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Outwardly Expanding Premixed Flames in Open and Confined Turbulent Environments

Moshe Matalon, University of Illinois at Urbana-Champaign

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Moshe Matalon

The propagation of centrally ignited premixed flames in open and confined, laminar and turbulent environments will be examined within the context of a hydrodynamic theory. The theory has been derived systematically from the general conservation equations of multi-components chemically reacting mixtures by exploiting the disparate length and time scales associated with the fluid dynamics, molecular and energy transport processes and chemical reaction rates. As such, it is based on physical first principles and is free of modeling assumptions and ad-hoc adjustable parameters commonly used in turbulent studies.

For the numerical implementation of the hydrodynamic theory, a hybrid Navier-Stokes/embedded manifold approach is being proposed. This methodology is adept at handling multiply folded surfaces, representing the highly corrugated flames that result from intrinsic combustion instabilities and turbulence, and disjointed surfaces such as detached flamelets that separate from the main flame surface and burn individually. 

This approach provides a tremendous opportunity to simulate the flame propagation, for different flow conditions, fuel types, mixture compositions and pressure levels, which due to the sheer numerical costs is impractical to study by Direct Numerical Simulations. A sensitivity analysis covering mixtures with various compositions, diffusion properties and heat release that characterize combustion systems, is to be performed to investigate flame kernel development and its long-time evolution in open space and in confined environments.

The focus will be to understand the effects of turbulence and combustion instabilities on the burning rate, the self-acceleration and fractal nature of the flame, and derive scaling laws for the turbulent flame speed that captures the flame-turbulence interactions. Outwardly propagating flames are encountered in numerous applications, from the design of practical engineering devices like the spark-ignition engine to predicting astrophysical events like exploding supernovae and are crucial to study from a safety perspective.