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spinning combustion chambers to make rockets more efficient?

Discussion in 'SpaceX' started by returnero, Jul 11, 2018.

  1. returnero

    returnero New Member

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    so i was thinking that rockets not only lift because heated molecules explode and bump against the bottom portion of the vessel, they rely on pressure, pressure out = pressure up(or lift), because as we all know rocket engines are designed to maximize pressure by limiting the exhaust area at the throat of the rocket

    another way to generate lift is with a propeller on a plane, pressing against the air, but not however in a way that generates pressure, so i think that rocket engines should be able to combine a physical force (like how a propeller would) against the combustion molecules as well as using the physical explosive force of the molecules against the rocket, to combine a fan and an explosive in one rocket

    the way that comes to mind is with a cone like structure with spirals in it and the cone spins very fast in a direction that forces gas downward to create pressure then out the holes designed like the "throat" of the rocket designed to maximize pressure of the combustion chamber in the image below

    [​IMG]

    so basically here are three images of how it could work and look etc. the overall rocket does not spin, just the cone part, i don't know exactly how it should look at all, i call it the dragon shell, kind of a stupid name, i'm sure it's been thought up before

    [​IMG]
    [​IMG]
    [​IMG]


    so in order to actually use this you need electricity and a liquid fuel source, the main uses of this type of "dragon shell" would need to be in the future if we ever get some source to generate electricity very efficiently to spin the shell structure with, so i definitely see this as a futuristic type of propulsion

    the only ways this could be useful now is with a electrical wire incredibly long and sturdy attached to the rocket as it was flying in the air

    another use is in space, using solar cells to generate electricity and periodically when enough electricity is gathered - spin the shells until they're spinning very fast and ignite the fuel. the spinning motion works against the fuel pressing it downward to increase pressure on the throat points. i didn't draw any nozzles below the throat holes and maybe i should have, also it's possible this would work better if the steel rod that delivers fuel/electricity is connected to the base but not any of the overall cone structure itself but i think that is unlikely

    anyway just looking to share ideas nothing else
     
  2. ccutrer

    ccutrer Active Member

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    This would be absolutely no use in space, as you suggest. There’s nothing additional besides the exhaust gases to push against, so your goal would be to push “harder” against them. I don’t know that even with infinite free electricity you would propel the exhaust gases any faster doing this than a current optimal nozzle. It certainly wouldn’t be worth the cost of whatever electrical system you’re going to send up, rather than more fuel.

    While still in the atmosphere, it fits in the entire category of ideas that try to use some traditional form of propulsion to avoid the rocket equation for as long as possible. It seems on the crazier end of the spectrum of what I’ve seen.
     
  3. returnero

    returnero New Member

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    the spinning motion presses against the exhaust to create additional pressure, the exhaust is the pressure, lift is a function of pressure

    if you have increased pressure at the throat, it should propel the gasses faster... i think
     
  4. returnero

    returnero New Member

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    either that or you can propel gases the same speed with less gas
     
  5. bxr140

    bxr140 Active Member

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    I'm always a fan of new and interesting ideas and definitely not a fan of a basic "pfft-it won't work" responses (though we don't see that kind of post too often on this subform). With that in mind, I think it is most important to consider the energy flow with respect to this concept, both from a physical perspective and from a mathematical perspective.

    Traditionally, rocket motors are designed to maximize the amount of energy within the propellant (that includes electric...) and their nozzles are designed to maximize the number of particles that exit straight out the back. Adding additional features to that physical energy flow will introduce inefficiencies the because particles are making additional 'bounces', and in doing so they're 'losing' more of their energy. The geometry complexity means there's also a higher probability that more of the particles will fly out the back at sub-optimal angles, which means the vehicle is not maximizing the energy exchange of those particles. So...the solution needs to overcome these inefficiencies.

    From a slightly different perspective, its all about pressure. A motor is designed to convert the high pressure in the combustion chamber to low pressure at the nozzle exit in the most efficient way possible, because that means the exhaust flow exchanged as much energy with the vehicle (in the form of thrust pushing the vehicle forward) as possible. (Its actually flow velocity you're optimizing, but, I digress...). So...this concept actually is at odds with the goal of the expanding nozzle, because it is based on increasing the pressure in the flow. That's not inherently a show stopper, but it makes the math really hard to close.

    Mathematically, any concept must not just explicitly add energy to the exhaust flow to be viable, but also add net force to the system. One of the reasons rocket fuel is rocket fuel (be it solid, liquid, or electric) is because of its energy density, and there's a reason that to-date we don't have any practical alternatives. Basically, the spinning nozzle requires its own energy (that it will transfer to the exhaust flow) to come from somewhere, and because every other option for "somewhere" includes a less energy dense source than rocket fuel, that's going to be a hard trade to close. In other words, even with a spinning nozzle that actually creates a net-positive thrust there's still a thrust-to-mass hurdle.

    Sort of going sideways, there's a practical constraint of hotspots, which are always a major concern with chambers/throats/nozzles. They would no doubt be amplified with non-symmetrical features and sharper than typical edges/corners, so this concept would also need some advancement on the materials side of things--advancement that would also raise the performance of 'traditional' nozzles, mind.

    There's an interesting controls problem with the concept as well; Newton's third adds another layer to the concept. Regardless if in atmosphere or space, any inertial forces from a spinning nozzle need to be accounted for in the opposite direction, which can potentially cost more energy. Two nozzles [spinning opposite directions] is an obvious starting point to investigate...one could also imagine using a fast spinning nozzle to create a slow [opposite] spin on the "main" part of the craft for stability/artificial gravity/thermal loading.
     
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  6. RDoc

    RDoc S85D

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    Basically this seems like a proposal to increase the exhaust velocity with a form of propeller. So the question is if the "propeller's" added thrust is more than the power required to run it, in short, does it have an efficiency >100%.

    The answer is no.
     
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  7. Grendal

    Grendal SpaceX Moderator

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    Computers can crunch flow mechanics and find the maximum efficiency. I believe that is some of what SpaceX has done to increase the power and efficiency of the Merlins over the years. Just looking at the beauty of the plume from last nights launch showed how well balanced those nine Merlins are.
     
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