A Comprehensive Model for Liquid Film Boiling in Internal Combustion Engines

International audienceIn 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.Un modèle complet pour l'ébullition de film liquide dans les moteurs à combustion interne-Dans cet article, les principaux processus physiques, régissant les régimes d'ébullition nucléée et de transition d'un film liquide, ont été examinés à partir des observations expérimentales disponibles dans la littérature. Les tendances physiques observées, ont été utilisées, pour développer un modèle phénoménologique complet pour l'ébullition de film liquide (LFB). Celui-ci permet le calcul de sa vaporisation, dans le régime d'ébullition nucléée, ainsi que, dans le régime d'ébullition de transition. Ces régimes sont identifiés par les températures de saturation, de Nukiyama et de Leidenfrost. L'estimation des températures de Nukiyama et de Leidenfrost, en fonction de la pression de gaz ambiante, a requis une attention toute particulière. Plusieurs courbes de durée de vie, de gouttes de grosse taille déposées sur une surface chaude dans diverses conditions, ont été choisies parmi celles qui sont disponibles dans la littérature récente pour la validation du modèle LFB. Les résultats numériques montrent que les ordres de grandeur et les tendances observées expérimentalement sont bien respectés. En particulier, le modèle LFB reproduit bien la disparition progressive du régime de Leidenfrost avec des pressions suffisamment élevées du gaz. D'autre part, l'augmentation progressive du taux de vaporisation du liquide avec la rugosité du mur, précédemment observée expérimentalement près du point de Leidenfrost, a été correctement prédite par le modèle LFB. Abstract-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