摘要:

Conduction heat transfer into a vertical free burning slab was measured as a function of time and distance from the leading edge, and its contribution to the known values of effective heat of gasification was analyzed. The present set of experiments was performed using clear and black PMMA (polymethylmethacrylate) samples. The heat conduction into the pyrolyzing surface was deduced from temperature measurements in the interior of burning slabs. The surface conduction heat flux decreased from 14 kW/m2for clear PMMA and 13kW/m for black PMMA att= 300s to almost 8kW/m2at around l = 1000s and then reached a plateau, indicating a substantial degree of unsteadiness in the early part of combustion of slabs. It is concluded that, when estimating burning rates in numerical calculations one has to be careful in selecting a value for the effective heat of gasification because of the generally unsteady nature of heat conduction into the solid interior.

ISSN:0010-2202    

DOI:10.1080/00102209008951666

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The explosion resulting from the mere mixing in an inert atmosphere of ternary systems using H2O2and N2H4(or MMH or UDMH) has been investigated. The composition ranges leading either to ignilion or to detonation have been experimentally determined. A correlation allowed the authors lo propose an isoenthalpy line which is used as the envelope for the self-detonation range. Reaclional processes are considered Intermediate chemical species are different for ignition and detonation. Additives may help in one case or the other.

ISSN:0010-2202    

DOI:10.1080/00102209008951667

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The lean flarnmability limit of a premixed flame was extended by forcing the initial shear layer of the jet. It was shown that this extension depends on the forcing frequency and amplitude. The most effective control was obtained using forcing in a Strouhal number range of 0.01 to 0.06 near the most amplified frequency of the shear layer as determined by the jet exit mean velocity profile and initial boundary layer thickness. The small-scale vortices generated in the shear layer by this forcing caused reattachment of the lifted flame and held it at the jet nozzle for equivalence ratio and mean flow rate which were significantly beyond the unforced flarnmability limits. Flame intensity was augmented as well at this forcing. An adverse effect of acoustic forcing was observed when the jet was forced at the preferred mode frequency. For this condition, the generated vortices had length scales which destabilized the flame, causing intermittent flameholding and reduction in heat release.

ISSN:0010-2202    

DOI:10.1080/00102209008951668

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The unique shear-flow characteristics of a triangular jet were used to suppress longitudinal pressure oscillations in a coaxial dump combustor. The asymmetric flow configuration enhanced fine-scale mixing in the corner flow, while maintaining large-scale mixing at the flat sides, as demonstrated in air and water flows with and without forcing. In a forced annular diffusion flame it was shown that the flat-side shear layers were dominated by reacting vortices which lead to periodic heat release and possible driving of pressure oscillations, while the combustion at the corners was more intense and free of periodicity because of highly three-dimensional flow with enhanced molecular mixing between the fuel and oxidizer. For a coaxial dump, the pressure oscillations were significantly reduced with a triangular inlet duct and corner injection, compared to a triangular inlet duct with flat-side injection and to a circular inlet duct.

ISSN:0010-2202    

DOI:10.1080/00102209008951669

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A numerical model of non-adiabatic flame propagation is used to examine the dynamic properties of premixed flames in mixtures near flammability limits in planar and spherical geometries. Using highly schematic thermodynamic, chemical and transport models, numerical results are found to be, in the limit of high activation energy, in good agreement with analytical solutions. With more detailed models representative of lean methane-air mixtures experiencing heat loss from CO2and H2O band radiation, numerical results for spherical geometry are found to be in very good qualitative and good quantitative agreement with results obtained in microgravity (μm) experiments. In particular, experimentally observed memory effects associated with the ignition process are reproduced. It is concluded that flame dynamics and extinguishment processes at μg are probably a result of the interactions of the Lewis number effect, flame front curvature and heat loss due to gas radiation.

ISSN:0010-2202    

DOI:10.1080/00102209008951670

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A parametric analysis is performed of the counterflow mixing of two gas streams having different temperatures, with density changes taken into account. Numerical integrations of the self-similar stagnation-flow equations are completed to provide velocity, temperature and mixture-fraction fields. Results are obtained that are needed in analysis of the structure and extinction of counterflow diffusion flames.

ISSN:0010-2202    

DOI:10.1080/00102209008951671

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The ignition and extinction of CO-flame over a carbon rod in an oxidizing, stagnation-flow environment is studied theoretically and experimetally. In the theoretical phase, by considering the surface C-O2and C-CO2reactions and the gas-phase CO-O2reaction, explicit ignition and extinction criteria are derived by using generalized species-enthalpy coupling functions. In the experimental phase, the ignition and extinction states are determined as functions of the surface temperature or the burning carbon rod, and the oxygen concentration and velocity gradient of the flow. Fair agreement exists between the experimental data and theoretical calculations obtained by using a restrictive set of kinetic and thermophysical parameters.

ISSN:0010-2202    

DOI:10.1080/00102209008951672

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209008951673

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Buoyancy is an important factor in the dynamic behavior of jet diffusion flames. In order to determine the exact role that buoyancy plays, a simple procedure is described for varying in isolation the relative buoyancy force in stationary laboratory jet diffusion flame experiments. This procedure, which is derived from a theoretical model of these flames, merely requires that background pressure be varied while maintaining constant mass flows of fuel and oxidizer into the burner. It is shown that the sole result of these pressure variations in the theoretical model is that the effective gravitational acceleration acting upon the flame varies as the square of the pressure. Comparisons are made between the structure of a low speed laboratory methane/air flame at various pressures and the results of a direct numerical simulation of the same flame with various gravitational accelerations. Similar evolutions in flame structure are observed in both cases.

ISSN:0010-2202    

DOI:10.1080/00102209008951674

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor