Atmospheric engines with canned oxidiser?

[FlyingPete]

I remember reading a thread a while ago about the potential for a sort of 'reversed jet engine' that instead of using liquid fuel and intake air, would take in a fuel-rich atmosphere and use onboard oxidiser for combustion. Is this at all realistic? To me it seems that all a jet engine is doing is using a combustion process to accelerate the reaction mass through the engine by raising its temperature. The efficiency comes from not having to carry the reaction mass. It shouldn't make any difference whether you're combining onboard fuel with an oxidising atmosphere, or combining onboard oxidiser with a fuel-rich atmosphere. The latter way would end up with a very rich mixture and probably a great cloud of smoke, but should work well enough as far as I can see.

What would need doing to make this viable? I like the idea of having engines that work only in the atmospheres of Eve and Jool From my limited knowledge of modding, I believe you could reconfigure the stock jet engines/intakes to run on oxidiser/'intake fuel' easily enough, but I've no idea how you'd specify which planets supply intake fuel as a resource.

[TimePeriod]

No.

Because a fuel air bomb combined with a jet aircraft stuck inside the cloud is a bad idea.

[Starwhip]

No.

Because a fuel air bomb combined with a jet aircraft stuck inside the cloud is a bad idea.

Yup. Light up the whole damn planet.

In fact, the atmosphere would probably be on fire anyways if there was any kind of lightning / internalized heating on the planet.

[AngusJimiKeith]

If there were no oxidizer in the atmosphere already, it wouldn't be a bomb...Titan's lower atmosphere, for example, is nitrogen/methane. If you had to supply the oxidizer, you would be fine.

Now, if the planet's atmosphere did have both fuel and oxidizer....bad, bad things.

[aleis]

So you want liquid oxygen and liquid fuel? Then you want to burn it to make thrust, sounds like a rocket.

Jets are efficient because they don't carry oxygen. Then they add a lot of complexity and weight to have to ability to gather air, compress it, and make it explode. Sounds a lot like a rocket

Unless they add in propellers, turbo props, or alternate fuels that use something in eves atmosphere + stuff you brought. Not very effective

[Tex_NL]

...

Now, if the planet's atmosphere did have both fuel and oxidizer....bad, bad things.

True. But this will never happen. They would slowly react with each other until either fuel or oxidizer was used up.

[FlyingPete]

So you want liquid oxygen and liquid fuel? Then you want to burn it to make thrust, sounds like a rocket.

Jets are efficient because they don't carry oxygen. Then they add a lot of complexity and weight to have to ability to gather air, compress it, and make it explode. Sounds a lot like a rocket

Nope, I'm talking about taking in an atmosphere that's rich in, say, hydrogen or methane (but no oxygen) and burning it with a liquid oxidiser you carry on board- no onboard liquid fuel needed. The exact reverse of taking in an atmosphere rich in oxygen and burning it with a liquid hydrocarbon fuel. In both cases you're providing thrust by gathering in a gaseous atmosphere and accelerating it, using a small part of that atmosphere as one of the combustion reactants. The other reactant is a liquid you brought with you. It makes no difference whether you're adding oxygen to a nitrogen/methane atmosphere or adding a hydrocarbon to a nitrogen/oxygen atmosphere.

I just think it would be an interesting addition to the game if some bodies (most likely Eve and Jool) had this environment.

[Tellion]

Well in theory it is the same principle as a jet engine, taking in some of your reaction mass from the environment and making the whole "moving forward by pushing stuff out backwards" a whole lot more efficient... But if this has any feasibility in practice I have no idea... I do not know enough about the exact reactions/mass ratios in common jet engines, but I would guess that carrying the oxygen around with you while getting the hydrogen from the atmosphere would be significantly less effective, than the other way around. Methane looks more interesting in that regard if i am correct - but that's in no way guaranteed Its a very interesting concept to speculate about though.

