Gasoline engine powertrain development for 2025 and beyond is focusing on finding cost optimal solutions by balancing electrification and combustion engine efficiency measures. Besides Miller cycle application, cooled exhaust gas recirculation and variable compression ratio, the injection of water has recently gained increased attention as a promising technology for significant CO2 reduction. This paper gives deep insight into the fuel consumption reduction potential of direct water injection. Single cylinder investigations were performed in order to investigate the influence of water injection in the entire engine map. In addition, different engine configurations were tested to evaluate the influence of the altering compression ratios and Miller timings on the fuel consumption reduction potential with water injection. Based on the single cylinder investigations, drive cycle simulations covering a low, intermediate, and high load profiles were performed to evaluate the fuel consumption reduction potential as well as the corresponding water consumption under varying load demands for the different engine configurations. Furthermore, these simulations were used to optimize the water injection rate for the altering boundary conditions regarding the trade-off between the fuel and water consumption by the comparison of different criteria. Finally, the most promising criterion regarding a maximal fuel consumption reduction at a given water consumption in all of the investigated driving cycles is used to calculate the trade-off curves between fuel and water consumption as well as possible ranges with for a suitable water tank size.
