摘要:

The ignition and the oxidation of tetrahydropyran have been studied in a single-pulse shock tube under reflected shock wave conditions, and also in a high-pressure jet-stirred reactor(JSR) These experiments cover a wide range of conditions: 2-10 atm, 0.5 ≤ 𝛗 ≤ 2.0,800- 1700 K. The ignition delays of tetrahydropyran measured in a shock tube have been used to propose an overall representation for the dependence of ignition delay time on the concentrations of each component in the ignitable gas mixture: τall= 10−13.6exp (15360/T5) [C5H10O]0.0026[O2]−0.868[Ar]0.0274(units: s, mole/dm3, K). Concentration profiles of the reactants, stable intermediates and products of the oxidation of tetrahydropyran were measured in a JSR. A numerical model, consisting of a detailed kinetic reaction mechanism with 507 reactions (most of them reversible) of 72 species describes the ignition of tetrahydropyran in reflected shock waves and its oxidation in a jetstirred reactor. A fairly good agreement between the experimental results and the model was observed. Detailed kinetic modeling identified the major reaction paths.

ISSN:0010-2202    

DOI:10.1080/00102209708935717

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Images of mixture fraction, temperature, scalar dissipation rates and OH concentrations in turbulent diffusion flames of methane-air and hydrogen-carbon dioxide are presented. The images are derived from Rayleigh scattering, fuel Raman scattering and OH-LIF. The images reveal that the reaction zones in these flames are strongly affected by the turbulence within them and that they become broadly distributed as the velocity is increased. The reaction zone width, as estimated from the measured OH profiles, is found to increase with the increase in jet Reynolds number of the flames. Local turbulence affects the OH profiles and causes a variation in the OH concentrations with little apparent variation in the corresponding mixture fraction and temperature images. This is seen in flames which are far from blow off and is not thought to be a local extinction effect but the direct influence of turbulence in the reaction zone. High scalar dissipation rates are not measured in the reaction zone where unburnt samples are encountered. Local nonburning may be due to a lack of ignition of premixed fluid or to local quenching by large eddy entrainment of cold fluid. The measured scalar dissipation rates do not increase significantly with an increase in the jet velocity. This may be due to the decrease in the gas diffusivity with decreasing temperature which offsets the increase in the spatial mixture fraction gradient. The scalar dissipation rates are believed to reduce in regions of local nonburning due to the associated reduction in the temperature.

ISSN:0010-2202    

DOI:10.1080/00102209708935718

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The results of large-scale experiments on combustion of local hydrogen-air mixtures in a chamber of 20 m3volume are presented. It has been shown that, for mixtures with a relatively high laminar burning velocity, containing 30% (vol.) hydrogen in air, the explosion pressure and the explosion pressure rise rate decrease more rapidly in the case where the vent area is located in the vicinity of a local combustion mixture. For mixtures with a relatively low laminar burning velocity, containing 10% (vol.) hydrogen in air, the more rapid reduction of an explosion pressure was observed at the location of a vent area far from a local combustible mixture. The mutual influence of repeated obstacles and gasdynamic disturbances, caused by a gaseous mixture motion lo a vent area, on the intensification of the local mixtures combustion has been investigated.

ISSN:0010-2202    

DOI:10.1080/00102209708935719

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Flame structure measurements, made using UV Raman scattering and OH laser induced predissociative fluorescence (LIPF), are compared to one dimensional (ID) numerical simulations. Three low stretch (far from extinction) flame conditions are measured: 1) 20%H2+ 80% N2 vs. air, a = 133s−1’; 2) 50%H2+ 50%N2vs. air, a=125s−1; 3) 100% H2vs. air, a = 100s−1. Comparisons of major species measurements with the 1D simulations are in excellent agreement for all cases. Measurements of OH in the 100% H2 flame are slightly lower than the numerical predictions. However, considering spatial averaging and measurement uncertainty due to OH calibration, the OH measurements are in good agreement with the numerical simulations. Mixture fraction measurements (based on atomic nitrogen and atomic hydrogen) agree with the numerical simulations and indicate that differential diffusion effects are important in flames where the primary reaction zone is in a region of low conveclive velocity (e.g., the vicinity of the stagnation plane).

