Soot free length fraction of buoyant turbulent non-premixed jet flames in normal- and a sub-atmospheric pressure

This work quantifies and compares experimentally the soot free length fraction (SFLF) of buoyant turbulent non-premixed jet flames in normal- (100 kPa) and in specially a sub-atmospheric pressure (64 kPa), for which there is still no data reported in the literatures. Four circular nozzles with different diameters (4, 5, 6 and 8 mm) are used to produce the non-premixed jet flames with propane as fuel. It is found that SFLF increases with the increase in heat release rate (fuel mass flow rate), meanwhile decreases with increase in nozzle diameter for a given heat release rate; however, being higher in the sub-atmospheric pressure (64 kPa) than that in the normal-pressure (100 kPa). Such evolution is then interpreted physically as attributed to the change of turbulent mixing at the nozzle of the flame base, which is evidenced by the successful collapse and correlation of SFLF by the source Reynolds number (Re) with a power law function (SFLF ∼ Re0.75) globally for the data all together of different fuel flow velocities and nozzle diameters in both pressures.