Jet engines on Eve (and Jool)

[Human Person]

I know the exact composition of Eve's atmosphere or its oceans is a mystery, but I like to think of it as some sort of organic chemistry, something that would burn If added Oxidizer.

How about jet engines would work there, but in reverse: Burning oxidizer in a fuel-rich environment instead of fuel in an oxidizer-rich environment.

I now this would change gameplay drastically. I'm curious about your opinions.

Edited February 27, 2017 by Physics Student

[Wjolcz]

What you're describing is either an air-augmented rocket engine or a regular rocket engine running on propellant and oxidizer.

EDIT: Ohhhh, whooops! I misunderstood what you meant. But even then Ox+Intake air doesn't make much sense.

There's also another way this could work: Thermojets. These would consume a lot of EC though, so IMO the best (and most realistic) way to do this would be electric propellers. They work perfectly fine IRL and NASA tested them so I see no reason why shouldn't we also have them in KSP.

Edited February 26, 2017 by Veeltch

[cratercracker]

Maybe it would be better to use electricity/intake air to make propellers. Propellers could be possible infinite propulsion but it will require a lot of energy and will produce small amoun of thrust. Maybe as a combination we will need balloons. They are used by NASA,Roscomos,ESA and even small compaines. USSR space program used balloons to explore Venus. And we could do so in KSP!

[Wjolcz]

4 minutes ago, cratercracker said:

Maybe it would be better to use electricity/intake air to make propellers. Propellers could be possible infinite propulsion but it will require a lot of energy and will produce small amoun of thrust. Maybe as a combination we will need balloons. They are used by NASA,Roscomos,ESA and even small compaines.

They would be pretty sluggish though. Pretty much the same case as it is with solar sails (except in atmosphere).

[JadeOfMaar]

@Physics Student Your ambition is already realized or provided for with the Karbonite mod by RoverDude. Karbonite is a biofuel with composition KaO₃ so technically you only need a spark plug instead of Oxidizer for it to burn. You'll get fans, a turbojet and rockets that all consume it, Monopropellant instead of EC from the rockets' alternators, scoops to harvest from atmosphere, drills of course, and the ability to refine into LqdHydrogen for cryogenic engines, and Oxygen for Kerbalism or TAC Life Support if you use those.

Karbonite defines Eve's atmosphere and oceans to be full of it so you'll never be dry. There's so much more you can do with it than you can with Ore, LiquidFuel or IntakeAir but there's no hype train. Most of it is on Eve, where most players don't go.

WIP Forum Thread, GitHub.

Edited February 26, 2017 by JadeOfMaar

[The_Rocketeer]

@Veeltch I'm still not sure you get it. He's saying you can flip the sources of the ingredients for combustion and still make propulsion:


On Kerbin:
Fuel (from tank) + Oxygen (from air) + ignition = propulsion.

On Eve/Jool:
Fuel (from air) + Oxygen (from tank) + ignition = propulsion.

Edited February 26, 2017 by The_Rocketeer

[Human Person]

2 hours ago, Veeltch said:

There's also another way this could work: Thermojets. These would consume a lot of EC though

A lot of EC is still an understatement, the amount needed would be ginormous, not realizable. However there have been concepts of nuclear jet engines working as thermojets.

2 hours ago, cratercracker said:

Maybe it would be better to use electricity/intake air to make propellers. 

Good idea, but you mentioned the disadvantages of propellers yourself. Also, you'll find other threads about this topic, balloons as well.

2 hours ago, JadeOfMaar said:

@Physics Student Your ambition is already realized or provided for with the Karbonite mod by RoverDude. 

WIP Forum Thread, GitHub.

I'm playing with that mod but it's not what is meant. This is an suggestion for the stock-game and it doesn't involve a completely new fuel system.

Edited February 26, 2017 by Physics Student

[Tex_NL]

10 minutes ago, The_Rocketeer said:

On Kerbin:
Fuel (from tank) + Oxygen (from air) + ignition = propulsion.

On Eve/Jool:
Fuel (from air) + Oxygen (from tank) + ignition = propulsion.

Exactly. As long as the atmosphere is dense enough to get compression it should not matter where the fuel and/or oxidizer comes from. Either one (or both) can come from a tank.

