The Air Multiplier Fan Principle, Applied To A Jet Engine

Many readers will be familiar with the Dyson Air Multiplier, an ingenious bladeless fan design in which a compressor pushes jets of air from the inside edge of a large ring. This fast-moving air draws the surrounding air through the ring, giving the effect of a large conventional fan without any visible moving parts and in a small package. It’s left to [Integza] to take this idea and see it as the compressor for a jet engine, and though the prototype you see in the video below is fragile and prone to melting, it shows some promise.

His design copies the layout of a Dyson with the compressor underneath the ring, with a gas injector and igniter immediately above it. The burning gas-air mixture passes through the jets and draws the extra air through the ring, eventually forming a roaring jet engine flame exhaust behind it. Unfortunately the choice of 3D print for the prototype leads to very short run times before melting, but it’s possible to see it working during that brief window. Future work will involve a non-combustible construction, but his early efforts were unsatisfactory.

It’s clear that he hasn’t created the equivalent of a conventional turbojet. Since it appears that its operation happens when the flame has passed into the center of the ring, it has more in common with a ramjet that gains its required air velocity with the help of extra energy from an external compressor. Whether he’s created an interesting toy or a useful idea remains to be answered, but it’s certainly an entertaining video to watch.

Meanwhile, this isn’t the first project we’ve seen inspired by the Air Multiplier.

Thanks [Baldpower] for the tip.

26 thoughts on “The Air Multiplier Fan Principle, Applied To A Jet Engine

  1. How, good to see an interest in this, few areas for potential covering diverse pressure vs flow mappings, nice post.

    Takes me back to my VL Calais days mid 1990’s, this is akin to an Air Motion Transformer (AMT) exploits gas laws and thus applicable to an internal combustion engine mostly easily a turbo diesel but, with some modifications also a naturally aspirated (n/a) petrol/gas engine. Results can increase power by as much as 50% before approaching mechanical design limits, good for short term over taking, not long term use. But tricky though as most cost effective method is have a scuba tank in the back Very Well secured and a couple of pressure regulators to drop the 3000 psi or so scuba pressure to something more manageable such as 50 to 100psi moderated by flow of course. An extra ECU essential for stoich with all sorts of safety limits especially rate of change not just flow but head temp too etc.
    If you have a small turbo diesel very easy to set it up, basically all needed is a scuba tank, modulated flow valve, safety cutoff & welding type oxy tank pressure regulator :-)
    Still considering swapping out a vehicle petrol n/a for a turbo diesel I can run cooking oil off, nice project if I can configure an AMT for that…
    Thanks for posting :-)

    1. This has nothing to do with AMTs (a kind of ribbon loudspeaker) nor do they in turn have anything to do with engines. You’re mashing together unrelated things in a word salad – I suggest seeing your doctor.

  2. The fundamental flaw in all these schemes is that they are intrinsically inefficient.

    The compressor produces pressure, which is converted into high-velocity airflow. So far, so good — this can be relatively efficient.

    The high velocity air flow then impinges on the low velocity air in the throat of the device. The *momentum* transfer is essentially 100% efficient here, but you lose most of the *energy* (or power) you gave to the high velocity flow in the process.

    For example, if you’re pushing 1 kg/s at 10 m/s from the compressor, that’s 50 watts of power (1/2 mV^2). If your air multiplier converts that into 10 kg/s at 1 m/s, that is 100% efficient at momentum transfer, but the power in that resulting air stream is just 5 watts.

    That’s a lousy 10% efficiency. The remaining 45 watts gets lost into heat and noise.

    You’d be far better off and move a lot more air with less power by just driving it directly with a propeller.

    1. The ‘air multiplier’ is like gearing though, right?
      Attach one to a a compressed airline and you have a usable, diffuse, low velocity, high volume air stream (e.g. for human cooling purposes).

      In that mode, it takes up less room, has no moving parts (air is already compressed) & uses something that may already be available.

      I don’t know about the efficiency numbers (if you have links, or a measurement setup, it would be cool to see it), but it doesn’t seem like the type of properties you want for a jet – it produces higher volume, but at lower velocity.

      I can’t think of a use case for a combustion-assisted version (there might be something, but nothing obvious I can think of).

        1. They didn’t say that they needed someone to perform like a clown to keep their attention for ~10 minutes, did they? Try reading it again. All they said was it made the watching enjoyable. They didn’t at any point say it was required to get through the video.

          It’s honestly sad you felt you had to respond and make yourself look this way.

  3. There are a few things wrong with this post

    – Resin 3d prints do not melt. They are thermoset plastics and they decompose / burn instead of melt.
    – Ramjets do not work like this. They use supersonic intake air and combusts within it, which multiplies the amount of gas in the output. The force of the intake air prevents the combustion from exiting in the front. This is why ramjets only work well at high speed. Currently this is the opposite in this, the combustion happens somewhere else, the gases are directed though a shaped area which drives the output direction.
    – Compressors for jet engines don’t work this way either. The rotation of the front propellers of the jet engine, forces air into a smal area for combustion (maximizing oxygen, etc), and then additional propellers direct the air out the back, which drives the shaft that is connected to the front propellers.

    It seems in an effort to make this post sound smart, you’ve misused several concepts and it shows a lack of knowledge.

    1. Aren’t the ‘additional propellers’ turbines that take energy from the expanding hot exhaust (after combustion) and transfer that back to the intake/compressor blades?

      (rather than being ‘additional propellers [which] direct the air out the back’ – I.e. the expanding gas is directed by the intake flow & the combustion expansion is what drives it ..?)

      Not trying to be an ass, just trying to clarify for other readers – the last part of the sentence suggest you understand it.

  4. This is NOT an engine, it is a poor design of a space heater. Replacing a fan with a compressor is hardly revolutionary. There are many ways of suppling air for combustion. This is the same as a rocket engine, since both fuel and air are externally supplied to the engine, so the engine is a rocket engine but with both ends open, it becomes nothing more than very inefficient space heater and produces very little thrust and even less static thrust. Just another braindead scam! There is a sucker born every second and the con artist to take him.

    1. I think it’s a good experiment for testing the heat and mechanical limits of resin prints. You’d be surprised what some resins can handle (I’ve worked with some that go up to 220c).

      This is a good example:

      In fact, there are resins out there that degrade gracefully (leaves behind no dust). Just opening the mind up for hot 3d applications is all.

  5. This ‘air multiplier’ technique was done long ago, decades before Dyson. Back in the 1950s there was the Jetex ‘jet’ engine for small free flight model aircraft. This used decomposing pellets activated by lighting a fuse.

    Now the interesting thing was that there was an attachment called the ‘augmenter tube’ that was basically a small lightweight aluminium tube with a bell end. The Jetex was set up so that the bell would be close to but not joined to the motor. The gas exhaust would pull in air from the bell opening and result in a (claimed) thrust increase from 2oz to a whopping 2.5oz.

    I had a Japanese copy of the Jetex back in the mid 70s made by Tiger. I fitted it to a freeform H-tail balsa jet of my own design and subsequently wasted a number of pellets just trying to trim it right. I never had an augmenter tube for mine, I don’t think Tiger made one. I still have the instruction sheet and what’s left of the engine after I tried my schoolboy approach of substituting home-made pellets made from KNO3, charcoal and (IIRC) chopped steel wool. It melted the motor case.

  6. Why not inject the fuel into the front of the ring? Simpler design and should produce decent thrust.

    If anyone remembers the external combustion aurora project (or the rumors thereof) or the new type external comparison rocket engine prototypes, it would be an inverted version of that.

    Maybe the ring wouldn’t even melt then. (Decompose, burn, whatever. I know someone will condescendingly correct me on that)

    1. Well this is a technical site for technical readers. Nothing wrong with being accurate. If we try to constantly appeal to the lowest audience, then we won’t be a technical site anymore. We’ll just be another gizmodo.

      Personally I think it makes sense, but not sure how practical it would be at that scale. It would need a lot of control regarding fuel / air mix else it would choke the small area there easily. In addition, at such small scales & speeds, the combustion could easily apply force in the opposite direction (forwards).

      Our conversation here is a great example of why I think it’s nice to be accurate. It makes for great conversation.

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