Forcing of a flame by a periodic flow in a Hele-Shaw burner

The parametric forcing of premixed flames is observed here in the geometry of a Hele-Shaw burner. Using a vibroacoustic coupling, we are able to study the thresholds of the parametric flattening (where the flame wrinkles are suppressed) and the parametric instability (where the flame wrinkles oscillate at twice the acoustic period) and compare the measured values to a low-frequency theory. It is shown that the dependency of the parametric threshold with equivalence ratio is lower than predicted, suggesting that the Markstein lengths are frequency dependent and that the flattening threshold is independent of the Markstein number and of the nondimensional forcing frequency, in agreement with the Bychkov limit.