A Comprehensive Model for Liquid Film Boiling in Internal Combustion Engines

In this paper, the main physical processes governing the nucleate and transition regimes of the boiling of a liquid film were reviewed from the available experimental observations in the literature. The physical tendencies observed in most experiments have been used to develop a comprehensive phenomenological Liquid Film Boiling (LFB) model which allows the calculation of the vaporization of liquid films in the nucleate boiling regime as well as in the transition boiling regime. These regimes are identified by the temperatures of saturation, Nukiyama and Leidenfrost. A particular attention has been made concerning the estimation of Leidenfrost and Nukiyama temperatures as a function of the ambient gas pressure. Several curves of lifetime of rather bulky droplets deposited on a hot surface under various conditions and chosen among those which are available in the recent literature have been used for the validation of the LFB model. The numerical results show that the orders of magnitude and the tendencies observed experimentally are well respected. Particularly, the LFB model reproduces well the progressive disappearance of the Leidenfrost regime observed in experiments with sufficiently high gas pressures. In addition, the gradual increase of the vaporization rate with wall roughness which was previously observed experimentally near the Leidenfrost point has been correctly predicted by the LFB model.