What’s so special about an M-shaped flame?

With significant military, industrial and domestic applications, it is important to understand the complexities of flame stabilization. Premixed flame stabilization schemes mainly use passive methods instead of active ones due to their relative simplicity.

Anastasia Krikunova compared inverted conical M-shaped flames to classical conical flames. She numerically and experimentally studied the two types of flames in terms of oscillation frequency, velocity flow field and flame front dynamics.

To compare the two flames, Krikunova used image-processing with numerical simulations. She showed the classical conical flame’s vertical displacements amplitude to be approximately 3.5 times that of the M-shaped flame oscillations. The M-shaped flame also oscillated both vertically and horizontally, compared to the classical conical flame tip which only oscillates vertically.

Although both flames proved similar in terms of velocity flow field and flame front dynamics, Krikunova found that when the fuel-oxidizer mixture equivalence ratio is varied, the M-shaped flame’s oscillation frequency remained constant, while the frequency for the classical conical flames changed. Fuel enrichment also did not affect the frequency of flickering in the M-shaped flame as compared to the classical.

“In my opinion, the most significant difference in conical and M-shaped flame behavior is the flickering frequency constancy under the different ratio of oxidizer and fuel,” said Krikunova. “These results can be taken into account in the design of burner devices using passive flame stabilization methods.”

Source: “M-shaped flame dynamics,” by A. I. Krikunova, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5129250 .