Following a configuration change of F110 engines in the IAF, fire balls had been seen during start-up in several engines. In the new configuration several components are replaced, including fuel nozzles (20 similar nozzles).
In order to prevent the fire balls appearance, it was chosen to replace the new fuel nozzles with the original nozzles configuration (16 standard nozzles and 4 pilot nozzles on both sides of the ignitors).
This work included assessment of the effect of the fuel spray characteristics on the appearance of fire balls during engine start-up as well as detailed examination of the spray process in the different nozzles and its effect on the characteristics and quality of fuel spray in jet engines. In this work experiments were performed in order to characterize the fuel spray in each type of nozzle. In addition, an analysis of the experimental results was done in order to identify a link between the different fuel spray characteristics and the appearance of fire balls.
The experimental results and analysis had shown that the new nozzles configuration provide inferior fuel spray characteristics comparing the old nozzles. The results showed better diameter distribution and velocity in the original fuel nozzles. Moreover, it was seen that the original pilot nozzle provides a “hollow cone” type of spray while the other types of nozzles provide mass flux mostly at the center of the spray.
The results showed that the original nozzles configuration, where pilot nozzles are located on both sides of the ignitors, provides a better fuel spray that allows for better combustion of the fuel droplets and as a result for better combustion of the entire spray. Furthermore, it was found that the fuel spray provided by the new nozzles configuration makes it harder for the combustion to consume all the fuel in the combustion case and therefore represents, in high probability, a potential cause for the appearance of fire balls in the engines.
Additionally, a review was done of all other changes that were done in the new engine configuration and their effect on appearance of fire balls. This work has focused on the replacement of the fuel nozzles and it was found that the original configuration allows for better combustion. However, it would seem that the fire balls appeared due to the combination of several changes in the engine, Therefore, further investigation is needed in order to explore the combined influence of the changes done in the engine on the fire balls appearance.
