Combustion of a Train in Tunnel: Rosseland Radiation

Rosseland Radiation Model, Combustion of Train in Tunnel

Description

This project simulates the combustion of a train within a tunnel environment using ANSYS Fluent, focusing on the resulting radiation heat transfer captured through the Rosseland radiation model — a method specifically suited to optically thick media such as the dense combustion products generated in this confined-space fire scenario.

The 3D geometry represents the tunnel interior with the train positioned inside, meshed using an unstructured grid totaling 372,705 cells.

Methodology

Combustion was modeled using the Species Transport model with a volume-based reaction definition representing diesel-air combustion. Radiation heat transfer was captured using the Rosseland approximation, a simplified form derived from the P-1 radiation model that becomes appropriate once the optical thickness of the medium exceeds approximately 3 — a condition well-suited to the soot- and combustion-product-laden atmosphere generated by a train fire within an enclosed tunnel.

Boundary conditions were configured to represent fuel leakage and its interaction with the surrounding air, coupling the combustion source with the broader tunnel airflow.

Conclusion

Results include detailed contours of temperature distribution, velocity fields, radiative heat flux, and mass fractions of fuel, carbon dioxide, oxygen, and water vapor. Together, these results characterize how combustion and radiation heat transfer interact within the confined tunnel geometry, illustrating how the Rosseland approximation captures radiative heat exchange through the optically thick combustion products generated by the fire.

These results are directly relevant to tunnel and railway fire safety assessments, offering insight into thermal and radiative conditions during a train fire event that can inform tunnel safety design, ventilation strategy, and emergency response planning.