摘要:

The identity and concentration of bothsmall and large positive ions have been determined in rich and sooting ethylene and acetylene premixed flames. These ions are formed in two independent ionisation zones. The first one is the classical chemi-ionisation zone which produces the small ions (between 12 and ≃300 a.m.u.), and which importance decreases when the fuel equivalence ratio increases. The second one appears later, at the early stages of the soot formation, where larger species are formed. The size and concentration of these large ions can be explained by the direct thermoionisation of large polynuclear aromatic molecules and carbon particles less than 20 Ȧ diameter of low ionisation potentials, which concentrations increase as the flame becomes richer

ISSN:0010-2202    

DOI:10.1080/00102207908946906

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The applicability of the Method of Averaging (MOA) in the analysis of nonlinear axial combustion instabilities in solid propellant rocket motors is investigated. An approximate technique utilizing the Galerkin Method was first developed in order to reduce the computer time and core storage required to perform the stability calculations, which involve solving the conservation equations describing the two-phase unsteady flow of gases and particles in solid rocket combustors. At the expense of additional approximations, further reductions in computation time were obtained by using the MOA to solve the Galerkin equations. Solutions obtained with both the Galerkin Method and the MOA are compared with the “exact” numerical calculations for the simple case of the linear attenuation of small amplitude waves in a gas-particle mixture in a closed-ended chamber. For this simple problem, a one-mode approximation was used in the Galerkin and MOA analyses, and heat transfer between the gas phase and the particles was neglected in both “exact” and approximate analyses. Comparison of the decay rates calculated with the Galerkin method and the MOA with those obtained with the “exact” analysis indicates that the MOA may yield erroneous results in certain cases. The inclusion of gas/particle heat transfer and nonlinear mode coupling in these analyses is not expected to eliminate these discrepancies, therefore caution should be exercised in the use of the MOA in solid rocket stability analysis.

ISSN:0010-2202    

DOI:10.1080/00102207908946907

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

This paper describes the results of an experimental study that was concerned with the quantitative determination of the capabilities of the combustion processes associated with coaxial gaseous propellant rocket injectors to drive combustor pressure oscillations. The data, obtained by employing the modified impedance tube technique with compressed air as the oxidizer and acetylene gas as the fuel, describe the frequency dependence of the admittance of the combined injector-combustion process. The measured data are compared with the predictions of the Feiler and Heidmann analytical model utilizing different values for the characteristic combustion time τb. The values of τbwhich result in a best fit between the measured and predicted data are indicated for different equivalence ratios. It is shown that for the coaxial injector investigated in this study the τbvaries between 0.7 and 1.2 msec for equivalence ratios in the range of 0.57 to 1.31. In addition, the experimental data clearly indicate that the tested injector system could drive combustion instabilities over a frequency range that is in qualitative agreement with the predictions of the Feiler and Heidmann model.

ISSN:0010-2202    

DOI:10.1080/00102207908946908

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The unsteady one-dimensional interaction of a planar laminar isobaric flame (propagating at Lewis number unity through a fuel-lean uniform premixture) with a parallel end wall is described. The reaction rate is characterized by large dimensionless Arrhenius activation energy, such that the reaction zone of the flame structure is very thin. Accordingly, the reaction zone is modeled for convenience as a planar interface that is a Dirac-delta-function-type sink for reactants and a source for chemical heat. The result is a tractable Stefan-type problem, in which regions of unsteady convective diffusion are solved subject to suitable continuity conditions holding at a moving boundary (the flame). The increase in flame speed as the wall is approached is quantitatively described. A'systematic program for utilizing this thin-flame formulation for investigation of more general flame/wall interactions in premtxtures, analogous to the adoption of the Burke-Schumann diffusion flame for vigorously burning unpremixed reactants, is outlined.

ISSN:0010-2202    

DOI:10.1080/00102207908946909

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The definition of a flammability limit still remains a most important fundamental problem of the combustion theory. The data on limits are needed in practice in determining the fire- and explosion-proof conditions. However, there is yet no universal answer to the main question of the applicability of the data obtained in standard tubes to large confined and unconfined clouds. This paper is concerned with results obtained after the publishing of the first review by Lovachevet al. in 1973.

ISSN:0010-2202    

DOI:10.1080/00102207908946910

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The effects of the attenuation of the radiation by the decomposition products in the gas phase on surface temperatures of PMMA and red oak were studied by using a CO2laser in the radiant flux range from 7 to 18 W/cm2irradiating normally downward to the horizontally mounted sample. It was observed that the attenuation of the radiation caused by the decomposition products in the gas phase was significant enough to affect surface temperature. Maximum surface temperature of PMMA rises to about 400°C during the pre-ignition heating period and tends to be independent of the initial radiant flux. Surface temperature at ignition is in the range of 375 to 410°C and remains fairly constant from 8 to 19 W/cm2for piloted-ignition and auto-ignition. However, the maximum surface temperature of red oak during the preignition heating period tends to increase with the decrease in the initial radiant flux. Surface temperature at ignition increases from 400°C at 16 W/cm3 to 575°C at 8 W/cm2for auto-ignition and from 420°C at 15 W/cm28 to 500°C at 7 W/cm2 for piloted-ignition.

ISSN:0010-2202    

DOI:10.1080/00102207908946911

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

A modified laser schlieren and fast Fourier transform analysis system has been developed and applied to the study of vortex frequencies in a lean, premixed prevaporized combustor. The system is sensitive to the passage of vortex structures which dominate the flow in the combustor studied. The frequency spectra of the passage of vortices show distinct frequency peaks which are postulated to be characteristic of the processes triggering the vortex shedding. The method provides additional information which should aid in the characterization and understanding of shear flows.

ISSN:0010-2202    

DOI:10.1080/00102207908946912

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor