摘要:

About a quarter century ago, Rodenberger carried out preliminary tests on a novel chemical-propulsion gun for accelerating a practical-sized projectile to muzzle velocities on the order of several kilometers per second in a cylindrical tube, within conventional peak-barrel-pressure constraints. The tube was continuously lined with a thin film of solid propellant that underwent very-high-burn-rate deflagration immediately after projectile passage. The generation of combustion-product gases along the tube was to maintain a higher pressure on the base of the projectile than was attained by the conventional procedure of confining the propellant to the breech. We undertake simple approximate analysis for a similar thin film of solid propellant, through one that sustains a relatively slow detonation wave. We suggest: (1) the thickness of the propellant lining should be tapered with distance along the barrel, but either the variation of the circumferential packing of propellant or the composition of the propellant may be designed to compensate, so that the mass of solid propellant per length of gun barrel is invariant, or even increases, with distance along the barrel; (2) a prolate conical base, not a flat base nor a recessed conical base, accommodates the objective of maintaining a constant base pressure on the projectile, since combustion-product-gas generation at a site along the tube is initiated immediately after projectile passage; and (3) relatively modest, partial evacuation of gas from the portion of the tube ahead of the projectile significantly alleviates the shock-induced pressure on the projectile nose, which acts counter to the accelerating pressure. We arrive at these considerations by examining a tractable inviscid model of the expansional flow of the combustion-generated gas near the base of the projectile, in conjunction with projectile dynamics.

ISSN:0010-2202    

DOI:10.1080/00102209508907707

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A flame ball growing into a turbulent mixture exhibits a speed which is proportional to its size - this effect is a consequence of the distorted flame surface: the inner flame regions “push” the outer regions, the magnitude of this velocity depends upon the flame surface density distribution. A simple two-dimensional, zero-thickness flame model interacting with defined eddies illustrates how rapidly this flame distortion occurs after a spark ignition. This distributed volume source effect is also the functional form of Groffs modified entrainment model of flame propagation. A result of this size dependent growth is exponential growth of flame area which is an essential feature of spark-ignition internal combustion engines.

ISSN:0010-2202    

DOI:10.1080/00102209508907708

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We establish a mathematical model for the ignition of a thermally thin polymeric material in the Cone Calorimeter (autoignition mode). The model contains equations for solid phase and gas phase variables, and the two phases are coupled nonlinearly. Of particular importance are the couplings through convective and radiative heat transfer. We use the model to evaluate the critical heat flux required for ignition and identify features of the model which require further experimental validation.

ISSN:0010-2202    

DOI:10.1080/00102209508907709

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We consider unconfined spherical flames which expand into reactive gaseous premixtures that are laden with inert solid particles. An overall one-step Arrhenius reaction is adopted as burning process and the radiative transfer among the emitting/absorbing particles is modeled by a differential approximation of the Eddington type. The formulation accounts for the differences in velocity and temperature between the phases. The system is analyzed by matched asymptotic expansions in a multiple-limit process which assumes large Zel'dovich numbers (activation to reaction temperature ratio), small Boltzmann numbers (radiant to convective heat flux ratio), small loading (solid to gas heat capacity ratio) by the particles and optically very thin flame fronts. Three main regions can then be distinguished in the flowfield: a thinreaction zone(dominated by molecular transports and reaction) embedded in a thicker quasi-steadyflame-front region (dominated by molecular transports, convection and affected by conductive exchanges between the phases): the latter is itself flanked by even thicker, unsteadyradiation-zones(dominated by radiative transfer and convection). We analytically show that, even for polydisperse particle-clouds, tabulating a one-parameter function once for all allows one to obtain an integral equation for the flame speed evolutions; the evolution equation is then solved numerically. Depending on the mixture and/or initial conditions, the interplays among nonlocal radiative-transfer, chemical nonlinearity, as well as momentum and conductive gas/particle exchanges, lead to smooth or abrupt flame accelerations, everlasting relaxation oscillations in flame speed or transient ones. Cases of trajectory multiplicity are also encountered.

