| The Effect of Water Injection on a Naturally Aspirated Spark-Ignited Engine
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| Woojae Kim , Jongwon Chung 1, Junghyun Kim1, Cha-Lee Myung1, Kyeonghyeon Lee2, Jongbum Park2, Kyungdoug Min1 |
1School of Mechanical Engineering, Seoul National University
2eP Drivetrain Test Team, Hyundai Motor Company |
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| ABSTRACT |
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Water injection (WI) is a well-known technique to mitigate knocking phenomena, reducing the in-cylinder gas temperature with a high heat of vaporization and specific heat of water. In this study, the effect of WI directly into the cylinder on fuel efficiency was investigated using a 2.0 L naturally aspirated (NA), four-cylinder, port fuel injection (PFI)-spark-ignited (SI) engine. Spray visualization of water injection by a commercial gasoline direct-injection (GDI) injector was performed to elucidate the water evaporation characteristics. In engine experiments, combustion characteristics were analyzed by adjusting the WI timing and amount. Synergistic effects with other gas dilution techniques, such as EGR and Lean burn, were also investigated. The spray image of WI showed poor evaporation of water compared to gasoline, even at high fuel temperatures. The optimal timing of WI was advanced up to the early intake stroke due to the harsh conditions of NA engines for water evaporation compared to turbocharged engines. With the combination of EGR, the optimal WI timing was advanced by the compression stroke, and further fuel efficiency improvement was achieved. In lean combustion, WI can improve both combustion stability and fuel efficiency.
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| Key Words:
Direct water injection · Naturally aspirated spark-ignited engine · Exhaust gas recirculation · Lean burn
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Corresponding Author.
Kyungdoug Min , Email. 
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