Notre-Dame de Paris as a validation case to improve fire safety modelling in historic buildings

The analysis of the thermal damages in Notre-Dame de Paris is necessary to estimate the impact of the dramatic 2019 fire on the remaining structure prior to reconstruction. In doing so, the large amount of data being generated creates a benchmark environment to test the relevance of numerical fire models in the unconventional configuration of a medieval roof. While being an uncontrolled and complex configuration, it can provide insights regarding the relevance of numerical tools for fire risk assessment in historic buildings. Analysing the thermal degradation of the Lutetian limestone in a vault of the choir, experimental techniques are developed to track the in-depth maximum temperature profile reached during the fire. Numerical simulations of the fire development in the roof space then aim at replicating the observations through the evaluation of the heat flux impinging the vaults during the fire. These simulations are carried out using Fire Dynamic Simulator, which requires a large range of assumptions prior to any simulation regarding materials, geometry, meshing and scale. These assumptions are described and pave the way to a future sensitivity analysis to confront the upcoming outcomes of the simulations with the experimental observations

NASA-ASEE Summer Faculty Fellowship Program at NASA Lewis Research Center

During the summer of 1996, a ten-week Summer Faculty Fellowship Program was conducted at the NASA Lewis Research Center (LeRC) in collaboration with Case Western Reserve University (CWRU), and the Ohio Aerospace Institute (OAI). This is the thirty-third summer of this program at Lewis. It was one of nine summer programs sponsored by NASA in 1996, at various field centers under the auspices of the American Society for Engineering Education (ASEE). The objectives of the program are: (1) to further the professional knowledge of qualified engineering and science educators, (2) to stimulate an exchange of ideas between participants and NASA, (3) to enrich and refresh the research activities of participants' institutions. (4) to contribute to the research objectives of LeRC. This report is intended to recapitulate the activities comprising the 1996 Lewis Summer Faculty Fellowship Program, to summarize evaluations by the participants, and to make recommendations regarding future programs

INCORPORATING DYNAMIC FLAME BEHAVIOR INTO THE SCALING LAWS OF WILDLAND FIRE SPREAD

A challenge for fire researchers is obtaining data from those fires that are most dangerous and costly. While it is feasible to instrument test beds, test plots, and small prescribed burns for research, it is uncommon to successfully instrument an active wildland fire. With a focus on very specific facets of wildland fire, researchers have created many unique models utilizing matchsticks, cardboard, liquid fuel, excelsior, plywood, live fuels, dead fuels, and wood cribs of different packing densities. Such scale models, however, only serve as valid substitutes for the full-scale system when all functional relations of the scale model are made similar to corresponding relations of the original phenomena. The field of study of large wildland fires therefore was in need of a framework that researchers could use to relate the results from many previous experiments to full-scale wildland fires; this framework was developed during the research for this dissertation. This further work developing laws for instability scaling in wildland settings was founded on the established work in dynamic similitude of G.I. Taylor, H. C. Hottel, F. A. Williams, R. I. Emori, K. Saito and Y. Iguchi. Additionally, in this work, a new dynamic flame parameter was incorporated into the scaling laws for fires that had not previously been assessed and proved to provide additional, important insight into flame spread. The new dynamic parameter enabled improved St-Fr correlations and was established for a wide range of fire sizes and fuel types

