Date of Graduation

2017

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Akkerman V'yacheslav

Committee Co-Chair

Patrick Browning

Committee Member

Yogendra Panta

Abstract

Boundary conditions constitute one of the key factors influencing combustion in chambers with large aspect ratios such as narrow channels or pipes. Specifically, the flame shape and propagation velocity are impacted by wall friction and heat transfer to the walls. Both factors continuously deform the flame front, thereby resulting in a larger surface area of the flame front as compared to a planar flame. Such a corrugated flame consumes more fuel per unit time and thereby propagates faster than the planar flame at the same thermal-chemical conditions. Consequently, a flame accelerates due to the boundary conditions.;In the recent years, there have been many studies scrutinizing the role of boundary conditions in the flame acceleration scenario by means of analytical formulations, computational endeavors and experimental measurements. However, the majority of these works was limited to equidiffusive flames, where the thermal-to-mass diffusivity ratio (the Lewis number; Le) is unity. In this respect, the present thesis removes this limitation by analyzing non-equidiffusive (fuel-lean, Le1) flames propagating in pipes of various widths. Specifically, a parametric study has been conducted by means of computational simulations of the basic hydrodynamic and combustion equations.;A fully-compressible Navier-Stokes solver available in Akkerman's group at West Virginia University was employed in the simulations. The embryo of this solver was originally developed at Volvo Aero and then upgraded by various research groups and adapted for parallel computations. In this study, specifically, two-dimensional (2D) channels with smooth walls and different thermal conditions such as isothermal and adiabatic walls, have been employed for various Lewis numbers in the range 0.2 ≤ Le ≤ 2.0, and the Reynolds number associated with the flame propagation in the range 5 ≤ Re ≤ 30.;As a result, a strong coupling between the wall conditions and Lewis and Reynolds numbers' variations is demonstrated. Specifically, it is observed that the increase in the Lewis number results in the moderation of flame tip acceleration. It is also found that there is a change in the burning rate and surface area of the flame front at the lower Lewis numbers, where flames appear unstable against the thermal-diffusion instability. Moreover, a significant difference between the situations of isothermal and adiabatic wall conditions is demonstrated. In summary, it is emphasized that the more we understand how flames behave at a fundamental level, the better we can employ them, constructively, in numerous practical applications.

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