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 Akkerman

Committee Co-Chair

Ali S Rangwala

Committee Member

Arvind Thiruvengadam

Abstract

To reveal the inner mechanism of gas explosion, the entire scenario of premixed flame front evolution within an accidental fire is prescribed, quantitatively, with the situation of a methane-air explosion in a mining passage as the primary application. Specifically, the key stages of flame evolution are scrutinized. First, a globally-spherical expansion of a centrally-ignited, embryonic flame, with a possibility of self-similar acceleration caused by the hydrodynamic (Darrieus-Landau) instability occurs. This stage provides an order of magnitude increase in the flame speed in realistically large mining passages. Second, a transition from a globally-spherical front to a finger-shaped one happens, when a flame starts approaching the passage walls. While this acceleration is extremely strong, it stops as soon as the flame touches the passage wall. This mechanism is Reynolds-independent; being equally relevant to micro-channels and realistically large tunnels. The flame speed increases by one more order of magnitude during this stage. Eventually, a flame may accelerate due to wall friction as well as in-built obstacles and wall roughness. While this scenario could be dominant at micro- and mesa-scales, it appears negligible in a mining passage because the influence of wall friction decreases, drastically, with the Reynolds number, and wall-attached obstacles are small in mines. Overall, we have identified the key characteristics of all stages such as the timing for each stage as well as the flame shapes, propagation speeds, acceleration rates, and flame-generated velocity profiles. The flame speed rises by orders of magnitude. Starting with laminar homogenously-gaseous combustion, the analysis is subsequently extended to dusty-gaseous environments. For this purpose, the dependences of the thermal-chemical flame parameters, such as the planar flame speed, versus the combustible and inert dust properties, such as the dust particles size and concentration, are incorporated into the formulation.

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