Numerical Modeling of High-Pressure Partial Oxidation of Natural Gas

High-Pressure Partial Oxidation (HP-POX) of natural gas is one of the techniques in the synthesis gas production by non-catalytic reforming. On the path to emissions reduction, all operating facilities must be optimized to satisfy environmental regulations. In a rapidly changing economic and political environment, technological development from lab-scale to demo-scale, and industrial-scale is no longer feasible. Therefore, new research and design methods must be applied. One of such methods commonly used in science and industry is numerical modeling, which utilizes Computational Fluid Dynamics (CFD), Reduce Order Models (ROMs), kinetic, and equilibrium models. The CFD models provide details about flow field, temperature distribution, and species conversion. However, the computational effort required to conduct such calculations is significant. The computationally expensive CFD models cannot be effectively used in the reactor optimization. Herewith, other modeling techniques utilizing kinetic and equilibrium models do not provide necessary details for process optimization and can only be used for adjustments of boundary conditions, investigation of specific processes occurring in the reactor, or development of sub-models for CFD. A numerical investigation was conducted to validate existing CFD models against benchmark experiments. The results reveled that the CFD model is sensitive to modeling parameters, when simulating complex flows where turbulence-chemistry interaction occurs. Moreover, it was shown that the results sensitivity increases along with the oxidizer/fuel inlet velocities ratio. Based on the conducted experiments, the CFD model validation resulted in definition of the modeling parameters suitable for modeling of HP-POX of natural gas. Based on the validated CFD model, a ROM for HP-POX of natural gas was developed. The model assumes that the reactor consists of several zones characterized by specific conversion processes. Moreover, the model considers inlet streams dissipation upon the injection, and includes several optimization stages that allows model adjustments for any reactor geometry and boundary conditions. It was shown that the developed ROM can reproduce global reactor characteristics at non-equilibrium conditions unlike other ROMs, kinetic, or equilibrium models. Moreover, the validation against CFD results showed that the ROM can correctly account for the \gls{rtd} in the reactors of different geometries and volumes without extensive additional optimization. Finally, new experiments were designed and conduced at semi-industrial HP-POX facility at TU Bergakademie Freiberg. The experiments aimed to study the influence of different oxidizer/fuel velocities ratios on the reactants mixing and process characteristics at high operating pressures. The high velocity difference between oxidizer and fuel was achieved by injection of High-Velocity Oxidizer (HVO). The experiments showed no significant influence of the HVO on the global reactor characteristics and overall species conversion process. However, the numerical analysis of the experimental results demonstrated that the oxidation zone is affected by the oxidizer inlet velocity, and becomes less efficient in the fuel conversion when the oxidizer/fuel inlet velocities ratio is increased. In summary, a sophisticated numerical model validation was conducted and sensitivity of the numerical results to the modeling parameters was carefully studied. The novel natural gas conversion technique was experimentally studied. Based on the conducted experiments and numerical evaluation a ROM was developed. The ROM is capable of producing high accuracy results and greatly decreases the computational effort and time needed for reactor development and optimization

Liquid Layer Combustion Instabilities in Paraffin-Based Hybrid Rocket Fuels

Hybrid rocket engines are a promising technology for a variety of applications, but their use has been hindered in the past due to some disadvantages derived from the characteristic diffusive flame mechanism. However, most of these drawbacks can be solved through a correct design process. In particular, the recent discovery of the so-called liquefying fuels allows to obtain higher regression rates due to a different combustion mechanism. The liquid layer combustion process of paraffin-based fuels in combination with gaseous oxygen has been visualized with different optical techniques in a 2D single slab burner at both sub- and super-critical pressure conditions. Fuel slab configuration and composition and oxidizer mass flow rate have been varied to understand their influence on the phenomenon. In all the tests, the flame is characterized by a wave-like structure, whose frequencies and wavelengths are determined by using decomposition algorithms. At elevated operating pressures, the flame becomes unsteady and highly turbulent

The spatiotemporal coherence as an indicator of the stability in swirling flows

Combustion has played a key role in the development of human society; it has driven the evolution in the manufacturing processes, transportation, and it is used to produce the vast majority of the global energy consumed. The emission of pollutants from the combustion of fossil fuels in power plants lead to the development of advanced clean energy technologies, such as carbon capture and storage. Oxyfuel combustion is part of the carbon capture and storage techniques, and consists in the replacement of the air as oxidiser in the reaction with a mixture of oxygen and recycled flue gas, thus allowing a rich CO2 out-flow stream that can subsequently be compressed, transported and safely stored. The number of phenomena in combustion that are inherently dynamic impede the convention of a unique conception of flame stability. However, the quantification of the flow repeatability can produce insights on the efficiency of the process. This thesis presents the assessment of the stability in swirling flows through the calculation of their spatiotemporal coherence. The experimental data obtained from a 250 kWth combustor allows the assessment of the flame by means of spectral and oscillation severity analyses. A similar methodology is developed to analyse the data from large eddy simulations. The spectral analysis, the proper orthogonal decomposition and the dynamic mode decomposition have been employed to account for the temporal, spatial and spatiotemporal coherence of the flow, respectively. The spatiotemporal coherence is employed as a comprehensive term for the characterisation of the dynamic behaviour in the swirling flows and as a measurable indicator of the stability. This concept can be incorporated into the design of novel combustion technologies that will lead into a sustained reduction in pollutants and to the mitigation of the noxious effects associated to them

