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Ionizing Air Going Through A turbojet engine... could it increase thrust?


Spacescifi
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If the air being sucked into a turbo jet engine was ionized before leaving as exhaust could magnetic technology be used to further increase thrust more than than you would get from chemical combustion alone?

 

And is that the same idea behind a plasma jet or not?

I was even thinking that same easy to ionize gases could be injected into the fuel stream as well to increase thrust.

I realize plasma is low thrust by nature but if the volume of air being turned into plasma is great enough then that could change.

 

 

 

Edited by Spacescifi
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Where would the energy to do this come from? In a normal turbojet almost all of the energy involved is from the heat of burning fuel, if you take energy from the fuel away to power the ionization system the heat taken out will not go towards the turbojets thrust, and per the second law of thermodynamics there is no way for the  energy added by the ionization system to be more than that taken out from the burning fuel

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Energy of normal ionization methods, like corona discharge or radioactive source, is negligible to energy of combustion. Ionized intake gas would give no benefits but corrode engine parts. Highly ionized gas is used for plasma cutting.

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22 hours ago, Spacescifi said:

If the air being sucked into a turbo jet engine was ionized before leaving as exhaust could magnetic technology be used to further increase thrust more than than you would get from chemical combustion alone?

You can always add thrust by adding energy to an exhaust stream. If you are getting that energy by taking it away from an earlier step in the process, it will make the whole engine less efficient. If you are getting that energy from a separate energy source then it will make the whole engine less efficient unless that separate energy source has better specific energy and energy density than the original engine. If the separate energy source has better specific energy and energy density than the original engine, just use that energy source to build an engine from scratch running only on that energy source.

22 hours ago, Spacescifi said:

I was even thinking that same easy to ionize gases could be injected into the fuel stream as well to increase thrust.

Once the easily ionizable gases are injected into the propellant flow (whether upstream or downstream of combustion), they will mix and will no longer be easily ionizable.

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3 hours ago, sevenperforce said:

You can always add thrust by adding energy to an exhaust stream. If you are getting that energy by taking it away from an earlier step in the process, it will make the whole engine less efficient. If you are getting that energy from a separate energy source then it will make the whole engine less efficient unless that separate energy source has better specific energy and energy density than the original engine. If the separate energy source has better specific energy and energy density than the original engine, just use that energy source to build an engine from scratch running only on that energy source.

Once the easily ionizable gases are injected into the propellant flow (whether upstream or downstream of combustion), they will mix and will no longer be easily ionizable.

 

I understand.

 

The problem comes right back to energy density and it not being enough for plasma to make a difference.

Yet the irony is energy density only gets you so far since too much melts your engine... because the fuel conducts excess heat to the walls of the combustion chamber.

 

Let us imagine a fictional engine that just might work... but I am not sure.

MHD Fusion Pulse Rocket:

So you have a detonation chamber lined with magnets cooled with circulating chilled liquid helium.

It is not a vacuum chamber though.

The magnets are powerful enough to compress a fusion fuel pellet into fusion, which blast out the rocket as exhaust.

The main show stoppers in real life would be energy density.

The very energy you need to get off the ground will melt your engine if the ship is too heavy.

 

So IRL I doubt we will ever see heavy scifi rocket SSTOs.

Only project orion... since rockets cannot handle tge POWAH!

 

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29 minutes ago, farmerben said:

Assuming we had a spectacular secondary  energy source, why not?  Cathode ray tubes can project electrons onto the afterburner plume.  This might give thousands of times more thrust than an ordinary TV set.

 

You must be joking.

In scifi sufficient power is always assumed.

 

My contention is that even having what we do not have... sufficient power, may not be enough.

I am betting the amount of electrons needed to provide sufficient thrust to tye exhaust stream would melt or blow them up.

Edited by Spacescifi
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15 hours ago, Spacescifi said:

The main show stoppers in real life would be energy density

Yeah, I'm gonna say you don't really understand what energy density means.

What's with the engine melting fixation?

Magnets are, despite what some may say, in fact, not magic.

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1 hour ago, Shpaget said:

Yeah, I'm gonna say you don't really understand what energy density means.

What's with the engine melting fixation?