ISSN:0010-2202    

DOI:10.1080/00102209508907710

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Highly overventilated laminar coflow diffusion flames in axisymmetric geometry are addressed for Lewis numbers of unity in the reaction-sheet approximation with effects of buoyancy taken into account. A simple method of numerical integration with the boundary-layer approximation in stream-function coordinates is given, and results for flame structures and for Lagrangian histories are presented for hydrocarbon-air flames. Computed flame heights are shown to be in good agreement with experiment. The computational approach can efficiently employ standard routines on low-power work stations and personal computers.

ISSN:0010-2202    

DOI:10.1080/00102209508907711

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In most vehicle airbag systems, the gaseous mixture which fills the airbag comes from rapid combustion of a condensed-phase propellant. An area of current interest in the development of airbag systems is the decomposition behavior of these condensed-phase propellants over a range of operating conditions. The purpose of this paper is to examine the performance of gas-generating propellants by comparing the theoretical combustion behavior of three condensed-phase propellants commonly used in the airbag industry. The propellants discussed in this paper are a sodium-azide (NaN3) propellant, a non-azide propellant containing azodicarbonamide (ADCA), and a double-base propellant (DB). The thermophysical properties investigated in this study include the flame temperature and chemical composition of the product gases, the number of gaseous moles produced per mass of condensed-phase propellant consumed, the condensed-phase (slag) production of each propellant, and the toxicity of gas-phase combustion products. Airbag inflator performance, which is a function of the propellant combustion behavior, is often measured by reacting a sample of condensed-phase propellant in a rigid combustion chamber initially filled with nitrogen or air and observing the pressure-time relationship, the temperature-time relationship, and the final product composition. Such investigations are commonly called tank tests and are widely used in the automotive industry to test and validate inflator performance. In this paper, the questionable validity of using such tank tests to adequately describe the deployment of an airbag will also be addressed.

ISSN:0010-2202    

DOI:10.1080/00102209508907712

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Use of reduced chemical mechanisms in combustion applications is becoming standard practice due to the reduced computational effort involved in simulating finite rate chemistry. Reduced mechanisms are developed with simplifying assumptions which limit the phenomena that can be studied. In this study, a comparison between a full, finite rate, chemical mechanism and a standard reduced mechanism for H2-air combustion and NO formation is made for nonpremixed, turbulent jet flames. The numerical simulations incorporate an innovative mixing model so that turbulent-chemistry interactions can accurately be captured enabling a critical evaluation of the assumptions made in the reduced mechanism. Results indicate that the reduced mechanism and the full mechanism with differential diffusion and variable Lewis number compare relatively well except for the radical species. NO emission index results also compare favorably even though substantial variations in Lewis number and differential diffusion effects are found to exist in the full mechanism results

ISSN:0010-2202    

DOI:10.1080/00102209508907713

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The complete equations of premixed flames are solved numerically, in the isobaric approximation and with a simplified chemical kinetics. A momentum-pressure formulation is proposed for solving non-constant density flows. The growth rates of the Darrieus-Landau instability are measured and compared to the linear theory. Large amplitude curved flames are obtained, as well as flames submitted to a shear flow.

ISSN:0010-2202    

DOI:10.1080/00102209508907714

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Is a bank of cables, with a dust layer evenly distributed on both sides of the cables, more or less dangerous than a bank of cables with the same amount of dust all on one side? This question is answered by explicitly calculating the critical conditions for spontaneous ignition for each case. In the usual situation, with low dust conductivity, the asymmetric situation is more stable. When the conductivity of the “dust” becomes comparable to that of the cable, the stability is reversed.

ISSN:0010-2202    

DOI:10.1080/00102209508907715

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Based on a conduction equation with an intrinsic reaction rate term, a methodology has been developed to systematically study the factors affecting the forced ignition of a long pellet compressed out of a mixture of titanium and carbon reactant powders. This methodology enables identification of the parameters that determine whether or not ignition would occur under a given set of conditions and the time to ignition if it occurs. The ignition process is accountable through four nondimensional parameters: the intensity of ignition source, the Damkohler number, a reaction energy parameter and the Arrhenius number. Sample calculations show that the methodology is physically reasonable.

ISSN:0010-2202    

DOI:10.1080/00102209508907716

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor