A. James Clark School of Engineering

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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    Interaction of Acoustic Waves with a Laminar Line-Flame
    (2016) Friedman, Adam Neal; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A systematic study was conducted to elucidate the effects of acoustic perturbations on laminar diffusion line-flames and the conditions required to cause acoustically-driven extinction. Flames were produced from the fuels n-pentane, n-hexane, n-heptane, n-octane, and JP-8, using fuel-laden wicks. The wicks were housed inside of a burner whose geometry produced flames that approximated a two dimensional flame sheet. The acoustics utilized ranged in frequency between 30-50 Hz and acoustic pressures between 5-50 Pa. The unperturbed mass loss rate and flame height of the alkanes were studied, and they were found to scale in a linear manner consistent with Burke-Schumann. The mass loss rate of hexane-fueled flames experiencing acoustic perturbations was then studied. It was found that the strongest influence on the mass loss rate was the magnitude of oscillatory air movement experienced by the flame. Finally, acoustic perturbations were imposed on flames using all fuels to determine acoustic extinction criterion. Using the data collected, a model was developed which characterized the acoustic conditions required to cause flame extinction. The model was based on the ratio of an acoustic Nusselt Number to the Spalding B Number of the fuel, and it was found that at the minimum speaker power required to cause extinction this ratio was a constant. Furthermore, it was found that at conditions where the ratio was below this constant, a flame could still exist; at conditions where the ratio was greater than or equal to this constant, flame extinction always occurred.
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    Measurements and Analysis of Extinction in Vitiated Flame Sheets
    (2009) Williamson, Justin Wade; Marshall, Andre W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Accidental fires present many challenging hazards to people and property. The thermal and toxic effects of fires are significantly affected by the ventilation conditions supplied to the fire. Vitiation is a consequence of limited ventilation, where the products of combustion mix with the unburned reactants prior to reaction. Vitiation results in diluting and preheating the reactants, significantly enhancing the behavior of the fire. An interesting effect of vitiation is the increased propensity of the flame to experience extinction, either locally or globally. Likewise, there are other factors that can increase the propensity for extinction, including losses due to incomplete chemical kinetics, radiation, and conduction. These extinction events have a direct impact on the thermal and toxic hazards associated with accidental fires by creating holes in the reaction surface. This research provides a detailed analysis of local flame extinction by examining the behavior of counterflow flames undergoing kinetic losses, radiation losses, and vitiation. A thorough review of flame extinction theory was conducted to determine the appropriate parameters necessary for characterizing local flame extinction conditions. Simple scaling arguments are presented to demonstrate that each of these parameters is significant in accidental fires. Counterflow methane-air diffusion flames have been studied experimentally and numerically with OPPDIF to systematically examine the effects of each parameter on local flame extinction. Furthermore, a model is presented, which uses reactant composition and temperature in the vicinity of the flame, net radiation losses from the flame, and the local scalar dissipation rate as inputs to model local extinction conditions. The proposed model is suitable for integration into Computational Fluid Dynamics (CFD) codes used to predict the hazards associated with accidental fires.