摘要:

Asymptotic methods for large Reynolds numbers are used to show that through displacement effects the heat release associated with both premixed and nonpremixed laminar flames in laboratory counterflow configurations result in significant alterations of the rate of strain attributed to the flow external to the flame. The analysis involves the classical sequence of calculating the first order inviscid flow, which in the present case yields the currently available expression for the rate of strain, the first order inner flow describing the structure of the flame including the displacement thickness of the flame and finally the second order outer flow yielding the correction to the rate of strain. Comparisons are made with some experimental and fully numerical results to demonstrate the significant alterations in the rate of strain produced by the displacement effects associated with heat release.

ISSN:0010-2202    

DOI:10.1080/00102209208947204

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A parametric study of the fundamental exchange processes for energy, mass and momentum between the liquid and gas phase of vaporizing, multicomponent-liquid droplets is presented. The applicable model, which examines an isolated, vaporizing, multicomponent droplet in a laminar, axisymmetric, convective environment, considers the different volatilities of the liquid components, the alteration of the liquid-phase properties due to the spatial/temporal variations of the species concentrations and also the effects of multicomponent gaseous diffusion. In addition, the model accounts for variable thermophysical properties, surface blowing and droplet surface regression due to vaporization, transient droplet heating with internal liquid circulation, and finally, droplet deceleration with respect to the free flow due to drag. The numerical calculation employs finite-difference techniques and an iterative solution procedure that provides time-varying spatially-resolved data for both phases. The effects of initial droplet composition, ambient temperature, initial Reynolds number, and volatility differential between the two liquid components are investigated for a liquid droplet consisting of two components with very different volatilities. It is found that hydrocarbon mixtures with higher concentration of the less volatile substance actually vaporize faster on account of intrinsically higher liquid heating rates. An evaluation of the potential for droplet microexplosion of some hydrocarbon mixtures shows that the liquid-droplet temperatures remain below the limit of superheat of the mixture, even when the calculated equilibrium vapor pressures exceed the ambient value.

ISSN:0010-2202    

DOI:10.1080/00102209208947205

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The problem of multistage metal particles combustion has been discussed in the present paper. Experimental research on metal particles burning has been undertaken on the basis of a new means of their formation and ignition by a pulse discharge

ISSN:0010-2202    

DOI:10.1080/00102209208947206

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The extinction of hydrocarbon flames which are subjected to a nonuniform electric field has been studied. The experimental system consists of a candle type burner having a hemispherical tip and a horizontal conducting plate situated above the flame. A direct current high voltage was applied between the burner head and the conducting plate. The voltage was gradually increased until flame extinction is observed. It was found that the extinction voltage depends on the field polarity, the distance between the electrodes and the burner head curvature. For a fiat head burner no extinction was observed up to the breakdown voltage. The extinction was observed to occur in two phases. In the first as the applied voltage increases, the luminous zone stretches upward up to a critical field strength for which a sudden flame contraction occurs. In the second phase the flame gradually contracts as the voltage is increased and is finally completely extinguished. It is concluded that the interaction between the electric field and the flame is associated with electric forces which are applied to the polarizable inetrmediate species in the flame zone. These forces are directed, irrespectively of the voltage polarity, away from the flame zone, mainly toward the burner tip where the intensity of the electric field higher.

ISSN:0010-2202    

DOI:10.1080/00102209208947207

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A two-dimensional adaptive finite-element code is used to numerically investigate the propagation of a laminar premixed flame in a closed rectangular chamber giving rise to the so-called tulip instability. The physical model includes a single one-step chemical reaction where the physical parameters involved in the model are chosen in order to adequately represent a stoichiometric methane-air flame. Attention is focused on the shape of the flame and the flowfield generated by the combustion process. A detailed comparison between the numerical results and available experimental data shows a very good agreement, for various sizes of the combustion chamber.