[FlyingPete]

So I've been digging through the parts config, and while it's a fairly simple matter to specify a new resource 'IntakeFuel', modify a jet engine to use it and Oxidiser, and an intake to collect it, the sticking point seems to be in making it work only in certain atmospheres. There's a 'check for oxygen' line to limit regular jets to Kerbin and Laythe, but I presume this sort of data is buried deep in the code somewhere, which I've no idea how to alter

On a practical side, I believe most jet engines run very lean as you're only burning some of the oxygen in the air you draw in. With the reversed cycle you'd effectively have a rich mixture, but how this would be affected by a gaseous fuel and liquid oxidiser I don't know.

Edited January 8, 2015 by FlyingPete

[Kerbart]

Consider the jet engine a device that takes atmospheric gas "A" and mixes it with a highly reactive agent "B".

It wouldn't really matter which one of the two is the oxidizer. However, my limited knowledge of rocket fuels suggests that it's usually the oxidizer that you need in larger quantities. That might be a bit of a limitation for this idea.

[Tellion]

Regarding Resources, maybe Regolith does atmospheric definitions? It should...

Then you could modify planet x to have resource y in its atmospheric definition, and basically use your custom intake as a efficient air scoop á la Karbonite... This is probably a pretty "unelegant" solution, but it doesnt require fiddling around with the stock code. I am not sure whether the modules that are responsible for that job in regolith take altitude/atm pressure into account though.

Also one would have to do all the number crunching and physics calculation for the exact reaction... Which sounds hard

Edited January 8, 2015 by Tellion

[aleis]

Nope, I'm talking about taking in an atmosphere that's rich in, say, hydrogen or methane (but no oxygen) and burning it with a liquid oxidiser you carry on board- no onboard liquid fuel needed. The exact reverse of taking in an atmosphere rich in oxygen and burning it with a liquid hydrocarbon fuel.

Ah, ok then yes in this case it would work just fine. However, you have to design a special jet that is made specificity for that type environment and flight profile.

It is certainly possible if there is a chemical that works in the atmosphere but it would take a lot of special work. The engineering that goes in to making jets function beyond the basics is staggering and precise to our atmosphere.

But technically possible, thoughthoughyou would need different engines with different fuels for each planet

[FlyingPete]

Ah, ok then yes in this case it would work just fine. However, you have to design a special jet that is made specificity for that type environment and flight profile.

It is certainly possible if there is a chemical that works in the atmosphere but it would take a lot of special work. The engineering that goes in to making jets function beyond the basics is staggering and precise to our atmosphere.

But technically possible, thoughthoughyou would need different engines with different fuels for each planet

I'd probably simplify things slightly, in the same way that standard jet engines work on both Laythe and Kerbin and burn liquid rocket fuel without oxidiser. I'd have reversed-cycle jet engines work on Eve and Jool, running on standard oxidiser without fuel. Perhaps a higher efficiency on Jool if this is possible. There has to be a balance between practicality and accuracy.

Eve has the obvious application of oxidiser-fueled, fuel-breathing aircraft for exploring the surface, while at Jool you could drop a manned capsule into the atmosphere and do science before boostng back out.

A part that would be needed/useful for this is a tank that holds only oxidiser. It would be handy for conventional SSTOs too as you could more easily adjust the fuel/oxidiser capacity.

Edited January 8, 2015 by FlyingPete

[aleis]

You have the idea but you're missing what I was saying. The oxydizer (oxygen) is the easy part, its the fuel that's the problem. Think about putting diesel in a gas car then multiply the engineering involved by 10. And that's assuming the atmosphere there is made of something that even reacts with oxygen

[FlyingPete]

And that's assuming the atmosphere there is made of something that even reacts with oxygen

That's the assumption I was making. The ideal would be a nitrogen/hydrogen atmosphere. Then you could use it as both reaction mass and fuel in a specially-designed engine. A hydrocarbon atmosphere might give you problems with soot contamination due to the unburnt carbon at part load. But then this is KSP, and based on the dropped resource plans, we can assume that the atmosphere contains a proportion of propellium which we can use as fuel. I've dropped a probe on Eve before that did atmospheric analysis, so we can assume that engineers on Kerbin can design an engine that will run in that atmosphere