Shall we fly into orbit with an impact ram? Credit: NASA / Daniel Rosato / UCF.
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Aircraft and spacecraft developers are appealing for new types of propulsion that will ensure very fast flights, both in the atmosphere and from Earth to orbit and back, without additional rocket stages. Promising in this respect is the drive, which relies on a continuous sequence of detonations. This surprisingly simple drive is hidden under a number of notable names. Probably the simplest to be called a “shock-ramjet engine”. Another option is the Shock-Induced Combustion Ramjet Engine, or Shcramjet or possibly the Oblique Detonation Wave Engine (ODWE) or also the Standing Oblique Detonation Ramjet (Sodramjet).
So far, it has been practically just a theory. The team of the American University of Central Florida recently committed an explosive experiment, which fundamentally opens the way to the development of technology and propulsion of an impact or detonation ramjet.
Detonation is a violent burning in which a shock (in this case also a detonation) wave propagates at supersonic speeds, as we have all had the opportunity to see, for example, during an extreme detonation last year in Beirut. And as was clearly seen, the detonation carries a tremendous amount of energy. It would be great to handcuff her to the propulsion of an airplane or spacecraft. The problem, however, is that detonations are inherently quite unmanageable.
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Logo. Kredit: University of Central Florida.
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Kareem Ahmed and his colleagues took a significant step towards the implementation of the shock ramjet. They set up an experiment that allowed them to tame the detonation. They were able to keep the detonation of the air-hydrogen mixture in a fixed form for a few seconds. This could become the basis for a future impact frame. As Ahmed says, their goal is to “freeze” the detonation in space and use its energy to drive as much as possible. If we can do that, we will fly ultra-fast.
Ahmed’s team’s experiment represents a breakthrough after decades of theoretical research into this type of drive. The shock drive works by flowing a mixture of fuel and air at a hypersonic speed. This creates shock waves, which quickly heat the mixture of fuel and air and thus ignite its detonation, during which they fly out of the engine at high flue gas velocity. The result of all this is a powerful drive thrust.
Scheme of experimental shock frame. Credit: University of Central Florida.
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Detonations of the fuel-air mixture ensure that this drive is extremely efficient. Almost one hundred percent. The impact ram could theoretically reach speeds around Mach 17. That should be enough to get the machine with this drive from the surface to orbit without the need to start on the rocket stage.
After the experiment of Ahmed et al. further drive development may follow. They will tune the fuel mixture, the velocity of the air in the propulsion, and the geometry of the propulsion to best stabilize the detonations and use them to create thrust. Ahmed makes no secret of the fact that after their success it will be more of a technical problem. Over time, the viability of the shock ramjet will become apparent.
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