There are many benefits to tunnels, but they can also be dangerous. One of these is the chance of tunnel fires. As technology for building tubes improves and more people move into cities, the number of tunnels in China is growing quickly. The CFD methods are substituted with upmarket experimental methods in this field. This is why, on account of the reference paper entitled “ Extended CFD models for numerical simulation of tunnel fire under natural ventilation: Comparative analysis and experimental verification”, the present CFD study is conducted.

Simulation Process

The model geometry is primarily created using Design Modeler. By taking proper blocking inside ICEM meshing software, a structured grid is performed. The tunnel was 9.0 m long, 0.6 m, 3 wide and 0.45 m high with a rectangular cross-section. The fire source was located in the center of the tunnel. A square ethanol pool fire with a side length of 0.2 m was used to simulate the fire source. The fuel thickness was maintained at 5 cm before ignition.
The combustion rate calculation method figures out the real rate of a chemical process. It uses the Eddy Dissipation model (ED). The chemical reaction can be described by Species Transport Module as:

C2H5OH(l) + 3(O2 + 3.76N2) == 2CO2 + 3H2O(g) + 11.28N2

As a simplification, air is ideally considered as oxygen.

Post-Processing

With appropriate approximation, the chemical reaction is simplified to:

C2H5OH(l) + 3(O2) == 2CO2 + 3H2O(g)

The c2H5OH reacts as it mixes with oxygen existing in the tunnel. This leads to a massive explosion that produces carbon dioxide and water vapor in the tunnel. The temperature rapidly increases in the tunnel, in some areas it reaches even 2000K. However, the pressure gradient hastens the transmission of hot air through outlets.