General Electric has taken the wraps off its research into pulse-detonation engines (PDE), which it believes could replace the turbomachinery cores in jet engines. The company sees potential for a 5-15% improvement in fuel burn, but acknowledges hybrid PDE-turbine aero-engines are still decades away.
A PDE is a pulsejet in which the fuel-air mix is burned through supersonic detonation rather than subsonic deflagration, allowing more energy to be added more efficiently. There are almost no moving parts, and an array of tubes would replace the high-pressure compressor, combustor and high-pressure turbine at the core of a jet engine.
GE's three-tube experimental PDE © GE Global Research Center
GE's Global Research Center in Nisakyuna, New York is preparing to mate its experimental three-tube PDE to a small turbine to see how effectively the axial turbine extracts power from the rapid pulses. Each of the tubes fires 20 times a second, sequenced to provide a 60Hz firing rate. The PDE will be mated to a 130mm (5in) diameter turbine and dynamometer for testing.
The supersonic detonation shockwave produces a pressure rise in the tube, "which is good, because we expand from higher pressure in the turbine and extract more work from the turbine", says Narendra Josh, technology lead for advanced propulsion systems. Testing will determine how much power the turbine can extract from the pulses produced by the PDE.
GE has already demonstrated the first multi-tube PDE-turbine engine under contract to NASA, says Josh. This had eight tubes in a can-annular arrangement integrated with a 1,000shp (750kW) single-stage axial turbine from a railway engine turbocharger. The hybrid engine produced 750shp for a short duration, 350shp for a longer duration and ran for a total of 144min, he says.
Initial testing is using ethylene as the fuel, but GE is focusing its research on diesel and jet fuel for aviation applications. Efforts are also under way to reduce the "deflagration-to-detonation time" so that the tubes can be shortened to reduce weight and increase the PDE's firing frequency.
According to Tony Dean, manager of the research centre's propulsion systems lab, GE believes pulse-detonation cores could be used in aero-derivative industrial gas turbines like its CF6-based LM2500 within 10 years, allowing it to gain operating experience before using the engines in aviation applications. A PDE-turbine hybrid could power and aircraft within 20 years, he says.
Source: Flight International
