Fire and Smoke in a Factory Building

Description

This project simulates the combustion reaction — fire and smoke — arising from a leaking pressure tank in a factory using ANSYS Fluent. The factory is modeled as a computational domain containing several elements such as tanks, plates, and boxes. A cylindrical pressurized tank develops a leak, releasing flammable methane gas into the surrounding environment; the contact of this methane with the free ambient air then leads to a combustion reaction.

The aim of the project is to investigate the behavior of the combustion flame and the path of smoke emission over time, so the simulation is carried out in a time-dependent (transient) manner.

The study proceeds in two steps. The first step examines only the leakage of methane from inside the tank into the surrounding space, with methane released gradually over time. The second step allows this leaked gas to react with the air and ignite, producing flame and smoke (carbon dioxide) through the combustion reaction. In the first step there is no need to define a chemical reaction — only air and methane are present, without reaction. Both the factory air and the methane inside the tank are under pressure; a groove at the top of the tank serves as the leakage point, and assigning a higher initial pressure to the methane drives its release into the outer environment. Once the release has fully developed, the combustion reaction between methane and the free air is defined using stoichiometric coefficients, with methane and oxygen as reactants and carbon dioxide and water vapor as products. A spark is also defined at the groove section of the tank to initiate combustion.

The geometry was created as a 3D model in Design Modeler, and meshing was performed in ANSYS Meshing using an unstructured grid of 124,162 cells.

Methodology

The viscous model used is RNG k-epsilon with standard wall functions. The solver is transient, and the energy equation is enabled to capture the temperature field. The Species Transport model is used to simulate the combustion reaction.

Conclusion

After the simulation, the behavior of the reactants and reaction products was examined. To study the flame, an iso-surface at a constant temperature was used, with the flame temperature taken as the measure representing the flame's extent. To investigate the smoke produced by combustion, the behavior of carbon dioxide — defined as a product of the reaction — was examined, using its mass fraction as the iso-surface measure. Similarly, the leaked methane was tracked using its mass fraction as an iso-surface measure. Methane leakage before combustion, and the flame and carbon dioxide emission after combustion, were all studied at different time instants and presented as animations.

In the first step, the results clearly capture the leakage process: methane first fills the pressurized tank, then, once the leak occurs, escapes into the surrounding environment at high pressure. In the second step, the results show the onset of the combustion reaction. The temperature rises sharply as a result of the explosion; the flame grows at the start of combustion and then gradually fades over time. Carbon dioxide is produced throughout the space, confirming that combustion has taken place, since this gas is the product of the reaction — it too erupts at the moment of ignition and diminishes in volume as time progresses.