Concentric elliptical jet diffusion flames with co- and cross-flows

摘要

The characteristics of concentric elliptical jet diffusion flames were addressed with co- and cross-flow streams for pollution reduction and more flexible industrial firing. The peak turbulent kinetic energy was maximized at the major axis tips to pronounce increased jet entrainment by 478% in comparison to concentric circular jets. Aided by a fuel jet Schmidt number less than 1.0, increasing the outer to inner velocity ratio to 1.6 recorded peak NOx emissions of 24. ppm. Increasing the aspect ratio from 1.5 to 3.3 nearly duplicated the peak turbulent kinetic energy and pronounced 9% increase in the combustion efficiency with 25% HC reduction. As dominated by the peak turbulent energy merging, the optimum angular positioning of the two jets was 35° for higher inner jet velocity. For lower inner jet velocity, the best angular positioning was 45° and 30° for higher and lower inner aspect ratio, respectively. By introducing radially opposing air jets, the optimum angular positioning decreased to 25° as the flame was shortened by 43%. The opposing flow increased the elliptical jet peak turbulent energy to 25 times, while the stability limits were extended by 45%. The multi-stage air cross-flow revealed more aerodynamic features. Using less number of stages and increasing the cross-flow admission distance to 20. cm at increased cross-flow percent to 70% minimized the average HC and NOx emissions to 0.15% and 10. ppm, respectively. The optimum performance was thus found when lifted flame premixing features were coupled with the impinging cross-flow stabilizing effects.