[Human Person]

Since it already has oxidizer-plumbing, the RAPIER-engine would be predestinated for this task.

[Human Person]

@The_Rocketeer

@Tex_NL

The remaining question is: Does Eves or Jools atmosphere contain burnable fuel?

[The_Rocketeer]

23 minutes ago, Physics Student said:

Since it already has oxidizer-plumbing, the RAPIER-engine would be predestinated for this task.

Actually the RAPIER would be massively over-engineered for this. A simpler approach would be to just fuel up any regular jet engine with Liquid Oxygen in the gas tank instead of fuel. I guess the mixture would need to be refined, but the RAPIER (or rather the SABRE) is a much more complex animal.

[The_Rocketeer]

14 minutes ago, Physics Student said:

Does Eves or Jools atmosphere contain burnable fuel?

The Karbonite mod would suggest probably yes, but who knows? Unless Squad confirms or denies it, you're free to assume anything you want and mod it accordingly.

[Tex_NL]

25 minutes ago, Physics Student said:

@The_Rocketeer

@Tex_NL

The remaining question is: Does Eves or Jools atmosphere contain burnable fuel?

Stock, no. With mods literally anything is possible. It's just code after all.

[Human Person]

1 hour ago, The_Rocketeer said:

Actually the RAPIER would be massively over-engineered for this.

"Well, it simply shuts the Air Intake and injects Oxigen into the afterburner, easy as that ... ehremmm i mean it's highly complex an takes the rawest materials as well as super expensive production techniques to create this remarkable piece of engineering!" -C7 Aerospace Division-

 

you're right though 

Edited February 26, 2017 by Physics Student

[Martian Emigrant]

Hi all.

 

Jupiter (And presumably Jool) has an atmosphere mostly composed of Hydrogen which can burn if Oxygen is combined to it.

It also as 10 % Helium but that's no worst than Earth's 78% of Nitogen.

Now, I am no chemist. No aeronautical engineer. But I think if you went low enough you could get "Lift" for your wings.

And if you compressed that denser atmosphere you could make it burn but.....

Isn't hydrogen poor, energy wise, compared to say Kerosene or even methane?

Seem to me to be "Realist" (I know it's a game) you would need more oxidizer flying around Jool than LF on Kerbin for the same work.

Also it seems to me that if you are now that low you will never get out again.

Combined with nowhere to go...What's the point? Send a one way probe.

 

As for Eve....IDK....Something similar I guess.

 

ME

Edited February 28, 2017 by Martian Emigrant

[Human Person]

1 hour ago, Martian Emigrant said:

Isn't hydrogen poor, energy wise, compared to say Kerosene or even methane?

Will do the maths on this as soon as i get home. Because of its low density, it takes a lot of energy to compress hydrogen gas compared to its chemical energy. 

Assuming Eves Oceans are liquified atmosphere, it can't be hydrogen. I'll also reserch possible composites for this case. No, I would have to make too many assumptions for that, it would be rediculus. 

Instead, let's assume it's not hydrogen, let's assume it's mostly ... Methanol? Maybe this is worth a seperate thread.

flying on Jool is pointless, that's why it's in brackets but Eve rules!

Edited February 27, 2017 by Physics Student

[Starman4308]

2 hours ago, Martian Emigrant said:

Isn't hydrogen poor, energy wise, compared to say Kerosene or even methane?

Not really; the only metric by which hydrogen has less energy is on a per-mol basis, and that is heavily misleading due to how many atoms methane and kerosene have. Hydrogen has a spectacular energy-to-mass ratio (part of why it's the most efficient practical chemical rocket fuel), with its primary disadvantages being that it's incredibly cryogenic and very low-density.

If I did the math right, hydrogen should provide 572 kJ of energy per mol of oxygen (assuming stoichiometric ratios), with methane providing 445.11 kJ per mol of oxygen consumed.

I can't necessarily address the energy needed to compress the intake gases, and I am pretty sure atmospheric fuel + oxidizer will be inferior to fuel + atmospheric O2, but it'd still be a great deal more efficient than rocketry would be.

