2014 Volume 56 Issue 175 Pages 15-22
The effects of pressure on spherically propagating laminar and turbulent flames are described in this article for various fuels, such as methane, propane and iso-octane. Spherically propagating flames have not only the properties of common premixed flames but also have unique properties not seen in steady premixed burner flames. Such natures of spherically propagating flames arise as a consequence of variations of their size and flame stretch during the flame propagation. The Markstein number is employed to quantify the effects of pressure on the laminar and turbulent flames. The burning velocities and the Markstein numbers of the laminar flames decreased with the increase in the mixture pressure. The laminar flames were more unstable at elevated mixture pressures. The ratio of turbulent and unsteretched laminar burning velocities increased with the mixture pressure. The burning velocity of the turbulent flames kept increasing during the flame propagation. This increase in the turbulent burning velocity during the flame propagation was attributed to the progress in the effective turbulence intensity.
