LFO atmospheric egines: Any existing mod?

[FeliusKerNes]

Is there any mod that creates (or just apply a module manager patch to stock) jet engines and other air dependent engines so that they can be used in atmospheres without oxygen. That is, taking three "propellants", LF and some type of intake atmosphere (like Firespitter does (or used to do) for electric propellers) to generate thrust, allowing it to operate in planets with atmosphere that aren't Kerbin and Laythe.

I mean, I suppose you could theoretically do it already by taking an electric engine, fuel tanks and a whole load of fuel cells to generate electricity, even with only Stock parts now with Breaking Ground, but I was hoping for a more elegant solution (specially with how much of a bloody effort it feels to me to actually try to control a propeller plane (and let's not even talk about helicopters) created through the new stock rotors) than that.

And for what seems a current question that seems to pop out in every past thread about it I found when doing a search: How is it different from a rocket engine? It's not creating thrust by expelling it's reactional mass, instead being essentially a normal internal combustion engine that is carrying it's own oxidizer to create torque for the engines, so as to push the (oxygen-less) air around it, generating thrust that way. And while it certainly is going to lose quite a bit of efficiency (considering the standard rates of LF to Oxidizer in KSP, a bit over half of it), it's still far more efficient than to generate thrust solely by pushing internally carried reaction mass out. I mean, half of the worst jet engines is still better than even the best of non-ion rocket engines, at approximately 3200/2 or 1600 ISP for the Rapier equivalent, compared to 800 for a stock nuclear engine (in a vacuum). And about 6000 ISP for a Goliath Equivalent (good luck hauling a plane using that to far planets though :P )

I know there's the Exploudium Breathing Engine mod, but that's not quite what I was hoping for, even if it gets a bit close. That just "inverts" the relation of what's being carried, oxidizer instead of LF, and makes it breath Eve's atmosphere, which it assumes to be some form of combustible compound. Is not a bad approach, mind you, but not what I was looking for either. So, is there anything else like I was hoping for?

 

[linuxgurugamer]

There are a couple of atomic jet engines available 

[Incarnation of Chaos]

tbh i think you would need some sort of "Pre-burner" before the intake of the jet engine; you can't just dump fuel and oxidizer into the intake and expect something to happen. You need flow to start the compression stages which then can become self-sustaining at a certain RPM; this is why on any airfield you're gonna see APU's they use to get them started (Sometimes these are intergrated into the planes themselves). So a modified Jet Engine that takes OX and LF would actually have what amounts to a very inefficient rocket placed in front of the intake; that would use a little bit of the fuel to create a stream of partially burned Fuel/Oxidizer and spin the turbines up. But this now presents an issue; because now the compression stages can pull fuel/oxidizer under their own power. So you would need a way to bypass the "Pre-burner" and allow the engine to operate somewhat normally.

All of this adds weight, complexity; that's even before considering the turbine blades likely won't enjoy this kind of operation. I feel like a realistic "Closed" turbine engine would actually be far less efficient than you seem to think.

[DStaal]

Ok, it sounds to me like you're basically thinking a of taking a high-bypass turbofan, and making it *all* bypass - burn the fuel from internal instead.

Which is really just an advanced prop engine using a rocket-turbine to turn the shaft.  And the question is if that's more efficient than using some other sort of engine to turn the shaft.  (Electric, a more conventional combustion engine, etc.)

That said - take a look at the Buffalo rover system.  It has some fuel cells and electric propellers designed for this type of application.

[Shadowmage]

6 hours ago, DStaal said:

And the question is if that's more efficient than using some other sort of engine to turn the shaft.

Something about the conservation of energy and laws of thermodynamics might have some input here

Taking mechanical energy from rocket exhaust and using it to spin a turbine, which then spins props to produce thrust, I cannot envision any method where it would be more efficient than using the reaction mass/exhaust directly.  The energy output from the combustion of fuel doesn't change, but you are introducing more inefficiencies through the mechanics of rotors, bearings, gears, etc (friction, drag).  The reason that jet-engines are 'more efficient' on Kerbin is simply that they don't need to carry (and accelerate) their oxidizer. 