ISSN:0010-2202    

DOI:10.1080/00102209208947208

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The fuel-lean oxidation of methyl chloride was investigated using flow tube kinetics experiments coupled with plug and laminar flow models that included detailed reaction chemistry. Acetylene, vinyl chloride, ethylene, methane and CO were observed as the major reaction products at partial conversion conditions. A sensitivity analysis combined with a rate of production analysis for key species observed experimentally was used to identify reaction bottlenecks in the initial literature model used. Rates for the CH2CL + CH2CL and CH3+ CH2CL recombination reactions were estimated using QRRK analysis. The modified model accurately predicted experimental measurements of both methyl chloride conversion and intermediate product species profiles as a function of temperature. Model and experimental results highlight the difference in oxidation pathway between lean and rich conditions. Oxidative pyrolysis speeds CH3CL destruction and enhances CH2CL production leading to formation of C2H3CL. C2 production is also enhanced due to the relative difficulty in oxidizing CH3CL compared to CH3. Both model and experimental results also demonstrate that high destruction levels for lean methyl chloride oxidation can be achieved at moderately high (< 1335 K) temperatures with low residence times (< 16 ms) assuming plug flow and hot wall conditions are maintained.

ISSN:0010-2202    

DOI:10.1080/00102209208947209

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Thermally-assisted laser induced fluorescence temperature measurements using upward vibrational transfer from υ' = 0 to υ' = I in A2Σ+ OH have been demonstrated in premixed nitrogen diluted flames of acetylene, ethylene, and methane over a wide range of equivalence ratios. Detection of the (0-0) and (1-0) vibrational bands was used to determine the relative populations of υ' =0 and I from which temperature was calculated assuming a simple Iwo level model incorporating the effects of vibrational energy transfer and quenching. It was found that collisional effects that are a source of systematic error can be accounted for through a calibration procedure for each fuel type. The resulting accuracy of the measurement is better than I00K as determined through comparison with sodium line reversal temperature measurements in flames that ranged in temperature from 1700 K to 2700 K. Similar results using detection of the (0-1) and (1-0) vibrational bands in order to minimize self-absorption effects were also obtained. Single-shot measurements using 0.7 mJ of laser energy were also demonstrated with a lσ precision of 5%.

ISSN:0010-2202    

DOI:10.1080/00102209208947210

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The combustion process of tetradecane in a direct injection diesel engine has been studied by means of fast sampling and chemical analysis of the combustion products collected inside the diesel chamber during the early stages of the combustion cycle. Soot and acetylene were the major pyrolytic products and both of their concentration rapidly increased just after the ignition point, although acetylene reached its maximum concentration before the maximum of soot. Polycyclic aromatic hydrocarbons were minor pyrolytic species produced during the combustion cycle and accounted for less than 20% of the heavy organic material, referred to as high molecular weight species, whose concentration was more than one order of magnitude lower than soot and C2H2concentration

ISSN:0010-2202    

DOI:10.1080/00102209208947211

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A method for deriving global ignition kinetics from a detailed chemical mechanism is described, with the lime-temperature range of applicability assessed. The computed ordering of simple hydrocarbons by ignition temperature is consistent with published data. Values of the global rate parameters were found to be only weakly dependent on gas mixing intensity, as determined by a comparison of results from a perfectly-stirred reactor model and plug flow reactor model. Major reaction pathways prior to and at ignition are presented for methane, ethane, ethylene and acetylene in stoichiometric air. Radical chain mechanism analysis of reduced reaction sets demonstrates that values of effective ignition activation energies are dependent almost entirely on one or two chain-branching reactions. These results suggest that the global chemistry representing the weakly reacting regime up to ignition may be determined independent of reactor fluid mechanics and utilized in the prediction of hydrocarbon auto-ignition.

ISSN:0010-2202    

DOI:10.1080/00102209208947212

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Minimum explosible concentrations (MEC) of dusts were measured in the Bureau of Mines 20-L chamber and in the Fike L-m3(1000-L) chamber. The MEC values for gilsonite dust and bituminous coal dust were measured in each chamber at several ignition energies. The explosibility of anthracite coal was also studied in the two chambers. Strong chemical ignitors with energies of 500 to 10 000 J were used in the tests. The uniformity of the dust dispersions in each of the chambers was studied by using optical dust probes. One purpose of the research was to determine if the 20-L chamber was “overdriven” at high ignition energies. The MEC-values measured in the 20-L chamber with 2500-J ignitors were comparable to those measured in the 1-m3chamber with 10 000 J ignitors. At higher ignition energies in the 20-L chamber, there was evidence of overdriving.

ISSN:0010-2202    

DOI:10.1080/00102209208947213

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor