摘要:

The ignition of tetrahydrofuran (THF) has been studied in a single-pulse shock tube under reflected shock wave conditions while the oxidation of THF was studied in a high-pressure jetstirred reactor (JSR). The present experiments cover a wide range of conditions: 2–10atm, 0.5≤ ≤2.0, 800–1800K. The ignition delays of THF, measured in a shock tube, have been used to propose an overall representation for the dependence of ignition delay time on the concentration of each component in the ignitable gas mixture: τall=10-14.4exp (19590/T5)[c4h8O]0.272[O2-0.984[AR]-0.189(units:s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of ThF were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 484 reactions (most of them reversible) of 71 species, describes the ignition of THF in reflected shock waves and its oxidation in a jet-stirred reactor. We observed a fairly good agreement between the experimental results and the computations. Detailed kinetic modeling enabled identification of the major reaction paths and sensitive kinetic parameters.

ISSN:0010-2202    

DOI:10.1080/00102209808924147

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The objective of this study was to estimate the efficiency of methane autoignition promotion by testing different ignition improvers including hydrogen, H2, hydrogen peroxide, H2O2, ozone,O3and dimethyl ether, DME, (CH3)2O. This was accomplished by computing ignition delays for CH4/O2/Ar or N2mixtures of various compositions, concentrations of the promoters, pressures and temperatures. Ignition delay times for additive-free mixtures were used for tuning a methane oxidation mechanism consisting of 185 reversible elementary reactions between 32 species. A selection of the reaction rate parameters available in the standard databases was made to optimize the agreement between simulation and experimental results for one particular set of test conditions (reference mixture) by refining the rate parameters of the most sensitive stages revealed by sensitivity analysis. The agreement achieved between model predictions and shock tube experimental data is very good. To investigate the effect of dimethyl ether on methane autoignition, the mechanism was extended up to 301 reactions and 53 species to predict the autoignition delay at high pressures. Methane autoignition promotion is proven to be much stronger for H2O2, O3and (CH3)2O additives than for H2. The mechanism of ignition acceleration is attributed mainly to the dominant role of the O and OH-radicals generated by the rapid decomposition of hydrogen peroxide and ozone, and to the peroxide intermediates and low temperature branching, in the case of dimethyl ether.

ISSN:0010-2202    

DOI:10.1080/00102209808924148

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Effects of radiative heat loss on temperatures and extinction characteristics of CH4/CO2air and CH4/CO2/O2counterflow premixed flames were numerically investigated by using the detailed chemistry and transport properties with emphasis on assessing the importance of radiation reabsorption. Radiative transfer was calculated using the discrete ordinate method along with the grey gas assumption. Results show that radiation reabsorption has little influence on the temperatures and extinction limits of CH4/ air counterflow premixed flames of low equivalence ratio. However the radiation reabsorption has a significant effect on the flame temperatures and extinction limits of CH4/CO2/air and CH4/CO2/O2counterflow premixed flames becomes smaller as the fraction of Co2added to air increases. Radiation extinction of CH4/CO2/O2flames occurs at higher stretch rates than that of CH4/air flames.

ISSN:0010-2202    

DOI:10.1080/00102209808924149

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A spontaneous vibrational Raman scattering technique is developed for simultaneous measurements of temperature and multi-species (C02O2, CO, N2, CH4, H20, H2, and OH) concentrations in premixed methane - air flames. The Raman spectra and spectral background are obtained using a narrowband tunable KrF excimer laser working at 248 nm and a spectrometer combined with an intensified CCO camera. Optimal tuning of the narrowband KrF excimer laser (248.632 nm) for minimization of OH A2Σ_X2П and 02B3Σu- X3Σg­fluorescence interference is determined from fluorescence excitation spectra. Laser emission spectra are made to ensure that the optimum wavelength of the laser is within a good locking region. Natural fluorescence spectra (without laser excitation) are used to determine the gate time of the ICCO camera. Measured Raman spectra demonstrate that single-pulse concentration and temperature measurements, with only minimal fluorescence interference, are possible for turbulent premixed methane-air flames. A time-averaged temperature measurement technique is presented that matches the theoretical spectra to the measured N2Stokes Raman spectrum. Methodologies for simultaneous temperature, major species, and OH concentration measurements in turbulent premixed flames are discussed.

ISSN:0010-2202    

DOI:10.1080/00102209808924150

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The influence of CO and CO2on hydrogen-air detonations in round tubes was studied numerically and experimentally. The quasi-one-dimensional Zeldovich model of detonation limits and a detailed kinetic mechanism of H2/CO oxidation (72 elementary reactions, 13 species) were used to estimate the detonation sensitivity to kinetic parameters and tube diameter. The numerical results were verified by comparison with various experimental data available for HC/air detonations and with our own measurements in 41-. 24-. and 14-mm i.d. tubes. For H2/CO/air and H2/CO/CO2/air detonations, we calculated and measured the concentration limits in a 24mm fixed-diameter tube at initial pressure 0.1 MPa and temperature 298 K. It is shown that the limiting concentration of hydrogen in lean hydrogen/air mixtures decreases from 15.5 to 2.4 vol% with addition of 20 vol% carbon monoxide. Dilution of the mixture with CO2results in a substantial shrinkage of the detonability domain. The numerical predictions are in reasonable agreement with the experimental results.

ISSN:0010-2202    

DOI:10.1080/00102209808924151

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Obtaining efficient and robust solutions to real reacting flow problems is a challenging task in numerical simulation due to severe nonlinearities in the conservation equations and the wide range of time scales of chemical reactions. However, there are many important industrial applications for such simulations, e.g., premixed and non-premixed combustion, catalytic combustion, or materials processing.

ISSN:0010-2202    

DOI:10.1080/00102209808924152

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The stabilisation region of turbulent lifted flames of methane has been investigated using simultaneous laser imaging of Rayleigh scattering, Raman scattering and OH·LIF. These images are used to derive mixture fraction, temperature, fuel mass fraction and OH concentration images. This enables the mixing field and the reaction zone of the lifted flames to be studied in detail.

ISSN:0010-2202    

DOI:10.1080/00102209808924153

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A laser-based measurement system has been developed that is capable of measuring the densities of all majority species. temperature and velocities simultaneously in turbulent hydrogen flames. The experiment aims on complete characterization of the instantaneous combustion situation in the probe volume. The measurement of these quantities is performed twice with a short time delay (µs-ems) using two iaser pulses. This double-puise technique is performed in order to monitor the temporal development of turbulent mixing and combustion. It is expected that the chain of cause and effect of mixing and combustion processes can be studied in detail by monitoring the situation over a sufficiently short time step. The novel measurement technique is discussed in detail and first experimental results arc presente

ISSN:0010-2202    

DOI:10.1080/00102209808924154

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

An extension of the BML model to the case of Combustion ol lean mixtures with variable equivalence ratio is presented in this paper. The Dilution of both burnt products are fresh reactants by the surrounding air is taken into account by introducing the mixture fraction f in addition to the progress variable c. Statistical analysis of the reactive flow is achieved by using a joint pdf of c and following calculation of mean quantities. Extinction of individual flamelets due to local dilution of fresh recants is also considered. The Influence of dilution, i.e. variable production rate is described. application of this modified model to the case of a stagnating turbulent flame stabilized close to a solid wall shows that the mean flame brush is predicated to be detached from the burner, in agreement with avaliable experimental observartions Qualitative and quantitative modifications of the mean structure of the flame due to dilution are also investigated.

ISSN:0010-2202    

DOI:10.1080/00102209808924155

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The present paper investigates the structure of turbulent spray diffusion flames by means of numerical simulations. The flamelet model for turbulent diffusion flames has recently been extended to turbulent spray diffusion flames. The model is suitable for considering detailed chemical reactions through use of a laminar flame library consisting of structures of laminar gas diffusion flamelets that are characterized by the mixture fraction and its scalar dissipation rate. The focus of the present paper is the implementation of laminar spray diffusion flames for use in turbulent flame computations. Since the structure of laminar spray flames is considerably different from that of their gaseous counterparts, new criteria need to be developed for the implementation of these structures. The present paper presents characteristics of laminar spray flames and their consideration in turbulent flame computations. Both the model predictions (using either laminar gas flames or laminar spray flames) are compared to experimental results of a turbulent, axisymmetric free jet where an air-assisted methanol spray is injected into air. The new model is free of parameters that need to be adjusted to predict experimental data, and it correctly predicts the principal structure of the turbulent spray flame. Two reaction zones are identified where the turbulent model using laminar gas flames needs an artificial cut-off temperature to predict the low temperature regime where liquid is present. Thus, the use of laminar spray flames is required for the prediction of turbulent spray flame characteristics within the vaporization zone.

ISSN:0010-2202    

DOI:10.1080/00102209808924156

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor