This study proposes a novel multi-injection strategy to enhance fuel atomization and combustion in a constant volume combustion chamber. By integrating a third injector into the conventional axis-opposed spray configuration and optimizing injection timing, the strategy significantly improves fuel–air mixing and ignition reliability, particularly under cold-start conditions. Two fuels with contrasting reactivity – n-hexadecane and iso-octane – were used to investigate spray and combustion characteristics. Laser diffraction analysis showed that the proposed strategy substantially reduced the Sauter Mean Diameter compared to single or impinging injection alone. Combustion experiments demonstrated improved ignition stability, advanced heat release phasing, and increased total heat release with the multi-injection approach. These effects were more pronounced for iso-octane, where ignition failure was frequent under baseline conditions. The results confirm that the proposed multi-injection strategy effectively stabilizes combustion and enhances thermal efficiency for both high- and low-reactivity fuels.