Investigation and Application of Fundamental Phenomena of Turbulent Premixed Combustion in a High-Pressure Environment

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Turbulent premixed flames stabilized in a high-pressure atmosphere was studied with the aim of basic elucidation of phenomena of the high-pressure turbulent combustion which has not been explored precisely. The relationship between turbulence characteristics and turbulent flame structure under high pressure was clarified. Investigation of pressure effect for the fractal properties and turbulent burning velocity under high pressure were also made.The laminar flow nozzle-burner is installed in the pressure chamber, and OH-LIF technique were investigated at pressures from the atmospheric pressure up to 3.0 MPa. (0, 0) band and (1, 0) band of the OH radical were excited by an OPO tunable laser and a dye laser pumped by a Nd-YAG laser. The relationship between OH-LIF intensity and pressure was examined. In addition, a simulation considering effects of the broadening of laser line width and absorption spectrum was made and also compared with the experimental result. As the result, it was cla … More rified that the effects of the absorption spectrum broadening was large for the LIF intensity degradation with the increase in pressure. Although the LIF intensity for larger laser line width is smaller than the case of smaller laser line width at atmospheric pressure, the decrease in LIF intensity with pressure is small for larger laser line width. It was proven that to estimate LIF intensity degradation under the high pressure was possible by calculating the overlap integral of laser spectrum profiles and absorption line spectral profiles. From these findings, guideline for the measurement condition of OH-PLIF at high-pressure was established.In continuing, the OH-PLIF method was applied to the instantaneous tomographic imaging of high-pressure turbulent flames. Especially, the fractal analysis of the OH-PLIF image was carried out as the technique which can quantitatively evaluate refinement and complication of the turbulent flame structure. As the result, it was proved that the fractal dimension for high-pressure flame was larger than atmospheric pressure flame even for equal u'/SィイD2LィエD2. The fractal inner cutoff decreased with pressure, but it was proven that the fractal inner cutoff was almost fixed in almost whole range of u'/SィイD2LィエD2 at high pressure. When various characteristic scales such as turbulent scales were compared with the fractal inner cutoff, it was proved that a characteristic instability scale, which corresponds to disturbance scale of maximum growth rate for the hydrodynamic instability, was well correlated to the fractal inner cutoff. These new findings which the hydrodynamic instability has dominant effects at high pressure were also confirmed by the observation of the flame instability with no initial turbulence in flow at high pressure. Less