Sinan Demir

Date of Graduation

2017

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

V'yacheslav Akkerman

Committee Co-Chair

Richard Bajura

Committee Member

Cosmin Dumitrescu

Committee Member

John M Kuhlman

Committee Member

Ali S Rangwala

Abstract

Accidental fires and explosions in gaseous environments with dust impurities constitute a tremendous hazard for dwelling and office buildings as well as for industries dealing with explosive materials such as flammable gasses and combustible dust. Among these industries, coal mining traditionally exhibits one of the highest occupational fatality and injury rates, often due to methane/air/coal-dust catastrophes claiming many lives every year world wide. There is therefore a critical need to reduce the risk of such accidents, or at least to mitigate their disastrous consequences. For this sake, the analytical and computational studies of the present Dissertation reveal the mechanism of flame evolution and acceleration in a coal mine combustion accident, thereby commanding both the practical relevance mentioned above as well as the fundamental interests. First, the key stages and characteristics of premixed flame front evolution---including the flame shapes, propagation speeds, acceleration rates and run-up distances---are scrutinized in two-dimensional planar and cylindrical geometries. Starting with gaseous combustion, the analysis is subsequently extended to gaseous-dusty environments, and the impacts of the size and concentration of the dust particles are quantified. Second, the effect of gas compressibility is incorporated into the theory of a methane/air/coal-dust fire in a mining passage. It is shown that gas compression moderates flame acceleration, and its impact depends on the type of the fuel, its various thermal-chemical parameters as well as the geometry of the problem. Third, spatial variations of laminar flame speed SL are studied to account for the potential impacts of pressure and temperature variations, as well as non-uniform distribution of the equivalence ratio and/or of combustible or inert dust impurities. Specifically linear, parabolic and hyperbolic SL -distributions are incorporated into the formulations of "finger" like flame acceleration. The conditions promoting or moderating flame acceleration are identified for these distributions. Finally, gaseous-dusty premixed combustion in a channel, resembling a methane-air fire scenario in a coal mine, is studied by means of computational simulations. The numerical approach employs a finite-volume, Navier-Stokes code solving for the reacting flow equations with fully- compressible hydrodynamics, transport properties, and an Arrhenius chemical kinetics model. The combustible dust particles are incorporated into the solver in such a manner that an "effective fluid", with locally-modified dust-induced flow and flame parameters, replaces a real gaseous-dusty environment. Specifically, flame acceleration due to wall friction is analyzed for linear, parabolic and cubic coal dust concentration spatial distributions. The similarity and differences in the evolutions of the flame morphology and velocity in each of these cases, as well as in the case of purely gaseous combustion, are identified. It is shown that a non-uniform dust distribution may result in an extra distortion or a local stabilization of the flame front, which respectively increases or reduces the total flame surface area, thereby promoting or moderating flame acceleration.

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