"Jet" engines on Eve for Alien Space Programs?

[Nicias]

On 4/7/2017 at 10:03 AM, Razorforce7 said:

In light of a collective desire to have atmospheric propulsion on Eve I say "aye" to any new propulsion method.
In light of a poor attempt to magicaly transform Jet engines into something fictional to meet the desire for having such propulsion I say "nay"

 

 

And I am going to bring up the "science behind" this idea. Not to convert you from the core idea of having atmospheric propulsion on Eve, in fact I'm encouraging you.
But I will attempt a reconsideraton of yours on what kind of propulsion this should be.

I'm not trying to convince people not to have their fun with a mod like this. If it entices you to have such a engine for Eve then go for it. Forget I ever replied and sorry for my post its length.
But in light of what I'm going to discuss I would recommend to go for atleast a theoretical propulsion design rather then a fictional hybrid jet engine for Eve. Because it makes no sense whatsoever.

Given the temperature and atmospheric conditions at Eve I can only think that explodium is a raw naturally occuring hydrocarbon.
Hydrocarbons are filthy in their raw form. They do not burn in a clean and controlled fashion, your engine will choke itself in case it does give you any ignition hicccup if it were to be fueled by it.
But it will never get to work because unrefined hydrocarbons are volatile, sticky, explosive, corrosive and unfit for controlled engine combustion.
Any raw material present is impure by the very fact that it is raw. Its why you bring your car to ExxonMobil instead of a oil well.
It is why water is purified in your local water treatment plant.

Also, explodium is present as lakes and atmosphere. So there is precipitation of explodium in the atmosphere. Meaning that the layer of combustable explodium is limited to the lowest part of Eve's atmosphere. And I would expect any such engine to choke itself from 8km altitude and quit alltogether at 10km.

Also, last time I checked turbofan combustion chambers have their fuel injected, not their oxygen.
If oxygen is to be injected then how could it guarantee proper chamber combustion when the chamber is expecting compressed oxygen to be ambient within the chamber itself?
How can you disperse oxygen to be ambient within a high pressure chamber that is designed to compress and exhaust as much ambient air as possible?
It would require a very sophisticated system that automaticaly injects the proper amount of oxygen before it is compressed in the turbines compressor.
Which needs to happen at the same pressure (which is high even in front of the compressor)
It also needs to happen very accurate or your engine will simply fail due to oxygen starvation.

How would that then be possible?
Also, oxygen requires heavy pressure tanks to be stored. For that reason I don't think it will fit any aicraft design since they'd be easily to heavy.

This engine would have the following miracle properties.

*Ability to feed injected oxidiser before it enters the engines compressor and have it computer controlled so that the engine keeps combustion stability at every turbine speed.
*Ability to refine the explodium fuel as it enters the intake (which requires a secondary intake) Because you need to store it first to refine it onboard.
*Very limited use since explodium is mainly liquid and only exists as a narrow lower band in the atmosphere as it is the densest gas available.
So realisticaly your engine should stall only a few kilometres above the surface and fail completely by going any higher then 10km altitude.

Carrying oxygen around is much heavier, a secondary intake and refinery is even more heavy. A modified heavier jet engine (if at all possible) is even more weight.
The point in case: You will never get of Eve's surface. This is like suggesting a alcubierre drive. Atleast from that one we agree it's fictional.
Since a Eve jet engine is the same ballpark I wonder why you don't simply theorize a fictional engine to begin with. Instead of something of which we know it can't be done. Or atleast not successful and for any existing purpose.
 

 

I don't buy these concerns. Whatever explodium is the substance in the ocean, is not the same as the substance in the atmosphere. If the oceans are filled with a reducer (like a hydrocarbon) then the atmosphere must not have any oxidizer in it. Otherwise the oceans would be on fire. So the most volatile elements of whatever is in the ocean will evaporate and rain down, like on Titan. So if the oceans are all kinds of hydrocarbon crud, the reactive portion of atmosphere is probably mostly things like methane, ethane, ethene, propane, etc. Which all burn fine. Don't think of using crude oil, think of using natural gas. Again, like Titan.

In terms of getting just the right amount to use, that is easy too. You don't. IRL, turbine engines aren't rune stoicometerically (sp?). They would melt if they did. So you throttle by controlling how much oxidizer you pump in.  

You also don't have to use LOX. (Assuming that is what oxidizer is). Hydrogen peroxide might be a better choice if you were actually making one of these.

Aside from the fact that LOX is cryogenic, I don't see any difference between a lox or peroxide jet in a mostly inert atmosphere with some light hydrocarbon and using a CNG turbine in a oxygen/nitrogen atmosphere.

