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Direct-injection (DI) in spark-ignition (SI) engines has been highlighted as an effective solution for improving engine performance. Since fuel is injected directly into the cylinder, a wide range of injection strategies can be applied. In this study, the aim was to improve air-fuel mixing by implementing a double injection strategy, with an interest in the effect of dwell time between the two injections performed during the intake stroke. To analyze the effects of split injection, a homogeneous-charge-type DISI gasoline engine with a side-mounted multi-hole-type injector was utilized. The second injection timing was swept in a wide crank angle degree range in an attempt to reach the optimal balance between performance and emissions. In particular, the reduction of soot formation in the combustion chamber was considered an important target. Thermodynamic analysis of in–cylinder pressure data and exhaust measurements were correlated to chemiluminescence results from spark ignition to the late combustion phase, thanks to the optical accessibility through the piston crown, rendering the combustion chamber visible from below.