Development of an improved liquid film model for spray/wall interaction under engine-relevant conditions

• An improved film dynamics model considering droplet/film interaction is proposed.
• The dissipative energy loss of the deposited droplet is taken into account.
• The improved model considers gas compressibility and non-unity Lewis number.
• The Lewis number significantly affects the film evaporation rate.

The dynamics and heat and mass transfer characteristics of the liquid film formed by spray/wall interaction have significant influences on the fuel/air mixing process in engines, which subsequently considerably affects engine combustion and emissions. In this paper, an improved liquid film model using the Lagrangian method was proposed with special emphasis on the engine-relevant conditions. By modifying the source term of the impingement momentum, the film dynamics sub-model was improved with consideration of the effect of droplet/film interaction on the film dynamics, as well as the dissipative energy loss during the expansion of the lamella formed by the deformation of the deposited droplet. Taking account of the effect of gas compressibility on the gas/film heat transfer and introducing the Chilton–Colburn analogy for calculation of the film evaporation coefficient, the film heat and mass transfer sub-models were further enhanced. By comparing with the available experimental data from constant-volume bombs and a diesel engine, it is found that the improved liquid film model is capable of satisfactorily reproducing the film dynamics, film/wall heat flux, and film evaporation rate under a wide operating range. Due to take the engine-relevant conditions into account, the predictions with the improved film model are in better agreement with the measurements in engines than that of the previous models.