OCR Text |
Show - 9 - studies with the hydrocarbon/chlorine systems may provide invaluable engineering data otherwise unobtainable. The use of oxygen enrichment has been advocated widely. For the mixtures studied here, as well as trichloroethylene, oxygen enrichment was essential to enable premixed flame combustion. As shown here, further increases in oxygen content, even under fuel-lean conditions appear beneficial. Equilibrium calculations suggest an increase in flame temperature of the order of 100 K for the range of oxygen levels considered here. Some simple considerations can be set forth which relate overall activation energies for each stage of the flame. From an approximate energy balance across a flame the following relation between flame speed and reaction rate can be derived [20,21] [1] where the reaction rate in tenns of mole fraction £ is dd£t = Ae -[JrJ £ "p ,,-1 . [2] A is the pre factor, E is the activation energy, n is the overall order of the reaction, p is the pressure, and a is the thennal diffusivity. For a steady-state flame, the continuity equation is ~ (Pit) = 0 [3] where p is the density and rt is the velocity vector. Considering a small quasi-planar area of a double flame where the two flames are close together and parallel, we only need to consider the flow perpen-dicular to the flames; the continuity equation ( 3) reduces to [4 ] where physical distances (S 1, S 2, S 3) are related to coordinates (x 1, X 2, x 3) through [5] |