Design fire curves for rail vehicles
IFAB produces CFD simulations for defining the design fire curves (HRR) for rail vehicles. Alternatively, experimental fire tests can be carried out, which is usually associated with significantly higher costs.
Detailed CFD models will be generated for the studied rail car type. The model is used to simulate specific fire scenarios in order to determine the heat release curve as function of time.
In order to allow for a simulation using CFD, the model has to be discretized; in this case using cuboid cells. The model is based on the detailed design with a sufficient resolution and is often based on a very small calculation grid.
Both outer structures and inner design are modelled in detail to simulate the fire development in a realistic fashion. Simplifications to the geometry or other discretisation sizes are leveraged to decrease computation time. The influence of said simplifications on the simulation result is individually and precisely evaluated in order to prevent a significant alteration of the results caused by discretisation failures.
Determination of material parameters
The accurate implementation of individual material properties and parameters is crucial in order to achieve good results. For this reason, material samples of the interior and exterior of the rail car have to be provided. These samples are tested in a cone calorimeter. The heat release rate as well as other parameters such as the heating value, ignition temperature and smoke production are determined with this procedure.
Determination of ignition position
The ignition position is crucial and can influence the fire behaviour significantly. Multiple ignition positions that are likely to produce different outcomes in regards to the fire spread behaviour, are determined and evaluated. The ignition source can represent a burning piece of luggage, which is positioned at different places, for example underneath a seat or in the gangway. The flame spread, smoke generation, temperature-, and pressure fields are used in order to assess the plausibility of the resulting design fire curves.
IFAB was contracted by the Berlin public transport system (BVG) to create a design fire curve for the metro vehicle types H and HK (large and small profile). This developed curve is used as a design fire curve for the smoke and evacuation simulations in all BVG stations in the future. The design fire curve is based on 4 different possible scenarios that all were simulated. The results of the most suitable scenario were chosen in order to create the final design curve.