Impact of cellularity in the flame front on the burning velocity acceleration of ethanol/air flames in constant volume combustion bomb

Abstract

The objective of this work was to characterize the impact of cellularity developed at the flame front on the burning velocity of ethanol/air flames in a constant-volume combustion bomb by varying the ethanol/air equivalence ratio (0.8–1.4), initial pressure (0.15–0.3 MPa) and initial temperature (343–373 K). Cellularity at the flame front was studied using instantaneous Schlieren images of flame morphology obtained with a high-speed camera. Results show that ethanol-air flames exhibit increased cellularity at the flame from as the equivalence ratio in rich mixtures ratio increases and with increasing initial pressure, thereby accelerating the burning velocity. Although acceleration of the burning velocity is observed in all experiments, not all of them develop in the same mode: there may be a relationship between the burning velocity profile and the type of cellularity (inherent instabilities) established at the flame front in each case. Three types of acceleration are considered and investigated: one-stage, two-stage and progressive acceleration. The flame front structure and the instabilities that give rise to the cellularity phenomenon during combustion may be important for understanding the transition to turbulent combustion. They also play a key role characterizing the increase in burning velocity and its acceleration in premixed flames, in comparison with laminar burning velocity obtained from kinetic modelling.