Characteristics of laminar gas jet diffusion flames under the influence of elevated gravity

Abstract

Laminar gas jet diffusion flames of hydrogen, methane, ethane and propane, stabilized on small cylindrical burners, were studied at elevated gravity to investigate the role of buoyancy in such flames. Greater than earth normal gravity levels were achieved in a 1.83 m diameter centrifuge. Photographic observation of the hydrocarbon flames indicated that length and carbon luminosity decreased with increasing buoyancy. Further, the flames eventually separated from the burner rim and finally extinguished as gravity increased. Hydrogen flames, however, did not separate or extinguish up to about 31 times earth normal gravity. Length data are reported and interpreted with the aid of a simplified model which views the flame as a heated vertical cyclindrical sheet to which oxygen is supplied by a free convection boundary layer. Results of the analysis produce a dimensionless group L/R 0 1/(Re 2 Fr) 1/3 where L and R 0 are flame length and burner radius and Re and Fr are the Reynolds and Froude number, which should tend to a constant if flame length is buoyancy controlled. Ethane and propane clearly demonstrate this limiting behavior. The stability data are also presented in dimensionless form and demonstrate a regime of buoyancy controlled flame lift for which gD/Su 3 =constant