Effect of backpressure on internal flow dynamics and spray characteristics of liquid swirl injector

A combined theoretical and numerical analysis was performed to explore the flow characteristics in liquid swirl injectors under a wide range of backpressure. Axial velocity in nozzle, surface wave speed and spray pattern were theoretically studied basing on existing theories. Numerical simulations basing on swirl axi-symmetric model were carried on by solving of the Navier-Stokes equations coupled with the VOF equation implemented with CICSAM surface tracking technique on adapted grids. The effects of inlet turbulent intensity and backpressure to the film thickness were investigated by analyzing the velocity component profiles. The results showed that it is the changes of velocity profiles caused by increased gas shear stresses following increased backpressure responses to the increasing to film thicknesses. Using a long nozzle makes this simulation study have the ability to catch the stationary surface wave which was not well investigated before. Mechanism of wave generation was explained by analogy with the classical gravity wave theories. The effects of backpressure to spraying cone of liquid swirl injector were also studied by combining theory with numerical simulation. It showed that the increasing pressure different between internal and external surface of spraying cone caused contraction. A model of spray patterns was established by relating pressure different to the velocity at surface of liquid sheet and showed a good agreement with experiment results.