Spray Behaviors and Gasoline Direct Injection Engine Performance Using Ultrahigh Injection Pressures up to 1500 Bar

Abstract

High fuel injection pressure systems for Gasoline Direct Injection (GDI) engines have become widely used in passenger car engines to reduce emissions of particulates and pollutant gases. Current commercial systems operate at pressures of up to 450 bar, but several studies have examined the use of injection pressures above 600 bar, and some have even used pressures around 1500 bar. These works revealed that high injection pressures have numerous benefits including reduced particulate emissions, but there is still a need for more data on the possible benefits of injection pressures above 1000 bar. This article presents spray and engine data from a comprehensive study using several measurement techniques in a spray chamber and optical and metal engines. Shadowgraph imaging and Phase Doppler Interferometry (PDI) were used in a constant volume chamber to interpret spray behavior. Particle Image Velocimetry (PIV) was used to capture near-nozzle air entrainment. Optical engine experiments were performed to visualize the spray's position relative to the piston at different start of injection (SOI) timings. A single-cylinder GDI engine was used to investigate the effects of injection pressure on emissions and combustion characteristics. The spray tests showed that high-pressure sprays tend to exhibit better atomization and create more air entrainment, accelerating evaporation and mixing. However, high pressures also cause high spray tip penetration due to the high spray velocity, potentially causing wall film formation. At commonly used SOI timings, the benefits of high-pressure injection are relatively insignificant. The improvements in combustion stability and emissions of hydrocarbon (HC) and particulates are greater when the SOI timing is advanced (≈340°bTDC) or retarded (later than 180°bTDC). Wall film occurs at advanced SOI timing for all injection pressures, but high injection pressures significantly reduce particle number (PN) emissions by affecting wall film formation. At late SOI timings, high injection pressures yield acceptable combustion stability and emissions because they shorten the injection and promote mixing. These results suggest that high-pressure sprays allow HC and PN emissions to be greatly reduced and increase flexibility with respect to injection timing without sacrificing engine performance or increasing other emissions. Fuel consumption is also improved, but the effect is more significant when the injection pressure is 1000 bar.