摘要:

The spectra of pressure oscillations in combustion chambers often contain large peaks at frequencies corresponding to chamber acoustic modes. Pulsed combustors are designed to operate with fixed amplitude oscillations but in many systems the oscillations have undesirable consequences. An understanding of the nonlinear mechanisms responsible for the limiting-amplitude behavior is therefore desired. This paper is divided into two parts. First, characterization of the oscillations in terms of attractors in mathematical phase space has been performed on pressure signals measured in a laboratory combustor of premixed gases. The results for one set of operating conditions show a quasiperiodic attractor of dimension two over an order of magnitude of scales. Next, the nonlinear combustion response to oscillations of a single acoustic mode are used to model autonomous or 'self-excited' behavior. Tho simple models of nonlinear combustion processes observed in the laboratory combustor result in unstable oscillations that reach limiting-amplitudes. With the variation of model parameters. the periodic limit cycles undergo subharrnonic bifurcations and transition to chaos.

ISSN:0010-2202    

DOI:10.1080/00102209308924107

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A new method for the determination of thermocouple time constants is described, which reproduces the large temperature differences between the thermocouple junction and ambient fluid that occur in premixed turbulent flame applications. Time constants measured while the thermocouple is both heating and cooling, as well as the dependency of the time constant on velocity and temperature, are reported. Velocities are varied from 0.6 to 5.5 ms-1, and junction temperatures range from 700K to ISOOK while heating and from 400K to llooK while cooling. Temperature differences between the thermocouple junction and ambient fluid up to 800K are achieved. Radiation losses from the junction are accounted for. Predicted time constants based on commonly used correlations for heat transfer from a cylinder in cross-flow are compared to the data, and it is suggested that free molecular flow effects are partially responsible for the systematic deviation of the data from the theoretical predictions.

ISSN:0010-2202    

DOI:10.1080/00102209308924108

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Abstract—A mathematical model is presented describing a physical system of detonation waves propagating in a solid particle/air mixture with a wide range of solid phase concentrations. The mathematical model was solved numerically using the Second Order Godunov method, and numerical solutions were validated for detonation waves propagating in mixtures with concentrations of solid phase from 0.75 kg/m3to 1000 kg/m. Numerical solution was obtained for detonation waves propagating in a system consisting of clouds with a small concentration of particles and a ground layer in which solid particle densities are three orders of magnitude larger than in the cloud. Three different particle concentration distributions in the ground layer were simulated and compared in terms of detonation wave structure and parameters.

ISSN:0010-2202    

DOI:10.1080/00102209308924109

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Abstract—A detailed experimental study of a turbulent premixed flame above a Bunsen burner is presented. First the mean velocity field and the turbulence field within the flame have been studied by L.D.A., including measurements of turbulent length scales. Secondly the flame is studied with quantitative planar imaging. These images lead to the knowledge of the mean and fluctuating progress variable, as well as length scales of the fluctuating field and the "flamelet length by unit surface area". The experimental results are discussed with respect to already existing measurements and theories. For the present turbulent flame, which can be classified as a "wrinkled flame" throughout most of the flow field, there is found a clear but slight influence of combustion on the turbulence kinetic energy. As determined from experiments the turbulent length scale increases when crossing the flame. The measurements of flamelet length by unit surface area has enabled us to directly obtain the mean reaction rate, because the local flamelet velocity has been found, in the mean, close to the laminar burning velocity within ± 5%. Existing models for calculating the mean reaction rate have been compared with these measurements, and it is found that the Eddy Break Up Model, or the Cant and Bray Model are in agreement, nearly equally well, with the experimental findings.

ISSN:0010-2202    

DOI:10.1080/00102209308924110

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The actual flame stretch rates of the stretched cylindrical premixed flame and counterflow twin flames were measured with LDV for the methane-air and propane-air mixtures over a wide range of equivalence ratios. The stretch rate at the flame center at the point of flame extinction was considered to be the maximum stretch rate for the existence of cylindrical and plane ftamelets. It was shown that the actual flame stretch rate at the point of flame extinction for the stretched cylindrical flame was smaller than that for the counterflow twin flames except for the case of very rich propane-air mixtures. The conditions for the existence of the cylindrical flamelet in turbulent premixed flames, which has a similarity to the fine structure of turbulent premixed flames proposed by Chomiak (1970, 1972, 1977), were discussed using the stretch rate data at the extinction point and the turbulence parameters. It was found that the cylindrical flame let could not exist in highly turbulent flames where the distributed reaction zones were realized because of the limitation of resistibility to the extinction due to local strain. Furthermore, the cylindrical flamelet should be limited to mixtures such as rich propane-air and lean methane-air in which the minimum flame diameter at the extinction point is comparable to the Kolmogorov microscale.

ISSN:0010-2202    

DOI:10.1080/00102209308924111

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Abstract–The formation of carbonaceous deposits in gas turbine combustion chambers has been studied at the Institute for Thermal Turbomachinery at the University of Karlsruhe. The deposits show differing chemical and physical properties over wide ranges. Consequently, different mechanisms of formation are considered. In investigating the dominant parameters for coke deposition the chosen approach was to study the formation process under well defined test conditions. These bench tests were followed by comparison with deposits derived from operating combustors using elementary analysis, gaschromatography, infrared spectroscopy as well as electron microscopy. The development of the deposits by fuel droplet impingement on the hot combustion chamber wall is simulated. In using both gas turbine fuels as well as pure hydrocarbons the influence of wall temperature and fuel composition is examined. As a result of the analysis, a characteristic temperature range for the coke deposition is found. In addition, the deposition-causing fraction of the fuel can be determined. Two different groups of deposits are identified under combustion chamber operation conditions. Deposit formation by droplet impingement accompanied with chemical reactions at the combustor wall is found in the primary zone of the combustor. This is confirmed by identical chemical characteristics between deposits of the bench tests and the combustion chamber deposits. Another typical deposit build-up is formed by adhesion of small particles formed in the reaction zone of the combustor. Based on our results, a scheme for the formation of deposits from the liquid fuel is formulated.

ISSN:0010-2202    

DOI:10.1080/00102209308924112

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An oscillating piezoelectric beam was used on the prefilming surface in a two-dimensional model of the prefilming-type aircraft fuel atomizer to interact with the periodic phenomena occurring inside the nozzle and just at the atomizing exit-edge of the prefilming surface. The oscillating beam was designed such thatits second mode of oscillation resonated at frequencies close to the above-mentioned periodic phenomena.It was shown that the spray Sauter Mean Diameter (SMD) and mean drop velocity profiles became more uniform at a distance of 50 mm from the nozzle for the condition tested. Cross-sectional-averaged SMD decreased slightly as a result of this novel feature.

ISSN:0010-2202    

DOI:10.1080/00102209308924113

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The weak thermal development of a reacting high speed high enthalpy hydrogen-air mixing layer which seems to depart from equilibrium only slightly in terms of reaction rates is analysed through the examination of stretch, and details of chemistry from the direct numerical simulations of the reacting mixing layer with full chemistry. The analysis of these parameters clearly indicates that the peak temperatures and the local composition depart from equilibrium significantly consistent with the high stretch even though the departures of the reaction rates from equilibrium apparently are not large. A serious consideration of chemical non-equilibrium effects in high speed mixing layers is called for.

ISSN:0010-2202    

DOI:10.1080/00102209308924114

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209308924115

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor