In modern fuel injection systems, the interaction between injector spray dynamics and in-cylinder airflow structures has a decisive influence on mixture formation and combustion stability. Rather than considering spray characteristics or air motion independently, it is increasingly recognized that their matching behavior determines fuel dispersion efficiency and combustion robustness. To quantitatively evaluate this interaction, Particle Image Velocimetry (PIV) was applied to study the coupling mechanisms between injector spray development and combustion chamber flow fields under different flow configurations.
The experimental setup consisted of an optically accessible combustion chamber capable of generating controlled swirl and tumble flows. A solenoid-driven common-rail injector was installed at varying orientation angles to simulate different spray–flow alignment conditions. Airflow was seeded with micron-sized tracer particles, and a high-energy laser sheet illuminated the measurement plane. Time-resolved PIV measurements were synchronized with the injection event to capture transient velocity fields before, during, and after fuel injection.
Unlike conventional qualitative observations, this study introduced dimensionless matching indicators to quantify spray–flow interaction. Parameters such as velocity alignment index, momentum ratio, and vorticity interaction factor were calculated based on PIV-derived velocity fields. The results indicated that when the spray momentum was comparable to the local airflow momentum, strong mutual interaction occurred, leading to enhanced spray deformation and accelerated fuel dispersion. Excessively dominant spray momentum, however, suppressed airflow structures and resulted in limited mixing efficiency.
Flow-field analysis revealed that different air-motion patterns significantly affected spray evolution. Under swirl-dominated conditions, the spray exhibited circumferential deflection and asymmetric penetration, whereas tumble flow promoted vertical dispersion and improved spray breakup. PIV-derived vorticity maps showed that effective spray–flow matching increased local vortex stretching and intensified small-scale turbulence near the spray boundary, which is beneficial for rapid evaporation.
Furthermore, temporal analysis demonstrated that early-stage matching between spray and airflow is critical. Poor alignment during the initial injection phase led to persistent inhomogeneities, even if later interaction conditions improved. This finding highlights the importance of injector orientation and injection timing in relation to in-cylinder flow development.
In conclusion, the PIV-based quantitative evaluation method presented in this study provides a systematic approach for assessing spray–flow matching in combustion chambers. By linking spray dynamics with airflow characteristics through dimensionless indicators, the results offer valuable guidance for coordinated injector and combustion chamber design. This methodology can support the development of advanced fuel injection strategies aimed at improving combustion efficiency and emission performance.
