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

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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.