[Gordon Fecyk]

On ‎4‎/‎9‎/‎2017 at 11:37 PM, JadeOfMaar said:

I don't know if machCurve works for the harvest module as it works for the intake module but it's quite worth a shot.

machCurve appears to be ignored by ModuleResourceHarvester. I took two shock cones, one with machCurve copied from the original shock cone intake and one without, and they harvested the same amount of ExpVapour at all altitudes up to 40 km and air speeds beyond Mach 5.

velCurve's copied from the original engines to the Exp/Ox versions. The Sphinx engine will flame out beyond Mach 3 like the Panther does above Kerbin normally, but Mach 3 is a different air speed above Eve depending on altitude.

I suppose the velCurve values from the original engines should be OK, but I could tune them to have less thrust to accommodate Eve's higher pressures, or give them low expansion nozzles like the Eve Optimized Engines... maybe this doesn't make sense on a jet engine but I could reduce the ISP somehow. Already these engines use 1.2x the oxidizer that the original engines use in liquid fuel, so that plus oxidizer being more massive (and weighing more on Eve's 1.7g) might be enough to emulate the desired efficiency and thrust.

The test craft was Thrimm's LTS Sparrow-FC, using Sphinx instead of Panthers, and either circular or shock cone harvesters instead of intakes. Source craft here. These craft won't make orbit from Eve of course, but they can exceed Mach 5 for engine and harvester tests.

I was thinking about oxidizers too. Oxygen is the most well known oxidizer but there are plenty of others; Nicias just mentioned Hydrogen Peroxide a moment ago as one example. KSP already simplifies liquid fuel into something that can be used with rockets, nuclear engines and jet engines, so oxidizer could likewise be simplified into something that can be used by rockets and these explodium-breathing engines.

Folks, if you feel brave enough to try out GregroxMun's Alien Space Programs and building jet aircraft with these parts on Eve, please let me know in the mod dev thread your suggestions for engine tuning.

[Update 21 APR] I did some math and came up with one set of numbers, then did some chemistry and came up with a different but still reasonable second set of numbers. Check out the mod dev thread for the math and chemistry, but the end result is the modded engines could use anywhere from five to seven times the amount of ExV than the corresponding jet engine would use in Intake Air.

Edited April 21, 2017 by Gordon Fecyk
Added progress on engine balancing

[Gordon Fecyk]

All right, here's some science. Chemistry, specifically.

I haven't done this sort of chemistry for decades, so corrections are wanted. I'm assuming that IntakeAir = 78% N₂ and 21% O₂, and LiquidFuel = 100% H₂. Dangerous stuff, but it's the only thing that could be simultaneously used in chemical rockets, jet engines, and nuclear rockets. I'll also assume, based on the KSP Wiki entry for Eve, is that ExpVapour is 90% CO₂ and 10% C₂H₆ (Ethane), and Oxidizer = 100% O₂. Also dangerous stuff in Eve's environment.

When reacting with O₂, H₂ and C₂H₆ provide different amounts of energy, here in megajoules:

Propellant	HHV (MJ/kg)	LHV (MJ/kg)
H2	141.80	119.96
C2H6	51.90	47.62

Already C₂H₆ is 36-40% as powerful as H₂. Fine, we just use more of everything. But then Eve's air has half of the C₂H₆ that Kerbin would have in O₂, so do we need to move twice as much air to get the same thrust? This is the first thing I don't know.

The lower heating value includes heat losses due to water evaporation. But Eve's air is above 100^OC already at altitudes 40 km or lower, so the water exhaust should already be vapour and I can use the high heating value.

I did a lot of math and chemistry to come up with a ratio of 38.1 U Intake Air to 1 U Liquid Fuel getting 100% usage, or 119.96 MJ/kg / 599.8 MJ/U LF based on Kerbin's temperatures being lower than 100^OC, assuming 1 U Intake Air has only 0.21 U O₂ in it. Some engines are more efficient than this (Wheesley, Goliath, Panther in Dry mode) and the rest are less efficient.

Spoiler

Clean burn needs 2 x H₂ + 1 x O₂ -> 2 x H₂O
H₂ atomic mass = 2, O₂ atomic mass = 32
2 kmol H₂ = 4 kg, 1 kmol O₂ = 32 kg
4 kg H₂ + 32 kg O₂ -> 36 kg H₂O + 479.2 MJ energy
4 kg H₂ + 152.38 kg IA -> 36 kg H₂O + 116.38 N₂ + 479.2 MJ energy
20 kg H₂ + 761.9 kg IA -> 180 kg H₂O + 581.9 N₂ + 2396 MJ energy
1 U H₂ + 38.095 U IA -> 9 U H₂O + 29.095 U N₂ + 599.8 MJ energy (Assuming 1U = 5 kg)

On Eve with its hypothetical 10% C₂H₆, to burn 1U O₂ I need 0.375U C₂H₆, or 1.875 kg. This gives me 97.31 MJ/U O₂ based on Eve's air being warmer than 100^OC up to 40 km up and the water already being vapour. This is 16.2% of the energy I get from H₂ and Intake Air back at Kerbin, even with vapour heating ignored. I'd need 6.16 times the resources to get the same energy. And then ExV being only 10% C₂H₆, I'd need 3.75U ExV.

