摘要:

In the present study, the unburned gas region of wrinkled laminar flame stabilized on a Bunsen burner was visualized by a laser tomography and the fractal analysis was applied to the flame boundaries to characterize the geometry of wrinkled laminar flame. The effects of mixture turbulence, laminar burning velocity and burner geometry on the fractal parameters were examined statistically. The fractal dimension D3was found to be expressed by non-dimensional parameter u’/SL, and to increase with the turbulence intensity from 2.17 to 2.32, approaching asymptotically to 2.36. Inner and outer cutoff scales are not directly correlated with typical turbulence scales of unburned mixture. The inner cutoff scale £, is affected by the flame properties as well as the turbulence characteristics. For the Bunsen burner flames, the outer cutoffscale ϵiwas found to be determined by the flame base diameter. The turbulent burning velocity can be estimated approximately by the equation, ST/SL= (ϵi/ ϵo,)2−D2

ISSN:0010-2202    

DOI:10.1080/00102209408907695

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Results from a computational model of transient droplet vaporization are presented. In this model, axisymmetric flows around translating single component droplets are assumed. The governing equations are expressed in finite volume form and solved numerically for transient velocity, species and temperature profiles. Fully variable properties in the gas and liquid phases are allowed (except for liquid densities, which are held constant), and pressures of 1 and 10 atm are considered. A unique feature of the calculations is the inclusion of surface-tension gradients resulting from droplet surface temperature variations. Results show that surface-tension gradients significantly affect droplet internal temperature and velocity fields even when initial droplet Reynolds numbers, based on droplet diameters and free-stream conditions, are as large as 50. When surface-tension gradients are allowed at high initial Reynolds numbers (SO), droplet internal circulation rates are found to be initially increased for a short period of time and then significantly reduced, causing bulk liquid temperatures and droplet vaporization rates to increase at smaller rates than when surface-tension gradients are neglected.

ISSN:0010-2202    

DOI:10.1080/00102209408907696

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The influence of the atomization characteristics on the combustion of heavy oil is investigated. Combustion tests are conducted in an experimental furnace with a thermal input of 0.33 MW. The characteristics of the spray produced by a simplex pressure-swirl nozzle are known in detail from a previous investigation in an atomization rig. Two cases are selected and tested under combusting conditions, while keeping constant the remaining experimental parameters. Reported results include extensive measurements of (he spatial distribution of the velocity field, temperalure and species (O2, CO, CO2, UHC and NOxinside the flame, as well as the emission of pollutants in the flue gases. The differences in the spray lead to changes in the fuel vapor distribution inside the flame. The consequences are important variations of the flame characteriscics and of the emission of gaseous and solid pollutants.

ISSN:0010-2202    

DOI:10.1080/00102209408907697

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

New informations on weakly-turbulent premixed flames in the cusped-flame regime are obtained upon studying a Michelson-Sivashinsky equation whose solution (the instantaneous flame shape) is excited by the influence of a weak, pseudo-random additive forcing, that is meant to mimic incoming velocity fluctuations. Attention is focused on the time-dependent mean spacing lc{t) between crests, in cases where the front is flat before forcing is switched on. Despite the complexity of each individual run, a surprisingly simple history Ac(t) always emerges upon averaging lc(t) over many realizations of the forcing function, especially in the limit of weak forcings: a noise-triggered linear stage is followed by a stage of crest-coalescence during which dAJdt is a constant and the direct role of forcing is minor; then, rather abruptly, an equilibrium stage is reached where Ac(t) acquires a time-independent value because the crest implants induced by the noise statistically equilibrate the coalescences. Improved or new scaling-laws, including dynamical ones, are suggested numerically and theoretically for each of the aforementioned stages.

ISSN:0010-2202    

DOI:10.1080/00102209408907698

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A single production cooktop burner was studied at three levels of thermal input, to determine the effects of load height on its efficiency and gaseous emissions. In this work, load height was defined as the vertical distance from the center of the base of the load vessel to the top of the burner ports. To simulate practical operation as closely as possible, the production gas injector was used, so that primary aeration varied with thermal input in these experiments. The Australian Gas Association regulations limit the operating range of load height for this burner to values between 7mm (CO/CO2<0.01) and 48 mm (efficiency > 40%). Minimum NO2emission rates of 8.7,8.0 and 8.8 ng/J were observed at load heights of 25, 40 and 48 mm respectively, at thermal inputs of 0.49, 0.83 and 1.65 kW respectively.

ISSN:0010-2202    

DOI:10.1080/00102209408907699

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We examine the stability of premixed flames in mixtures containing significant amounts of fine inert dust whose sole impact is upon the radiative transport. By using well-established modeling strategies together with a simple radiation model which preserves much of the essential physics, it is possible to explore to what extent radiative transport displaces the classical non-hydrodynamical stability boundaries of the plane deflagration. Analysis is possible for arbitrary values of both the Planck length and the Boltzman number. It is shown that the pulsating/traveling-wave instability is strongly enhanced by the presence of radiation, and can be present even if Le < 1. On the other hand, radiation tends to suppress the cellular instability normally associated with values of Le less than 1. The latter is consistent with preliminary experimental observations of Abbud-Madrid and Ronney.

ISSN:0010-2202    

DOI:10.1080/00102209408907700

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The oxidation of mixtures of n-heptane and iso-octane in a high-pressure jet-stirred reactor has been investigated experimentally in a wide range of conditions covering the low and high temperature oxidation regimes (550-1150K, 10 atm, ø=1). The cool flame and negative temperature coefficient regimes were observed below 750K, Above 750 K, the normal high temperature oxidation of both fuels was observed. Reactants, intermediates and final products have been measured providing a useful picture of n-heptane-iso-octane mixtures oxidation. Cyclic ethers resulting from the low-temperature oxidation chemistry of n-heptane and iso-octane were identified. The evolution of their concentration as a function of RON have been measured. These results are interpreted in terms of reaction mechanism. Tentative correlations between RON and CO, CO2and C2H4in the cool flame region and for the high temperature oxidation (normal combustion) are presented.

ISSN:0010-2202    

DOI:10.1080/00102209408907701

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The uncatalysed and catalysed heterogeneous oxidation processes of a batch of Fullerene have been investigated in Ihe range 25-900°C under various non-isothermal heatings. The results are compared to those obtained with more conventional and well characterized carbons. With respect to these, Fullerene shows higher reactivity in both uncatalysed and catalysed processes. It has been shown that the contact between catalyst and carbon material strongly affects the catalysed oxidation. A high selectivity of the catalyst toward carbon dioxide formation has been found and the ability of the catalyst to catalyse the gas phase reaction of carbon monoxide to carbon dioxide at the temperature higher than 400°C has been proved.

ISSN:0010-2202    

DOI:10.1080/00102209408907702

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The oxidation of n-decane in a high-pressure jet-stirred reactor (JSR) has been investigated experimentally in a wide range of conditions covering the low and high temperature oxidation regimes (550-1150K, lOatm, Ø = 0.1 to 1.5), Reactants, intermediates and final products have been measured providing a detailed picture of n-decane oxidation. Cyclic ethers resulting from the so-called Iwo-temperature oxidation chemistry of n-decane were identified. The results are interpreted in terms of reaction mechanism. A detailed chemical kinetic modeling of the high-temperature oxidation of n-decane is used to assess the influence of low temperature chemistry in the intermediate temperature range.

ISSN:0010-2202    

DOI:10.1080/00102209408907703

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor