摘要:

When a flame propagates in a nonuniform flow it experiences strain and curvature effects. The fractional rate of change of the flame area constitutes the flame stretch. This quantity is often used to describe the structure and extinction mechanisms of turbulent flames. It also occurs in many recent studies of premixed laminar flames. This article provides a unified view of this concept on the basis of a novel derivation of stretch in terms of strain rate and curvature. The flame stretch, the rate of change of the normal to the flame front and the rate of change of the curvature are deduced from a general transport theorem. As an illustration, the components of flame stretch are evaluated in the case of a direct numerical simulation of the interaction between a pair of vortices and a laminar flame. Another application of flame stretch concerns the determination of the available flame surface density. A balance equation is derived for this quantity and cast in various useful forms thus providing a basis for the turbulent combustion models which rely on a determination of the local density of flame area

ISSN:0010-2202    

DOI:10.1080/00102209008951608

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Measurement of the flame spread rate on single ponderosa pine needles as a function of angle of inclination and concurrent external flow speed arc reported. The ability to fit the orientation results with a single curve is of particular interest. Consideration of the results of previous experimenters concurs with this observation. Temperature measurements, visible observations and order of magnitude estimates are used to discuss the physical mechanisms for increasing flame spread rate with increasing angle from the downwards vertical, or with concurrent external flow speed. Volume expansion, species diffusion, finite rate gas phase kinetics, and buoyant convection are all thought to play a role

ISSN:0010-2202    

DOI:10.1080/00102209008951609

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The use of NO2for chemical kinetic analysis has been extended to the simplest of the alkylbenzenes—toluene. The results of a series of toluene oxidation experiments performed with and without NO2and over a range of initial oxygen concentrations have not only confirmed the conclusions of a prior series of benzene oxidation experiments but also added to the understanding of the toluene oxidation mechanism.

ISSN:0010-2202    

DOI:10.1080/00102209008951610

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Previous experimental investigations of turbulence measurements in conventional laboratory premixed flames are extensively reviewed. Because of numerous disadvantages of these configurations, primarily associated with flame stabilization mechanisms, a freely-propagating flame configuration is proposed for the study of flame-turbulence interactions. The unperturbed, unrestrained flow field in this configuration is ideal for measuring the effect of the flame on turbulence properties. Temporally resolved, ensemble averaged measurements of turbulence intensity, integral length scale, integral time scale, and energy spectrum have been measured both normal and parallel to the mean flame surface with laser Doppler velocimetry (LDV) in a propane-air flame at an equivalence ratio of 1.0, in a flow with incident turbulence intensity of 25 cm/s and length scale of 8 mm. The following changes in turbulence parameters were observed across the flame: a factor of five to six increase in the normal turbulence intensity, a factor of two to three increase in the parallel turbulence intensity, a factor of two increase in the density weighted lubulent kinetic energy, a 100% increase in the normal length scale, a 50% increase in the parallel length scale, an increase in turbulence time scale, and a slight shifting of turbulence energy towards lower frequencies in the normal component. These results indicate that turbulence production in the flame is significant, and is anisotropic in nature

ISSN:0010-2202    

DOI:10.1080/00102209008951611

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Computed vorticity-flame interactions in two-dimensions suggest that a wrinkled flame is a common occurrence in reacting turbulent flow and that these wrinkles are formed in a small fraction of an eddy turn-over time. An experiment in which the Tsuji porous-cylinder burner is spinning may be a way to achieve a steady, wrinkled diffusion flame under laboratory conditions. The wrinkled flame differs from the previously studied stagnation, counterflow flame in that the former has a large spatial variation in diffusive gradients near the wrinkle. These gradient variations may explain the extinction observed in unsteady, pulsed jets by Lewis et al

ISSN:0010-2202    

DOI:10.1080/00102209008951612

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The critical value of the dimensionless heat loss parameter is determined for a thermal explosion with reactant consumption. The critical phase trajectory of the system contains an unstable integral manifold as its own portion. Initial conditions corresponding to this trajectory conform to the explosion limit. The technique of asymptotic expansions is used to derive a critical explosion parameter

ISSN:0010-2202    

DOI:10.1080/00102209008951613

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209008951614

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor