摘要:

A simulation procedure capable of handling transient compressible flows involving combustion is presented. The method uses the velocity components and pressure as primary flow variables. The differential equations governing the flow are discretized by integration over control volumes. The integration is performed by application of up-wind differencing in a staggered grid system. The solution procedure is an extension of the SIMPLE-algorithm accounting for compressibility effects. Turbulence is treated by solving the equations of kinetic energy of turbulence and of dissipation rate of kinetic energy of turbulence. The combustion model incorporates solution of balance equations for the mixture fraction and the mass fraction of fuel. The rate of combustion in the latter equation is modelled according to the “eddy-dissipation model” of Magnussen and Hjertager. A validation calculation of the classical shock-tube problem is performed and good agreement between analytical solution and computed predictions is found. Flame acceleration by repeated obstacles is also modelled, and comparisons with large-scale and small-scale experimental data are encouraging.

ISSN:0010-2202    

DOI:10.1080/00102208208946985

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Experiments have been conducted to determine the global kinetics for lean-fuel propane oxidation on a transition metal oxide catalyst. The catalyst used was composed of chromium and cobalt oxides (Cr2O3, CO3O4) deposited on alumina washcoated honeycomb ceramic substrates.

ISSN:0010-2202    

DOI:10.1080/00102208208946986

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The rate of oxidation of pyridine and the nitrogen containing products formed during the oxidation were studied in the temperature range of 675–775° C using a Vycor, stirred-flow reactor. The rate was found to be half-order in pyridine, first-order in oxygen and half-order in oxygen consumed for both rich and lean mixtures. The activation energy and log frequency factor were 54·0 kcal/mole and 14·9 (using M-1sec-1), respectively. Coating the reactor wails with KG had no significant effect on reaction order or activation energy, although the rate was increased by about a factor of two. An alternative to the apparent autocatalysis factor, ( δO2)1/2, could be that the rate of radical escape was competitive with that of chemical termination. The treatment using this assumption was applied to the data, however, the scatter prevented drawing a definite conclusion concerning these two alternatives. Product determinations indicated that nitrogen was accounted for by the HCN and N2formed for lean mixtures when oxygen concentration was 7·0 mole percent or below; significant nitrogen appeared in the smoke for rich mixtures. However, at higher oxygen concentrations, N2O and NO became more significant as products. The mechanistic implications of these observations are discussed.

ISSN:0010-2202    

DOI:10.1080/00102208208946987

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Steady and pulsating modes of flame propagation through a premixed combustible mixture are studied for the case in which the flame is characterized by the sequential production and depletion of a significant intermediate species. We employ the method of matched asymptotic expansions to derive a model valid for large activation energies, and show that the pulsating solution is the result of a supercritical Hopf bifurcation from the steadily propagating solution (which becomes unstable). Through a nonlinear bifurcation analysis, we calculate the pulsation amplitude and other characteristics of the flame along the bifurcated branch. It is shown that the average thickness of the pulsating flame, by which we mean the average effective separation distance between production and depletion of the intermediate species, is greater than that predicted by a steady-state theory. In addition, we find that the mean propagation speed is less than that of the steadily propagating solution, but that the instantaneous peak concentration of the intermediate species is a constant equal to its steady-state value.

ISSN:0010-2202    

DOI:10.1080/00102208208946988

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The induction period of a high activation energy thermal explosion in a confined, rigid, nondiffusing, combustible material is considered. A method-of-lines approach is used to develop numerical solutions for the infinite slab, infinite cylinder and spherical geometries. When the dimensional initial and boundary temperatures are equal, results are obtained for a wide range of supercritical values of the Frank-Kamenetskii parameter S, and for arbitrary values of the ratio of the chemical heat release and the initial internal energy. The time-history of the spatially variable temperature distribution is described. At a common value of S the thermal runaway time is largest for a sphere and smallest for a slab, with the cylindrical system between. The explosion location re is found to move away from the symmetry point when the wall temperature is made sufficiently large compared to the initial temperature. A further increase in the former moves the value of r" toward the hot boundary. The dependence of the explosion time on the incremental difference between the boundary and initial temperatures and on a modified Frank-Kamenetskii parameter is described in detail. The time-history of an off-center explosion is shown to produce precisely the same kind of highly localized hot spot as that found when the temperature difference is zero.

ISSN:0010-2202    

DOI:10.1080/00102208208946989

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

SO2was used as a tracer gas in an experimental study of turbulent air jets and propane diffusion flames in cross-flow. Measurements of the SO2concentration field were used to obtain data on the shape and size of the bent-over plumes in the vortex zone, between 60 and 220 diameters downwind of the discharge. Data on the variation of plume cross sectional area with distance led to estimates of the variation of entrainment with distance. It appears that for turbulent diffusion flames in cross-flow, in which both initial jet momentum and flame buoyancy are significant influences, the trajectory can be expressed by a power law of the form [Ztilde]=M X¯nin which the distances are nondimensionalized by the momentum length scale and n is a function of the Froude number. Even though the wind tunnel was too short to permit it, the SO2tracer technique seems to be useful also for studies of the buoyant plume several hundred discharge diameters downwind of the flame.

ISSN:0010-2202    

DOI:10.1080/00102208208946990

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The calculation of the shock Hugoniot of a composite propellant from the experimental Hugoniot of the components is discussed. The calculated Hugoniot of a composite HMX explosive-polyurethane binder propellant is shown to be in good agreement with experiment. The homogeneous shock temperature of the bulk propellant and its components is calculated numerically using the Walsh-Christian equation, but including the effect of temperature on heat capacity. The shock temperature of the binder is greater than that of the explosive. The factors that control the energy partition in an impacted or shocked composite propellant are discussed. It is shown how the addition of a polymeric binder to an explosive reduces the shock temperature, which in turn reduces the sensitivity of the material to impact or shock ignition.

ISSN:0010-2202    

DOI:10.1080/00102208208946991

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An experiment has been conducted to determine the variation in light scattering characteristics of refractory oxide particles (TiO2and AI2O3) as they pass through a laminar pre-mixed hydrogen-air flame. It was found that AI2O3was not affected by the flame but Ti02 particles exhibited a substantial reduction in scattered light intensities. In addition the effect of agglomeration on particle light scattering measurements of the fluctuating concentration field in a turbulent flame was evaluated with the use of Mie scattering computations. The broadness of the initial particle size distribution was found 1o be a dominant parameter. Measurements using nearly monodisperse aerosols were most sensitive to agglomeration

ISSN:0010-2202    

DOI:10.1080/00102208208946992

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor