Swirler structure and air distribution effects on the atomization of a dual-stage counter-rotating nozzle

The dual-stage counter-rotating nozzle, developed using lean direct injection technology, aims to reduce combustion emissions. This study investigates the effects of swirler structure and air distribution on atomization characteristics by combining experimental and numerical methods. Numerical simulation accuracy was validated using a laser particle size analyzer and particle image velocimetry, revealing velocity and particle size errors of 6.7% and 6.3%, respectively. The results indicate that the dual-stage counter-rotating swirler enhances droplet breakup, reduces the spray cone angle, and significantly lowers the Sauter mean diameter (SMD). Under baseline conditions, SMD increases with axial and radial distance, with droplet sizes ranging from 38.5 to 58.7 μm. Increasing the inner swirler vane angle enhances swirl intensity, enlarges the spray cone angle, and reduces SMD, with 50° identified as optimal. Conversely, increasing the outer swirler vane angle enlarges the spray cone angle but increases SMD, with 45° being optimal. Increasing vane number reduces the flow passage area, accelerates airflow, and decreases the spray cone angle, with minimal impact on SMD. The optimal inner-to-outer air flow rate ratio is found to be 3:1. A high proportion of outer swirl airflow increases droplet radial velocity, hindering spray cone formation. As total air flow increases, the spray moves downstream faster, and SMD reaches its minimum value of 41.16 μm at 6.3 g/s.