摘要:

We present an experimental study of CO and NOxemissions from a controlled-air burner. Burners of this type are used throughout industry for direct heating of gas streams. A small scale research burner is used which emulates the key geometric features of a typical production burner. Exhaust measurements based on parametric variations of burner operating conditions are combined with insights gained from in situ measurements and from visual observations of flame structure to develop a description of the key mechanisms controlling pollutant production.

ISSN:0010-2202    

DOI:10.1080/00102209508907721

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A model taking account of condensation and evaporation within damp combustible material is considered where the fibres are considered completely covered by water liquid so that the evaporation term is not dependent on the amount of liquid present This leads to a simpler equation set and highlights the important findings that (a) greater dampness can induce an ignition event (even in the absence of a wet hygroscopic reaction) and (b) there can be situations where ignition takes place after quite a sharp (initial) temperature decrease.

ISSN:0010-2202    

DOI:10.1080/00102209508907722

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A field-parametrized model termed the Inter-Layer Diffusion Model (ILDM) is developed and is implemented for the probabilistic description of scalar mixing in homogeneous turbulent flows. The essential element of the model is based on the lamellar theory of mixing in the context developed by Kerstein (199 la), and proposes that there are two coupled mechanisms by which the mixing process is described. These mechanisms are due to: (1) local events and (2) integrated global events. The mathematical formalities by which the closure is invoked are described and it is shown that the conditional expected diffusion of the scalar field depicted by the model depends more directly on the local events. With the manipulation of each of these two mechanisms, several families of scalar probability density functions (pdf's) are generated. These families include some of the distributions generated by other mixing closures. The similarity of local events imply the similarity of the conditional expected diffusion as generated via these models. The global events manifest themselves by the evolution of the tonditional expected dissipation, and also the boundedness of the composition domain. While the pdf's generated in this way are very different, their applications for modeling of mixing limited reactions do not yield significantly different results.

ISSN:0010-2202    

DOI:10.1080/00102209508907723

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The study of the ignition of a combustible mixture induced by means of an unsteady gas jet, at an initial temperature ranging from 700 to 3000 K, requires the construction of an original test facility which consists of a shock tube connected to a combustion chamber via an injector. With this new experimental setup, the ignition conditions of hydrogen-air ( + carbondioxide) mixtures, induced by a hot hydrogen-argon mixture, have been extensively studied, resulting in the determination of the ignition limits of these combustible mixtures, at an initial pressure and temperature of 100 kPa and 403 K respectively.

ISSN:0010-2202    

DOI:10.1080/00102209508907724

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It has been shown that pressure waves can have a large effect on the burning rate of flames. For sharp changes in pressure, recent studies by Batley, Mcintosh and Brindley [2] have indicated that the mass flux is dependent on the origin chosen as the frame of reference. Consequently, the structure of the flame is altered by the passage of a pressure disturbance as gas flows at different rates through different locations of the flame.

ISSN:0010-2202    

DOI:10.1080/00102209508907725

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A turbulent combustion model based on the coherent flamelet model was developed in this study and applied to diesei engines. The important physics involved in each phase of diesei engine combustion were defined and modeled as directly as possible. The combustion event was broken into three phases: low temperature ignition kinetics, high temperature premixed burn kinetics, and diffusion burn. Two transition steps were developed to model the progression of combustion between each of these phases. The ignition phase was accomplished using the Shell ignition model. The transition to the high temperature premixed burn kinetics was accomplished using a criteria based on heat release rate and temperature. The high temperature premixed burn kinetics were modeled using a global Arrhenius equation for the rate of reaction. The transition to the diffusion burn was based on a critical Damkohler number. Finally, the coherent flamelet model was used as a foundation for the diffusion burn portion of the model. The model was implemented into the multidimensional computational computer code KIVA-II. The sensitivity of the combustion events to several of the model parameters was examined and the results were used to pick the optimum settings for the model. Previous experiments on a Caterpillar model E 300, # 1 Y0540 engine, a Tacom LABECO research engine, and a single cylinder version of a Cummins N14 production engine were used to validate the cylinder averaged predictions of the model. The characteristics of the modeling approach were also addressed by examining the spatial resolution of the model results inside the engine cylinder. The location and magnitude of model heat releases, flame areas, and equivalence ratios were examined. The results of this approach to the modeling of diesei engine combustion could be used to enhance to modeling of engine emissions.

