Understanding and Modeling Flame Displacement Speed 

Background:

Turbulence and Combustion are two highly complex and nonlinear phenomena; their interaction is all the more fascinating. When turbulence interacts with flames, the flame gets stretched, wrinkled, corrugated at a multitude of length scales and these interactions happen at different timescales. Understanding these interactions are scientifically fascinating as well as technologically important.

Why did we solve this problem?

Premixed flames have a propagation speed of their own. For example, when a premixture is ignited using a sparkplug in an SI engine, the flame quickly engulfs the cylinder volume to generate hot gases. While the flow field in the cylinder is not stationary, the tendency of the flame to run towards the fresh mixture and convert it into products would still be there. Similarly in a lean-premixed combustor, the flame consumes fresh reactants and at times may flashback into the fuel-air mixture injection manifold. Therefore, one important question is how fast a flame moves when it interacts with a turbulent stream of fresh reactants. This is precisely the question that we've addressed in our research along with additional questions. 

What did we find?

We found out that premixed flames on interacting with a turbulent stream fresh reactant continuously gets destroyed and generates. The generation sites and destruction sites are primarily different - generation usually happens in the regions that are convex (positively curved) to the oncoming stream of fresh reactants while destruction usually happens in the regions that are concave (negatively curved) - at least for the premixed flame interactions with moderate levels of turbulence. We also found that there are some existing flame speed models known as Markstein length models that can model the flame speeds in the quasi-steady or slowly varying regions of the flame. However, the flame destruction events, especially through flame-flame interactions, are usually very transient and pose challenges to quasi-steady Markstein length models. We developed a flame interaction model for modeling flame speed in those regions.

Impact

Our research has helped in improving our understanding of complex turbulence premixed flame interactions and answered few of the challenging questions on the dynamical behaviour of premixed flames. This can be useful for modeling flame stabilization, understanding flame stabilization mechanisms, developing scientific machine learning applications for reduced-order modeling of turbulent combustion.

You can read more about this topic in the following references. Additionally, if this research theme piques your interest and you want to know more, learn more, and contribute more on this topic, please feel free to write.

References:

[1] Dave, Himanshu L., Abinesh Mohan, and Swetaprovo Chaudhuri. "Genesis and evolution of premixed flames in turbulence." Combustion and Flame 196 (2018): 386-399.

[2] Dave, Himanshu L., and Swetaprovo Chaudhuri. "Evolution of local flame displacement speeds in turbulence." Journal of Fluid Mechanics 884 (2020): A46.

[3] Uranakara, Harshavardhana A., Swetaprovo Chaudhuri, Himanshu L. Dave, Paul G. Arias, and Hong G. Im. "A flame particle tracking analysis of turbulence–chemistry interaction in hydrogen–air premixed flames." Combustion and Flame 163 (2016): 220-240.

[4] Yuvraj, Song, Wonsik, Himanshu Dave, Hong G. Im, and Swetaprovo Chaudhuri. "Local flame displacement speeds of hydrogen-air premixed flames in moderate to intense turbulence." Combustion and Flame 236 (2022): 111812.