Backlit images (shown here under 1g) reveal the receding of droplet as the burning progresses.
Effect of gravity on burning rate
Fluctuations in the regression of droplet diameter are due to initial transients.
The burning rate of droplet under normal gravity is higher than that of micro gravity.
Buoyancy under normal gravity results in increased motion of fuel vapors inside the droplet. Thus, heat transfer inside and transport of fuel vapors to the flame front is enhanced and burning rate increases consequently.
Effect of pressure on burning rate
Normal gravity droplet burning exhibits higher burning rate compared to the microgravity case due to buoyancy effects as seen in the ambient pressure case. Similar trends are observed at higher pressures of 4 and 8 bar in the above figures.
Burning rate of droplet increases with chamber pressure due to enhanced vaporization rates and reaction rates. In case of normal gravity, increased buoyancy at higher pressure also causes enhancement in the burning rate.
