General Electric has been working on a Pulse Detonation Engine combined with a turbine section to create a hybrid that may produce a fuel savings of 5% or more.
Pulse detonation engines are powered by exploding fuel which then exit the detonation tubes as exhaust producing thrust. The advantage is that this allows the engine to harness the power of the detonation of the fuel and the large pressure increase that occurs with it, rather then the less energetic combustion, or burning, of the fuel.
This type of engine differs from the pulse jet, used on the German V-1 in WWII, is that unlike the pulse-jet, whose exhaust exits the tube sub-soniclly, the PDE creates a supersonic explosion, which consumes the fuel more efficiently. For comparison, the compression ratio of a pulse-jet is around 2:1, while the PDE typically achieves a 100:1 ratio, resulting in a huge increase in efficiency.
Long-EZ PDE Demonstrator
In 2008, the Air Force Research Laboratory and Innovative Scientific Solutions, Inc., flew a 4 tube pure PDE in a converted Rutan Long-EZ. The aircraft’s takeoff was rocket assisted to improve margin but the engine’s 200lbs of thrust provided more than enough power to keep the plane aloft.
GE is taking the concept a step further by using the result of the detonation, the exhaust, and coupling it with a more traditional turbine section. The intent is to simplify the internal components of the engine, while making the engine lighter as well as retaining or increasing the efficiency. GE is currently using ethylene as the fuel, but will focus on using kerosene or jet fuel in the future. The company, though, admits that the technology is still 10-15 years away from being produced for commercial applications.