FORMATION DE GELS ET D'ÉMULSIONS DANS LE CIRCUIT DE BLOW-BY DES MOTEURS A COMBUSTION INTERNE
Experiments and models were used to understand the ice and emulsion formation within blow-by pipe. These phenomena consist of phase change of water vapor from moist gas in oil polluted media (particles and oil film). Condensation occurs if gas temperature, humidity, wall temperature and gas flow rate are high enough. Though condensate doesn't lead to pipe obstruction, one has to take into account its ability to build up and to freeze if any tube related parameters change (direction, shape,..). In the presence of oils, condensation is coupled with emulsion formation. The latter may plug the pipe due to its viscosity and its ability to retain water until freezing. At a cooler environment, water liquid, frost and ice appear simultaneously. They make pressure rise promptly. When oil particles are present, condensate that are located near the entrance of gases tend to become an emulsion. It may solidify as time increases. In cold environment, frosting prevails. Frost causes pressure to rise slowly. It is not affected by oil presence as particles acts as inert foreign material within the frost layer. Water mobility and plug location are used to describe all phenomena that occur during experiments. These parameters can be correlated with operating conditions (inlet gas dew point, inlet gas flow rate, pipe cooling temperature, pipe size) and with heat and mass transfer related parameters namely the condensate flow rate and the wall temperature distribution. Nusselt number correlations were used to emphasize the contribution of each parameter to heat transfer. In order to understand the heat transfer phenomenon, enthalpy correlation was carried out. Heat and mass transfer models were built by combining the heat and mass transfer analogy with fogging and isothermal condensation of supersaturated air related theories. The risk of blow-by pipe plugging and the prevailing phenomena can be predicted according to the wall temperatures distribution and the condensate flow rate. These two parameters are easily available by using models that were built during this study.