If you wanted a minimally-cheaty probe to send as deep into Jool's atmosphere as possible and still return, these engines would be an excellent choice to get you out to upper atmosphere. When it comes to Eve: its closest analog (Venus) has mostly just inert atmospheric gases (carbon dioxide and nitrogen), both of which could be used as reaction mass for an air-assisted rocket, nuclear turbine, etc, but could not contribute as either fuel or oxidizer to a chemical reaction.

[natsirt721]

For Jool, a H2 scoop would amount to either an infinite duration NTR burn or, if combined with oxidizer, a plain-old chemical rocket engine.  Either way, not particularly appealing as 1) NTRs have terrible atmospheric isp and 2) oxidizer is heavy, and chemical rockets have terribly isp anyway - doubling your mass ratio isn't going to be terribly useful unless your ship is gargantuan.

[Zeiss Ikon]

19 hours ago, natsirt721 said:

1) NTRs have terrible atmospheric isp and 2) oxidizer is heavy, and chemical rockets have terribly isp anyway - doubling your mass ratio isn't going to be terribly useful unless your ship is gargantuan.

If you have an NTR that can also be run as a thermal turbine/jet, any atmosphere that can be compressed would work as reaction mass -- Jool's (presumed) hydrogen-helium, Eve's (presumed) carbon dioxide/nitrogen, or Duna's (presumed) thin carbon dioxide/nitrogen.  You'd need a variable geometry compressor and nozzle to have a single engine work in all three locations,  but that's not a hard problem (compared to actually getting the ship there in the first place).  If Jool's atmosphere is, in fact, mostly hydrogen, any oxidizer ought to work with it -- and oxidizer isn't significantly heavier than (presumed) kerosene to run a conventional jet on Laythe.  The big issue you'd have with this nuclear thermal jet is Eve -- if the atmosphere is mostly CO2, it might well be compressing to a liquid at the surface (that's about 800 psi at room temperature, though much above room temperature you wind up supercritical before it properly liquefies -- so you don't get a well defined surface like the "water" on Eve).  Compress that, anywhere near "sea level", and you'll find it liquefying in the compressor; you'd have to preheat it in order to compress it, then heat it still more to get it to provide turbine energy (to run the compressor stage) and give a pitiful little bit of jet thrust.  I'm afraid that on Eve, at least down low, a propeller is likely to be the most efficient way to move something in the air -- and then you'll want wings to hold it up, so TWR less than one won't keep you grounded.  A Rankine cycle turbine (steam turbine, though it could run on anything that has a convenient boiling point) running off your nuclear thermal source is probably the best way to do that -- and that engine will work anywhere there's atmosphere to push and a way to get rid of waste heat.

Edited March 1, 2017 by Zeiss Ikon
typos\

[natsirt721]

3 hours ago, Zeiss Ikon said:

If you have an NTR that can also be run as a thermal turbine/jet, any atmosphere that can be compressed would work as reaction mass

Well, almost any atmosphere.  Want to guess what 3000K oxygen radicals do to an improperly shielded NTR?  And you can't shield for all reaction masses at the same time (on one part) due oxidization and reduction reactions and all that. Although, for Kerbal's sake this could probably be overlooked.

3 hours ago, Zeiss Ikon said:

If Jool's atmosphere is, in fact, mostly hydrogen, any oxidizer ought to work with it -- and oxidizer isn't significantly heavier than (presumed) kerosene to run a conventional jet on Laythe. 

Well sure, but you're still burning hydrogen and oxygen in a conventional rocket engine, isp in the 300-400s range.  Turbojets get like, what, 9500s?  It's still going to chew through the onboard oxidizer at a steady clip. 

With regards to the Eve CO₂ ramjet, depending on the compression ratio of the turbojet it could operate in the 5-15km altitude range where ambient pressure isn't too large (less than 2atm).  But a compression ratio over 30:1 or so would still push the incoming air supercritical at 5km, so it would have to be operated in a pretty narrow envelope.  Then again, with a lower ratio (5:1 or so) turbojet you could conceivably operate at or near sea level, but the thrust would be pitiful.  I'm not aware of how Eve's elevation is distributed, if there is enough land above 5km it might be practical, but I suspect that this is not the case.

