Abstract
The stability limits of a jet flame can play an important role in the design of burners and combustors. This study details an experiment conducted to determine the liftoff and blowout velocities of oblique-angle methane jet flames under various air coflow velocities. A nozzle was mounted on a telescoping boom to allow for an adjustable burner angle relative to a vertical coflow. Twenty-four flow configurations were established using six burner nozzle angles and four coflow velocities. Measurements of the fuel supply velocity during liftoff and blowout were compared against two parameters: nozzle angle and coflow velocity. The resulting correlations indicated that flames at more oblique angles have a greater upper stability limit and were more resistant to changes in coflow velocity. This behavior occurs due to a lower effective coflow velocity at angles more oblique to the coflow direction. Additionally, stability limits were determined for flames in crossflow and mild counterflow configurations, and a relationship between the liftoff and blowout velocities was observed. For flames in crossflow and counterflow, the stability limits are higher. Further studies may include more angle and coflow combinations, as well as the effect of diluents or different fuel types.
Highlights
A multitude of studies have been performed on lifted jet flames and their behavior in various air flow configurations
Liftoff and blowout jet velocities were measured under four ambient flow velocities: 0, 0.25, 0.4, and 0.6 m/s. (Note: the velocity of 0.25 was chosen due to physical limitations of the blower motor.) twenty-four flow configurations are established
Based on the results obtained from this experiment, a number of conclusions may be drawn regarding the stability of oblique jet flames in coflow
Summary
A multitude of studies have been performed on lifted jet flames and their behavior in various air flow configurations. Their results confirmed the theory proposed by Vanquickenborne and van Tiggelen: blowout occurs when the local flow velocity exceeds the turbulent burning speed of the flame They investigated the role of large-scale eddies, concluding that they are responsible for flame propagation in the interior of the jet. By measuring the jet velocity at which blowout occurs (at the lower limit), Kalghatgi concluded that jet flames are less prone to blowout as the burner angle increases from 0◦ to 180◦ He discovered that the lower blowout limit does not always exist under low wind speeds. Hasselbrink and Mungal performed a similar study in which the velocity fields of transverse (0◦) jet flames were measured using PIV [13] Overall, they noted greater flame/flow interaction near the base of the lifted flame than at downstream locations. By consolidating the overall results, an optimal burner configuration may be chosen based on desired stability and blowout parameters, as well as a relationship between the flame liftoff velocity and blowout
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