Magnets are, despite what some may say, in fact, not magic.

 

I know magnets are not magic... magnets require power too... and create waste heat too.

The reason rocket engines do not melt is because they carry the heat away with the exhaust through the propellant.

But even that has it's limits... since if the energy injected into the propellant is so high that the mass flow rate is not enough to reduce the heat to a safe level... bad things happen.

Basically, a way to still use absurdly high energy exhaust with traditional combustion rocketry would be to increase the mass flow rate to match the energy being dumped into the flow. Which increases thrust but reduces efficiency a great deal.

The NSWR got around this thorny issue I think by having the nuclear reaction take place near or at the nozzle as the exhaust was already leaving, so it allowed it to behave like a torch drive... just an absurdly dangerous one since it did not need to worry about dumping heat as much.

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29 minutes ago, Spacescifi said:
2 hours ago, Shpaget said:

What's with the engine melting fixation?

The reason rocket engines do not melt is because they carry the heat away with the exhaust through the propellant.

But even that has it's limits... since if the energy injected into the propellant is so high that the mass flow rate is not enough to reduce the heat to a safe level... bad things happen.

Unless you're dealing with an actual torch drive, the heat capacity of the propellant flow will always be far greater than the heat rejection needs of your engine.

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On 9/11/2022 at 7:35 PM, Spacescifi said:

And is that the same idea behind a plasma jet or not?

Absolutely not. Lookup the Microwave Air Plasma Thruster. The only use of a turbine here is as the pump for compressed air into the ionizing chamber. It's a concept tech that promises to take electric aviation to serious heights (metaphorically and literally).

Side note: It would be useless, possibly even subtractive, to try to combust ionized air. The ions might be resistant to combustion or could produce less net thrust or would gain the energy necessary to corrode the engine parts. And there's the pointless added engineering complexity of trying to make a hybrid engine.

On 9/11/2022 at 7:35 PM, Spacescifi said:

If the air being sucked into a turbo jet engine was ionized before leaving as exhaust could magnetic technology be used to further increase thrust more than than you would get from chemical combustion alone?

Amusingly, this is exactly how the original creator of the OPT Spaceplane mod figured the 2.5m Nebula jet engine would work.

Edited by JadeOfMaar
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One may have either physics or chemistry, but not both.

Either accelerated ions with applied energy from external source, or molecules of exhaust gas giving that energy.

The ion can't be at the same time a part of molecule and free.

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5 hours ago, JadeOfMaar said:

Absolutely not. Lookup the Microwave Air Plasma Thruster. The only use of a turbine here is as the pump for compressed air into the ionizing chamber. It's a concept tech that promises to take electric aviation to serious heights (metaphorically and literally).

Side note: It would be useless, possibly even subtractive, to try to combust ionized air. The ions might be resistant to combustion or could produce less net thrust or would gain the energy necessary to corrode the engine parts. And there's the pointless added engineering complexity of trying to make a hybrid engine.

Yes, problem with the Microwave Air Plasma Thruster is that you need lots of power and batteries has an low energy density. Now if you have very good fusion this is not an issue but in this case you might use plasma from the fusion reactor to heat air via a plasma window. You could add some reaction mass if you needed some more trust say for takeoff or passing the sound barrier. 

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13 hours ago, JadeOfMaar said:

It would be useless, possibly even subtractive, to try to combust ionized air. The ions might be resistant to combustion or could produce less net thrust or would gain the energy necessary to corrode the engine parts. And there's the pointless added engineering complexity of trying to make a hybrid engine.

On 9/11/2022 at 7:35 PM, Spacescifi said:

If the air being sucked into a turbo jet engine was ionized before leaving as exhaust could magnetic technology be used to further increase thrust more than than you would get from chemical combustion alone?

Amusingly, this is exactly how the original creator of the OPT Spaceplane mod figured the 2.5m Nebula jet engine would work.

Also keep in mind that for any ion-based propulsion system to work, you have to have a way for your net exhaust to be electrostatically neutral, or you end up with charge buildup on your vehicle. For ion thrusters, this is accomplished by firing a beam of electrons into the exhaust stream. It doesn't add any thrust but it keeps you electrostatically neutral:

1920px-Ion_engine.svg.png

Also in an ion engine the actual acceleration is produced by an electrostatic field (between the positive and negative grids) while the magnetic field is what does most of the work to ionize, not the other way around.