Edited March 1, 2017 by natsirt721
increased humility

[Zeiss Ikon]

My recollection from the Eve SSTO discussion is that there are a few peaks that reach as high as 7.5 km -- which strongly implies little land above 5 km.

As for 3000K oxygen, fluoride passivation is a marvelous process.  But as you note, that doesn't help much for a hydrogen atmosphere.  And running at lower temperature to ensure material compatibility cuts deeply into the efficiency of a Brayton cycle (gas turbine/turbojet).  I think we're back to a closed-circuit "steam" system driving a propeller (or ducted fan) for loiter and to get high enough (in Jool and Eve atmosphers) for rockets to work at departure.

Or just not trying to land on Eve or Jool...

Edited March 1, 2017 by Zeiss Ikon
Complete idea

[JacobJHC]

On 2/26/2017 at 3:39 PM, Physics Student said:

@The_Rocketeer

@Tex_NL

The remaining question is: Does Eves or Jools atmosphere contain burnable fuel?

I think not because if it did would it not burn when a usual rocket engine burns in the atmosphere or ocean? 

[Human Person]

22 hours ago, JacobJHC said:

I think not because if it did would it not burn when a usual rocket engine burns in the atmosphere or ocean? 

Fuel cannot burn without oxidiser. The whole point of rocket engines is that they mix just enough fuel and oxidiser that it all burns up.

Rocket-Engines in the real world leave a trail of fire because they burn a fuel-rich mixture. That tiny amount of left-over fuel (usually a few % of the exhaust gasses) creates the visible jet of fire. Because the mixture is fuel-rich, there is absolutely no unburned oxidiser left, just burn-products and fuel. Nothing of this would further react with a fuel containing atmosphere.

Edited March 2, 2017 by Physics Student

[JacobJHC]

48 minutes ago, Physics Student said:

Fuel cannot burn without oxidiser. The whole point of rocket engines is that they mix just enough fuel and oxidiser that it all burns up.

Rocket-Engines in the real world leave a trail of fire because they burn a fuel-rich mixture. That tiny amount of left-over fuel (usually a few % of the exhaust gasses) creates the visible jet of fire. Because the mixture is fuel-rich, there is absolutely no unburned oxidiser left, just burn-products like CO2 and H2O and fuel. Nothing of this would further react with a fuel containing atmosphere.

Good point, although considering that this is Kerbal technology we can't be sure they aren't venting trace amounts of oxidizer without realizing it.

[Zeiss Ikon]

9 hours ago, JacobJHC said:

Good point, although considering that this is Kerbal technology we can't be sure they aren't venting trace amounts of oxidizer without realizing it.

Real world rocket engines are always run slightly fuel-rich for two reasons.  One is to ensure that the exhaust is rich in carbon monoxide, and poor in carbon dioxide; this is done because CO, with its lighter molecular weight, gives better exhaust velocity (= Isp) than the heavier molecules of CO2 (as well as about double the gas volume).  The Isp levels of most of the engines in the game are inconsistent with a CO2-heavy exhaust, but right in line with a fuel-rich combustion giving mostly CO (in addition to the water vapor).

The other reason is that a fuel rich combustion is far easier on the materials of the combustion chamber and nozzle -- metals in general are subject to oxidation, because they're fully reduced.  As a result, a reducing environment tends to leave the metal mostly unchanged, while an oxidizing environment tends to rapidly eat away at the metal.  You see much the same thing in oxy-acetylene welding; you'll prefer your flame to be slightly on the reducing side of neutral, rather than slightly oxidizing, for most welding processes, and this is why.

The F1 engines in the Saturn V first stage were actually "film cooled" -- they used an injection system that put a film of kerosene vapor along the combustion chamber and nozzle wall.  Without enough oxygen present to fully combust the hydrocrabons, this film left the chamber without reacting, and carried away heat from the chamber and nozzle in the process.  Look at video of a Saturn V startup and you can see the blackish layer partially obscuring the bright core of the exhaust -- that's the cooling film.  This method has been used in many hydrocarbon fueled engines, because it's cheap, fairly simple to implement, and works pretty well.