Spoiler

Clean burn needs 2 x C₂H₆ + 5 x O₂ -> 4 x CO₂ + 6 x H₂O
C₂H₆ atomic mass = 30, O₂ atomic mass = 32
2 kmol C₂H₆ = 60 kg, 5 kmol O₂ = 160 kg
60 kg C₂H₆ + 160 kg O₂ -> 176 kg CO₂ + 108 kg H₂O + 3114 MJ energy
600 kg ExV + 160 kg O₂ -> 176 kg CO₂ + 108 kg H₂O + 540 kg CO₂ + 3114 MJ energy
120 U ExV + 32 U O₂ -> 35.2 U CO₂ + 21.6 U H₂O + 108 kg CO₂ + 3114 MJ energy (Assuming 1U = 5 kg)
3.75 U ExV + 1 U O₂ -> 1.1 U CO₂ + 0.675 U H₂O + 3.375 U CO₂ + 97.31 MJ energy (Assuming 1U = 5 kg)

Now take the Panther, with its 40:1 usage in Dry mode that closely matches the clean burn of 38.1:1. To get 599.8 MJ on Eve I'd need to burn 6.16 times the OX and 6.16 times the ExV, giving me a ratio of 23.1:6.16. The Panther is slightly more efficient, so the Sphinx would have 1.04 times the 23.1, or 24.0:6.16. Or maybe that needs to be inverted to be 4% less efficient? 22.2:6.16?

I tried increasing the ratio of OX in the engines to see what using six times the oxidizer would do, but KSP seems to ignore this and instead adjusts the ExV usage. I suppose I could change the ratio to be 3.60:1 and then increase the resource use by 6.16 times. Not sure where to set that; looks like it's in atmosphereCurve. It's in atmosphereCurve alright; I can set the ratio to be some fraction of 3.75:1 and then reduce the ISP value in atmosphereCurve to have it use 6.16 times the oxidizer. The poor Hades turned into a pig with only 990 seconds ISP and a ratio of 2.2:1, compared to the Juno's 6400 seconds and 22:1 ratio.

Edited April 23, 2017 by Gordon Fecyk
Figured out how to edit resource usage! And Grammar.

[Wadusher0]

What happens to the thrust of your engines under those assumptions? Does it increase or decrease at 1 atmosphere of Expoldium compared to the stock jet engines? From a gameplay perspective I would expect these engines to sacrifice efficiency for a massive increase in thrust over stock jets, especially at Eve sea level's 5 atmospheres  - otherwise they'd be completely unusable - but you're the one with the chemistry knowledge...

[Gordon Fecyk]

15 minutes ago, wadusher1 said:

What happens to the thrust of your engines under those assumptions? Does it increase or decrease at 1 atmosphere of Expoldium compared to the stock jet engines?

If I take a craft with Hades engines up to about 15 km up where it's one atmosphere, the thrust feels like the stock engine thrust. I'm getting about 18-20 kN thrust at that altitude like the Juno does at Kerbin sea level. Thrust isn't decreasing at lower altitudes, but the air pressure does so the craft will slow down.

I kept the existing atmCurve and velCurve values for the stock engines. The Hades barely scrapes Mach 1 at 15 km up and slows right down to Mach 0.2 at 2 km up.

31 minutes ago, wadusher1 said:

From a gameplay perspective I would expect these engines to sacrifice efficiency for a massive increase in thrust over stock jets, especially at Eve sea level's 5 atmospheres  - otherwise they'd be completely unusable.

By trying to keep the energy levels the same as the stock engines using that baseline of 599.8 MJ/U, these engines would burn 6.16 times as much oxidizer as the stock engines would burn liquid fuel to get the same thrust. So there is a sacrifice in efficiency to be sure; a huge one. What I am gaining though, is a lot of lift.

Having made the changes and experiencing the very pathetic ISPs, I'm wondering if I should increase the ISPs and actually reduce the thrust. At 5.7 atmospheres I don't need nearly as much speed to climb as I would with 1.0 atmospheres, even with 1.7g surface gravity. I'm launching and flying with 1/3rd throttle just to avoid pushing against the thick air too much, using less oxidizer while doing so. Maybe change that baseline to 300 MJ/U, cut the thrust values in half, and double the ISP values. You just don't need the thrust in 5 atmospheres, and in fact more thrust is wasteful.

