Experimental study on flow and burning behaviors of pool fires under ventilation conditions inside an engine compartment

Despite the considerable body of work on pool fires taking place in confined and mechanically ventilated environments, there are still important uncertainties in our comprehension of such phenomena and in our ability to forecast their behavior. In this context, experiments are carried out to investigate the impact of airflow velocity on the flow and thermal characteristics of a heptane pool fire in a full-scale engine compartment of an industrial vehicle. The particle image velocimetry (PIV) technique is employed across several areas of interest to investigate the effect of airflow velocities (0, 1.6, 3.2, and 6.4 m/s) on the flow properties in the flame's neighborhood. An analysis of these zones can provide a representation of the global average velocity fields, which are not often documented in the existing literature for this type of enclosure. The burning characteristics, such as flame shape, mass loss, heat release rate, total heat flux, temperature profiles, and gaseous species concentrations, are investigated and compared among different ventilation conditions. The PIV results exhibit detailed flow structures around the flame in terms of direction and intensity. Vertical and horizontal velocity components are sensitive to changes in ventilation rate and the exhaust hood's position. Experimental findings reveal the formation of a large corner vortex at low velocity magnitudes. Thomas' predictions show reasonable agreement with flame height measurements compared to Heskestad's correlation. A high ventilation rate can lead to a significant increase in both heat release rate and total heat flux. Increasing ventilation rates results in a more significant temperature decrease in the intermittent zone compared to the continuous flame zone. A high ventilation speed of 6.4 m/s does not decrease O2 concentration as expected, possibly due to the fan's blowing effect and the dilution of fresh air with combustion product gases. This study enhances the physical understanding of fire behavior in ventilated engine compartments, leading to improved fire safety measures and the design of effective extinguishing systems.