Researchers from the Korea Advanced Institute of Science and Technology (KAIST) and the Advanced Gasoline Engine Development Team at Hyundai Motor Company report on the effects of water direct injection on a gasoline engine under high-load conditions in a paper in the International Journal of Engine Research.
The precisely controlled injection of water into engine cylinders produces a cooling effect that boosts power and torque, particularly when operating at or near full throttle, while at the same time reducing fuel consumption and emissions. BMW (earlier post), Bosch (earlier post) and FEV (earlier post) have all reported efforts in this area.
The KAIST/Hyundai researchers directly injected water into the cylinder with an injection pressure of 5 MPa to investigate its effect on engine performance and emissions in a gasoline engine. The test engine was a 1.6-L naturally aspirated prototype engine equipped with water direct injection and port fuel injection systems.
The engine featured a compression ratio of 13.5. Commercial gasoline direct injection injectors were used for the water, which was injected at a fixed timing of −120 crank angle degrees after top dead center.
The researchers found that the addition of water showed potential to mitigate the knock occurrence at part-load condition where the knock initially started to occur due to the high compression ratio. Water injection allowed a further advance of spark timing; thus, the brake-specific fuel consumption was improved.
They investigated the effects of water injection under full-load condition within the engine speed range of 1500–3000 rpm. Under this condition, the water effectively reduced the in-cylinder temperature and the exhaust gas temperature; therefore, charge cooling through over-fueling (fuel enrichment) was eliminated with reduced brake-specific fuel consumption.
Increasing the injected water mass resulted in further spark advance without knock occurrence and provided room for further brake-specific fuel consumption reduction.
They also determined that an optimum water mass existed; too much water deteriorated the combustion efficiency, burn duration, and cycle efficiency. The positive effects of water injection were dulled with increased engine speed because the knocking resistance was already high intrinsically with the higher engine speed.
Jaeheun Kim, Hyunwook Park, Choongsik Bae, Myungsik Choi, Younghong Kwak (2015) “Effects of water direct injection on the torque enhancement and fuel consumption reduction of a gasoline engine under high-load conditions” International Journal of Engine Research doi: 10.1177/1468087415613221