摘要:

—We derive two different asymptotic models which describe the nonsteady, nonplanar burning of certain types of homogeneous solid propellants. Motivated in part by recent work on ammonium perchlorate deflagration, we assume, in the first model, that a fraction of the pro-pellant is pyrolyzed directly to product gases at a solid/gas interface, while the remainder sublimes and burns in the gas phase. In the second model, there is a thin liquid layer between the solid and gas, with combustion occurring in both the liquid and gas phases. Our analysis exploits the largeness of activation energies to derive flame sheet models analogous to those derived for strictly gaseous and strictly condensed deflagrations. For the special case of steady, planar burning, we obtain expressions for the regression rate eigenvalue as a function of the various parameters in the problem. However, a linear stability analysis of this basic solution shows that, for sufficientlylarge values of a certain grouping of parameters, it is unstable to small perturbations which correspond to pulsating, cellular modes of burning.

ISSN:0010-2202    

DOI:10.1080/00102208608923862

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

— Axial velocities in the recirculation zone of circular cylinders were measured using laser velocimetry in cold flows and flows with premixed combustion. Free stream turbulence with an intensity of 4 percent was introduced by an upstream grid. The mean free stream velocity and the equivalence ratio were fixed at values of 2.6 m/s and 0.65, respectively. The flow over a circular cylinder was studied at Reynolds numbers of 1000 and 2000. Profiles of mean velocity and turbulence intensity were determined from the data. The results indicate that the effect of combustion for the conditions of the study is to increase the length of recirculation zones, to dampen velocity fluctuations and to increase the magnitude of recirculating velocities. Comparison with reported data for similar cold flows suggests that the increase in length of the recirculation zone and the decrease in velocity fluctuations is in part due to a delay in transition in the wake of the cylinder and the suppression of vortex shedding.

ISSN:0010-2202    

DOI:10.1080/00102208608923863

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An apparatus has been built and utilized to study stabilized, premixed particle-cloud flames in each of the following three modes: upward propagation or downward propagation under normal gravitational conditions, or microgravity conditions. Results for lycopodium-air flames are reported. The upstream boundary hcat loss measurements have been utilized, along with detailed flame temperature structure, to deduce prominent aspects of the axial and of the omnidirectional heat transfer modes. For lycopodium-air flames, it is found that microgravity conditions yield the highest peak flame temperatures and that downward propagating flames display the lowest peak flame temperatures. Radiative losses are found to be more significant determinants of extinction limits than the axial conductive losses to the flameholder.

ISSN:0010-2202    

DOI:10.1080/00102208608923864

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We study a non-linear evolution equation which describes a non-adiabatic flame nearthe propagation limit due to heat losses, and takes into account the cellular instability of thermal and diffusional origin:Using numerical integration and shooting methods, we show that:i) Heat loss induced regime multiplicity also exists for cellular fronts, even when the cell size is prescribed.ii) Extinction by heat losses still occurs when cells are present, but is shifted; the new limit changes with the cell size.iii) Cellularity widens the propagation range, the shift being larger for lighter fuels.iv) For a fixed lateral flame dimension, many steady cellular patterns coexist for the same heat loss intensity, each one having its own velocity and propagation limit.

ISSN:0010-2202    

DOI:10.1080/00102208608923865

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The combustion wave structure of ammonium perchlorate (AP) composite propellantswas observed by microphotographs and the heat transfer process from the gas phase to the con-densed phase was determined by microthermocouples. Since the thickness of the combustion wave increased with decreasing pressure, the experiments were conducted at low pressures below I atm in order to examine the structure as detailed as possible. It has been determined that the reaction zone in the gas phase consists of heterogeneous flamelets produced by the decomposed AP monopropellant flames and the decomposed gases of polymeric fuel binder. The thickness of the reaction zone decreases with decreasing the concentration of binder at a constant pressure. The heat feedback from the gas phase to the condensed phase and the heat release at the burning surface are very dependent on the type of binder used. The reaction rate in the gas phase is greater and the heat release at the burning surface is smaller for the binder (HTPE) which contains higher oxygen concentration in its structure when compared with the binder (HTPB) which contains lower oxygen concentration in its structure.

ISSN:0010-2202    

DOI:10.1080/00102208608923866

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The results of a linear stability analysis of a stationary premixed plane flame attached to a porous plug burner are presented. A dispersion relation derived by Buckmaster (1983) is used to define the neutral stability curve in the wave number vs. Lewis number plane. The nature of this curve is analyzed as the characteristic parameters of the burner and the standoff distance of the flame are varied. It is shown that the neutral stability curve may have multiple brancheswhere pulsating flames become unstable. Depending on the parameter values, the burner mayhave a stabilizing or destabilizing effect.

ISSN:0010-2202    

DOI:10.1080/00102208608923867

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The spatial stability of a two-dimensional wake undergoing finite-rate kinetics is studied for both neutral and amplified antisymmetric disturbances. For inviscid flows, a gen-eralized stability equation is derived that reduces to the classical inviscid stability equation for non-reactive flows. Numerical calculations are presented for both non-reactive and reactive wakes and, for no chemical reactions, excellent agreement with calculations by Lees and Gold 1964) is obtained. For reactive flows, the neutral phase velocity is shown to be a function of both the free stream Mach number and the wake centerline temperature excess, in contrast to on-reactive flows, where it is independent of Mach number. The reactive stability problem is hown to be quite different from the non-reactive stability problem for both neutral and amplified isturbances.

ISSN:0010-2202    

DOI:10.1080/00102208608923868

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor