This study investigates if particulates from a GDI engine can be significantly suppressed by use of ultra-high injection pressures under 2 different engine conditions known to be associated with high particulate numbers (PN): warm-up and transients. Experiments were carried out in a single-cylinder GDI engine equipped with an endoscope connected to a high-speed camera to enable combustion visualization. To mimic the warming-up, the coolant temperature was varied between 20 °C and 90 °C. A Diesel injector with modified nozzle was used and the injection pressures were varied between 400 and 1500 bar.
The results revealed that increasing the fuel injection pressure decreased engine out HC and PN under warming-up conditions. However, the coolant water temperature was the most dominant factor affecting the emissions. For coolant temperature of 20 °C, the use of 1500 bar fuel injection pressure in comparison to lower fuel pressures resulted in significantly lower PN.
The simplified load transients were studied with motoring followed by combustion. The results revealed that increasing the fuel pressure significantly suppressed the occurrence of luminosity from soot. After ca 40 combustion cycles, the luminosity had decreased significantly due to increased combustion surface temperatures and the decrease was more significant when the fuel pressure was increased. Overall, the results suggested that an increased fuel injection pressure is beneficial under warming-up and simplified load transient conditions as well as under hot conditions.