Research Group for Combustion
Hong Kong
Many important industrial devices involve circular or annular fluid systems consisting of many identical units symmetrically arranged in a circle or ring shape, for example, gas-stove ring burners, turbomachine rotors, can-annular combustors in gas-turbine engines, and Chevron-type primary exhaust nozzles for aircraft engines.
The N-periodic systems of flickering buoyant diffusion flames, as simplified prototypes of flame oscillators in annular combustors, are studied to experimentally observe collective dynamical modes, computationally reproduce major modes, and theoretically establish a predictive vortex-dynamical model.
The relevant works have been published in Physical Review Fluids, Proceedings of the Combustion Institute, Combustion and Flame.
Single Flickering Buoyant Diffusion Flame
Dual Flickering Flames
In-phase
Anti-phase
Independent
Poster in China National Symposium on Combustion 2022
Triple flickering buoyant diffusion flames in an isosceles triangle arrangement, as a nonlinear dynamical system of coupled oscillators, were experimentally studied. The focus of the study is two-fold: we established a well-controlled gas-fuel diffusion flame experiment, which well remedies the deficiencies of prevalent candle-flame experiments, and we developed a Wasserstein-space-based methodology for dynamical mode recognition, which is validated in the present triple-flame systems but can be readily generalized to the dynamical systems consisting of an arbitrary finite number of flames. By use of the present experiment and methodology, seven distinct stable dynamical modes were recognized, such as the in-phase mode, the flickering death mode, the partially flickering death mode, the partially in-phase mode, the rotation mode, the partially decoupled mode, and the decoupled mode. These modes unify the literature results for the triple flickering flame system in the straight-line and equal-lateral triangle arrangements. Compared with the mode recognitions in physical space and phase space, the Wasserstein-space-based methodology avoids personal subjectivity and is more applicable in high-dimensional systems, as it is based on the concept of distance between distribution functions of phase points. Consequently, the identification or discrimination of two dynamical modes can be quantified as the small or large Wasserstein distance, respectively.
The relevant study has been published in Combustion and Flame.
Recent Progress on Torsional Anharmonicity of Large Molecules in Partition Function Calculation Using the Metric-based Multi-Structural Method
Calculating partition function plays an important role in the high-level chemical kinetics of large molecules, in which the conformational torsional anharmonicity needs to be correctly treated. The multi-structural approximation with the torsional anharmonicity (MS-T) method proposed by Truhlar and his collaborators has been widely used. Regardless of the noticeable success of the MS method and its variants, some questions about the implementation of these methods need to be answered. First, whether we need a complete set of distinguishable torsional conformers? Second, how to find an appropriately chosen small subset of distinguishable torsional conformers which can significantly reduce the computational cost while retaining acceptable accuracy? Last and more important, how to find a general approach to assess the performance of various subsets?
The recent work aimed to propose a systematic method to assess and explain the performance of various variants of the MS-T method. It is worth emphasizing that the proposed method provides a mathematically rigorous and computationally effective diagnostic tool to assess various MS-T methods dealing with the torsional anharmonicity of large molecules in partition function calculation. The work, “A Metric-based Assessment Method for MS-T Formalism with Small Subsets of Torsional Conformers”, has been published in The Journal of Physical Chemistry A, DOI: 10.1021/acs.jpca.2c04724