摘要:

A new mechanical technique for the production of well characterized small diameter isolated free droplets of multi-component and emulsified liquids is described. The technique is employed in development of an experimental facility to generate, inject, and combust free droplets of liquid fuels in a well defined, hot convective atmosphere. Initial observations of the burning characteristics of isolated free droplets of water in pure n-paraffin emulsions are reported. The existence of free droplet secondary atomization and the importance of fuel physical characteristics, water content, and internal phase structure to optimizing this phenomenon are confirmed. Observations are found to be in agreement with earlier predictions of the required internal phase super heat (Avedisian and Andres, 1978) and results suggest previously published suspended droplet combustion data on emulsified fuels to be of limited quantitative value. Observations are compared with the prediction of and physical models used in recent analytical studies of water-in-pure fuel emulsion droplet combustion.

ISSN:0010-2202    

DOI:10.1080/00102207908946913

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The burning rate of a fuel-oxidant mixture is invariably found by experiment to have a maximum slightly on the fuel-rich side of stoichiometry. The usual explanation is that the maximum adiabatic flame temperature is shifted there by dissociation of the products. However, several aspects of this explanation are unsatisfactory: the burning rate depends on other factors than the flame temperature, especially near stoichiometry; verification is always numerical and hence for a limited range of parameters; and cool flames, where dissociation is negligible, are excluded. The present paper is an analysis of a two-reactant model, with not necessarily equal Lewis numbers K and L for oxidant and fuel (respectively),in the absence of dissociation. In particular, it is found that the phenomenon occurs whenever K is large enough and L smallenough, the precise conditions nearly always being met in practice. In other words, diffusion alone provides a satisfactory explanation. Part II will incorporate dissociation to show that, while it does explain the shift in maximum temperature, it has a subsidiary effect on the maximum burning rate.

ISSN:0010-2202    

DOI:10.1080/00102207908946914

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

A model, based on the two phase theory of fluidization, is presented for calculating carbon load and spatial oxygen concentration in a fluidized bed combustor operated with multisized coal feeds. It accounts for both the cases of complete mixing and piston flow of gases in the particulate phase and uses the number of transfer units X between the bubble and the particulate phases as a parameter. Allowance is made for the different burning rates of volatiles and carbon, and temperature effects on the latter are reconsidered. Experimental data of previous authors are used to test the proposed model. Values of X required to fit these data are compared with those expected from the flow characteristics of the bubbling bed.

ISSN:0010-2202    

DOI:10.1080/00102207908946915

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

A theoretical model of catalytic combustion is developed which allows calculation of temperature and reactant/product distribution in a tubular duct with catalytic walls. Under adiabatic conditions, as prevail in the central ducts of a catalytic monolith combustor, and in the absence of heat conduction along the reactor walls, the model provides an analytic solution. It exhibits the existence of multiple steady states and, for gas mixtures with low Lewis number, temperature excursions in excess of the adiabatic reaction temperature, Gas-phase reactions are shown to increase the fuel consumption in a given length of catalytic duct but leave unchanged the relations between the temperature and species distributions. The model is applied to a series of experimental results obtained with different fuels in tubular reactors. Satisfactory agreement is found between theoretical and experimental data when account is taken of the effects of heat loss from the reactor to the environment.

ISSN:0010-2202    

DOI:10.1080/00102207908946916

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Flammability limits of both premixed and diffusion flames for n-alkanes and n-alcohols found in the literature are assembled. Several sets of theoretical flame temperatures and combustion stoichiometrics corresponding to the limits are denned and tabulated. These data are used to discuss the implication of the commonly accepted view that extinction (i.e., limit of flammability) occurs at temperatures at which the flame reaction rates become too low to overcome the dissipation processes. It is shown that the customary assumption of thermodynamic equilibrium at the limits leads to two serious difficulties in interpretation: (i) the inference that in fuel-rich regions the flame reactions are favored by a decrease of oxygen concentration, which is unreasonable from the kinetic point of view; and (ii) the indication that, in the case of several fuels, diffusion flames have a wider range of stability than their premixed counterpart. Thus, the assumption of thermodynamic equilibrium at the limits is unrealistic. It is also shown that when the assumption of equilibrium is replaced by an alternative assumption of incomplete reaction in a way suggested by chemical-kinetic considerations, a simple qualitative explanation of the limit phenomenon, removing both difficulties, becomes apparent. It is concluded that experimental measurements of combustion-product concentrations and temperatures near the limits are needed for quantitative explanations of the observed phenomena.

ISSN:0010-2202    

DOI:10.1080/00102207908946917

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

An essentially monosized ambient temperature and pressure fuel mist in air was generated by vaporizing and then condensingn-dodecane in nitrogen gas and later adding oxygen. Drop size was determined from the Fraunhofer diffraction pattern produced by passing a light beam through the mist. Oxygen concentration in the air around the drops, overall air-fuel ratio and fuel burning rale were measured. Oxides of nitrogen from the laminar mist flames, expressed as an emission index—milligrams of NOxas NO per gram of fuel burned—ranged from 0.1 to 3 and increased rapidly as droplet size was varied from 6 to 20 μm, The rate of increase for sizes from 20 to 35 μm was less rapid. Heterogeneous burning, with visible centers of combustion in a non-luminous flame was observed for all drop sizes. Probe results showed NOxwas formed in the thick flame zone. The NO2/NOxmole ratio increased with drop size, reaching 0.99 for the drops of 35 μm diameter.

ISSN:0010-2202    

DOI:10.1080/00102207908946918

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Numerical predictions are made of the radial and temporal variation of species concentration and temperature in a combustible gas around a hot, inert, spherical particle. The governing equations are integrated in dimensionless form, and ten dimensionless parameters are found to govern the solution. Five gas species were modeled: fuel, oxidizer, water, carbon dioxide, and nitrogen. Predictions are made of the critical particle diameters and temperatures above which a propane/air mixture is ignited by a particle which has the density and specific heat of aluminum. From the results of the model and from experimental results cited in the literature, it is argued that an aluminum particle formed by abrasion must be larger than 800 μm in diameter to ignite a stoichiometric propane/air mixture.

ISSN:0010-2202    

DOI:10.1080/00102207908946919

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

This paper deals with the detonability of unconfined clouds of natural gas and air. The effect of the presence of ethane in methane air clouds was experimentally studied. All tests were conducted using stoichiometric fuel-air mixtures where ethane was varied between 0 and 5.66 percent by volume of the total mixture. A detonation is characterized in the experiments by a non-decaying constant velocity wave propagation. Plots of critical initiation energy versus percent C2H6show that very small amounts of ethane have a significant effect on the detonability of methane-air clouds.

ISSN:0010-2202    

DOI:10.1080/00102207908946920

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The predictions of Thomas's Hot Spot Theory of the self-heating of volumes of hot material in a cool environment have been examined experimentally for a 0.61 m cube of mixed hardwood sawdust. Thomas's theory agrees well with the experimentally determined critical ignition temperature for a given size of cube.

ISSN:0010-2202    

DOI:10.1080/00102207908946921

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor