Flowfield-flame structure interactions in an oscillating swirl flame

A swirling methane-air diffusion flame at atmospheric pressure is stabilized in a gas turbine model combustor with good optical access. The investigated flame with a thermal power of 10 kW and an overall equivalence ratio of 0.75 exhibits pronounced thermoacoustic oscillations at a frequency of 295 Hz. The main goal of the presented work is a detailed experimental characterization of the flame behavior in order to better understand the flame stabilization mechanism and the feedback loop of thermoacoustic instability. OH* chemiluminescence imaging is applied for determining the flame shape and estimating the heat release rate. Laser Raman scattering is used for simultaneous detection of the major species concentrations, mixture fractions, and temperature. The velocity fields are measured by particle image velocimetry (PIV) or stereo PIV, simultaneously with OH planar laser-induced fluorescence. The dynamic pressure in the combustion chamber is determined by microphone probes. The flow-field exhibits a conically shaped inflow of fresh gases and inner and outer recirculation zones. The instantaneous flame structures are dominated by turbulent fluctuations; however, phase-correlated measurements reveal phase-dependent changes in all measured quantities. The paper presents examples of measured results, characterizes the main features of the flame behavior, explains the feedback loop of the oscillation, and discusses the flame stabilization mechanism.     

电真空玻璃熔窑内三维数学模型研究

电真空玻璃熔窑内三维数学模型研究祁建伟，胡桅林，过增元（清华大学工程力学系　１０００８４）ＴｈｒｅｅＤｉｍｅｎｓｉｏｎａｌＮｕｍｅｒｉｃａｌＳｉｍｕｌａｔｉｏｎｉｎａｎＥｌｅｃｔｒｉｃＶａｃｕｕｍＧｌａｓｓＭｅｌｔｉｎｇＦｕｒｎａｃｅ￥ＱｉＪｉａｎｗ...     

Propagation of an optical flame along a tube

Conclusions In the present study we have, for the first time, experimentally observed and investigated an optical discharge in a slow-combustion regime under gas-dynamics conditions close to the one-dimensional (plane) case, when there are no solid objects in the laser beam. We have shown that after the initial acceleration of the plasma there is a stationary regime of propagation of the discharge, characterized by a motion of the discharge front through the gas compressed by a shock wave that moves at high velocity. This regime was observed over an intensity range of 0.4–4 MW/cm². In this same range we detected deviations from the continuity of discharge propagation (jumps of the front). The characteristics obtained for the discharge propagation are in satisfactory agreement with the calculations carried out according to the one-dimensional model. When I_av 4.3 MW/cm², we observe a transition to a photodetonation regime.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 22, No. 3, pp. 18–29, May–June, 1986.     

Refining of Silicon Using an Induction Furnace in the Fractional Melting Process

A new fractional melting process using an induction furnace and a centrifugal system has been developed for metallurgical-grade silicon (MG-Si) refining. An induction furnace enables rapid heating and therefore reduces the total refining process time. Impurity-rich liquids can be ejected effectively from the MG-Si by the centrifugal force induced by a motor. The impurity behaviors of the refined samples are observed by scanning electron microscope (SEM). The refining efficiency, which depends on sample size and centrifugal force, is evaluated using inductively coupled plasma atomic emission spectroscopy (ICP-AES) and inductively coupled plasma mass spectroscopy (ICP-MS). The purity of the refined silicon increases with the centrifugal force. The correlation between the centrifugal force and silicon purity is rationalized using the surface tension of impurity-rich liquids. In spite of the rapid heating rate by induction furnace, the MG-Si is refined and 96.7% of the impurities are removed at rotation speeds of 3000 rpm.     

Diffusion flame in an electric field with a variable spatial configuration

The influence of an electric field whose intensity vector rotates around the flame axis on the shape of the diffusion flame of propane is experimentally studied. Application of spectrozonal registration makes it possible to obtain information about the radiation intensity distribution at wavelengths of intermediate reaction products (OH, CH, and C₂). Different positions of the peak intensity of the own radiation of the flame at different wavelengths testify to the influence of such an electric field on the mixing processes, namely, mixing is more intense than that in the regime without application of the electric field. This feature may turn out to be useful for increasing the efficiency of combustion of gaseous hydrocarbon fuels.