Pulse detonation engines (PDE) can achieve a maximum of 50% efficiency verus 30% for conventional jet engines Pratt & Whitney and General Electric now have active PDE research programs in an attempt to commercialize the designs with high pulse rates of 50-100 times per second to allow for less vibration. Some of the top scientists and engineers in the field say that with the right economic incentives and a few well-placed technology leaps, they could get to a flight-ready system in five years. (Air and Space magazine sept 2007). They are 3 to 4 on the technology readiness scale (working in the lab).
The pace of current research and development points the way to three phases of pulse detonation engine technology, each a bit more complex than the one preceding it.
The first phase could be called the “pure PDE”: Essentially it focuses on developing the detonation tube, which would power a very-high-speed, air-breathing missile. In this application, engineers and scientists can punt on two of the biggest technology problems—life, or the durability of the system, and noise. The missile has to fly only once, so long life for the metals or components is not a concern. And at the high speeds—around Mach 6—and altitudes in which the missile would operate, less noise is also moot. This is the area in which Adroit Systems, and later Pratt & Whitney, made the most strides. It was their machine that would have been flown on NASA’s F-15B.
The next phase could involve using pulse detonation engines to address another pressing issue in combustion: afterburners for fighter aircraft. Today’s fighter engines simply spray aerosolized fuel into a long tube aft of the turbine section, literally dumping extra fuel-air mixture into the hot gas stream for a brief extra kick of speed. Engineers think that if they add pulse detonation technology to a low-bypass-ratio turbine engine—the modern fighter jet engine—they can get the efficiency benefit of pressurized, shockwave combustion. It’s relatively simple because the pulse detonation tube would be at the end of the engine and not in the middle of the turbo-machinery. Here again, life and noise are less of an issue than they might be in a commercial aircraft. Fighter pilots only fly on afterburner about five percent of the time, and anyone who has seen an airshow knows fighter jocks usually don’t worry about making a racket.
The third phase is where it gets most complicated, but is the one that may offer the biggest payoff: pulse detonation in the middle of the engine. Having a compressor upstream and a turbine downstream, says GE’s Dean, is a potential high-value payoff that keeps his company attracted to PDE development. A PDE-based combustor is one of the main areas of work for a young researcher on Dean’s team named Adam Rasheed. Rasheed is chronicling his work on a publicly available blog, “From Edison’s Desk” (www.grcblog.com). The publicity seems to have done him some good: The Massachusetts Institute of Technology’s Technology Review magazine in 2005 named Rasheed one of under the age of 35.
Like everyone else, Rasheed has his eyes on a jet engine that burns five percent less fuel—an enormous leap compared with today’s fuel-saving techniques. In a world in which efficiency improvements of even 0.2 percent are considered a major breakthrough, “PDEs represent a possible game-changing technology that could revolutionize aerospace propulsion,” Rasheed writes. Even a one percent improvement would save hundreds of millions of dollars in fuel.the world’s top 35 researchers