A study of the mixture formation process for a third-generation conical spray applied in HCCI diesel combustion

The purpose of this study is to investigate the mixture formation processes of a third-generation spray (TGCS), an impinging spray that is intended to be applied in mixture preparation for homogeneous charge compression ignition (HCCI) diesel combustion. The spray visualization is performed in a constant-volume vessel by high-speed photography, to investigate the characteristics of the TGCS, and also to provide a validation for numerical models. Then the behaviors of spray and mixture formation process in a constant-volume vessel and diesel in-cylinder conditions were examined numerically by FIRE v8.5 package. Results of the high-speed photography indicated that the TGCS is characterized by a flexible spray tip penetration and circumferential angle, depending on the impinging angle of the TGCS nozzle. Findings of the numerical simulations in a constant-volume vessel under the spray visualization conditions revealed that after the fuel jets had impinged on the guide wall, the TGCS has a much smaller fuel mass fraction compared with a free spray. Furthermore, simulation results under diesel engine conditions demonstrated that for the TGCS, the fuel–air mixture can achieve circumferential homogeneity at 2° CA after the start of injection (ASOI), and form a comparatively homogeneous lean mixture at 20° CA ASOI.