The small enhanced technology that synergizes in-cylinder direct injection and turbocharging has good power and fuel economy, and has become a trend in the development of gasoline direct injection engines. However, the enhanced technology has sharply increased the thermal load in the cylinder. It is easy to cause engine knocks, which is currently one of the main limiting factors in improving the performance of direct injection gasoline engines. This paper discusses the influence of direct injection of water into the cylinder on the combustion of gasoline direct injection engines through numerical simulation. The gasoline engine is induced to knock by increasing the compression ratio and advancing the ignition timing. The influence of the water injector (six nozzle holes) layouts (direct water injection in the cylinder) and the water temperatures on the water movement in the cylinder and on the combustion and knock is explored. The in-cylinder water injector and the fuel injector are injected with two nozzles. Results show that when the water injector is arranged in the center of the cylinder head, the water evaporation in the cylinder before ignition is faster. Most of the water is located near the cylinder wall surface, which can reduce the temperature near the wall surface as much as possible and suppress the knock. Therefore, the effect of suppressing knocks is better. The injecting water is advantageous to make the mixed gas distribution uniform and the turbulent kinetic energy high when its temperature is low.

This paper explores the effects of six different cases of port water injection on the combustion, knock suppression and emissions of a supercharged gasoline direct injection (GDI) engine through numerical simulation. The six different intake port water injection cases included three vertical distances from cylinder center to water injector and two different injection directions. The results showed that cases 2 and 4 allowed more water and air to enter the cylinder and thus suppressed the knock, so the pressure oscillation was small. Case 2 had the largest turbulent kinetic energy in the center of the cylinder, which in turn facilitated the propagation of flame to the cylinder wall and suppressed the knock. The water injection cases shortened the combustion delay period compared to the no water cases. At the same time, the strong low temperature reaction of the end mixture produced a large amount of CH2O that decomposed into HCO. A high concentration and a large area of HCO distribution can predict the occurrence of a knock. In addition, the water injection cases (except for case 6) reduced the in-cylinder soot, unburned hydrocarbon (UHC) and CO emissions compared to the no water cases, but it increased NOX emissions.

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