M.Sc Thesis

M.Sc StudentMarcovici Dafna
SubjectThe Influence of Injector's Configuration on the Fuel Spray
Quality During Start Up in Jet Engines
DepartmentDepartment of Aerospace Engineering
Supervisor PROFESSOR EMERITUS Yeshayahou Levy
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Following a configuration change of IAF's F110 engines, fire-balls had been seen during start-up in several engines. The configuration change included replacements of several engine components, including fuel atomizers (The new configuration contains 20 type C atomizers, the original configuration contains 16 type A atomizers and 4 type B atomizers on both sides of the ignitors).

In order to prevent the fire-balls appearance, it was chosen to replace the new fuel atomizers with the original configuration (16 A and 4 B atomizers).

This work included an assessment of the effect of fuel spray characteristics on the appearance of fire-balls during engine start-up, as well as detailed examination of the spray process in different atomizers and its effect on the characteristics and quality of fuel spray.

In this work two experiments were performed in order to characterize the fuel spray in each type of atomizer - one to identify the pressure at which the atomizers transition from primary spray to secondary spray; and another to examine each atomizer's spray characteristics and compare the performance of the atomizers. 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 configuration of atomizers (20 C atomizers) provides inferior fuel spray characteristics compared to the original configuration (16 A and 4 B atomizers). The results showed better diameter distribution and velocity in the original fuel atomizers. Moreover, it was seen that the original pilot atomizers provide a "hollow cone" type of spray while the other types of atomizers provide mass flux mostly at the center of the spray.

The results showed that the original configuration of atomizers, provides a better fuel spray that would allow for better combustion of the droplets and, as a result, a better combustion of the entire spray. Furthermore, it was found that the fuel spray provided by the new configuration would probably make 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.

Additionally, a study was performed of all other changes that were done in the new engine configuration and their potential effect on the appearance of the fire-balls. One of the changes reviewed is the replacement of the Low Pressure Turbine shaft which is heavier in the new engine configuration. The different shaft could possibly influence the moment of inertia and therefore influence its acceleration and consequently the fuel supply and the fuel-air ratio in the combustor.

In conclusion, this work focused on the replacement of the fuel atomizers and the results showed 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.