Date of Graduation

2015

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

V'yacheslav Slava Akkerman

Committee Co-Chair

Patrick Browning

Committee Member

Arvind Thiruvengadam

Abstract

Accidental gas and dust explosions constitute a tremendous hazard for personnel and equipment in industries dealing with flammable gases and explosive materials. Historically, the coal mine industry has one of the highest occupational fatality and injury rates, claiming hundreds of miners' lives every year. To reduce the risk of mining scenarios, a joint team of West Virginia University and Worcester Polytechnic Institute are developing a comprehensive analytical, computational and experimental platform that will eventually be able to quantify the probability of a fire initiation and/or a deflagration-to-detonation transition as well as the methodologies how to terminate or, at least, mitigate these disasters. Within the frame of this research, a predictive scenario of a methane-air fire in a dusty-gaseous environment of a mining passage is being developed. Among various mechanisms responsible for the flame acceleration such as combustion instability, turbulence, acoustics, and wall friction, the acceleration due to a finger-shaped flame front plays a dominant role here, because this mechanism is scale-invariant and, thereby, Reynolds-independent. This finger-flame acceleration is very powerful, promoting the speed of the fire spreading by an order of magnitude. However, this acceleration scenario is limited in time: it is terminated as soon as the flame skirt contacts a passage wall. While the existing analytical formulation of this predictive scenario is based on the incompressible approximation, in this particular study, the effects of gas compressibility on the mining fire scenario are quantified by means of the analytical and computational endeavors. It is shown that gas compressibility generally moderates the flame acceleration, and the result depends on various thermal-chemical parameters. While the effect of compressibility is minor (say, providing a 3-5% reduction) for lean and rich methane-air pre mixtures, thereby justifying the incompressible formulation in that case, it appears significant (provides a reduction of 10-20%) for near-stoichiometric methane-air combustion, and therefore should be incorporated into a rigorous formulation. Starting with gaseous fuels, the formulation is then extended to dusty-gaseous flows. Specifically, the effects of equivalence ratio and dust size/concentration on the flame characteristics, such as the flame speed and temperature, are systematically investigated. In this respect, combustible and inert dusts, as well as their mixture, are studied.

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