High fidelity simulations of reactive liquid-fuel jets
- Most of the propulsion combustion engines, due to weight and volume restrictions, rely on liquid phase combustion processes. The multi-physics aspect of liquid phase combustion introduced by the fuel evaporation along with combustion in a highly-turbulent environment makes experimental investigation of such a system a very challenging endeavor. This lack of high fidelity experimental data explaining complex interaction between different physical mechanisms motivates the need for detailed simulations in order to improve our understanding and thereby advance model development. Traditionally in turbulent combustion research, focus is directed towards understanding the fully burning state. However our understanding of the transition from an unburnt state to a fully burning state is relatively underdeveloped and therefore is the focus of the present work. While most of the industrial combustion devices rely on either an external ignition source or auto-ignition to start combustion, this work will solely focus on understanding and modeling auto-ignition in liquid hydrocarbon fuel jets. To study the phenomena of auto-ignition we have performed three-dimensional high fidelity simulations of reacting n-heptane liquid-fuel temporal jet in Diesel engine type conditions. In these simulations the continuous phase is described using an Eulerian representation whereas Lagrangian particle tracking is used to model the dispersed phase. The chemical kinetics are described using a reduced n-heptane chemical mechanism with 42 species and 304 reactions. The results from the simulations are used to characterize auto-ignition in turbulent spray flames. Auto-ignition kernels are first seen in fuel-lean mixture fraction regions. The role of scalar dissipation rate on auto-ignition is highlighted. Auto-ignition is observed only in the regions of low scalar dissipation rate. Subsequent to formation of auto-ignition kernels, reaction fronts propagate towards the fuel-rich regions and establish regions of increased reaction rate. Dominance of partially premixed mode of burning is also noted. Finally, the flamelet combustion models are analyzed using the simulation database. The a-priori tests highlight the deficiencies of premixed progress variable based model in reproducing auto-ignition. The a-priori tests also reveal the superior performance of non-premixed progress variable model in capturing the auto-ignition behavior.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Stanford University, Department of Mechanical Engineering
|Mungal, Mark Godfrey
|Mungal, Mark Godfrey
|Statement of responsibility
|Submitted to the Department of Mechanical Engineering.
|Thesis (Ph.D.)--Stanford University, 2012.
- © 2012 by Shashank Shashank
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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