The interaction between fuel spray and in-cylinder airflow is a highly transient process that evolves rapidly during the injection event. In modern engines, not only the spatial alignment but also the temporal matching between the injector spray field and combustion chamber flow field plays a crucial role in determining mixture formation efficiency. To investigate this dynamic interaction, Particle Image Velocimetry (PIV) was employed to analyze the time-resolved coupling behavior between spray-induced flow and pre-established air motion.
In this study, a transparent constant-volume combustion chamber was used to generate controlled airflow conditions prior to fuel injection. Swirl-dominated and quiescent flow fields were established using adjustable air inlet configurations. A high-pressure injector was triggered at specific phases of the airflow development, allowing the investigation of spray–flow interaction under different temporal matching conditions. PIV measurements were performed at multiple time instants during the injection and post-injection periods to capture transient velocity and vorticity fields.
The results showed that the timing of injection relative to the airflow evolution significantly influenced spray dispersion behavior. When injection occurred during the peak airflow momentum phase, the spray experienced strong lateral deflection and rapid deformation, leading to enhanced entrainment of surrounding air. This condition promoted fast fuel–air mixing but reduced spray penetration depth. In contrast, injection during the decay phase of airflow resulted in more stable spray penetration but weaker turbulence generation, potentially leading to locally non-uniform mixtures.
Time-resolved velocity field analysis revealed that spray momentum initially dominated the local flow field near the nozzle exit. However, as injection progressed, the interaction region expanded, and the pre-existing airflow structure gradually reshaped the spray plume. PIV-derived vorticity maps indicated that favorable temporal matching increased vortex stretching and intensified small-scale turbulent structures around the spray boundary, which is beneficial for atomization and evaporation.
Additionally, the study found that mismatched timing between spray injection and airflow development led to inefficient momentum exchange. In such cases, the spray either excessively disrupted the airflow or failed to utilize available air motion, resulting in reduced mixing effectiveness. These findings highlight that optimal spray–flow matching is a time-dependent process rather than a purely geometric one.
In conclusion, PIV-based time-resolved measurements provide valuable insight into the temporal coupling mechanisms between injector spray fields and combustion chamber airflow. Proper synchronization between injection timing and airflow evolution can significantly improve mixture preparation quality. The results offer experimental guidance for injection strategy optimization and air-motion design in advanced combustion systems.
