A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Water Mist Suppression in a Turbulent Line Burner(2016) Keller, Elizabeth; Marshall, Andre W; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental study of water mist fire suppression in a buoyant, turbulent diffusion flame is presented. An existing turbulent line burner facility was modified to allow for water mist suppression. These modifications include streamlining the oxidizer delivery system, facility improvements to increase mist generation efficiency, as well as the addition of a mist containment system and an enhanced exhaust flow to homogenize the water mist in the flame region and reduce secondary flows. Following these improvements, the capabilities of the water mist generation system were characterized both using a classical mass balance approach and using more modern advanced diagnostic techniques. The turbulent line burner facility fitted with the water mist improvements were applied to suppress a 50 kW methane flame. Species-based calorimetry was used to evaluate the global heat release rate and combustion efficiency to evaluate suppression behavior. Detailed local measurements of flame temperature were also performed and provide a useful data set for the evaluation of flame suppression response and for the validation of CFD fire models.Item Measurement and Simulation of Suppression Effects in a Buoyant Turbulent Line Fire(2016) White, James Patrick; Sunderland, Peter B; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An experimental and numerical study of turbulent fire suppression is presented. For this work, a novel and canonical facility has been developed, featuring a buoyant, turbulent, methane or propane-fueled diffusion flame suppressed via either nitrogen dilution of the oxidizer or application of a fine water mist. Flames are stabilized on a slot burner surrounded by a co-flowing oxidizer, which allows controlled delivery of either suppressant to achieve a range of conditions from complete combustion through partial and total flame quenching. A minimal supply of pure oxygen is optionally applied along the burner to provide a strengthened flame base that resists liftoff extinction and permits the study of substantially weakened turbulent flames. The carefully designed facility features well-characterized inlet and boundary conditions that are especially amenable to numerical simulation. Non-intrusive diagnostics provide detailed measurements of suppression behavior, yielding insight into the governing suppression processes, and aiding the development and validation of advanced suppression models. Diagnostics include oxidizer composition analysis to determine suppression potential, flame imaging to quantify visible flame structure, luminous and radiative emissions measurements to assess sooting propensity and heat losses, and species-based calorimetry to evaluate global heat release and combustion efficiency. The studied flames experience notable suppression effects, including transition in color from bright yellow to dim blue, expansion in flame height and structural intermittency, and reduction in radiative heat emissions. Still, measurements indicate that the combustion efficiency remains close to unity, and only near the extinction limit do the flames experience an abrupt transition from nearly complete combustion to total extinguishment. Measurements are compared with large eddy simulation results obtained using the Fire Dynamics Simulator, an open-source computational fluid dynamics software package. Comparisons of experimental and simulated results are used to evaluate the performance of available models in predicting fire suppression. Simulations in the present configuration highlight the issue of spurious reignition that is permitted by the classical eddy-dissipation concept for modeling turbulent combustion. To address this issue, simple treatments to prevent spurious reignition are developed and implemented. Simulations incorporating these treatments are shown to produce excellent agreement with the experimentally measured data, including the global combustion efficiency.Item Large Eddy Simulation of Fire Extinction Phenomena(2015) Vilfayeau, Sebastien; Trouve, Arnaud; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The simulation of fire phenomena using classical Computational Fluid Dynamics (CFD) methods has made remarkable progress in the past 20 years. However, the occurrence of flame extinction is still a challenge for combustion modeling in general, and for fire modeling in particular. The study is performed using FireFOAM; FireFOAM is an advanced Large Eddy Simulation (LES) fire modeling software developed by FM Global and is based on a general-purpose open-source software called OpenFOAM. A new flame extinction model based on the concept of a critical value of the flame Damk ̈ohler number is incorporated into FireFOAM. The objective of the present study is to evaluate the ability of CFD-based fire models to simulate the effects of flame extinction in two different configurations (under-ventilated compartment fire and turbulent line fire in controlled co-flow, i.e. nitrogen or water-mist). Comparisons between experimental data and numerical results provide a suitable test bed to evaluate the ability of CFD-based fire models to describe the transition from extinction-free conditions to conditions in which the flame experiences partial or total quenching.