Fire performance of residential shipping containers designed with a shaft wall system

seven story building made of shipping containers is planned to be built in Barcelona, Spain. This study mainly aimed to evaluate the fire performance of one of these residential shipping containers whose walls and ceiling will have a shaft wall system installed. The default assembly consisted of three fire resistant gypsum boards for vertical panels and a mineral wool layer within the framing system. This work aimed to assess if system variants (e.g. less gypsum boards, no mineral wool layer) could still be adequate considering fire resistance purposes. To determine if steel temperatures would attain a predetermined temperature of 300-350ºC (a temperature value above which mechanical properties of steel start to change significantly) the temperature evolution within the shaft wall system and the corrugated steel profile of the container was analysed under different fire conditions. Diamonds simulator (v. 2020; Buildsoft) was used to perform the heat transfer analysis from the inside surface of the container (where the fire source was present) and within the shaft wall and the corrugated profile. To do so gas temperatures near the walls and the ceiling were required, so these temperatures were obtained from two sources: (1) The standard fire curve ISO834; (2) CFD simulations performed using the Fire Dynamics Simulator (FDS). Post-flashover fire scenarios were modelled in FDS taking into account the type of fuel present in residential buildings according to international standards. The results obtained indicate that temperatures lower than 350ºC were attained on the ribbed steel sheet under all the tested heat exposure conditions. When changing the assembly by removing the mineral wool layer, fire resistance was found to still be adequate. Therefore, under the tested conditions, the structural response of the containers would comply with fire protection standards, even in the case where insulation was reduced.Postprint (published version

On the prediction of combustion products and soot particles in compartment fires

In fire simulations, one of the most critical challenges is the incorporation of detailed chemical description for the combustion process where intermediate chemical products are formed through a series of elementary reactions. It is essential to apply a comprehensive reaction scheme that fully describes the oxidation processes of the parent fuel and the formation processes of major intermediate chemical species. A novel in-house fire field model based on Large Eddy Simulations (LES) approach incorporating fully coupled subgrid-scale (SGS) turbulence, combustion, soot formation and radiation models for the interactive and non-linear nature of the turbulent reacting flow in compartment fire phenomena has been developed in this dissertation. It uniquely embraces the detailed reaction mechanisms for the chemical processes involved during combustion. Since the modelling of hydrocarbons by-products are enabled when considering the full chemical profile, the formation of soot particles can be related to the concentration of main incipient such as acetylene, which provides an appropriate representation of nucleation, surface growth processes. Furthermore, two alternative SGS turbulence models: Vreman model (VM) and Wall-Adapting Local Eddy Viscosity model (WALEM) are incorporated and examined for compartment fire simulations. Parametric studies have been performed in two large-scale compartment fire tests. It is found that the turbulent Prandtl and Schmidt numbers of 0.3 respectively and the Smagorinsky constant of 0.2 should be applied to correctly model the flow and thermal diffusivities. Furthermore, temperature and velocity field predications accuracies are enhanced using WALEM, owing to the wall adaptive features and the consideration of both strain and rotational rates of the turbulent field. The importance of incorporating the detailed reaction mechanisms in compartment fire simulations has been confirmed by comparing with experiments. It is discovered that species concentrations especially CO2 and CO are more accurately predicted by the detailed scheme comparing to the multi-step scheme, since the formation of hydrocarbons and nitrogen oxides are considered. This also improves the replication of the flame structure as the fire is chemically-driven within the combustion zone. In addition, the evaluation of soot particle content is also enhanced with the consideration of acetylene as the precursor