The role of atomization in the coupling between doped droplets dynamics and their flames

TL;DR

This study experimentally investigates how atomization influences the coupling between doped droplet dynamics and flame chemiluminescence, revealing that atomization events significantly affect oscillation frequencies and flame behavior in graphene oxide doped diesel.

Contribution

It provides new insights into the role of atomization in droplet-flame coupling, especially in doped fuel droplets, with detailed frequency analysis of oscillations.

Findings

Atomization events cause oscillations at ~25 Hz and ~5 Hz.

Doping concentration correlates with oscillation intensity.

Atomization influences the frequency coupling between droplets and flames.

Abstract

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.