摘要:

During the last decade various laser spectroscopic techniques have shown great potential for combustion diagnostics. The largest advantages with these techniques are that they permit non-intrusive measurements with high spatial, temporal and spectral resolution. The most important parameters measurable are; species concentration, temperature and velocity. In the present review some developments and applications will be briefly described. This includes Laser-Induced Fluorescence, LIF, Coherent anti-Stokes Raman Scattering, CARS, and Polarization spectroscopy, PS

ISSN:0010-2202    

DOI:10.1080/00102209908952096

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The application of Cavity Ring Down Spectroscopy for the quantitative determination of CH densities in atmospheric flames has been investigated. Two different atmospheric flames have been studied: a premixed burner stabilised flat CH4/air flame and an oxyacetylene flame from a welding torch, which is used for diamond deposition. For the methane flame density profiles of CH are obtained and compared with densities calculated by De Goey and Van Oijen (1998). The temperature is derived from the measured Boltzmann distribution. The data from the oxyacetylene flame are compared to LIF profiles measured by Klein-Douwel et al. (1995).

ISSN:0010-2202    

DOI:10.1080/00102209908952097

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We present an experimental study of the growth rate of the Darrieus-Landau instability on propane-air and on oxygen enriched propane-air flames using a two-dimensional inverted-“V” flame on a slot burner. We use a novel system of electrostatic deflection to produce an initial perturbation of controlled wavelength and amplitude. The growth rate of this spatially growing perturbation is measured as a function of wavenumber of equivalence ratio and of oxygen enrichment using high speed flame imaging. The results are analyzed using the Clavin-Garcia laminar flame stability theory (including temperature dependent diffusivities). The dependence of the growth rate on wavenumber and flame speed is reasonably well represented by this theory. As a by-product of this analysis, we obtain values of the Markstein number, which, for rich flames, are found to decrease with equivalence ratio and to increase with oxygen concentration

ISSN:0010-2202    

DOI:10.1080/00102209908952098

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A detailed N/O kinetic mechanism has been developed and tested in comparison with experimental data for N2O ignition, NO and NO2decomposition at high temperatures. It consists of 27 reactions among 11 species. A sensitivity analysis reveals which reactions are critical for the quality of the modeling in particular experimental conditions. The choice of the rate constants for these reactions is discussed. Good agreement has been obtained for the ignition delays in the pure N2O and its mixtures with Ar, decomposition rates of the NO and NO2in static reactors and behind shock waves. The modeling using recently suggested controversial rate constants for the key reactions N2O + O = N2+ O2N20 + O = NO + NO has been performed as well. It is demonstrated that the use of too-low or too-high values of the reactions (8,9) rate constants is incompatible with available experimental data

ISSN:0010-2202    

DOI:10.1080/00102209908952099

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Detailed modeling of soot formation and destruction was carried out using a model which consists of a relatively large reaction gas phase mechanism and of a mechanistic soot model. The objective of the present study is to validate a comprehensive gas phase reaction mechanism for soot precursor species from experiments of sooting flames for pressures up to 15 bar and to identify dominant pathways in the soot model.

ISSN:0010-2202    

DOI:10.1080/00102209908952100

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A mathematical model for two-phase turbulent reactive flows is presented which is based on considering both phases in Lagrangian manner. The mechanical and thermodynamical properties of the two-phase mixture are calculated along the trajectories of ”particles” representing the system. Similar to Monte-Carlo methods for solving a high dimensional joint velocity-composition probability density function, the turbulent gas phase is described by means of stochastic calculus. The deterministic equations for individual solid particles can be treated directly. In this approach, the interaction between both phases is not smeared over computational ceils but restricted to the vicinity of solid particles by the definition of an “action-sphere“ which is attached to every solid particle. Applications of the method to isotropic, homogeneous turbulence indicate that it is capable of providing information on the local structure of combustion zones with species formation and transport. The results show that the method is applicable independent of the combustion modes in the gas phase and it provides extensive statistics of various correlations of properties.

ISSN:0010-2202    

DOI:10.1080/00102209908952101

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A recently developed two-dimensional optical technique has been applied for measuring two-dimensional maps of soot volume fractions, particle number densities and mean particle radii in a turbulent acetylene-air diffusion flame. The technique is based on the simultaneous detection of Rayjeigh-Scat-tering and Laser-Induced Incandescence (LII) in combination with the detection of the extinction from one single laser pulse (RAYLIX-technique). Single shot experiments in the investigated flame exhibit small particles in zones of high panicle number densities and vice versa. Mean values and standard deviations are obtained by averaging 1000 single laser shots. The results reveal large relative fluctuations of soot volume fractions, number densities and particle radius in the outer region of the flame due to its turbulent structure. Two-dimensional probability density functions (PDFs) of number density and particle radius are obtained, which provide a useful data basis for future modeling of turbulent flames by means of PDF-models. Finally turbulent length scales are determined from autocorrelation functions. This information is important for engineering and also modeling purposes.

ISSN:0010-2202    

DOI:10.1080/00102209908952102

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The soot formation process in the high temperature - high pressure pyrolysis of ethylene has been studied in a conventional diaphragm-type shock lube behind reflected shock waves. The investigated ranges of temperature and pressure were 1600-2200 K and 9-13 bar, respectively. Light scattering/extinction measurements in the visible, and extinction measurements in the near infrared have been analysed to characterise the soot formation process. Pyrolytic products, formed prior lo sool particles, have been evidenced by continuous absorption measurements, with high time/spectral resolution, in the UV-visible range. The absorption spectra have been analysed according to the Tauc optical band-gap model. In the investigated experimental conditions, the characteristic optical band-gaps of aromatic structures with 2-4 rings at most have been observed before soot-inception. After the soot-inception, a sharp decrease of the band-gap has been revealed, indicating a high degree of aromaticity of sool particles

ISSN:0010-2202    

DOI:10.1080/00102209908952103

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Freely propagating and counterflow laminar premixed steady hydrogen/air and methane/air flames are investigated numerically using complex chemistry and detailed transport models. All the transport coefficients in the mixture, including thermal diffusion coefficients, are evaluated using cost-effective, accurate algorithms derived recently by the authors from the kinetic theory of gases. Our numerical results provide a quantitative assessment of the impact of thermal diffusion on planar flame speed as a function of equivalence ratio and on extinction limits of counterflow flames as a function of either strain rate or equivalence ratio. In some cases, such as rich hydrogen/air flames, the effect of thermal diffusion is actually opposite to the one expected from a qualitative viewpoint or obtained with empirical models. In addition, we observe relevant effects of thermal diffusion on extinction of methane/air counterflow flames

ISSN:0010-2202    

DOI:10.1080/00102209908952104

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A mass-based stretch rate is introduced. Combining this stretch rate with the conservation equations for premixed flames gives a set of quasi-one-dimensional flamelet equations, which describe the structure and the mass burning rate of these flames. An integral analysis is applied to the flamelet equations and subsequently a general expression for the mass burning rate of stretched flames is derived. Finally, the mass burning rate is computed for weakly stretched methane/air flames

ISSN:0010-2202    

DOI:10.1080/00102209908952105

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor