The fuel-air mixing procedure and equivalence ratio distribution were highly dependent on the injection timing. The early injection cases formed a homogeneous mixture because the fast intake flow at around ATDC 45-90 CA spread out the fuel spray. The interaction between the intake flow and the fuel spray was a key factor in forming a homogeneous
mixture. Conversely, the late injection (during the slow intake flow) formed an inhomogeneous mixture, and the fuel-rich region was formed in the intake side.