Investigation of Micro-Scale Structure in Turbulent Premixed Flames and Its Control

本文研究了湍流预混火焰的微观结构，以期为燃气轮机燃烧室内观察到的湍流燃烧提供有效的控制方案。对氢气/空气和碳氢/空气湍流预混火焰进行了直接数值模拟，考虑了详细的动力学机制以及输运和热性质与温度的关系。为了从实验上研究湍流预混火焰的微观结构，还发展了激光诊断仪，如OH和CH同时的PLIF和时间序列PIV。结果表明，湍流强度和长度尺度等湍流特性对预混火焰的微观结构、NOx的生成机理、燃烧室的发声机理以及湍流预混火焰的真实三维特性都有一定的影响。所得结果也证实了仅从量纲论证提出的湍流燃烧图。为了开发基于湍流相干细尺度结构的湍流燃烧控制方案，对均匀旋转湍流中的湍流预混火焰进行了数值模拟。结果表明，预混火焰的微观结构和湍流燃烧速度与系统旋转方向有关，可以根据微观结构对湍流燃烧进行控制。通过建立湍流旋流燃烧器，研究了燃烧室内微尺度火焰结构与压力脉动的关系。在微观尺度上，压力波动与火焰结构有关，并通过在回流区引入二次喷油来控制微尺度结构。结果表明，二次喷油控制微尺度结构可以抑制燃烧噪声和NOx排放。

In this study, micro-scale structures of turbulent premixed flames are investigated to develop effective control schemes for turbulent combustion observed in gas turbine combustors. Direct numerical simulations (DNS) of hydrogen/air and hydrocarbon/air turbulent premixed flames are conducted by taking into account detailed kinetic mechanisms and temperature dependence of transport and thermal properties. To investigate the micro-scale structure of turbulent premixed flames experimentally, laser diagnostics such as OH and CH simultaneous PLIF and time-series PIV are also developed. From the results of DNS and CH/OH PLIF, effects of turbulence characteristics such as turbulence intensity and length scale on the micro-scale structure, NOx formation mechanism, sound generation mechanism from combustors and the real three-dimensional feature of turbulent premixed flames are shown. The obtained results also confirmed the turbulent combustion diagram which has been proposed only from dimensional arguments. To develop the control schemes for turbulent combustion based on coherent fine scale structure of turbulence, DNS of turbulent premixed flames in homogeneous rotating turbulence are conducted. It has been shown that micro-scale structure of premixed flame and turbulent burning velocity depend on the direction of the system rotation, which suggests that turbulent combustion can be controlled based on the micro-scale structure. By constructing turbulent swirl burner, the relation between micro-scale flame structure and pressure fluctuation in combustor is investigated. The pressure fluctuation is related with flame structure in micro scales and controls of micro-scale structure by introducing second fuel injection into recirculation zone are conducted. The results show that the control of micro-scale structure by second fuel injection can suppress the combustion noise and NOx emission.