At least that is my understanding of the physics of it (someone please correct me if I'm wrong on any of those points).  Would love to check the ISP of a jet engine converted to burn LFO at the same total mass-flow-rate as the atmo equivalent (assuming IntakeAir uses something approximating a sane density/mass value).

[DStaal]

22 minutes ago, Shadowmage said:

Taking mechanical energy from rocket exhaust and using it to spin a turbine, which then spins props to produce thrust, I cannot envision any method where it would be more efficient than using the reaction mass/exhaust directly.  The energy output from the combustion of fuel doesn't change, but you are introducing more inefficiencies through the mechanics of rotors, bearings, gears, etc (friction, drag).  The reason that jet-engines are 'more efficient' on Kerbin is simply that they don't need to carry (and accelerate) their oxidizer. 

I was thinking there had to be some effect, as most real-world jet engines these days use a high-bypass tubofan design, where most of the thrust comes from the fan/props instead of the direct exhaust.

A bit of careful reading leads me to believe it's because they can manipulate the compression ratio easier that way - making the combusting turbine more efficient and more than making up for the mechanical losses.  This wouldn't apply to a rocket-turbine as we're discussing, so that is out.  The only other reason would be to add remass - but the fan isn't actually needed for that, just some careful ducting as you'll want the remass heated and added to the exhaust flow just after combustion.

[Incarnation of Chaos]

11 hours ago, DStaal said:

Ok, it sounds to me like you're basically thinking a of taking a high-bypass turbofan, and making it *all* bypass - burn the fuel from internal instead.

Which is really just an advanced prop engine using a rocket-turbine to turn the shaft.  And the question is if that's more efficient than using some other sort of engine to turn the shaft.  (Electric, a more conventional combustion engine, etc.)

That said - take a look at the Buffalo rover system.  It has some fuel cells and electric propellers designed for this type of application.

I'm more saying that you have to have something to get the compression stage up to speed; that in a closed system that would basically be a rocket. Once started you can bypass the pre burner in theory and feed ox/fuel directly into the system. But that's all weight, energy losses to heat, friction etc; so basically you end up with a heavy, complex engine that I question if it would be worth it. I'll look into your rover though since it sounds pretty interesting.

I just wish there was a software for rapidly prototyping jet engines sometimes xD

4 hours ago, DStaal said:

I was thinking there had to be some effect, as most real-world jet engines these days use a high-bypass tubofan design, where most of the thrust comes from the fan/props instead of the direct exhaust.

A bit of careful reading leads me to believe it's because they can manipulate the compression ratio easier that way - making the combusting turbine more efficient and more than making up for the mechanical losses.  This wouldn't apply to a rocket-turbine as we're discussing, so that is out.  The only other reason would be to add remass - but the fan isn't actually needed for that, just some careful ducting as you'll want the remass heated and added to the exhaust flow just after combustion.

The J58 used on the SR-71 almost obtained 50% of it's thrust from airflow at mach 3; but that's a ramjet/turbojet hybrid.

[FeliusKerNes]

6 hours ago, Shadowmage said:

Taking mechanical energy from rocket exhaust and using it to spin a turbine, which then spins props to produce thrust, I cannot envision any method where it would be more efficient than using the reaction mass/exhaust directly.  The energy output from the combustion of fuel doesn't change, but you are introducing more inefficiencies through the mechanics of rotors, bearings, gears, etc (friction, drag).  The reason that jet-engines are 'more efficient' on Kerbin is simply that they don't need to carry (and accelerate) their oxidizer.  

