摘要:

Abstract –The rate of interpenetration of two initially separated gases of appreciably different molecular weight is studied analytically and numerically. The gases are confined between two infinite parallel impervious planes situated perpendicular to the gravitational acceleration; the lighter gas is initially confined to a horizontal layer,which lies (a) adjacent to the upper plate, and (b) adjacent to the lower plate. The initial stratification in (a) is relaxed by Fickian diffusion, with barodiffusion found to be relatively ineffectual in maintaining the initial distribution, especially for smaller plate separations. In the far more unstable stratification in (b), in which a Taylor-type instability related to the acceleration of a density interface toward the heavier medium arises, diffusional processes playa perturbational role relative to inertial processes, except at small disturbance wavelengths. An energy approach to describing the finite-amplitude overturning of case (b) is suggested as a means of estimating the width of protuberances which grow to large size.

ISSN:0010-2202    

DOI:10.1080/00102207708946773

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102207708946774

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract – A sensitivity test procedure developed by Shuler and co-workers for obtaining systematic estimates of the sensitivity of the solution of coupled sets of non-linear differential equations to variations in parameters is applied to a 23-equation methane oxidation mechanism. The sensitivity method is based on varying each rate constant sinusoidally with a specific frequency assigned to each rate constant over an arbitrary range. The results are Fourier analyzed to determine quantities which measure the uncertainty in the solution as well as the individual contributions from each rate constant. By application of this procedure, we obtain estimates for the sensitivity of species concentrations of reactants, products and free radicals which occur in the CH4-02-Ar system subject to a simultaneous variation of all rate coefficients over a ± 50 percent uncertainty range. We present results for a stoichiometric reaction of the CH4-02-Ar system at 2000° K for a time corresponding to ignition. Jt is found that of the 23 reactions (plus their reverse) included in the mechanism, only about 5-7 reactions (depending on the species in question) strongly affect the concentration of that species. For the specific case of the Ο-atom concentration, we find that our six most sensitive reactions include the five reported previously by Bowman in the Fifteenth Symposium (International) on Combustion. For the ±50 percent variation in rate constants, we find deviations from the mean concentration ranging from ∼3 to ∼71 percent, depending on species.

ISSN:0010-2202    

DOI:10.1080/00102207708946775

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract-An analytical investigation of an acceleration-induced burning rate increase of solid propellants is presented. The analytical model includes the pit formation on an accelerated combustion surface, the growth of agglomerated globules, the heat feedback by an agglomerated globule and the growth of pits. A set of equations expressing these processes is integrated with respect to burning time in order to quantitatively estimate the acceleration sensitivity of burning rate. Analytical results are compared to the experimental results with regards to aluminized and non-aluminized composite propellants. The proposed model adequately explains the observed effects of acceleration, burning pressure, static burning rate, aluminum content and transient phenomenon of burning rate augmentation. And it clarifies the relationship in the roles of aluminum particles and ammonium per-chlorate (AP) particles in this phenomenon. The results on post-fire residues are also discussed in light of the proposed model.

ISSN:0010-2202    

DOI:10.1080/00102207708946776

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract-The high-temperature decomposition kinetics of nitric oxide have been investigated in shock-heated mixtures of NO, H2, and either argon or krypton. Initial NO:H2 ratios ranged from 1:2 to 2:1, with the inert diluent making up 90 percent of the test gas in all cases. Two high-speed infrared detectors were used to monitor the infrared emission from nitric oxide and water vapor. Calculations using a seventeen-reaction kinetic model indicate that the rate-limiting reaction for NO decomposition is the reaction of NO with atomic hydrogen,Math The chemical rate constant for this reaction, k1, could be determined accurately by optimizing agreement between calculated and measured emission records for NO and H2O. The Arrhenius-type expression which best tits the data from 21 shock tube experiments in the temperature range from 2400 K to 4200 K is Math.

ISSN:0010-2202    

DOI:10.1080/00102207708946777

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract-The amount of exhaust gas recirculation (EGR) which a single-cylinder engine tolerated without misfire increased when the duration of the spark was increased. Also, when minimum spark advance for best torque was maintained, engine efficiency improved as EGR increased. In addition to misfire, two other engine combustion problems were identified: partial combustion, and excessively slow combustion. Low flame speeds associated with high EGR probably caused these other problems, which could be prevented with advanced spark timing. Misfire, partial combustion, and excessively slow combustion were detected by monitoring with an oscilloscope the output of a bare wire thermocouple located in the exhaust port of the engine. This simple method could be suitable for quantifying combustion problems in multi-cylinder engines.

ISSN:0010-2202    

DOI:10.1080/00102207708946778

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

It is shown that the formation of cellular structure in a flame is conditioned by diffusion and heat conduction effects and is independent of the hydrodynamics of the perturbed flame. It is proved that cellular flames are formed only when a sufficiently light reactant of the combustible mixture is present in a low concentration. If there is an excess of the light reactant, a plane flame front is absolutely stable (in the framework of the diffusional-thermal model) or shows a noncellular periodic structure (hydrodynamic model)

ISSN:0010-2202    

DOI:10.1080/00102207708946779

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract-Data are presented on the structure of propane diffusion flames burning in a concentric stream of air, with and without the addition of diluents (carbon dioxide and nitrogen) to the fuel jet and air stream. The flame length and the fraction of heat release radiated are documented as functions of diluent concentrations in fuel jet and air stream. The effects of diluent addition on the temperature profiles, composition profiles showing species CO2, H2O, CO, N2, O2, C3H8,NO and pyrolysis species of C3H8 and axial profiles of radiant power emitted are also presented. The results show that the diluents reduce flame length, stability, radiation and concentrations of nitric oxide in the flames. The effects of diluents on the flame structure can be attributed primarily to the changes in concentrations of various species rather than to the changes in temperature. The problems of using flue gas recirculation in large combustion systems are indicated.

ISSN:0010-2202    

DOI:10.1080/00102207708946780

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Abstract-The ignition behavior of laminated propellants composed of ammonium perchlorate (AP) single crystal oxidizer and carboxyl terminated polybutadiene (CTPB) fuel-binder slab, has been studied by means of CO2laser under sub-atmospheric pressure. The ignition is initiated by the reaction of carbonaceous material on AP surface with AP decomposition products and ambient helium gas has appreciably preventive influence on propellant ignition, compared with Ar and N2 gases. These phenomena might be explained by a comprehensive ignition model.

ISSN:0010-2202    

DOI:10.1080/00102207708946781

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor