Ventilation effects in confined and mechanically ventilated fires

• A reduced-scale enclosure is designed using a Froude scaling law.
• Heptane and dodecane pool fires are performed in this enclosure.
• Influence of ventilation on the heat release rate is investigated.
• Different cases can be distinguished according to oxygen concentration.

The main objective of this work is to study underventilated and highly underventilated fires in a compartment equipped with a mechanical ventilation network. Heptane and dodecane pool fire experiments are performed in a reduced-scale room. A changing-scale analysis is performed in order to obtain species concentrations and temperature levels at a larger scale. Carbon dioxide concentration increases linearly with the decreasing of oxygen concentration. Heat release rate depends on ventilation condition in the compartment and we can distinguish three cases. The first one corresponds to sufficiently ventilated fires, where heat release rate is higher or equal to the one of an open fire and where the reaction is almost complete. The second one includes underventilated fires for oxygen concentration ranging between the Minimum Oxygen Concentration of the given fuel and around 7% (this value corresponds to the Minimum Oxygen Concentration of carbon monoxide). At this percentage of oxygen, the Heat Release Rate is lower than the one of an open fire and the carbon monoxide production is proportional to oxygen concentration. The third one corresponds to very underventilated fires for oxygen concentration lower than 7%, and where the fire can stop due to a lack of oxygen. In this case, carbon monoxide concentration increases strongly with the decrease of oxygen concentration.