Water injection for gasoline direct injection engines: fundamental investigations in an evaporation chamber

Today’s combustion engine development is strongly driven by reduction of \(\hbox {CO}_2\) and exhaust gas emissions. Modern turbocharged downsizing concepts with gasoline direct injection are well established in all major markets and contribute to current and future mobility as a cost attractive and efficient solution. Further improvement of gasoline engine efficiency and performance is mainly limited by knocking. Water injection (WI) has the potential to reduce knocking significantly. To improve the effectiveness of water injection, fundamental knowledge of the thermodynamic process has to be built up. Therefore, a zero dimensional evaporation model was developed and simulations were carried out. This model was derived and validated on the basis of measurements which were carried out on a specifically designed and assembled WI evaporation chamber. Conditions in terms of temperature and pressure were varied to determine the evaporation behaviour of water droplets influenced by temperatures of e.g. air or water. The model describes the process of droplet heating and finally the evaporation of the droplets depending on their size at relevant engine boundary conditions. The simulation results support interpretation of engine measurements and allow further optimization of water injection concepts.