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This study investigated the influence of different rear bottom wall lengths on the blow-out limit, flame shape, flame mean length, and flame tilt angle of jet diffusion flames under cross-wind conditions. The experimental results reveal that the bottom wall had a significant effect on the flame blow-out limit. The flame blow-out velocity was maximum only when the front bottom wall existed, and all jet diffusion flames had similar blow-out velocity under the influence of the rear bottom wall. Once the length of the rear bottom exceeded a certain value, the jet diffusion flames were prone to lift-off. Moreover, the jet diffusion flames adhered to the bottom wall, which is attributed to the Coanda effect. The flame length significantly increased under the influence of the bottom wall. Additionally, under the influence of the front bottom wall, the flame length was maximum when the cross-wind velocity was higher. Under the influence of different rear bottom wall lengths, the flame tilt angle was divided into two variation regions. Among them, the flame tilt angle affected only by the front bottom wall was minimum. The flame tilt angle was maximum when the rear bottom wall length was 20 cm. Finally, the empirical formula of the jet diffusion flame tilt angle was obtained by analogy analysis and exhibited good correlation with the experimental data.

Four nozzle types were used to investigate the blow-out limit, flame shape, flame mean length, and flame tilt angle of jet diffusion flames under cross-wind conditions. The experimental results revealed that the nozzle geometry had a minor influence on the flame blow-out limit when the fuel jet velocity was low. As the fuel jet velocity increased, the nozzle geometry had a significant influence on the flame blow-out limit, the blow-out velocity of the triangle nozzle was the maximum, and the rectangular nozzle was minimum. The nozzle geometry had a significant influence on the down-wash and lift-off of the flame under cross-wind conditions. The triangle nozzle was prone to the appearance of the down-wash phenomenon, and the rectangular nozzle flame easily exhibited the lift-off phenomenon. Additionally, the effect of the nozzle geometry on the flame blow-out limit and flame shape was explained from a moment of inertia viewpoint. The flame length of the rectangular and cross nozzles monotonously increased with the increase of the momentum flux ratio of the fuel jet to the cross-wind. However, two growth curves occurred as the flame length of the circle and triangle nozzles increased with the momentum flux ratio of the fuel jet to the cross-wind. Additionally, for the jet diffusion flames under cross-wind conditions, the nozzle geometry exerted a smaller effect on the flame tilt angle.