Fuel Injection System for Improved Fuel Mixing and Distribution into Hypersonic Jet Engines

Injects Fuel into a Jet Engine's Airflow Upstream of the Combustion Chamber to Improve Fuel Modulation and Combustion Efficiency

This fuel injection system places a porous injection strut upstream from the combustion chamber inside of the inlet and/or isolator. This positioning improves fuel distribution throughout the flowpath during the flight regime, provides improved energy management during flight maneuvers, and achieves better fuel mixing, which leads to increased combustion efficiency.

Researchers at the University of Florida have developed a fuel injection system that increases the fuel residence time by injecting part of the fuel upstream of the combustion chamber, leading to better fuel and air mixing prior to its entrance into the combustion chamber. A porous strut extending across the engine’s inlet and/or the isolator improves mixing, providing greater control over fuel distribution throughout the entire flight regime of hypersonic aircraft. Porous injectors of this kind can also find a positive application with gas-turbine injectors in addition to this application for hypersonic propulsion using supersonic combustion.

Application

Fuel injection system for hypersonic jet engines that introduces fuel into the airflow inside of the inlet and/or the isolator to improve fuel mixing and provide greater control of fuel distribution at the combustion chamber entrance

Advantages

• Increases residence time of fuel in the airflow, improving quasi-premixed air/fuel conditions upstream of the combustion chamber
• Adds an additional location for fuel injection, improving the capability to modulate fuel injection along the flight path for better energy management
• Incorporates fuel injectors into the structural design of the propulsion system, reducing overall weight for reduced weight leading to improved performance
• Allows for a smaller combustion chamber as a result of improved fuel mixing, reducing system weight and thermal stresses to further enhance engine performance
• Injects fuel into the core of the airstream, avoiding the inlet walls to eliminate the risk of flashback

Technology

The primary component of this fuel injection system is a fuel injection strut extending between the opposing walls of the engine’s inlet and/or the isolator. A porous material which meets the thermal and structural requirements for fuel injection, such as the superalloy inconel, forms the surface of this strut. The strut injects fuel into the incoming airstream as it flows through the center of the porous surface thus maintaining the fuel away from the slow flow in the boundary layer formed along the walls. This eliminates the danger of “seeding” the boundary layer with a fuel-air mixture that might otherwise present the danger of upstream flame propagation. The strut has a porosity of 20 to 100 pores per square inch, depending on the vehicle mission design, thus providing a distributed fuel injection over a larger area in the core of the incoming airflow. Upstream injection coupled with the extended residence time leads to partially premixed fuel as it arrives at the combustion chamber. Structurally, the fuel-injection strut, or struts, depending on the engine cross-section design selection, is also temperature and corrosion resistant due to internal cooling by the injected fuel.