Intermittent flame lengths of buoyant jet flames in reduced and normal pressures: Experiments and theoretical analysis

Quantifying the intermittent flame length scale of buoyant jets is valuable for the understanding of the physical mechanisms of flame stabilization, risk assessment of fuel leakage fire in storage facilities, as well as the practical design of effective industrial burners. In this work, experimental studies are conducted to study the intermittent flame lengths in both reduced (0.64 atm) and normal (1.0 atm) pressures. The intermittent flame lengths are quantified by flame probability contours of propane flame using five nozzles with different diameters ranging from 4 to 10 mm with different heat release rates ranging from 4.31 kW to 49.52 kW. The intermittent flame lengths are found to be positively related to the heat release rate Q˙ and nozzle diameter d. Besides, results show that lower ambient pressure can bring about significantly higher intermittent flame lengths as compared with the results obtained in normal pressure. Moreover, based on physical analysis of the flow character of unburned fuel pressure dependence of flame length scale, a general model coupling with Froude number and nozzle diameter (d) and pressure effect (P∞/1.0atm)2/3 is established as Δlf/d(P∞/1.0atm)2/3=C1Frm−0.4(2−C2Frm−0.6) for the quantification of the intermittent flame lengths in both pressures. And the correlating results show that all the data in both pressures and those from previous literature can be well normalized with a satisfactory agreement. The current work can provide some supplemental knowledge on flame instability in the reduced pressure environment, a scientific evaluation model of fire length scale in fire safety strategies in fuel storage facility leakage cases, and good data reference for CFD validation.