Turbulent premixed flames propagating in homogeneous isotropic turbulent flows were simulated with a singlestep irreversible reaction. Two cases were calculated: case H, with a high-density ratio of flame ρ_u/ρ_b = 7.53, and case L, low-density ratio of flame ρ_u/ρ_b = 2.50, while u'/u_L was nearly equal to unity. We obtained databases of fully developed stationary turbulent flames. We investigated transport properties in turbulent kinetic energy and turbulent scalar flux by analyzing the transport equations, and we modeled the important terms in the transport equations. Analysis based on the Favre-averaged transport equation for turbulent kinetic energy showed that pressure related terms produced kinetic energy in the flame brush. The mean pressure gradient term, pressure dilatation term and additional dissipation components were modeled and these models well mimicked DNS. On the other hand, analysis based on the Favre-averaged transport equation for turbulent scalar flux showed that pressure concerning terms and velocity-reaction rate correlation term were positive sources to produce counter-gradient diffusion. The mean pressure gradient term, fluctuating pressure term, dissipation terms and velocity-reaction rate correlation term were modeled and these models well represented DNS.

Experimental and numerical studies on laminar burning velocities of a stoichiometric H₂/O₂ mixture, which was diluted by helium in order to exclude flame instabilities, were performed in the pressure range of 0.1 to 1.0 MPa and in the preheated-mixture temperature range of 300 to 500 K. Measurements of laminar burning velocities were conducted by a technique which measures the instantaneous local burning velocity using particle tracking velocimetry (PTV) and planar laser induced fluorescence (PLIF) simultaneously for burner-stabilized flames in a high-pressure chamber. Experimental results were compared with numerical results obtained considering some existing detailed reaction mechanisms, and the verification of reaction mechanisms was performed. A modification of the reaction mechanism was also conducted using the mechanism of Allen et al as a starting mechanism for the application in high-pressure and high temperature condition, and the modified mechanism was in good agreement with experimental data in the pressure dependency of laminar burning velocity.