Effects of pressure on laminar and turbulent burning velocity of outwardly propagating propane-air flame

The effects of pressure on outwardly propagating laminar and turbulent flames were studied for propane-air mixtures at the equivalence ratios from 0.8 to 1.3 and the initial pressures from 0.10 to 0.50 MPa. Turbulence intensity, u′ was set to 0.80 and 1.59 m/s. The Markstein number was employed to quanify the effects of the equivalence ratio and the pressure of the mixture on laminar and turbulent burning velocities. Turbulent burning velocities, u _tn did not become small with the increase in the mixture pressure although the unstertched laminar burning velocities, u_l decreased with the mixture pressure. The ratios of turbulent burning velocities to unstretched laminar ones, U_tn/u_l increased as the mixture pressure increased. They also increased with the increase in the equivalence ratio. We found that u_tn/u_l increased with the decrease in the Markstein number irrespective of the equivalence ratio, the initial mixture pressure and the turbulence intensity if u′/u_l did not vary so much. Turbulent burning velocities were affected not only by turbulence but also by the thermo-diffusive effects and flame instabilities both related to the Markstein number.