  The droplet and flame chemiluminescence dynamics as well as their coupling
during atomization events of graphene oxide doped diesel are investigated
experimentally. The tested doping concentrations are 0, 0.001, 0.005, 0.01, and
0.02% by weight. To minimize heat transfer between the droplet and its
suspension mechanism, small diameter fibers are used for the droplet
suspension. Separate shadowgraphy and OH* chemiluminescence measurements are
performed at 4000 Hz to study the droplet and flame dynamics, respectively. The
results show that both the droplet diameter squared and the flame
chemiluminescence feature intermittent oscillations. The droplet diameter
squared oscillations RMS is positively related to the number and intensity of
the atomization events and the graphene oxide doping concentration. The
probability density function of the inverse of the time separation between two
consecutive atomization events and the power spectrum density of the droplet
diameter squared oscillations feature dominant large probabilities and powers
at about 25 Hz prior to the occurrence of the first intense atomization event.
After the occurrence of the first intense atomization event, this frequency
decreases to about 5 Hz for both. Although the intense atomization triggers the
large amplitude oscillations at 5 Hz, it was argued that the retracting motion
of the igniter induces the oscillations at 25 Hz. Our findings suggest that the
atomization events are the root cause of the smaller frequency coupling between
liquid fuel droplets doped with graphene oxide and their flames. This has
implications for spray combustion research.
