Abstract
Increasingly stringent emission norms have always brought forth innovative measures to improve engine efficiency. Spark-ignited engines have been limited in efficiency, traditionally by knock, and more recently by preignition too. Water injection has recently regained interest as a knock suppressant. The current work explored water injection via port and direct injection at a fixed engine speed of 2000 rpm and varying engine loads. The data presented in this work emphasize that the gains from using water injection are best realized at a specific injection timing (neither too early nor too late), and the effectiveness of water in suppressing knock decreases rapidly with increasing water mass injected. In general, direct water injection offers a more significant knock reduction because of better utilization of the charge cooling effect than port water injection. Engine-out emission confirms a reduction in NOx and CO, while the HC emissions increased when using water injection. No preignition events were observed at the engine load up to 27 bar. Chemical kinetics simulations confirm the role of water in suppressing reactivity under the operating conditions considered in the current study.