Pockets in Highly Turbulent Premixed Flames: Physics and Implications on Modeling
Abstract
The research project comprises two phases that focus on flame kernels in subsonic and supersonic premixed combustion environments. The objective of the first phase is to understand the underlying physical processes of two types of pockets that are observed within the thin reaction zones regime and the broken reaction zones regime, including fresh-mixture pockets surrounded by the product of the flame (termed as FiP) and product pockets surrounded by fresh mixtures (termed as PiF). Subsequently, phase II focuses on understanding the fundamental physical processes of the initiation and propagation of auto-igniting kernels within highly compressible shock-laden environment, such as in detonation. Direct numerical simulations (DNS) are employed in both phases to minimize errors arising from subgrid phenomena. During phase I, numerical experiments are designed to discern impacts of laminar flame speed and extinction strain rates on the quenching of a turbulent PiF flame kernel and a FiP flame kernel. It has been found that laminar flame speed is a critical canonical property that determines the displacement speed in strained laminar flame and in the turbulent flame studied here. The extinction strain rate plays a secondary role in determining the probability of global extinction, and reformation of fresh mixtures by quenched flame kernels is not significant enough to alter the qualitative behavior of flame kernels. Turbulence-chemistry interactions are found to be manifested through modification of the curvature stretch instead of changing tangential strain rates. Additionally, it is determined that FiP pockets have low probability of developing into an auto-igniting hot spot in atmospheric methane/air flames, due to the much shorter time scale of flame propagation and diffusion compared to autoignition.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 18, 2024
- Accession Number
- AD1230631
Entities
People
- Xinyu Zhao
Organizations
- University of Connecticut