Flame heights of line-source buoyant turbulent non-premixed jets with air entrainment constraint by two parallel side walls

- Line-source slot burner buoyant turbulent non-premixed jets.
- Air entrainment and flame height with two parallel side walls clarified.
- Critical wall distance correlated by free flame height.
- A non-dimensional correlation proposed for flame height at various wall distances.

This paper investigates the flame height of line-source buoyant turbulent non-premixed jets with air entrainment constraint by two parallel side walls at various separation distances. Laboratory-scale experiments are carried out by employing two line-source nozzles (2 mm × 142.5 mm and 2 mm × 217 mm) using propane as fuel. The nozzles are arranged with two kinds of orientations relative to the side walls, i.e. with its longer or shorter side perpendicular to the side wall. The flame heights are measured for various fuel supply exit velocities and side walls separation distances. Results show that the flame height changes little with side walls separation distance when the longer side of the nozzle is perpendicular to the side walls; meanwhile decreases with increase in side walls separation distance and finally approaches the value of a free jet after the separation distance beyond a critical value when the shorter side of the nozzle is perpendicular to the side walls. This confirms the physics that the air entrainment into the buoyant turbulent non-premixed jets for such line-source nozzle is mostly from the longer side; meanwhile rarely from the shorter side. The air entrainment per height is reduced hence the flame height increases with decrease in side walls separation distance when the shorter side of the nozzle is perpendicular to the side walls. The critical side walls separation distance normalized by the nozzle width is found to be linear function of the non-dimensional fuel exit velocity normalized by the buoyancy induced air entrainment velocity using the flame height of the free jet as characteristic length. Finally, a non-dimensional correlation is proposed to characterize the flame heights for various side walls separation distances when the shorter side of the line-source nozzle is perpendicular to the side walls.