  Effects of graphene oxide nanomaterials addition and oxidation level on
ignition delay and burning rate of ethanol droplets are experimentally
investigated. Three graphene oxide samples are synthesized and characterized.
Separate high-speed OH* chemiluminescence and high-speed shadowgraphy images
are collected. The results suggest that increasing the loading concentration
from 0 to 0.1% generally increases the ignition delay, except for ethanol doped
with the highly oxidized graphene. The probability density function of the
atomized baby droplet diameter, initial projected velocity, and length of the
projected trajectory are similar for all tested conditions and independent of
the oxidation level and loading concentration of the additives. The joint
probability density function calculated for the atomization-related parameters
against one another suggests that the majority of the baby droplets feature a
relatively short lifetime, indicating they may potentially burn inside the
flame envelope. Using droplet surface regression curves versus time, the
burning rate for periods in which the atomization does not occur, and for the
periods that the atomization is present are estimated. The former burning rate
is shown to enhance by increasing the loading concentration and reducing the
oxidation level of graphene. However, it is found that a maximum increase in
the latter burning rate for both loading concentrations occurs for ethanol
doped with the graphene oxide that features maximum amount of infrared
radiation absorption. It is shown that relatively intense atomization
suppresses the mass loss. Doping ethanol with graphene oxide and increasing the
loading concentration from 0.01 to 0.1% enhances the overall burning rate, with
a maximum enhancement of 8.4% pertaining to addition of reduced oxidized
graphene oxide and for the loading concentration of 0.1%.
