Effect of Fuel Nozzle Geometry on the Stability of a Turbulent Jet Methane Flame

The effect of asymmetric fuel nozzles on the stability of turbulent jet methane flame discharging into still air is investigated experimentally. The emphasis of this study is however, more on the flame liftoff height and velocity, as well as reattachment and blowout velocities. Five nozzles; a pipe, a contracted circular, a triangular, a rectangular and a square, which all have an equivalent diameter of approximately 4.50 mm, are tested. The experimental results reveal that asymmetric nozzles reduces the jet flame liftoff height, and hence stabilizes the flame base closer to the nozzle compared with conventional circular nozzles. This finding correlates well with the entrainment rate of the corresponding non-reacting jets. That is, the flame liftoff height decreases as the jet entrainment increases. Furthermore, the asymmetric nozzles are found to significantly influence the blowout, liftoff and reattachment velocities. The blowout is believed to be primarily governed by the far-field local mixing rate.