Water injection represents a promising tool to improve performance of spark-ignition engines. It allows reducing in-cylinder temperature, preventing knock risks. Optimizing the spark advance, water injection allows obtaining an increase of both efficiency and power output, particularly at medium and high loads. Water can be injected into the intake port or directly into the combustion chamber.
In this paper, the authors investigated the effects of both direct and port water injection in a downsized PFI spark-ignition engine at high load operation. Different water-to-fuel ratios have been analyzed for both configurations. For the experimental analysis, low-pressure water injectors have been installed in the intake ports of the engine under study, upstream of the fuel injectors. Experimental tests have been carried out at various operating points. Furthermore, engine operation with port water injection has been simulated by means of the AVL Fire 3-D code. The numerical analysis has been also used in order to simulate the direct water injection in the same engine. A 6-hole high-pressure water injector has been implemented within the 3-D model of the engine combustion chamber. Water spray has been validated against available literature data. High load engine operating points with in-cylinder water injection have been simulated. CFD analysis allowed to deeply investigate the evolution of water spray and its cooling effect on the air-fuel mixture for both direct and indirect water injection configurations. For each configuration, main engine performances have been compared to those obtainable in dry engine operation.