摘要:

The fire hazard of a combustible material may be ranked according to its ignition and flame spread characteristics. For chemically reacting flow systems, the spread rate assumes a special significance because the rate is usually faster than for stagnant systems. What fuel parameters significantly control the flame spread rate? In this paper, we focus our attention on the production of “excess fuel,” “excess flame length” due to burning of excess fuel, the heat fluxes to the burnt region and unburnt regions which raise the temperature of virgin surface to the gasification level, and finally the flame spread rate. In Part I, we have used integral techniques to obtain simple results for excess fuel and heat fluxes to the burning surface for buoyant, forced convection and stagnation flow systems; explicit but approximate results are provided for each parameter of interest and they are compared with numerical results and with experiment to provide a check on the present results. In Part II those results are utilized to obtain approximate but explicit expressions for excess Same length and flame spread rate in terms of known fuel and oxidizer properties.

ISSN:0010-2202    

DOI:10.1080/00102207908946878

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

In the previous paper (Part I), results were given for unburnt fuel fraction and wall heat flux for boundary layer flows with combustion. In the present paper, a highly simplified model of the combusting plume region and the previous unburnt fuel results are used to obtain analytical results for the ratio of flame to gasification heights in terms of the parametersrandB. It is found that these analytical results can be correlated by a simple formula which depends only on the ratior/B. These results are compared with the predictions of other theoretical work and with available experimental measurements. The flame height results and the heat flux results from Part I are then combined with a simplified physical model to obtain an explicit result for laminar flame spread on thermally thick surfaces. Using this explicit result the effects of varying parameters such as ambient oxygen concentration, heat of combustion and heat of pyrolysis on the flame spread rate are described. The importance of choosing proper initial conditions when comparing experimental data with theory is discussed, and comparisons with measurements for upward burning on vertical walls are given.

ISSN:0010-2202    

DOI:10.1080/00102207908946879

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The mechanisms of inhibition and catalysis at high degrees of conversion are analysed. A complete set of isothermal kinetic equations for inhibited hydrogen oxidation is computed. The inhibition efficiency is considered as a function of pressure, temperature, initial composition, and degree of conversion. The regions of no inhibition or of catalysis of hydrogen oxidation in the presence of hydrogen bromide are found. The contributions from regeneration of initial HBr and of the secondary inhibitor Br2are discussed. The parametric dependences of inhibited hydrogen oxidation rates are investigated for a number of elementary rate constants. The potential efficiency of inhibition with bromine compounds is evaluated.

ISSN:0010-2202    

DOI:10.1080/00102207908946880

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The results of an experimental investigation of the effect of supplemental hydrogen (up to 30 percent of the total fuel energy) on the combustion process in a CFR engine are reported. The hydrogen was added under otherwise constant conditions so that chemical properties were varied under constant hydrodynamic conditions. Calibrated cylinder pressure traces, averaged over many cycles, were incorporated into a two-zone thermodynamic analysis to determine the mass fraction burned as a function of crankangle. The techniques employed enabled changes in the induction period and combustion duration of the order of 0.1 ms to be resolved. The added hydrogen resulted in significant reductions in ignition delay or induction times, especially in lean mixtures. Reductions were greater with increased fractions of hydrogen. Once a turbulent flame was well established, the hydrogen had a relatively small effect on the burning rate. The results are consistent with a description of the combustion process which includes an induction period dominated by chemical dynamic effects and a turbulent burning period dominated by turbulent transport effects. Added hydrogen also led to improved efficiency and less cycle-to-cycle pressure variations.

ISSN:0010-2202    

DOI:10.1080/00102207908946881

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

A semi-empirical model is developed to describe the structure of porous coal char. The pores are assumed to be cylindrical tubes of lengthlpand radiusrp. The number of pores whose radius is betweenrpandrp+drpis denoted by a pore distribution function. A statistical theory and the available data suggest arp−3distribution of pore number density. The pore length is expressed as a collision integral over the distribution function and is shown to be proportional to the pore radius. Each pore that reaches the exterior surface of the char particle is depicted as the trunk of a tree. Each tree trunk of radiusrtis associated with an internal structure whose surface area is proportional tort3. The theory suggests that the structure of this “pore tree” resembles that of an ordinary tree or river system.

ISSN:0010-2202    

DOI:10.1080/00102207908946882

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

A mechanistic model has been constructed to describe pore combination during char gasification. The engulfment of the smaller pores by the larger ones is responsible for the relative depletion of the small pores and enhanced growth of the large pores. Pore volume distributions demonstrate qualitative agreement with laboratory measurements. Pore combination reduces the internal area by the factor (1 − θ), where θ is the porosity, and the θ dependence of the internal surface area is in approximate agreement with the data. However, the magnitude of the internal area is under predicted by a factor of 1.5 to 2. It is apparent that the influence of the parent coal and the effects of pyrolysis and pore growth during gasification are as significant as the effect of pore combination and must be considered before the time history of the pore distribution may be accurately predicted. It is demonstrated that these effects are responsible for an “order one” perturbation to the 1/rp3law derived in Part I.

ISSN:0010-2202    

DOI:10.1080/00102207908946883

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The transient ignition process of a stagnant combustible mixture by a stationary, isothermal flat plate or spherical particle is studied using matched asymptotic technique in the realistic limit of large activation energy. Results show that for a sufficiently-reactive mixture the flow field consists of a locally-similar reactive-diffusive region next to the hot surface and a non-similar transient-diffusive region external to it; that the ignition lag is usually much shorter than the characteristic diffusion time and hence can be considered to be instantaneous; and that the ignition process is only minimally affected by the geometry of the body. An explicit expression for the ignition delay has also been derived, enabling a priori assessment of its magnitude and its functional dependence on the various system parameters of interest.

ISSN:0010-2202    

DOI:10.1080/00102207908946884

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102207908946885

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Experimental measurements of the time required for disruption of unsupported residual oil/water and residual oil/methanol emulsion drops passing through hot combustion gases are presented. The effects of varying the weight fraction of internal phase, initial diameter of the drop, size of internal phase drops, initial temperature of the drop, ambient temperature, and relative velocity between the drop and ambient gases on drop disruption time have been investigated.

ISSN:0010-2202    

DOI:10.1080/00102207908946886

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

One of the methods contemplated for reducing the potential spill hazards posed by large accidental spills of energy fluids such as Liquefied Natural Gas is to reduce the quantity of spill or prolong the duration of spill of a given volume. These are to be achieved by appropriate changes in the design of ships. To assess the potential hazards from spills of various sizes and spill rates using existing models, classification of spills into instantaneous and continuous types are essential. A time criterion is derived which differentiates the spills into the two classes. If the dimensionless duration of spill is less than 2 × 10−3the spill is classified as instantaneous spill. It is seen that this cross-over time is essentially indpendent of LNG spill volumes in the range 1000–50,000 m3.

ISSN:0010-2202    

DOI:10.1080/00102207908946887

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor