Bibliography - J. Yuan

1. Yuan, J., Y. Ju, and Chung K Law, 2007: On flamefront instability at elevated pressures. Proceedings of the Combustion Institute, 31(1), doi:10.1016/j.proci.2006.07.180 1267-1274
   [ Abstract ]

   Effects of pressure up to 3 atm on flame-front instability were numerically investigated for both linear and nonlinear growth stages at sub-unity and unity Lewis numbers. A sixth-order compact scheme and non-reflecting boundary conditions were used to capture the evolution of the flame front. Results show that in the linear instability growth stage, elevated pressure can extend the unstable range of flame-fronts and generate the fine flame cell structure. This effect can be qualitatively predicted by the theories when Le = 1.0; however the theories diverge at sub-unity Lewis numbers (e.g. Le = 0.7). In the nonlinear growth stage, the critical wave number (k_c) from the linear dispersion relation can be used as a reference length scale for the evolution of the flame cell structure. Since elevated pressure increases the critical wave number, small flame cells appear over large flame cells (deep folds) at high ambient pressures. Furthermore, flame-front hydrodynamic instability is excited when the lateral domain is enlarged.

2. Yuan, J., Y. Ju, and Chung K Law, 2005: Coupled hydrodynamic and diffusional-thermal instabilities in flame propagation at large Lewis numbers. Physics of Fluids, 17(O74106), doi:10.1063/1.1964845
   [ Abstract ]

   The dynamics of flame cell evolution due to the coupling between hydrodynamic and diffusional-thermal instabilities in subunity Lewis number flames was simulated using a sixth-order central difference scheme and newly developed nonreflective boundary conditions. Results show that the interaction between these two modes of instabilities yields distinct evolutions of cell splitting, merging, growth, local extinction, and lateral motion, leading to fluctuations of the flow and species concentrations as well as substantial increase in the flame speed. The study also demonstrates that small computational domains cannot correctly predict cell merging and transverse motion.

3. Yuan, J., S. D. Tse, and Chung K Law, 2002: Dynamics of Flame Ball Formation from Localized Ignition: Effects of Elevated Pressure and Temperature. Proceedings of the Combustion Institute, 29(2), doi:10.1016/S1540-7489(02)80305-4 2501-2507
   [ Abstract ]

   A computational study was conducted on expanding spherical premixed flames to investigate the dynamics of flame-ball formation at elevated temperatures and pressures. Lean H₂/air mixtures were investigated using a time-dependent, spherically symmetric code with detailed chemistry, transport, and radiation submodels. Results show that, with increasing pressure, both the steady-state flame-ball radius and the H₂ consumption rate for a given mixture composition decrease monotonically up to 50 atm, varying approximately as p^-0.57. Furthermore, a window of pulsating flame behavior, near the upper dynamic flame-ball limit, was discovered and investigated. Within this window, an outwardly propagating flame begins to self-extinguish due to radiative losses but revives suddenly due to low-Lewis-number effects and evolves into a flame ball. More than one such cycle of behavior can occur for a given mixture concentration. Results further show that as the ambient mixture temperature is increased, the initial trend is a downward shift of the upper dynamic flame-ball limit. With reduced radiative loss, spherical flames continue to propagate outwardly for leaner mixture compositions without degenerating into flame balls, but at the same time, expand themselves into radiative extinction. Again, the role of radiative loss as both the requisite mechanism for and the limiting mechanism against the dynamic transformation of spherically propagating flames into flame balls is emphasized. Nonetheless, as the ambient temperature is increased to near 700 K (in an attempt to investigate the boundary defining the flameless combustion regime), steady flame balls are no longer attainable, with chemical reactions occurring at the boundary.

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