Effects of nozzle configuration on internal flow and primary jet breakup of flash boiling fuel sprays

Fuel spray plays more vital role in governing fuel economy and emission quality of IC engines due to the wide application of direct injection system in automotive engines. High temperature fuel spray, namely flash boiling spray, has been documented to improve fuel atomization and evaporation with less energy consumption compared with high pressure fuel spray. It is because the hot exhaust gas and coolant are two potential energy sources can be used to heat the fuel. Most of existing research works of flash boiling spray focus on investigating the spray behavior outside the nozzle, and limited studies can be found about the in-nozzle superheated flow. In this study, a two-dimensional transparent slit nozzle was designed to reveal the in-nozzle flow under various superheated conditions. Both internal flow and near-nozzle fuel jet were investigated using high-speed backlit imaging technique to acquire a better understanding of the primary breakup process of flash boiling sprays. The slit thickness was 40 μm with well-adjusted nozzle length and inlet corner radius to investigate the effects of nozzle configuration. The ambient pressure ranged from 40 kPa to 190 kPa, and fuel temperature varied from 41 °C to 71 °C, which produced a wide range of superheated conditions. N-pentane was chosen as test fluid with an injection pressure of 0.6 MPa. Experimental results showed that the bubbles occurring inside the nozzle near the nozzle exit affected the near-nozzle fuel jet characteristics. Stronger superheated conditions resulted in larger in-nozzle bubbles, which facilitated the jet break-up process significantly. Longer nozzle and nozzle with sharp inlet corner led to larger inner bubble volume fraction and narrower liquid core of near-nozzle fuel jet. In summary, the effects of nozzle configuration on in-nozzle flow and near-nozzle fuel jet were revealed with more fundamental understanding of the primary breakup process of flash boiling sprays.