球状伝播予混合乱流火炎の燃焼速度および火炎面形状の有効乱れ強さによる変化

<p>Turbulent burning velocity of spherically propagating premixed turbulent flame keeps increasing during flame propagation although that of steady flame is constant for a given turbulence intensity. In this study, the variation of turbulent burning velocity of spherically propagating turbulent flame during flame propagation was investigated. As the size of flame becomes larger, scales of turbulent eddies effective to turbulent burning velocity may vary. The effective turbulence intensity was adopted in order to evaluate the energy of these eddies only among the entire energy of turbulence. The flame front area is considered to be one of the dominant parameters for turbulent burning velocity. The perimeter of cross-sectional image of turbulent flame which may correlate with the turbulent flame front area was evaluated using effective turbulence intensity. Experiments were carried out for stoichiometric iso-octane/air flames at initial mixture pressures of 0.10, 0.25 and 0.50 MPa. The cross-sectional images of spherically propagating premixed turbulent flame were obtained by laser tomography technique. It was found that the ratio of the perimeter of cross-sectional image of turbulent flame to that of laminar one increased with the increase in effective turbulence intensity. The increase in turbulent burning velocity of spherically propagating premixed turbulent flame during flame propagation may be caused by the increase in the ratio of turbulent flame front area to laminar one during flame propagation.</p>