Abstract
The formation of a fine spray at ultra-low liquid flow rates remains a long lasting challenge that limits the use of liquid fuels in various science and engineering applications. This work demonstrates the spray formation for liquid flow rate nearly 25 times lower than those reported in the literature for similar studies. The experiments are carried out at liquid flow rates of 2.78-41.7 mg/s (2.78-41.7 mu L/s) with air flow rate varying from 0.01 to 0.1 g/s (8.33-83.3 mL/s). This study reveals that for ultra-low liquid flow rates, air entrainment and development of slug bubble inside the liquid tube helps in the formation of a high shear zone, resulting in the formation of a uniform spray. Three spray regimes: (i) bubble bursting, (ii) weak spray, (iii) fully developed spray are observed with a gradual increase in air flow rate due to a distinct liquid-gas interaction inside the injector. A fine spray formation with Sauter Mean Diameter (SMD) similar to 32-76 mu m was observed in fully developed spray regime. Coarser droplets with SMD greater than 200 mu m were observed to form in the weak spray regime. A new SMD correlation in terms of governing parameters is proposed for fully developed spray regime. The analysis of the experimental results show that an atomization efficiency of 0.1% can be achieved for ultra-low flow rate conditions through the application of a flow-blurring atomization concept.