the precursor particles that previously have been found to contain multiring polycyclic aromatic hydrocarbons (PAHs). These results are consistent with the hypothesis of Oberlin (1984) that PAHs in carbonizing hydrocarbon pitches are assembled in parallel layers to produce diffraction peaks. The more intense display of diffraction maxima is evident in DFTEM when the particles sampled from flames undergo the transformation from isolated precursor spheroids to clustered aggregates during the carbonization process. These results support the view that the PAHs initially formed in the gas phase combustion processes undergo a series of transformations in which the hexagonal geometry is preserved and form the basal planes of the crystallites found carbonaceous soot particles. This description evidently applies to the formation of soot from a wide variety of hydrocarbon fuels burned in various combustion devices ranging from gaseous-fueled laboratory burners to diesel engines.

ISSN:0010-2202    

DOI:10.1080/00102200008935779

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Recent pollution requirements and stringent operating conditions for gas turbine engines has prompted the need for real-time feedback control of combustion processes for power production and propulsion. NO and CO pollutants from gas turbine engines have been die focus of many researchers for some time. By accurately controlling the equivalence ratio (EQR), fluctuations to disturbances may be avoided so as to maintain desired levels of NO and CO. In this paper, we develop a feedback technique based on CH chemiluminescence for real-time control of EQR in combustion processes. We focus on a continuous combustor for experimental modeling and implementation. An in-depth presentation is given of model development and digital controller design. An experimental step response and pressure disturbance test is provided for experimental validation of the EQR controller. Equivalence ratio control produces over a 700% decrease in NO emissions for large pressure disturbances. A 1.18 second settling time with only 6.7% overshoot is achieved for EQR commands.

ISSN:0010-2202    

DOI:10.1080/00102200008935780

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Near-surface laser-induced fluorescence (LIF) measurements of OH axe performed in the post-flame region of low pressure hydrogen/oxygen flames in stagnation flows above catalytic and non-catalytic surfaces. Measurements of the normalized gradient of the OH number density near the surface are shown to be sensitive to changes in surface reaction rates, and thus can be used as a test of surface chemical mechanisms. In addition, such measurements do not require an absolute calibration, which increases the accuracy of the comparison. A comparison of the observed results for varying substrate temperature, system pressure, and flame equivalence ratio suggests that the recombination probability of OH on platinum is overpredicted in general by current surface models, and that the dependence of recombination on pressure is stronger than predicted. The qualitative trends for OH recombination with temperature and equivalence ratio are similar to predicted trends.

ISSN:0010-2202    

DOI:10.1080/00102200008935781

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Computational and experimental studies on the effects of oxygenated fuels with single and split high-pressure fuel injections were conducted at both high and low load engine operating conditions. The oxygenates were a long chained ester and ether blended with conventional diesel fuel. An improved version of the KIVA-II multidimensional engine code was used in the study, and the soot model was modified to account for the influence of the oxygenate.

ISSN:0010-2202    

DOI:10.1080/00102200008935782

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Laminar flow reactors are frequently used to experimentally study an isolated elementary reaction step as well as chemical kinetic mechanisms of many coupled reactions. This classical method is effective in measuring kinetic rate parameters when the effects of mass diffusion and wall surface reactions can be neglected or accurately assessed. We perform a series of two-dimensional direct numerical simulations to investigate issues related to the operation of this classical apparatus. By utilizing a well-established gas phase kinetic mechanism for moist CO oxidation and a commonly used sub-model for multi-component diffusive transport, we investigate a virtual elementary kinetic experiment. In particular, we extract data from the simulations and evaluate the rate parameters of the reaction CO + OH ⇄ CO2+ H as one would in an actual experiment. We show that under appropriate operating conditions, the desired elementary reaction rate parameters can be recovered accurately with minimal efforts in analyzing the experimental data. We also demonstrate that two-dimensional simulations can be useful in refining the operating conditions of an experiment to minimize uncertainties in the determined rate parameters. Numerical results confirm that operating conditions that differ from the classical “plug flow” condition can yield more accurate results. Finally, we investigate laminar reactor operating conditions typical of those used in the literature to study reacting systems of many coupled elementary reactions. Using the same CO oxidation mechanism as an example, we show that for oxidation experiments conducted at one atmospheric pressure, the coupling between transport and chemical kinetics results in a highly two-dimensional reacting flow field. Interpreting these results on a one-dimensional basis can lead to significant inaccuracies in the evaluated rate parameters.

ISSN:0010-2202    

DOI:10.1080/00102200008935783

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor