Effect of split injection on fuel adhesion characteristics under non-evaporation and evaporation conditions

Spray/wall interaction cannot be avoided in direct-injection spark-ignition (DISI) engines. This leads to the formation of fuel adhesions on the piston head and cylinder wall. The fuel adhesion has a negative impact on combustion and emissions. In the present study, the aim is to investigate the effect of split injection on fuel adhesion characteristics under non-evaporation and evaporation conditions. The fuel adhesion of single, double and triple injections was measured using the refractive index matching (RIM) method. Results show that under the non-evaporation condition, split injection decreases the adhered mass ratio from 15.6% to 12.2% at 30 ms after start of injection (ASOI). Two possible reasons can be concluded as "splashing" and "suction" effects. However, under the evaporation condition, split injection increases the adhered mass ratio slightly. The "heat transfer" has the advantage over "splashing" and "suction". The main reason is that the fuel adhesion of split injection has short time for heat-transfer with the hot wall and high-temperature ambient gas, leading to more adhesion left on the wall. Furthermore, split injection promotes the uniformity of the fuel adhesion on the wall under non-evaporation and evaporation conditions. Finally, these results could provide data for the development of simulation models.