摘要:

Experimental studies were made on supersonic combustion in a two dimensional combustor using Hydrogen as fuel. A Hydrogen vitiation air heater with oxygen replenishment was used for simulating high temperature air entering the supersonic combustor. Transverse fuel injection was employed from the walls (Single wall and Double wall)of the combustor at upstream (Pilot injection) and downstream (Primary injection) of backward-facing step. Experiments were also conducted with single wall injection and in the absence of step and pilot injection. Ignition and pressure drop characteristics of the combustor were determined. Wall static pressures were considered as a measure to find the advantages of pilot and double wall injections. The effects of pilot injection, double wall injection and the step on the performance of the supersonic combustor were studied in terms of combustion efficiency and stagnation pressure drop. It is found that the combustor with pilot fuel and step configuration, employing double wall injection yielded better results.

ISSN:0010-2202    

DOI:10.1080/00102209808952008

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new class of pentacyclic hydrocarbon compounds with high-energy/high density have been synthesized to be used as fuels or fuel additives, with the expectation that their inclusion in the fuel mixture will result in a net increase in volumetric efficiency of the current generation of powerplants. These compounds exhibit high density and contain a moderate amount of strain energy which contributes to the energy output during combustion. Through direct measurements, melting and boiling points, specific heats and latent heats of fusion were determined. Droplet combustion experiments with binary solutions of solid high-energy fuels in kerosene indicated increased effervescence and higher heat output. The liquid high-energy-density formulations exhibited microexplosive combustion behavior.

ISSN:0010-2202    

DOI:10.1080/00102209808952009

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Particle data on a 160 MWecorner-fired, pulverized-coal fired boiler operated by New York State Electric and Gas (NYSEG) were collected as part of a comprehensive series of measurements taken to better understand the complex phenomena involved in pulverized-coal combustion, and to develop information suitable for model validation of comprehensive combustion codes. Changes in operating conditions involved variations in coal type, the amount of overfire air, load, and burner tilt. The measurements discussed include those of particle size, velocity, concentration, and an analysis of the concentration probability density function. The particle data were collected using the laser-based PCSV (Particle Counter Sizer Velocimeter) probe. PDF calculations were based on particle velocity distributions measured with the PCSV probe and particle data rate statistics measured with a frequency-to-voltage converter connected to the signal processing system. Measurements for this test series were collected primarily in the radiant section of the boiler and showed that both particle size and velocity were sensitive to the boiler operating conditions. Particle sizes generally decreased with increasing vertical distance, and measured velocities were influenced by the location of air inlets at most locations in the boiler. In contrast to the measured particle sizes and velocities, cumulative number densities and the associated PDF's showed little sensitivity to the variables investigated during this test. Concentration levels were fairly constant in the radiant section of the boiler, and then dropped significantly above the nose. Analysis of the probability density functions showed that the log-normal distribution function best fit the experimental concentration probability density functions at all locations in the boiler.

ISSN:0010-2202    

DOI:10.1080/00102209808952010

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A tunable KrF excimer laser operating at 248  nm is used for visualization of water vapor (H2O) at engine-like conditions by two-photon laser-induced fluorescence (LIF). The effects of two-photon absorption in water, laser sheet focusing and two-dimensional fluorescence imaging conditions are discussed, and an estimation of the reliability of the image data is given. The water vapor content measured close to the spark plug prior to ignition in a high-pressure combustion cell is correlated to the ensuing combustion rate, which is determined from the evolving pressure during combustion. The combustion rate is shown to be dependent on the water vapor concentration close to the spark plug prior to ignition, where a high water concentration yields a slow combustion. Using two-photon LIF of water vapor, the influence of residual gases on cycle-to-cycle variations is also investigated in a running spark-ignition (SI) engine. With a low inlet manifold pressure, a correlation coefficient of 0·6 is found between the combustion rate and the residual gas concentration close to the spark plug at the time of ignition. Further, a fast combustion in one cycle is found to yield more residual gases in the subsequent cycle.

ISSN:0010-2202    

DOI:10.1080/00102209808952011

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Active control has been pursued vigorously for combating thermoacoustic instabilities in combustion processes. Most experimental investigations employ empirical design procedure for determining the characteristic parameters of the filter and phase-shifter of the controller. Such procedure has been observed to result in resonance at frequencies which were not excited in the power spectrum of the uncontrolled combustor, though the dominant thermoacoustic instability was suppressed. In this paper, we present an alternative design methodology which is based on the underlying physical model of the combustor and modern control theory. We show that using this methodology, one can avoid the generation of secondary peaks and achieve short settling time using small control energy. The physical model takes into account multiple acoustic modes, the heat release dynamics of a premixed flame, and the effect of an actuator such as a loudspeaker, on the flow variables over a wide range of frequencies. The model-based control strategy consists of optimizing a quadratic cost function of the pressure response and the control input, and leads to a straight forward selection of the parameters of the active controller. The resulting controller is compared to those obtained using empirical designs and is shown to modulate the gain-phase characteristics of the combustor over a wide range or frequencies thereby leading to a better performance and no secondary resonances.

