摘要:

—We examine unstable overdriven detonations with one-step Arrhenius' kinetics in the limit of infinite activation energy. For the one-dimensional problem we show how a ccrtain class of initial disturbances lead to thermal runaway for the entire detonation structure, with thc shock temperature and pressure increasing several-fold in an extremely small time interval. This behavior resembles the sharp transients reported by others in numerical computations. For the two-dimensional problem, run-away occurs at discrete points distributed along the plane of the shock with spacing determined by the initial disturbance. This description is characterized by very large transverse pressure gradients which, in turn, will give rise to the transverse shock waves that are a familiar feature of unstable multidimensional detonations.

ISSN:0010-2202    

DOI:10.1080/00102208808915754

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

—Here we have analyzed the governing equations of reacting low Mach number flow ror plane premixed flame structures in non-unirorm flow fields given that the activation temperature of the mixture is large compared to the temperature of the remote reactants. An extinction mechanism is uncovered Tor flames with Lewis numbers less than one thal cannot be round through the use of activation energy asymptolics, a limit where the activation temperature of the mixture is large compared lo the burned gas temDerature.

ISSN:0010-2202    

DOI:10.1080/00102208808915755

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

—Counterflow diffusion flames burning undiluted and diluted methane-air and propane-air mixtures have been computed using global reaction schemes involving only major species. Agreement for the undiluted methane-air and propane-air flames has been found to be excellent and realistic variations of species profiles with increasing rates of strain are obtained. Computations of diluted methane-air flames at different rates of strain confirm the experimental findings that the critical parameter determining name extinction is the maximum reaction zone temperature, which is found to be in acceptable agreement with measurements. The critical fuel concentration at the limit of low strain for the case of fuel diluted with nitrogen is also in acceptable agreement with measurements. Effects of varying degrees of approximation of transport properties is also investigated, including the common approximation of unity Lewis numbers. Implications of the results as regards to the inclusion of direct kinetic effects into turbulent computations and to the generation of laminar flamelets are also discussed.

ISSN:0010-2202    

DOI:10.1080/00102208808915756

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

—The isolated effects of fuel dilution and flame temperalure variation on soot formation have been investigated experimentally for counterflow dilTusion flames. The methodology of isolation through temperature adjustment involves changing the concentration of the fuel by diluting it with nitrogen, and then incrcasing the maximum temperature of the diluted flame back to that of the undiluted Rame by replacing a portion of the nitrogen in the oxidizer flow with an equal portion of argon. Soot quantities are determilied by using light-scattering and extinction techniques, flame temperatures by thermocouple measurements, and velocities by LDV mapping. Results on ethylene show that both temperature and dilution contribute to a reduction in the soot volume fraction and dilution accounts for a substantial amount of this reduction. I t is further found that the soot formation rate and specific surface area are linearly dependent on the initial fuel concentration, while the specific surtace growth rate is insensitive to its variation. Finally, the soot formation process is insensitive to a wide range of fuel ejection rates for the present counterflow diffusion flame established in the forward stagnation region of a porous cylinder.

ISSN:0010-2202    

DOI:10.1080/00102208808915757

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A mathematical model is presented in this paper which can be used as the theoretical foundation of a new method for interpreting flame propagation data in a multiphase system. In this method the global kinetic parameters are estimated by comparing computed pressure histories with those obtained experi- mentally. The model is essentially a homogeneous multiphase transport model for turbulent dust explo- sions. The turbulent transport is modeled employing an eddy diffusivity correlation for confined turbulent premixed gaseous flames. The performance of the mathematical model is compared with the experimental data of an aluminum dust explosion conducted in a twenty-liter sphere with central ignition. Parametric sensitivity of the model is briefly discussed and model limitations are identified.

ISSN:0010-2202    

DOI:10.1080/00102208808915758

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The deformation of diffusion flames by a vortex pair flowfield is examined analytically, in which emphasis is placed on the elfect of heat release due to chemical reaction on the straining of and reactant consumplion by the flames. Two types of initial geometry are considered: one in which a diffusion flame bounding a semi-infinite fuel strip is distorted by the vortex pair, and one in which two infinite diffusion flames bounding an infinite fuel strip interact with the flowfield; these situations are similar to those considered in earlier isodensity modeling (Karagozian and Manda (1986). The chemical reaction is again assunled to be difusion controlled. The procedure for calculating flame deformation. reactant consumption, and the distribution of products about the flame surface accounts for motion of the flame due to the sloichiometry as well as the flowfield. When heat release due to thechemical reaction is represented in terms of local source terms. a significant complication is introduced to the problem, in that the streamlines of the flowfield are not closed. as they are in the isodensity case. The size of the burned core. comprised mostly of combustion products. is much larger when heat release is taken into account, and the effective flame lengths and rates of reactant consumption are reduced, since the flames arc translated radially outward from each vortex struclure. Because the degree of heat release significantly affects the streamline pallern for the vortex pair flowfield, heat release is observed, with stoichiometry, to strongly impact the determination of the "limiting" reactant in reacted core formation.

ISSN:0010-2202    

DOI:10.1080/00102208808915759

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor