A Numerical Study for the Effect of Liquid Film on Soot Formation of Impinged Spray Combustion 2021-01-0543

Spray impingement is an important phenomenon that introduces turbulence into the spray that promotes fuel vaporization, air entrainment and flame propagation. However, liquid impingement on the surface leads to wall-wetting and film deposition. The film region is a fuel-rich zone and it has potentials to produce higher emission. Film deposition in a non-reacting spray was studied previously but not in a reacting spray. In the current study, the film deposition of a reacting diesel spray was studied through computational fluid dynamic (CFD) simulations under a variety of ambient temperatures, gas compositions and impinging distances. Characteristics of film mass, distribution of thickness, soot formation and temperature distributions were investigated. Simulation results showed that under the same impinging distance, higher ambient temperature reduced film mass but showed the same liquid film pattern. During the film evaporation, the flame temperature was reduced and a transition region was observed between the film region and the soot region. Under different impinging distances, longer ones significantly reduced the film formation. The pattern of the liquid film was also changed under different impinging distances. Ambient gas compositions did not directly affect the evaporation process of the film, however, higher oxygen levels reduced ignition delays and increased flame temperatures, which subsequently reduced the film mass compared to lower oxygen levels.