Will the Rotating Detonation Engines Enable Hypersonic Planes?

Disk rotating detonation engines could provide engines that are 10% more efficient, which could enable hypersonic planes. The USA, China, and Russia will be ramping up hypersonic weapon and hypersonic plane spending over ten billions per year each.

Combustion can be performed in two different modes (deflagration and detonation). Deflagration is usually treated as approximately isobaric combustion. For detonation, its propagating velocity can reach the order of kilometers per second.

Three kinds of detonation based engines are most studied. They are standing detonation engine (SDE), pulse detonation engine (PDE) and continuously rotating detonation engine (CRDE).

* Internal combustion engines are less than 25 percent efficient.
* best aero-derivative gas turbines, such as the H series turbines used for electric power generation, might break 40 percent.
* major challenge for a single-cycle heat engine of any type to achieve 50 percent.
* Gas turbine and steam combined cycles can approach 60 percent.
* With enough pre-compression and efficient components, an RDE (rotating detonation engine) gas turbine by itself might top 50 percent.
* A combined-cycle RDE plant could possibly reach 70 percent efficiency, a goal of current DOE research.

The promises of increased efficiency, simplicity, and high power density are driving the current research focus on rotating detonation engines (RDEs). An engine that uses detonation rather than deflagration could have some key advantages. If harnessed in a gas turbine or rocket, detonation could reduce the need for some expensive hardware, lighten engine weight and increase power output and efficiency.

There is work on annular flow disk rotating detonation engines and radial flow disk rotating detonation engines.

A Disk Rotating Detonation Engine Part 1:Design and Buildup

A Disk Rotating Detonation Engine Part 2: Operation (2018)

15 thoughts on “Will the Rotating Detonation Engines Enable Hypersonic Planes?”

  1. This could good for prop planes, only maybe cause the future of prop planes is going to be 100% electrical at one point.. Has nothing to do with Hypersonic Planes…

  2. Complexity is an issue with gas turbines because it decreases reliability. For an example look at using gearing in the initial compression stage for high bypass engines and the reluctance in adopting it.

  3. This is one way around heat generated by shock diffusion within a turbine inlet. The velocity is reduced / compression achieved by applying an MHD effect to a non-thermal plasma generated ahead of the engine. The electrical energy extracted ahead of the engine is in turn added to the engines exhaust in a reversed MHD process, which boosts velocity of gas exiting the nozzle.

    The Effect of Magnetohydrody
    namic (MHD) Energy Bypass on
    Specific Thrust for a Supers
    onic Turbojet Engine


  4. Now the interesting part here is gas turbines, yes hypersonic planes are cool but gas turbines live by efficiency and going from 60 to 70% is huge, they also don’t care about weight complexity is not an major issue.
    So higher chance of it getting developed.

  5. However rocket engines has to carry its oxidizer who makes them very inefficient compared to planes as its don’t use the oxygen in the air, in fact most of your mass will be oxidizer.

    Now rockets has some benefits like not require air who is handy in space.
    But if you could reach mach 15 in air you would just need a bit oxygen to reach orbit or you can drop an tiny upper stage or an bomb who land on another continent.

  6. Hard to start (get lit) and keep the detonation propagating. Screeches like a mofo. Very cool. Not new… perhaps useful in the future.

  7. Normal rocket engines have thermodinamic efficiency over 60% right now. Rockets engines are the most efficient engines that uses chemicals. I think it is not necessary to change this technology for rockets.

  8. Your carnot cycle theoretical limit on a combustion engine is limited by the ratio of the temperature of the hot part of the cycle to the temperature of the cold part of the cycle.

    Minus all the losses, of which there are many.

    So to push the theoretical limit up higher, you want to increase the temperature of the combustion part of the cycle (because there’s not much you can do to lower the temperature of the cold bit, (though engineers work on that too).

    You also want to have the combustion occur at high pressure which both increases the combustion temperature (because you are compressing air which heats it before you ignite the fuel) and the expansion of the compressed gas means you can get the energy out of the process more efficiently (because the expanded gas is now cooler, which is the other side of the equation.)

    A big way of doing this is to compress the air before using it to burn the fuel. This is already done to a big extent in a big gas turbine, it runs through multiple rows of high speed compressor blades and you get compression numbers like 50:1 That is super high by piston engine standards, but of course they would like even more.

    Increasing mechanical compression has a number of costs and disadvantages, but the detonation engine uses the combustion process itself to send a compression shockwave through the fuel/air mix, which adds another high compression factor on top of the existing one.
    Still, 70% is going to be a remote target.

  9. Can someone explain to me why thermodynamic limitations (which seem likely to me to top out way shy of the 70% figure that is the highest efficiency mentioned above) either don’t apply or else have a much higher ceiling than I am expecting?

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