摘要:

Direct flame imaging through a transparent cylinder liner has bee´n used to study the final phase of lean combustion in a spark-ignition four-stroke optical engine. Two image-intensified video cameras record instantaneous lean flame radiation at two preset times to examine the structure and development of the flame as it approaches the wall to complete the flame travel. There is one peripheral spark plug on the side of the cylinder opposite the cameras, so that combustion completion images capture only one flame thickness and provide a unique map of flame intensity. These flames have highly structured intensity patterns on all of the scales associated with in-cylinder turbulence. Although the large-scale pattern of burning results from the flame shape early in the cycle, intensity variations of the flame images indicate that the burning rate varies significantly over the flame area on both large and small scales, indicating that the flame front is not a uniformly propagating sheet.

ISSN:0010-2202    

DOI:10.1080/00102209508907736

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of periodic oscillations of the rate of stretch on the extinction of lean methane-air and butane-air premixed flames in stagnation-point flow and counterflow is experimentally investigated. The periodic variation of the rate of stretch is achieved by means of two speakers that are attached to the conventional counterflow burners. It is found that for a given frequency, increasing the amplitude of the velocity oscillations tends to weaken the lean flames such that the critical minimum fuel concentration at extinction increases. The effects of oscillating stretch rates on flame position and extinction characteristics are found to diminish with the frequency. The extinction data are also obtained as a function of the frequency of velocity oscillations for given mean flow through the burners. Higher frequency flow oscillations are found to render more robust premixed flames since larger amplitudes of velocity oscillations are needed to extinguish the flames. For the counterflow methane-air and butane-air premixed flames the temperature profiles between the opposing burners with and without periodic velocity oscillations are determined. Periodic velocity fields arc found to reduce the temperatures throughout the flow field resulting in closer approach of the counterflow flames to the stagnation plane.

ISSN:0010-2202    

DOI:10.1080/00102209508907737

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A strategy is described for the computational prediction of strongly sooting turbulent non-premixed flames in which are coupled a comparatively detailed model of soot formation and oxidation together with significant radiative heat loss. The considerable computational simplifications introduced by mixture fraction-centred flamelet modelling to address turbulence interaction effects are extended to embrace soot source term modelling through the introduction of a family of flamelet profiles, each characterised by varying radiative loss. Encouraging comparisons with experimental measurement are reported for single and multiple flamelet representations in turbulent jet flames of ethylene and pre-vaporised kerosine.

ISSN:0010-2202    

DOI:10.1080/00102209508907738

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The aim of this research was to examine the possibilities of NOx, emission abatement from high temperature industrial furnaces by controlling the gasdynamic parameters of natural gas flames. The following parameters were investigated: air and gas velocity at burner exit, air swirl angle, position of the burner nozzles and air staging. It has been shown that moderate swirling of the combustion air enhances the level of NOxthe lowest NOx, emissions are observed for parallel air and gas flow burners. It is also demonstrated that to attain successful NOx, abatement it is necessary to realize sufficient mixing of the flue gases with the combustion air before the flame temperature reaches its maximum value. The developed burner, enabling successful abatement of the maximum flame temperature, presents a large potential of industrial applications as a tool for NOxemission reduction from high temperature furnaces.

ISSN:0010-2202    

DOI:10.1080/00102209508907739

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Naturally occurring oscillations in ducted premixed flames have been controlled by imposed oscillation of the fuel. The flames were stabilised behind a bluff-body and a step with methane as the main fuel and kerosene as the oscillated secondary fuel and with heat release rates of up to 150 kW. Some experiments with oscillation of gaseous fuel were performed to supplement and to complement earlier results

ISSN:0010-2202    

DOI:10.1080/00102209508907740

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A model is proposed for heterogeneous ignition and extinction in terms of the dynamics of a thin inert layer covering the surfaces of condensed-phase components in a combustion reaction, the layer consisting of reaction products or impurities which collect in the reaction surface. Heterogeneous ignition then is associated with the formation and the spreading of ruptures and punctures in the surface layer, whereas extinction is associated with the formation and the spreading of layer fragments in the form of “caps” or “islands”. For a liquid layer, the model describes the dynamics of a liquid edge where the layer thickness changes from macroscopic to microscopic values. Such a description is in terms of ordinary hydrodynamics only for layer thicknesses which are large enough. Consequently, an intermediate “mesoscopic” range exists which separates macroscopic from microscopic thicknesses, designating the transition range where ordinary hydrodynamics changes over into different forms of transport. Those parts of the liquid edge which are primarily affected by these different forms of transport comprise the socalled “precursor” for which the layer thickness assumes mesoscopic or microscopic values, Recently, major progress in the field of liquid films lead to a much improved understanding of the wetting dynamics for nonvolatile precursors on inert isothermal surfaces. These results are generalized to include nonisothermal reacting surfaces covered by films for which formation and evaporation is admitted. Conceptually, heterogeneous ignition and extinction are shown to be associated with the nucleation and spreading of precursors with thickness profiles representing self-similar surface waves.

ISSN:0010-2202    

DOI:10.1080/00102209508907741

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A modified three-dimensional version of the turbulence k—ε model is applied to simulate the transient fire-induced air flow and smoke movement in a full scale ventilated tunnel. The mode! adopts the general curvilinear coordinate system to preserve the actual geometry of the tunnel. A modified elliptic grid generation method is introduced to specify all of the boundaries in terms of grid distribution, grid size and angle of intersection. The effects of the buoyancy and mean streamline curvature on turbulence are accounted for in the model. The smoke concentration is expressed in terms of smoke obscuration and is calculated by a conservation equation. The QUICK discretization scheme is used. The predictions are shown to be in reasonable agreement with reported experiment data. Application of the mixed convection parameter Gr*/Re5/2Hhas been extended and this is confirmed by the observed temperature stratification of the heated air flow in the full scale tunnel.

ISSN:0010-2202    

DOI:10.1080/00102209508907742

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This report compares temperatures measured with the suction pyrometer and coherent anti-Stokes Raman spectroscopy (CARS) techniques in turbulent, swirling, coal and No. 2 oil flames. The flames were generated in a horizontally fired, cylindrical (1.0 m dia. by 5.0 m long), axi-symmetric, tunnel furnace (firing rate l,000M.J/h). A broadband USED-CARS system was employed to make several, one thousand shot acquisitions in the furnace before and after the suction pyrometer measurements. These experiments indicate that the CARS technique can successfully be applied to practical flames to make temperature measurements. It is demonstrated that these measurements are more meaningful and more reliable than temperatures measured using a suction pyrometer.

ISSN:0010-2202    

DOI:10.1080/00102209508907743

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Soot formation under isothermal conditions during pyrolysis was investigated for the following hydrocarbons: methane, acetylene, benzene, toluene and p-xylene. Over the temperature range 1150- 1400°C the soot particle number density was shown to depend linearly on the hydrocarbon concentration for all hydrocarbons investigated. Activation energies of soot particles aerosol formation were demonstrated to be within the limits 313—340 kJ/mol. Expressions to calculate the particle number density and the soot surface area were obtained.

ISSN:0010-2202    

DOI:10.1080/00102209508907744

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor