On display at the USAF Museum (in the experimental plane annex…. ya gotta take a bus) is the Air Force Research Lab/Innovative Science Solitions Inc. “Borealis,” a Scaled Composites Long-EZ kit plane with substantial modifications. The propellor and associated propulsion system were replaced with an experimental pulse detonation engine, necessitating substnatiall changes to the airframe, including the massive bulge visible on the underside. PDE’s work by spraying small puffs of fuel into an air-filled tube and detonating them, rather than simply burning the mix. In principle this leads to simpler engines with greater fuel savings compared to conventional turbojets. So far, though, the engines look to be pretty damned heavy.
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2 Responses to “Pulse Detonation Engine testbed: “Borealis””
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Looking at the length of the pipes on the back and my knowledge of pipe organs my guess as to the frequency of the pulses was about 100 to 120 hertz. Wikipedia says the engine ran at 80 hertz. Dunno if those tubes need to be tuned to the frequency of the pulses, but it kind of makes sense.
I’d love to see some more shots of the plumbing of the engine. It looks like a simple 4 cylinder DOHC heads connected to the exhaust tubes. Seems pretty straight forward. There would be four valves per exhaust tube. I wonder if they all close or open at the same time or in sequence. If they are timed to all open at once, that would have them operating at 4800 RPM which is probably about the max those automotive valves and heads could manage (equivalent to a car engine running at 9600 RPM).
If valves are opening in sequence it would be equivalent to the car engine bopping along at 2400 RPM. Given that Goldbergian belt drive assembly slower is perhaps more reasonable.
1st time I’ve seen close-up pics of a working PDE, cool 🙂
I expect in about 10-15 years, these may show up at Oshkosh / EAA.