The effects of pressure on laminar and turbulent burning velocities of spherically propagating iso-octane flames

Spherically propagating laminar and turbulent flames at elevated pressures in a large volume bomb were studied using iso-octane / air mixtures. The properties of the iso-octane flame at elevated pressures, especially the burning velocity and the effects of the flame stretch acting upon it are quite important to the modeling of combustion in internal combustion engines. Turbulent burning velocity correlations with the turbulence Karlovitz and Markstein numbers were proposed in this study. Experiments were carried out in the wide range of the equivalence ratio from 0.8 to 1.4 at two turbulence intensities of 0.80 and 1.59m/s varying the initial pressure from 0.10 to 0.50MPa. The Markstein number decreased for increasing pressures and for large equivalence ratios. The ratios of turbulent to unstretched laminar burning velocities at a constant Peclet number increased with increasing turbulence Karlovitz number and decreasing Markstein number at a constant pressure. However, the burning velocity ratios did not increase with increasing pressure although the Markstein number reduced with pressure. Turbulence spectrum affecting flames at higher pressures might be limited due to the smaller flame radii under the condition of a constant Peclet number.