摘要:

This paper addresses the behavior of a candle flame in a long-duration, quiescent microgravity environment both on the space Shuttle and the Mir Orbiting Station. On the Shuttle, the flames became dim blue after an initial transient where there was significant yellow (presumably soot) in the flame. The flame lifetimes were typically less than 60 seconds. The safety-mandated candlebox that contained the candle flame inhibited oxygen transport to the flame and thus limited the flame lifetime. The flames on the Mir were similar, except that the yellow luminosity persisted longer into the flame lifetime because of a higher initial oxygen concentration. The Mir flames bumed for as long as 45 minutes. The difference in the flame lifetime between the Shuttle and Mir flames was primarily the redesigned candlebox that did not inhibit oxygen transport to the flame. In both environments, the flame intensity and the height-to-width ratio gradually decreased as the ambient oxygen content in the sealed chamber slowly decreased. Both sets of experiments showed spontaneous, axisymmetric flame oscillations just prior to extinction.

ISSN:0010-2202    

DOI:10.1080/00102200008947294

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The suppression of pressure oscillations in combustion chambers through the use of active feedback control is a new technology with high potential. In this article, we present a feedback control strategy based on an Internal Model Control System for nonlinear plants that uses artificial neural networks. This control system uses two neural networks: The Internal Model which approximates the plant forward dynamic; and a controller which gives the appropriate control input. The controller's parameters are updated adaptively for that purpose. We demonstrate numerically the capabilities of the developped control system in a numerical simulation of control of combustion instabilities. Then, we demonstrate the ability of this neural networks based control system to actively damp instabilities in a Rijke-tube burner.

ISSN:0010-2202    

DOI:10.1080/00102200008947295

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The oxidation of iso-octane has been studied in the past, primarily under stoichiometric conditions. Due to significant heat release from the oxidation of iso-octane in the intermediate temperature regime, excessive nitrogen was added to ensure safe operations and to slow the reactions in the use of flow reactors. Under these diluted stoichiometric conditions, all of the concentrations of iso-octane, oxygen, and nitrogen are significantly different from those in actual stoichiometric conditions. In this study, lean oxidation experiments of iso-octane in air (φ = 0.05) are performed in a high pressure flow reactor at 3, 6, and 9 atm in the intermediate temperature regime with reaction temperature in the range 915--950 K. Twenty-three hydrocarbon and oxygenated hydrocarbon intermediate species are identified and quantified as a function of time. A detailed chemical kinetic model is used to simulate these experiments. Comparison of predicted and measured species profiles shows that the model predicts the experimental data well including the shapes of species profiles. Based upon modeling results, the major chemical pathways are described.

ISSN:0010-2202    

DOI:10.1080/00102200008947296

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A comparison of different experimental techniques for metallic particle size evaluation including light diffraction, scanning electron microscope analysis and nitrogen adsorption is presented. Nitrogen adsorption as an appropriate experimental method for particle size evaluation is proposed. Certain aspects of chemical reactivity of micron and submicron aluminum powders in the air, using thermogravimetry and differential thermal analysis (TG/DTA), are discussed.

ISSN:0010-2202    

DOI:10.1080/00102200008947297

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This article reports observations of structures consistent with triple flame reaction zones in the stabilization region of turbulent nonpremixed jet flames. Previous studies of laminar mixing layers and nonpremixed jets show Hi brachial structures, however reports of triple flame structures in turbulent flowfields are sparse, The asymmetric coflow, which facilitates visualizing the luminous flame structure, is described and the observed double and triple flame structures are discussed. Flame luminosity data is presented and the relevance to CH planar laser-induced fluorescence (PLIF) studies of leading edge flame structures is discussed. Furthermore, connection is drawn to select theoretical studies of triple flames and partially premixed combustion.

ISSN:0010-2202    

DOI:10.1080/00102200008947298

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The present study numerically investigates the turbulent nonpremixed hydrogen jet flames. The turbulent combustion processes are represented by the reaction progress variable model coupled with the presumed joint probability density function. The reaction progress variables are derived assuming the radicals O, H, and OH to be in partial equilibrium and additional species HO2and H2O2in steady state. The turbulent combustion model is extended to nonadiabatic flame by introducing additional variable for the transport equation of enthalpy and radiative heat loss is calculated using a local, geometry independent model. The predictive capability of the RPV combustion model has been validated against the detailed experimental data involving the distribution of temperature, major species, radicals, and NO. Effects of the HO2/H2O2chemistry and radiative heat loss on the thermal NO formation are discussed in detail. In order to examine the validity of the optically thin radiation model in conjunction with the improved RPV model, the present numerical results for the radiant fraction have been compared with measurements and other computational results. Furthermore the capability of the present RPV model reproducing the NOx emission index (EINOx) is critically evaluated.

ISSN:0010-2202    

DOI:10.1080/00102200008947299

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An experimental investigation of the combustion phenomena of gel fuel droplets was conducted using a computerized video system. The ignition and combustion processes were viewed and recorded while the droplet and flame temperatures were measured simultaneously. A parametric investigation was conducted to evaluate the effect of the gellant content in the fuel, the ambient pressure and the oxygen mass fraction on the droplet burning rate. The heat of vaporization of gel fuels was measured and was found to increase with increasing the gellant content. The experimental results correlate well with the d-law and indicate that gels burn similar to liquids, however at lower burning rates. Ignition of gels was more difficult in comparison to liquids, especially at relatively high pressures.

ISSN:0010-2202    

DOI:10.1080/00102200008947300

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A three-dimensional model for oxidation of unburned hydrocarbons at the SI engine exhaust port has been developed. The computational mesh with a moving grid for the valve motion is constructed for the port geometry of a single-cylinder research engine. A 4-step oxidation model is used to predict the HC oxidation and the coefficients of the model are modified for the port oxidation environment with the results of a full chemical kinetic mechanism. The measured THC concentrations at the cylinder exit (3 positions) are used as the inlet concentration for the simulation and the temperatures of the core gases and boundary zone gases in the cylinder are obtained from a three-zone cycle simulation.

ISSN:0010-2202    

DOI:10.1080/00102200008947301

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The ignition characteristics of heated C2H2counterflowing against heated air were numerically investigated in the presence of additives such as NO, F2, and H2C2H4and air temperatures were chosen to resemble conditions relevant to high-Mach number, air-breathing propulsion. The numerical simulations were conducted along the stagnation streamline of the counterflow and included detailed descriptions of chemical kinetics and molecular transport. Addition of NO, at concentrations of about 10,000 ppm (1%), results in a substantial increase of ignition strain rates, from 300s−1to values up to 32,000s−1, This ignition promotion is caused by enhanced radical production, initiated through the interaction between NO and HO2. Further increases in NO amount lead to reduced improvements. Small additions of F2and H2were also found to promote ignition, but to a lesser extent compared to NO. Results also show that with the addition of F2in the presence of NO, ignition promotion is further enhanced. The system becomes hypergolic for F2and NO concentrations larger than 25,000 ppm. The present investigations suggest that the use of C2H2. NO, and F2may permit ignition at conditions of relevance to SCRAMJET's.

ISSN:0010-2202    

DOI:10.1080/00102200008947302

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An augmented reduced mechanism (ARM) for methane oxidation, consisting of 16 species and 12 lumped reaction steps, was developed from GRI-Mech 1.2. It showed excellent performance in reproducing the global response of a wide varieties of combustion phenomena including auto-ignition, laminar flame propagation, and counterflowing non-premixed systems under extensive thermody-namical parametric variations including those of temperature, pressure, and composition. The present study extends the rigor of validation of this reduced mechanism to the next level by showing that good reproduction still exists for the detailed evolutionary and spatial structures of these phenomena. Validation comparisons have also been conducted for the two skeletal mechanisms developed by Kazakov and Frenklach, showing that DRM-22, which consists of 23 species and 102 elementary steps, appears to be the minimum size for a skeletal mechanism to approach the comprehensiveness of the 12-stepARM.

ISSN:0010-2202    

DOI:10.1080/00102200008947303

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor