Jet flame heights, lift-off distances, and mean flame surface density for extensive ranges of fuels and flow rates

Abstract

An extensive review and re-thinking of jet flame heights and structure, extending into the choked/supersonic regime is presented, with discussion of the limitations of previous flame height correlations. Completely new dimensionless correlations for the plume heights, lift-off distances, and mean flame surface densities of atmospheric jet flames, in the absence of a cross wind, are presented. It was found that the same flow rate parameter could be used to correlate both plume heights and flame lift-off distances. These are related to the flame structure, jet flame instability, and flame extinction stretch rates, as revealed by complementary experiments and computational studies. The correlations are based on a vast experimental data base, covering 880 flame heights. They encompass pool fires and flares, as well as choked and unchoked jet flames of CH4, C2H2, C2H4, C3H8, C4H10 and H2, over a wide range of conditions. Supply pressures range from 0.06 to 90 MPa, discharge diameters from 4 × 10−4 to 1.32 m, and flame heights from 0.08 to 110 m. The computational studies enabled reaction zone volumes to be estimated, as a proportion of the plume volumes, measured from flame photographs, and temperature contours. This enabled mean flame surface densities to be estimated, together with mean volumetric heat releases rates. There is evidence of a “saturation” mean surface density and increases in turbulent burn rates being accomplished by near pro rata increases in the overall volume of reacting mixture.