摘要:

This paper presents a numerical study of the stratified flow situation that exists in a corridor in which hot exhaust gases from a fire enter at the top of one end and cool air feeding the fire enters at the low side of the other end. It is seen that a temperature difference of 40 to 8O°C will cause the turbulence to disappear in the separation region. The gradient Richardson number gives the best physical insight into the flow and the critical value is about 0.5 for Reynolds numbers of 3000.

ISSN:0010-2202    

DOI:10.1080/00102208408923774

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Influences of upstream versus downstream volumetric heat loss/gain on the linear stability of laminar premixed flames are investigated. A single-step irreversible reaction governed by Arrhenius-type rate law is considered within the framework of a diffusional-thermal stability model. The resulting dispersion relations show that while both upstream and downstream losses enhance the tendency towards instability, downstream loss is more effective in promoting instability.

ISSN:0010-2202    

DOI:10.1080/00102208408923775

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The turbulent boundary layer arising from the injection of cold reactants into a hot product stream is studied theoretically. By treating the rate of growth of the boundary layer as a small parameter and by assuming power law variations of global features of the layer the equations of a Reynolds stress closure are reduced to similarity form. A combination of the aerothermochemical model of premixed turbulent combustion due to Bray-Moss-Libby and standard models for pressure fluctuations and dissipation results in a closed set of equations which are solved numerically. The predictions are compared with available experimental data.

ISSN:0010-2202    

DOI:10.1080/00102208408923776

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

An analysis is conducted of the structure of a premixed flame stabilized in the boundary layer flow over a hot, impermeable, flat plate. The cases of a noncatalytic and catalytic plate are considered. The governing equations are solved by series expansion of a small parameter that controls the longitudinal diffusive processes. The zeroth order solution corresponds to the boundary layer approximation and the first order solution gives the correction to that solution for the distributions of pressure, velocity,temperature and fuel concentration. The magnitude of the correction is largest in the vicinity of the flame leading edge and depends on the plate temperature or equivalently on the activation energy of the chemical reaction. These last parameters also affect the character of the correction and, consequently, the aerodynamic structure of the flame. For low plate temperatures a region of elevated pressure is generated in front of the flame leading edge. This region becomes weaker and is displaced above the flame and downstream from its leading edge as the plate temperature is increased. The perturbed velocity field is in agreement with the pressure distribution with regions of low longitudinal velocity appearing wherever elevated pressures are present. The presence of low gas velocities favors the longitudinal diffusion of heat and mass. These diffusive processes, and in particular the upstream diffusion of combustion products, affect the rate of the chemical reaction. The interaction between diffusive and chemical kinetic effects is of primary importance in the determination of the final structure of the flame.

ISSN:0010-2202    

DOI:10.1080/00102208408923777

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Results are presented of a study in which schlieren photographs of the flame in a special visualization spark ignition engine were taken, with first propane and then hydrogen as fuel, under conditions where the flow field, total energy released and geometric constraints were closely comparable. It is shown that the rate of development of the flame from its inception is much faster for hydrogen, that the cycle-to-cycle variations for hydrogen are substantially less, and that the thickness of the hydrogen turbulent flame is about one-third to one-quarter that of propane. Application of a wrinkled laminar flame model to these results shows that the characteristic burning time of the hydrogen flame is one-sixth that for propane, and that the characteristic scale of the wrinkling for hydrogen is 0.6 that for propane. Both the appearance of the two flames, and their turbulent flame speeds in relation to their laminar flame speeds, indicate that the two flames fall in different turbulent flame regimes (Ballal and Lefebvre, 1975).

ISSN:0010-2202    

DOI:10.1080/00102208408923778

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Experiments have been designed and executed to answer the following specific questions about the role of hydroxyl and pressure in the formation/destruction mechanism for combustiongenerated soot: (a) what effect, if any, does sub-atmospheric pressure have on the stoichiometry for the onset of soot; (b) is there really a limiting pressure below which soot fails to form, even though the flame was sooting at a higher pressure; and (c) if the limiting pressure does exist, is there any correlation between the disappearance of soot and the hydroxyl radical concentration as a function of pressure? From measurements on quenched, premixed flat ethane/air flames, which are the first of their kind, the answers of these questions were learned to be none, yes, and yes, respectively.

ISSN:0010-2202    

DOI:10.1080/00102208408923779

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102208408923780

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor