Effect of port water injection on the characteristics of combustion and emissions in a spark ignition direct injection engine

Port water injection techniques, considered as a potential solution to further enhance the combustion performance of internal combustion engines, can suppress engine knock by reducing the cylinder temperature so that the spark timing can be advanced. Although previous literature has discussed some aspects of utilizing port water injection techniques, thorough investigations on port water injection strategies, such as injection schemes, water/fuel mass ratio, etc. and their impacts on engine power output, thermal efficiency, and emissions are still not well understood. This work implements a three-cylinder engine installed with a port water injection system to investigate water injection strategy systematically. Various parameters, such as in-cylinder pressure, exhaust temperature, fuel combustion emissions, engine work, etc., were recorded for analysis. Different engine conditions were tested and recommendations were provided in optimizing the water injection design. Furthermore, this work finds that with knock suppression, port water injection can lead to 3.4%-16.7% improvements in the brake thermal efficiency under different engine operating conditions. Via the cooling effect on the exhaust gas, fuel enrichment strategy used under high speed, full load conditions can be eliminated so that particulate number emissions can be reduced by up to 96.0% with proper water injection.