Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science in Aeronautics and Astronautics

Department

Aeronautics and Astronautics

Committee Chair

Robert P. Lucht

Committee Member 1

Paul E. Sojka

Committee Member 2

Jay P. Gore

Abstract

Alternative fuel is an area of combustion research gaining increased attention within the aviation industry. These fuels can provide many benefits over standard aviation fuels such as lower prices, supply diversity, and improved emissions. The current focus of alternative fuel research is on producing fuels similar to aviation standards, so that they can be implemented in existing infrastructure and gas turbine engines without significant modification to those systems. These fuels are known as ”drop–in” fuels, and undergo an extensive, costly certification process outlined in ASTM D4054–14 in order to be considered suitable for commercial use.

The National Jet Fuels Combustion Program (NJFCP) is conducting research to streamline the ASTM certification process through the use of standard laboratory tests and computer models to determine how the proposed alternative fuels will perform in gas turbine applications rather than costly combustor rig testing. Multiple areas of research are being performed in different areas of the program to accomplish this goal including an area focusing on the atomization of alternative fuels.

This study investigates alternative fuel blends and standard aviation fuels for the NJFCP at a variety of conditions using a hybrid airblast pressure–swirl atomizer to determine the spray characteristics of different fuels. This data is then provided to computer modelers at Stanford University as validation for their models. The sprays were investigated under conditions representative of lean blowout and cold start conditions of a gas turbine engine. For each of these conditions, the injection pressure differential (ΔPpilot) and pressure drop across the air swirler (ΔP/P) were varied to investigate their effect on the atomization of different fuels. Spray characteristics were measured using phase Doppler particle anemometry (PDA) at three locations downstream from the injector exit: 0.5 inch (12.7 mm), 1.0 inch (25.4 mm), and 1.5 inch (38.1 mm).

The study found that the ΔPpilot had no significant effect on the spray produced by the hybrid atomizer for any fuel. The swirler pressure drop ΔP/P was observed as having a significant effect on the spray. Increases in ΔP/P resulted in significant decreases in droplet size and increases in velocity magnitude throughout the spray for all fuels. Comparison of the fuels found that some differences occurred between the alternative fuels and the aviation standard fuels depending on the location within the spray and the operating conditions. Overall the standard and alternative fuels produced sprays similar to each other. Spray characteristics were obtained along multiple planes downstream of the injector exit. Comparison of the characteristics on these planes showed that the largest drops in the spray continue to spread radially outward as they travel further downstream from the injector exit. Secondary atomization was also investigated. It was found that, if secondary atomization occurs, it must be at a location closer to the exit of the injector than the 0.5 inch (12.7 mm) plane.

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