Experimental Investigation of Puffing/Microexplosion in Fuel Droplets and Effects of Injection Modes on It

Puffing/microexplosion potentially increases atomization and enables better air–fuel mixing in sprays, thereby improving combustion. In this paper, we have investigated the physics leading to puffing and microexplosion in fuel droplets and identified factors such as droplet detachment modes and droplet-air interaction that influence puffing/microexplosion. A microsyringe is used to inject droplets as small as 100 μm radius in a control volume chamber maintained at 500 ℃ and atmospheric pressure. Droplet dynamics are captured using high-speed camera coupled with a long-distance microscopic lens using backlight illumination technique as the droplet traverses and undergoes puffing and microexplosion. In-house image processing codes are used to track droplet motion and compute its geometrical parameters, which enable us to decipher microexplosion dynamics. During this study, two significant factors were identified to cause puffing/microexplosion; thinning of droplet shell and interfacial instabilities. A general trend of increasing puffing times was observed with increasing droplet radii. The modes of detachment do affect the instabilities at the droplet surface which further amplify them and causes early puffing. Furthermore, the rate of bubble growth was amplified for the droplets traversing at higher Reynolds number.