ISSN:0010-2202    

DOI:10.1080/00102209708935720

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Recently, Majda and Souganidis have presented a rigorous asymptotic theory governing the large-scale renormalized flame front dynamics for a reaction-diffusion-advection system involving KPP type chemistries and small scale turbulence. This theory is valid in the context of an infinitely thin reaction layer. Embid, Majda and Souganidis have explored this rigorous theory within the context of a shear layer flow geometry, and demonstrate that the enhanced burning speed is sensitively dependent upon the presence of a mean wind transverse to the direction of the flame propagation. Here, we address the effect that a thin reaction layer may have on the enhanced flame propagation for the case of a small scale shear layer with and without a transverse mean wind. We show through high resolution numerical simulations that the enhanced burning speed is sensitively dependent on the presence of a transverse mean wind in a qualitatively similar fashion to the asymptotic theory; but further, we exhibit that a finite reaction zone yields effective burning speeds which aresmallerthan the theoretical predictions for infinitely thin flame fronts and that the decay of these corrections depends upon the relative scale separation between the reaction layer scale, the turbulence scale, and the integral scale.

ISSN:0010-2202    

DOI:10.1080/00102209708935721

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A numerical approach for predicting multi-dimensional reacting flows is presented. The various interacting processes which occur during combustion are considered: turbulent transport, chemical reaction, and radiative heat transfer. The formulation is based on time-averaged transport equations. Turbulent transport is modeled with thek-ε turbulence model, chemical reactions are considered using the eddy dissipation concept (EDC), and radiative heat transfer is modeled with the discrete ordinates method. The EDC includes influences of both local turbulence and finite-rate chemical kinetics on the reaction rates, and is applicable to general,n-step, elementary reaction mechanisms. The model is applied to two swirling natural gas flames. Predictions are presented for several detailed and reduced reaction mechanisms including the 279-step GRI-Mech. Results indicate that the use of intermediate and detailed reaction mechanisms with the EDC significantly reduces uncertainty associated with simple one- and two-step chemistry, but also thatk-ε model underpredicts turbulent transport in the considered flames.

ISSN:0010-2202    

DOI:10.1080/00102209708935722

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Simultaneous two-dimensional Rayleigh and fuel Raman images have been collected in air-diluted methane and hydrogen jet diffusion flames. Temperature, fuel mass fraction and mixture fraction images are derived by a two-scalar approach based on one-step chemistry and equal species diffusivities. This enables calculation of two components of the scalar dissipation rate x-The inherently weak Raman signal has been maximised by intra-cavity measurements, using a flashlamp-pumped dye laser. In addition, the Raman signal-to-noise ratio is drastically improved by a novel contour-aligned smoothing technique which exploits the high correlation between the Rayleigh and Raman signals.

ISSN:0010-2202    

DOI:10.1080/00102209708935723

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Planar laser-induced fluorescence (PLIF) imaging of the OH radical is used to investigate the structure of the OH fields in turbulent H2/Ar jet diffusion flames. Flames are investigated at moderate to high Reynolds number (Red=3×l04, 7.5×l04, 1.5× 105), and PLIF images are obtained over the full length of the flames. For the lowestRedcase, in agreement with previous studies, the images reveal OH zones that appear as thin filaments connected by diffuse regios. For the highestRedcases, over the entire length of the flame, the OH zones are broader and appear to be more influenced by small-scale turbulence. The images also show that for the highestRedcases the large-scale turbulent structure, as defined by OH, appears to be less prevalent upstream of the flame tip, but after the flame tip a clear large-scale apparently helical instability is present. Statistics generated from the OH PLIF signals show clear changes with increasing Reynolds number. RMS OH signal radial profiles show that over the entire extent of the flame, fluctuations are largest for the lowRedcase, owing to large fluctuations in the thin OH zones. At highRedfor the lower half of the flame, the RMS profiles exhibit a double peak which results from the distributed OH zones combined with small-scale mixing on the rich and lean sides of the reaction zone.

ISSN:0010-2202    

DOI:10.1080/00102209708935724

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A review of the brief history of catalytic combustion in internal combustion (IC) engines suggests that catalytic combustion may aid in fuel ignition, but can also cause increased flame-quenching because of surface catalytic oxidation of unburned fuel in the gas boundary layer. The effect of catalytic combustion on heat transfer measurements in engines is also discussed, with the controversial Woschni effect, wherein thermal insulation appears to increase heat rejection from the combustion chamber, being shown to be probably only a manifestation of catalytic combustion.

ISSN:0010-2202    

DOI:10.1080/00102209708935725

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The acetone vapor concentration between two neighboring droplets in a droplet stream is measured using laser induced fluorescence. It was found that a cylindrical region of high vapor concentration surrounds the droplet stream. As the droplet spacing decreases the minimum concentration between droplets increases because of limited entrainment towards the stream axis from lower concentration regions.

ISSN:0010-2202    

DOI:10.1080/00102209708935726

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor