Study on the impact of ventilation on heat release rates of propane fires in tunnels

The heat release rates (HRRs) in fire experiments with gaseous fuels in tunnels were generally determined by the product of supplying fuel rates and their heat of combustion with the assumption that gaseous fuels could combust completely irrespective of ventilation conditions. In this paper, systematic calibration of the HRRs of propane fires at varying ventilation conditions in a tunnel was conducted by using the oxygen consumption method. Firstly, the HRRs of propane fires were calibrated in open space and the calibrated values agreed well with the theoretical ones. Then, a series of fire experiments were conducted in a 1:20 reduced-scale tunnel. The supplying fuel rates varied from 2.0 l/min to 27.7 l/min, corresponding to theoretical HRRs of 2.8 kW to 39.1 kW, at ventilation velocities from 0.01 m/s to 2.27 m/s. The results showed that the ventilation velocities have a marked impact on the HRRs of propane gas fires. The HRRs for a flow rate of 11.9 l/min at velocities of 0.74, 0.19 and 0.06 m/s were around 19.4, 15.3 and 5.9 kW respectively. At a velocity of 0.06 m/s, the HRR was around 30% of the HRR in open space. The HRRs increased with velocity at low ventilation velocities and they were independent of ventilation velocity at higher ventilation velocities, An outer envelope of HRRs given by an empirical equation, which represented the achievable maximum HRRs at given velocities, was proposed for propane fires. The applicability of using a fuel-to-air equivalence ratio to represent the status of ventilation conditions for gaseous combustion was discussed.