GAS PROPERTY EFFECTS ON DROPSIZE OF SIMULATED FUEL SPRAYS

Two-phase flow in pneumatic two-fluid fuel nozzles was experimentally investigated to determine the effect of gas properties on liquid-jet breakup in sonic-velocity gas flow. Dropsize data were obtained for the following atomizing gases: nitrogen, argon, carbon dioxide, and helium. The ratio of liquid-jet diameter to Sauter mean diameter (SMD) D0/D32 was correlated with aerodynamic and liquid-surface forces based on the product of the Weber and Reynolds number WeRe and gas-to-liquid density ratio with breakup forces produced by using different atomizing gases, a molecular-scale dimensionless group was derived, (rho-l)V3/g mu-g. As a result, a semiempirical correlating expression was obtained that can be used in the design of fuel injectors for gas turbine and rocket combustors. This expression for liquid-jet breakup in two-fluid atomizer shows that D32 approximately (rho-(g)V(c))-1.33, where (rho-g)V(c) is gas mass-flux at sonic velocity, and this agrees well with atomization theory for liquid-jet breakup in high velocity gas flow. Also, it was found that at the same gas mass-flux (rho-g)V(c), helium was considerably more effective than nitrogen in producing small droplet sprays with SMDs in the order of 5 mu-m. This was attributed to the high acoustic velocity of helium.