It must be to some degree, otherwise there'd be no point at all to making propellers and turbofans, just rocket engines that gather oxidizer from the air as they go (which is, as I understand, a standard ramjet engine). And the Isp of at least some airbreathing engines compared to rockets certainly wouldn't be as good as they are now. I'm not sure of the actual numbers and specific physics involved, but certainly, there must be some reason why they are better than just pushing reaction mass out, at least under some conditions. Or rather, some reason why turbofans can cross 10k Isp (in real life, not any KSP specific engine) while even cryogenic rocket engines (again, speaking of real life rocket engines) are under 500 Isp

If nothing else, there must be some way of getting better efficiency than standard rockets in inert atmospheres, even if not strictly a turbofan that feeds oxidizer into the intake (although that would probably be the limit of my modding skills if I ever get the patience to try my hand at creating something for this).

[Incarnation of Chaos]

56 minutes ago, FeliusKerNes said:

It must be to some degree, otherwise there'd be no point at all to making propellers and turbofans, just rocket engines that gather oxidizer from the air as they go (which is, as I understand, a standard ramjet engine). And the Isp of at least some airbreathing engines compared to rockets certainly wouldn't be as good as they are now. I'm not sure of the actual numbers and specific physics involved, but certainly, there must be some reason why they are better than just pushing reaction mass out, at least under some conditions. Or rather, some reason why turbofans can cross 10k Isp (in real life, not any KSP specific engine) while even cryogenic rocket engines (again, speaking of real life rocket engines) are under 500 Isp

If nothing else, there must be some way of getting better efficiency than standard rockets in inert atmospheres, even if not strictly a turbofan that feeds oxidizer into the intake (although that would probably be the limit of my modding skills if I ever get the patience to try my hand at creating something for this).

I'm going to say your best bet would be something like the J58; where even when the compression stage is idle it's designed to essentially become a ducted fan. Then you could have Bypass Tubes (Represented in KSP by a mode switch) that could go around the core and dump OX and Fuel directly into the afterburner; the only issue would be starting the turbine but if the air is inert anyway then that's not an issue. The "Afterburner" would just need to provide enough thrust to get up to at least Mach 1; where the effects begin to show.

Only issue is i'm not sure how KSP would handle this; if it could at all. The J58 didn't have a hard cutoff; it just became more and more of a ramjet up until the flow thru the turbines resembled a ducted fan instead of a turbojet. A thrust curve could be written for that i suppose; i'm just not familar enough with it's engine code to suggest how. What you want IS possible; it's just hard to conceptualize. 

Edited August 2, 2019 by Incarnation of Chaos

[steve_v]

10 hours ago, Shadowmage said:

Taking mechanical energy from rocket exhaust and using it to spin a turbine, which then spins props to produce thrust, I cannot envision any method where it would be more efficient than using the reaction mass/exhaust directly.

Free and unlimited reaction mass, at a nice low (close to vehicle) velocity. Next to free oxidiser, 'tis the second reason you see few rocket-planes and many turboprops, and why high-bypass turbofans are more fuel-efficient than turbojets.
For pure chemical to thermal/kinetic energy conversion a rocket is going to win hands-down, but effective propulsive efficiency in atmosphere is more complicated.

On the OP, M2X has LFO lift-fans IIRC.

Edited August 2, 2019 by steve_v

[DStaal]

10 hours ago, Incarnation of Chaos said:

I'm more saying that you have to have something to get the compression stage up to speed; that in a closed system that would basically be a rocket. Once started you can bypass the pre burner in theory and feed ox/fuel directly into the system. But that's all weight, energy losses to heat, friction etc; so basically you end up with a heavy, complex engine that I question if it would be worth it. I'll look into your rover though since it sounds pretty interesting.

And the real question in that is: Why are you feeding something you're not planning on burning any part of into the combustion chamber?    All that's likely to do is interfere with the combustion - we have enough problems with that on air-breathing engines already, but at least we are planning on burning 20% of the air.

[Incarnation of Chaos]

8 hours ago, DStaal said:

And the real question in that is: Why are you feeding something you're not planning on burning any part of into the combustion chamber?    All that's likely to do is interfere with the combustion - we have enough problems with that on air-breathing engines already, but at least we are planning on burning 20% of the air.

....the compression stage would ignite the unburnt exhaust once it spun up; the preburner is feeding the gasses in so you can burn them. This is a closed system; we can't depend on an exposed intake to do the job.