ISSN:0010-2202    

DOI:10.1080/00102209508907726

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A comprehensive review of the experimental conditions that have been used in flame impingement studies is given here. It concerns experiments in which heat transfer rates were measured. The objective of this review is to define the experimental conditions that have been used. A companion paper contains part 2 of the review (Baukal and Gebhart, 1995a). The objective of that review is to specify the diagnostic techniques and measurements used in the tests.

ISSN:0010-2202    

DOI:10.1080/00102209508907727

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper is the second part of a comprehensive review of flame jet impingement studies. The first part concerned the experimental conditions that were used in those studies. This part concerns the measurements that were made in those studies. Both reviews describe studies where the heat transfer to a target was measured. The geometries include flames impinging: 1( normal to a cylindrical surface, 2( normal to a hemisphericaliy-nosed cylinder, 3( normal to a plane surface, and 4( parallel to a plane surface. Total heat flux to these targets has ranged up to 41 M W/m2. Three steady-state methods have been used to determine the heat fluxes: uncooled target, cooled target and cooled heat flux gage. Two transient methods have been used: an uncooled target and an uncooled gage. In these studies, the gas temperatures have ranged from 292 to 3200 K. These have commonly been measured with bare wire thermocouples and line reversal techniques. Measured gas velocities have ranged from 0.3-1400 m/s. These have commonly been measured with Pilot tubes and laser doppler velocimeters. The static pressure distribution near the stagnation point has been measured. This was used to determine the velocity gradient which is used in the semi-analytic heat transfer solutions. In a few studies, the thermal radiation from the flame to the target has been measured. The gas composition of the impinging jet has been measured in some of the studies. Other measurements, such as soot concentration and flame visualization, are also briefly reviewed. The advantages and disadvantages of each measurement technique are briefly considered. Recommendations for improved techniques are given.

ISSN:0010-2202    

DOI:10.1080/00102209508907728

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The small scale structure of premixed methane/air flames, stabilized on perforated or porous flat-flame burners has been studied numerically. The two-dimensional combustion equations have been solved, using the vorticity-stream function formulation for the flow field and two different chemistry models: the skeletal mechanism for lean methane combustion and a one-step scheme. The curvature of the flames, predicted by both models is comparable. The range of pore sizes, porosities and mixture velocities, which can be used to create practically undistored flat flames has been determined. It is found that more-dimensional transport effects are negligible in flames, stabilized on the flat-flame burners recently introduced by (Maaren van, 1994) for measuring burning velocities with the Heatflux method. This guarantees that the measurement data are not obscured by small scale distortions and can be compared with ID modeling results.

ISSN:0010-2202    

DOI:10.1080/00102209508907729

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A methodology for deriving material pyrolysis properties is proposed and validated by using three charring materials (pure cellulose, and two different particle boards designated as N and F). The methodology uses experimental data obtained in a pyrolysis apparatus together with an accurate integral thermal pyrolysis model for the charring pyrolysis process (see CST, 88, 309-328, 1993). The effects of various parameters on pyrolysis rates and surface temperatures are investigated by applying the integral pyrolysis model. This analysis shows that, in addition to the unpyrolyzed (virgin) material thermal properties, char conductivity (kc) and heat of pyrolysis (L) are adequate to describe the transient pyrolysis process for a charring material. The thermal capacity of char is shown to have negligible effects on the pyrolysis process because surface radiation loss from the hot char surface is the dominant mechanism causing the reduction of pyrolysis rates in charring materials.This result, which is for the first time documented definitely, is a significant achievement in characterizing the pyrolysis properties for charring materials. The thermal properties of the virgin material(kρc)c, and the pyrolysis temperature,Tp, are determined from surface temperature and mass loss histories during the heat-up period until pyrolysis starts. The char conductivity (kc) is derived from the surface temperature histories during pyrolysis while the heat of pyrolysis is derived from the mass pyrolysis rate histories by comparison of the experimental data and the results from the integral model.

ISSN:0010-2202    

DOI:10.1080/00102209508907730

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor