High-Fidelity Simulations to Study Spray-Induced Extinction and Particulate Formation Characteristics of Nonpremixed Ethylene-Air Flames.

[摘要] This work developed and employed high-fidelity direct numerical simulations to investigate fundamental flame behavior in laminar and turbulence nonpremixed flames. The scope of the work includes several advances in computational algorithms such as improved Navier-Stokes Characteristic Boundary Conditions (NSCBC) for mass additive systems and advanced soot models. In addition, detailed investigations into the effects of thermal quenching were conducted in an effort to understand ways of accurately describing the nature of flame extinction comprehensively. As an application to fundamental and practical combustion problems, the study investigates the interaction of water spray and turbulence with nonpremixed diffusion flames. The simulations incorporate detailed chemistry of ethylene flames, the chemistry of which is recognized as an important chemical pathway for combustion processes. A unified extinction condition that accounts for thermal quenching and strain induced quenching simultaneously is demonstrated to be effective at capturing the moment of extinction and tracking extinction holes in turbulent flames. The findings show that in the formation of edge flames, the evolution leading to the flame recovery or total extinction is found to depend strongly on the temporal history of the local strain rate as well as the presence of the spray droplets. While turbulent mixing leads to the formation of the edge flames, the presence of spray droplets suppresses the ability of edge flames to heal extinction holes.The final part of this study examines the dynamics of soot formation in ethylene-air nonpremixed flames using a Method of Moments with Interpolative Closure (MOMIC) approach. A number of technical challenges related to the simulation of soot and gas phases were addressed. The treatment of the interpolation moments, which play a role in the diffusion of soot as well as the soot reaction source terms, was found to be consistent with the mathematic description of MOMIC, and was shown to be consistent with the conditions of statistical realizability of the soot moments for the reaction test cases. The results of this study provide the Direct Numerical Simulation (DNS) community with a numerical framework towards the development and implementation of high-fidelity soot sub-models.

[发布机构] University of Michigan

[效力级别] Navier-Stokes Characteristics Boundary Conditions

[关键词] Direct Numerical Simulation;Navier-Stokes Characteristics Boundary Conditions;Method of Moments With Interpolative Closure;Mechanical Engineering;Engineering;Mechanical Engineering