Abstract
Characteristics of lifted flames in nonpremixed jets were studied experimentally with emphasis on the effects of the entrained flow field which was varied by placing a plate near the nozzle and by confining the jet. Results show that lifted flame behavior in a confined jet is drastically different: from that of a free jet. In the confined jet, the liftoff height is linearly proportional to the nozzle diameter and the flow velocity, while the liftoff height is independent of the nozzle diameter in the free jet. The ratio of the liftoff height at blowout to the nozzle diameter maintains a near-constant Value of 50 for both the free and confined jets. The blowout velocity is linearly proportional to the nozzle diameter in the free jet, whereas it is independent of the nozzle diameter in the confined jet. The jet Velocity at liftoff maintains a near-constant value for the free jet, while the liftoff velocity decreases with the increase in the nozzle diameter for the confined jet. The blockage effect of the plate near the non;le exit systematically reduces the liftoff height and a criterion is proposed to include such an effect in interpreting liftoff behavior.