High-Speed Imaging Studies of Gasoline Fuel Sprays at Fuel Injection Pressures from 300 to 1500 bar 2018-01-0294
High-pressure gasoline fuel injection is a means to improve combustion efficiency and lower engine-out emissions. The objective of this study was to quantify the effects of fuel injection pressure on transient gasoline fuel spray development for a wide range of injection pressures, including over 1000 bar, using a constant volume chamber and high-speed imaging. Reference grade gasoline was injected at fuel pressures of 300, 600, 900, 1200, and 1500 bar into the chamber, which was pressurized with nitrogen at 1, 5, 10, and 20 bar at room temperature (298 K). Bulk spray imaging data were used to quantify spray tip penetration distance, rate of spray tip penetration and spray cone angle. Near-nozzle data were used to evaluate the early spray development.
The bulk characteristics of the high pressure gasoline sprays were consistent with trends previously observed at lower fuel injection pressures, e.g. spray tip penetration distance increased with increased fuel injection pressure after the spray break-up time and sprays with higher cone angles were produced with increasing chamber pressure at constant fuel injection pressure. The spray break-up time was a strong function of the chamber pressure at lower fuel injection pressures, but the sensitivity to chamber pressure was negligible for fuel injection pressures over 1200 bar. The experimental results for spray tip penetration distance, spray tip penetration rate and spray break-up time were compared with several correlations from the literature. For the majority of the conditions, the spray tip penetration distance was under-predicted and the spray break-up time was over-predicted. Cavitation was not observed at any condition; however, the near-nozzle imaging results showed evidence of vapor pre-jets. The frequency of occurrence of the pre-jets transitioned from no observations at a chamber pressure of one bar to ~80% for chamber pressures of 20 bar, regardless of fuel injection pressure.