ISSN:0010-2202    

DOI:10.1080/00102209808952012

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The influence of initial droplet diameter on the sooting and burning behavior of isolated droplets under microgravity conditions was investigated by measuring soot volume fraction, ƒv, soot mass,ms, sootand burning rate. Theƒv, andms, sootwere measured using a full-field light extinction and tomographic inversion technique. The experiments were conducted at the NASA-Lewis 2·2 second droptower in Cleveland, OH.

ISSN:0010-2202    

DOI:10.1080/00102209808952013

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

For convenient diagnostic probing and analysis of the fundamental properties of the laminar burning of initially separated fuel vapor and gaseous oxidizer, the counterflow affords the advantage of planar symmetry; the key dependent variables depend on a single Cartesian coordinate only. However, in the diffusion-flame limit, in which the most vigorous and spatially intense chemical conversion occurs, the counterflow becomes unstable. As the strain rate goes to zero, the residence time of the throughput increases, so that, in earth gravity, small disturbances grow to finite amplitude during transit of the counterflow burner, and the planar symmetry is disrupted. Accordingly, in previous work, we have explored the properties of a fully developed, strain-rate-free planar diffusion flame in microgravity, with emphasis on the realistic case of differing species diffusivities (unequal Lewis-Semenov numbers). However, previously we dealt only cursorily with how such a planar diffusion flame might beinitiatedwithin a finite impervious noncatalytic isothermal container, and how the flameinteracts with the wallsof the container. Here, we discuss the triple-flame-related phenomena associated with the rapid constant-speed withdrawal, by translation in its own plane, of a thin planar interface, initially separating the contents or a half volume containing fuel vapor (diluted with an inert gas) from the contents of a half volume containing gaseous oxidizer (diluted with another inert gas)We also address the thickness of, and temperature fields within, near-wall flame-quench layers, which complement the vigorous burning in the interior of the container (until depletion of fuel and/or oxidizer effects extinction in the interior). For these studies, we formulate and solve simplistic models that straightforwardly extend the classical Shvab-Zeldovich/Burke-Schumann treatment of vigorous burning in unpremixed gaseous reactants with equidiffusion for species (equal Lewis-Semenov numbers).

ISSN:0010-2202    

DOI:10.1080/00102209808952014

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Evolution and combustion of fuel gas discharged into the atmosphere is simulated numerically. Finite-duration vertical releases are considered, the ignition occurring on the axis at some elevation above the source. The main stages of the release and burning are discussed, spatial distributions of concentrations, temperature and reaction rate in the fireball are presented at various stages of evolution, from ignition up to total burnout. Influence of the release parameters (fuel mass, injection velocity, orifice size, ignition source height) on the lifetime of the fireball is studied for methane and propane releases. The dependence of the fireball burning time on the Froude number (defined as the square of the ratio of the release velocity and the characteristic buoyant velocity) is obtained. The effect of the source size and ignition source location is shown to be much less significant. The results of calculations are compared with the experimental dataonsmall-scale methane and propane fireballs. Fairly good agreement on the fireball geometry and burning times is obtained. Applicability limits of the results obtained are discussed.

ISSN:0010-2202    

DOI:10.1080/00102209808952015

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The most important reactions in the reduction of NO in reburn zones have been identified for several reburning fuels at low temperatures. This has been accomplished through the analysis of reaction rates and sensitivity in kinetic plug flow calculations simulating the gas reburning process. The kinetic model developed is evaluated through comparisons with experimental data. Acetylene, ethylene, ethane, methane, and natural gas have been studied at various temperatures between 973 and 1373  K., The major NO removal pathway is found to be the HCCO + NO reaction in all cases. Critical to the modeling are the branching fraction of this reaction and the competition for vinyl between dissociation and reaction with molecular oxygen. These points are discussed in detail.

ISSN:0010-2202    

DOI:10.1080/00102209808952016

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This work is concerned with the applicability of modelling swirling pulverised coal flames with ideal chemical reactors. The objectives were to predict the emissions of NO and CO, and the burnout of char. The fluid dynamics were simplified by use of a system of ideal chemical reactors. The near burner zone was modelled as a well-stirred reactor, the jet expansion as a plug flow reactor, the external recirculation zone as a well-stirred reactor, and the down stream zone as a number of well-stirred reactors in series. A reduced model of a detailed reaction mechanism was applied to model gas phase chemistry and a novel model was developed for soot oxidation. A population balance was used to keep track of size and density changes for the char combustion. Individual particle temperatures were calculated for each size fraction. The model includes only one burner specific calibration parameter which is related to the mixing of air and fuel. The model was validated against experimental results from a 160kWthpulverised coal burner. For single staged combustion at varying stoichiometries, for two stage combustion, and for different coals good agreement between model and experiment was obtained for NO emissions and carbon in ash. This work also indicates that the interaction between the homogenous gas phase chemistry and the heterogeneous chemistry (soot and char), due to recombination of radicals on the surfaces, is of importance for the nitrogen chemistry in coal flames, especially for ammonia formation.

ISSN:0010-2202    

DOI:10.1080/00102209808952017

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor