Experimental and Numerical Investigation of Dispersed and Continuous Liquid Film under Boiling conditions

In this work, both experimental and numerical investigations have been carried out in order to improve the modelling of the vaporization of wall liquid-deposits in internal combustion engines. A comprehensive model is suggested for the vaporization of liquid films in the different boiling regimes, including nucleate boiling regime, the Leidenfrost boiling regime, as well as the transition boiling regime occurring between the two latter. This work extends the validity of the Liquid Film Boiling model (Habchi, Oil & Gas Science and Technology Rev. IFP, Vol. 65, No. 2, 2010) for dispersed liquid films that may be formed when a dilute spray impinges a wall. A sub-grid liquid film is indeed considered when the wetted-area is smaller than the wall cell-face area. A sessile droplet model is used to estimate the wall area wetted by the liquid film and whether it is resolved by the grid or located in the sub-grid scale (SGS). In addition, a novel Leidenfrost vaporization model is proposed for spray droplets located near a hot wall. The above vaporisation/boiling models has been implemented in the Large-Eddy simulation (LES) AVBP code. The validation has been carried out using two different experiments. First, the experimental lifetime curve of a sessile droplet (Stanglmaier et al., SAE paper 2002-01-0838) has been used for a quantitative validation in the different boiling regimes. Second, the wall impingement of a heptane spray from a typical gasoline injector from Continental Automotive, has been simulated. The numerical results obtained under boiling conditions, are compared to the liquid film footprints and lifetime provided by the Refractive Index Matching (RIM) experiment which is described in this article.