Detonation is chaotic and much harder to control

Wednesday, May 27th, 2020

A type of rocket engine once thought impossible has just been fired up in the lab:

Engineers have built and successfully tested what is known as a rotating detonation engine, which generates thrust via a self-sustaining wave of detonations that travel around a circular channel.

As this engine requires far less fuel than the combustion engines currently used to power rockets, it could eventually mean a more efficient and much lighter means of getting our ships into space.

“The study presents, for the first time, experimental evidence of a safe and functioning hydrogen and oxygen propellant detonation in a rotating detonation rocket engine,” said aerospace engineer Kareem Ahmed of the University of Central Florida.

The idea of the rotating detonation engine goes back to the 1950s. It consists of a ring-shaped — annular — thrust chamber created by two cylinders of different diameters stacked inside one another, creating a gap in between.

Gas fuel and oxidiser are then injected into this chamber through small holes and ignited. This creates the first detonation, which produces a supersonic shockwave that bounces around the chamber. That shockwave ignites the next detonation, which ignites the next, and so forth, producing an ongoing supersonic shockwave to generate thrust.

This should produce more energy for less fuel compared to combustion, which is why the US Military is investigating and funding it; this new research was funded by the US Air Force, and it’s not the only such project the military are looking into.

In practice, however, there’s a reason rockets are generally powered by internal combustion instead, in which the fuel and oxidiser are mixed to produce a slower, controlled reaction to generate thrust.

Detonation is chaotic and much harder to control. In order for the whole thing to not blow up — very literally — in your face, everything needs to be precisely calibrated.

(Hat tip to Hans Schantz.)


  1. Kirk says:

    It’s all well and good until you lose control of the process. After that, well… Yeah.

    The border between detonation and deflagration still isn’t well-understood or entirely predictable, to this day, even when discussing supposedly well-understood phenomenon like small arms propellants. You spend an hour or two dealing with the things that the typical Quality Assurance Specialist Ammunition Surveillance tech type does, and you’ll soon gain a hell of a lot of humility.

    I don’t doubt that the guys working this field can make it work, but I think we’re a long, long way from seeing actual effective engines based on this principal anywhere in the near future. I’d lay odds that they don’t perfect this until well after conventional rocket engines are replaced by something like those nifty “magic” mass drivers, or some other technology we don’t have a clue about.

    Conventional rocket engine just runs. These things require extensive management, control, and perfect awareness of what’s going on in the motor. It’s like the difference between what Ford put into a Model T, and what Ford today is putting into a pickup truck. I don’t see this getting fielded during the current technical generation.

    Whole thing reminds me of the aerospike engines–Yeah, they work, they’re technically way more sophisticated and efficient, but are they buildable and economic?

    The traditional rocket motors may well be the QWERTY keyboards of aerospace technology, and anything trying to supplant them is going to fail simply because they have the established installed base in the technologic ecology.

  2. Harry Jones says:

    No numbers here — no specific impulse, no thrust-to-mass ratio. I smell hype.

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