Numerical Study of the Effects of Droplet Size Distribution on Fuel Transport and Air-Fuel Mixing in a Gasoline Direct-Injection Engine

Numerical simulations are performed to investigate the effects of droplet size distribution on fuel transport and air-fuel mixing in a gasoline direct-injection (GD-I) engine. The engine grid was generated using the K3PREP grid generator and the simulations were carried out using the KIVA-3V Release 2 code. Three size distribution functions were considered, namely the Chi-squared (χ²) and two Rosin-Rammler functions with dispersion parameter, q of 3.5 and 7.5 (RR_q=3.5 and RR_q=7.5). A new subroutine, which arranges the fuel droplets into a spherical cloud of droplets, was developed to allow the in-cylinder placement of fuel droplets with different droplet size distribution. Two cases of intake valve timing were considered. Results of the simulation showed droplet size distribution to affect fuel dispersion under the influence of the in-cylinder gas flows. Spatial and temporal differences in droplet transport due to the differing size distributions used were found to have some influence on the quantity of liquid fuel deposited on in- cylinder surfaces as well as the degree of fuel vaporization. However, overall these effects were minor; thus, the results suggest that droplet size distribution has little influence on the formation of air-fuel mixture when considered independently of the injection event.