摘要:

A simple model of the initiation and propagation of gas phase detonations is developed to treat the dependence of detonation thresholds on initiator characteristics. The initiator is modeled as a supersonic spherical piston which imparts the initiating energy to the gas over a finite and variable space and time. The model is applied to the development of scaling laws for the important class of the relatively slow explosions common in accident scenarios. The results are verified by comparison to available experimental data and to detailed computations performed by numerical simulation of the full governing equations.

ISSN:0010-2202    

DOI:10.1080/00102208008946934

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

An exact solution of simultaneous integral equations is obtained for the turbulence-corrected Arrhenius law in the asymptotic limit of high activation energy. The reaction rate is shown to be bimodal, namely, having the form of arithmetic means of two Arrhenius formulae corresponding to temperatures higher and lower than the average by the root-mean-square of the fluctuation. This formula explains experimental evidence of speeding up the reaction rate beyond the value calculated by first order perturbation of the turbulence intensity. Also, turbulence is shown to play the role of selective enhancement only for reactions with a high energy barrier.

ISSN:0010-2202    

DOI:10.1080/00102208008946935

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A simple method has been proposed to estimate the drag coefficient for bluff bodies in high velocity streams. The estimated values for the drag coefficient agrees well with the measured values. The bluff body shapes considered are the flame holder shapes and blockages employed in jet engine after burners. It has been found that over a range of inlet conditions, the drag coefficient remained fairly independent of Reynolds number. An approximate method of estimating the drag coefficient for staggered flame holder is indicated.

ISSN:0010-2202    

DOI:10.1080/00102208008946936

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A quantitative description of the eddy structure that occurs in turbulent combustion processes can be obtained by the use of laser velocimetry, as shown in this work. The mean eddy length scales, eddy lifetimes, and turbulent diffusivity have been determined in a spray combustion flame for the first time. Velocity data was obtained at various locations within the flame, and standard correlation techniques were modified and then applied to reduce the data. In order to assess how the spray burns, the measured eddy lifetimes were compared with the relevant reaction times and drop lifetimes. Conditions that are conducive to group combustion of the droplets, rather than individual droplet combustion, were found to exist in the upstream region of the spray. Local measurements of the hydrocarbon concentration also support the conclusion that the majority of droplets undergo group combustion. However, the data indicate that some of the larger drops can survive the initial burning region and form a dilute spray downstream, where conditions favor individual droplet combustion.

ISSN:0010-2202    

DOI:10.1080/00102208008946937

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

An atmospheric combustor has been developed to investigate the details of pulverized coal combustion. Gas and char samples were obtained from the combustor with water-quench probes. An argon tracer was used to determine the extent of gas mixing while the extent of particle dispersion and the extent of particle reaction were determined from measured char quantity and composition. Secondary air velocity and injection angle and initial coal size were varied in 28 tests. Secondary velocity had a significant impact on gas mixing rate while particle dispersion was not influenced significantly by changes in test variables. Rates of the several processes which influence pulverized coal combustion were determined. Gas mixing, coal particle heat-up, particle dispersion and coal particle reaction times were all of comparable magnitude and were all reduced by use of smaller coal particles. Measured profiles for mixture fraction, gaseous species, particle flux and coal burnout percentage provide data for combustor model evaluation.

ISSN:0010-2202    

DOI:10.1080/00102208008946938

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

摘要:

A model of the four-stroke S.I. engine cycle has been developed which predicts fuel consumption, NOxand HC emissions as a function of engine design and operating conditions. The model is primarily thermodynamic in nature containing no formal spatial dependence. The major new features of the model are: first, a treatment of heat transfer which confines heat losses to a boundary layer region surrounding a central adiabatic core; second, an integral boundary-layer analysis of in-cylinder burnup of quenched hydrocarbons; and third, a calculation of exhaust port HC oxidation which considers the temperature history of each element of gas leaving the cylinder. The main adjustable parameters of the model relate to the rate of heat transfer and the ratio of the two-plate quench to the single-wall thickness. An extensive comparison of model predictions with experimental CFR engine data is presented. The results show excellent agreement between predicted and experimental fuel consumption and NOxemissions. Predicted trends of HC emissions were excellent for variations in spark timing, EGR, and A/F ratio for stoichiometric and lean conditions, while under rich conditions, predicted HC levels fell below experiment. Only fair agreement with experiment was obtained for HC predictions under conditions of varying speed und load. The adjusted ratio of initial one-wall to two-plate quench thickness in the present calculations was found to be six times the expected laminar value, suggesting that the actual process of quenching and in-cylinder burnup is more complex than the essentially laminar, single-step kinetics treatment employed or that additional sources of HC are present which have not been taken into account in the model.

ISSN:0010-2202    

DOI:10.1080/00102208008946939

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208008946940

出版商:Taylor & Francis Group    

年代:1980

数据来源: Taylor