My background is physics, not pchem, but it could be possible to use exotic propellants and a multistage combustion chamber to generate two ionized exhaust streams rather than a single electrostatically-neutral exhaust stream. If you then had some outside source of electrical energy, you could use electrostatic fields or magnetic fields to accelerate those two exhaust streams and produce additional thrust.

However -- and this is critical -- you must have some outside source of electrical energy. You cannot get the energy from your propellants. An engine which produces two ionized exhaust streams will always be less efficient than an engine using the same propellants which simply allows them to fully combust, because two ionized exhaust streams still have residual potential energy until they react with each other.

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In a high thrust high flow engine, screens are bad.  The flame in a conventional rocket is plasma and conduct electricity quite easily.  Smaller ring shaped anodes and cathodes could run a discharge current with as much power as you have.  

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21 minutes ago, farmerben said:

In a high thrust high flow engine, screens are bad.  The flame in a conventional rocket is plasma and conduct electricity quite easily.  Smaller ring shaped anodes and cathodes could run a discharge current with as much power as you have.  

Who is correct however current ion engines are low trust. For high trust you probably want something more like the vasmir engine or if your have fusion use the ion stream from that 
Yes you could beam power but think vasmir works out better 

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electrical power is ultimately the limiting factor in the performance of ion/plasma thrusters. you could make some stupid powerful thrusters if you had a megawatt or more to pump into them. right now all the means to generate more power means more weight. more solar panels, a big collector for beamed power, or a nuclear reactor an all the radiators you need to make it work. fission-electric may turn out to be a dead end. you might be better off using the nuclear reactor to initiate a fusion thruster.

Edited by Nuke
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So there are two ways to increase thrust.

 

1. Increase the mass flow... which we do not want to do if you want a heavy SSTO that is not totally a fuel tank.

2  Increase the speed of the exhaust... which requires more energy applied to it.

 

Seems to me that if an 8000 ton scifi SSTO had sufficient power, it would just pulse fire an uber laser into the rocket exhaust stream.

So at first you would see a normal rocket plume, but the moment it is shot through with an uber laser it would stretch much longer while granting exceptional thrust before receding back again.

This would happen repeatedly till orbit.

And if you wonder why I am a fan of pulsed energy it's because it is far more within our reach than continous uber power.

 

 

Edited by Spacescifi
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38 minutes ago, Spacescifi said:

Seems to me that if an 8000 ton scifi SSTO had sufficient power, it would just pulse fire an uber laser into the rocket exhaust stream.

This would do nothing useful for the rocket propulsion wise.

For dumping raw energy/heat into the exhaust to be useful, it needs to be before the throat of the engine, which in turn is before the nozzle. 

But you can only do this up to the point where the throat of your engine starts to melt, and this is a point that we already reach quite easily with just chemical combustion.

Shooting a laser into the exhaust of your rocket is functionally equivalent to mounting a small, off-center photon engine next to your chemical engine: lots of complexity for no practical gain.

43 minutes ago, Spacescifi said:

And if you wonder why I am a fan of pulsed energy it's because it is far more within our reach than continous uber power.

If you are adding magical uber-power sources without associated magical uber-materials, and also constrain those uber-power sources with a destructively-high minimum functional output, then you have basically re-skinned the nuclear fission bomb.

The only use-case where pusher-plates make sense is when you are limited to fission bombs or a close analog, with no materials or propulsion technologies significantly in advance of 50 years ago. 

 

Just remember: using an Orion engine in an atmosphere will cause significant damage to both the vehicle and the planet, so they are only of use once you are already in-orbit, where things like ion or plasma propulsion can get similar ISP with far less engineering and damage, even if the thrust is much lower.

 

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1 hour ago, Terwin said:

This would do nothing useful for the rocket propulsion wise.

For dumping raw energy/heat into the exhaust to be useful, it needs to be before the throat of the engine, which in turn is before the nozzle. 

 

 

Are you sure that is true? Superheating the exhaust could have a positive thrust.

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