I have Ferram Aerospace installed on my test bed for this mod, so the aero is a little more realistic.

Chemistry I seem to have figured out. Aerodynamics and fluid dynamics in Eve's air? That's another problem.

[qzgy]

26 minutes ago, Gordon Fecyk said:

By trying to keep the energy levels the same as the stock engines using that baseline of 599.8 MJ/U, these engines would burn 6.16 times as much oxidizer as the stock engines would burn liquid fuel to get the same thrust. So there is a sacrifice in efficiency to be sure; a huge one. What I am gaining though, is a lot of lift.

Having made the changes and experiencing the very pathetic ISPs, I'm wondering if I should increase the ISPs and actually reduce the thrust. At 5.7 atmospheres I don't need nearly as much speed to climb as I would with 1.0 atmospheres, even with 1.7g surface gravity. I'm launching and flying with 1/3rd throttle just to avoid pushing against the thick air too much, using less oxidizer while doing so. Maybe change that baseline to 300 MJ/U, cut the thrust values in half, and double the ISP values. You just don't need the thrust in 5 atmospheres, and in fact more thrust is wasteful.

I have Ferram Aerospace installed on my test bed for this mod, so the aero is a little more realistic.

Chemistry I seem to have figured out. Aerodynamics and fluid dynamics in Eve's air? That's another problem.

Hi. Not a modder. Haven't been on eve before. So completely unqualified. But I don't mind giving a bit of input. It seems like the atmosphere is super thick. Personally, I would do what you suggest, and reduce the thrust values for an (proportional-ish)increase in ISP so that the lift values themselves are so that aerodynamic craft performance is about the same on Eve as on Kerbin. Nobody (i think) would reasonably go too fast to avoid overheating.

Edited April 23, 2017 by qzgy

[Wadusher0]

25 minutes ago, Gordon Fecyk said:

If I take a craft with Hades engines up to about 15 km up where it's one atmosphere, the thrust feels like the stock engine thrust. I'm getting about 18-20 kN thrust at that altitude like the Juno does at Kerbin sea level. Thrust isn't decreasing at lower altitudes, but the air pressure does so the craft will slow down.

I kept the existing atmCurve and velCurve values for the stock engines. The Hades barely scrapes Mach 1 at 15 km up and slows right down to Mach 0.2 at 2 km up.

By trying to keep the energy levels the same as the stock engines using that baseline of 599.8 MJ/U, these engines would burn 6.16 times as much oxidizer as the stock engines would burn liquid fuel to get the same thrust. So there is a sacrifice in efficiency to be sure; a huge one. What I am gaining though, is a lot of lift.

Having made the changes and experiencing the very pathetic ISPs, I'm wondering if I should increase the ISPs and actually reduce the thrust. At 5.7 atmospheres I don't need nearly as much speed to climb as I would with 1.0 atmospheres, even with 1.7g surface gravity. I'm launching and flying with 1/3rd throttle just to avoid pushing against the thick air too much, using less oxidizer while doing so. Maybe change that baseline to 300 MJ/U, cut the thrust values in half, and double the ISP values. You just don't need the thrust in 5 atmospheres, and in fact more thrust is wasteful.

I have Ferram Aerospace installed on my test bed for this mod, so the aero is a little more realistic.

Chemistry I seem to have figured out. Aerodynamics and fluid dynamics in Eve's air? That's another problem.

Oh ok. If lift is more important then I wouldn't mind decreased thrust. ISP definitely needs to increase, but there is an approximate thrust curve when you graph the relation between isp and stationary thrust of all the stock jet engines that you may want to roughly preserve with Explodium engines. I suggest figuring out your isp values and then figuring out your thrust levels.

Also, since FAR is only a dev build for 1.2.2, it might help to test your engines separately for stock and FAR, as many Explodium Engine users will not be using it.

[Gordon Fecyk]

Hydrogen vs RP-1

I based all of this chemistry off in-game Liquid Fuel being hydrogen, thinking no one's going to use a hydrocarbon in the LV-N nuclear rocket. The KSP Wiki suggests it's closer to RP-1, refined kerosene, which gets used in chemical rockets and jet engines. That's a closer match to ethane for high heat value, and I'd be able to re-balance the Explodium engines with significantly higher specific impulse using a lower energy baseline.

I don't know what RP-1's chemical composition is, and neither does Wikipedia apparently, with the closest single match being dodecane (C₁₂H₂₆). Even if it's a mix of different hydrocarbons, they all burn to CO₂ and water vapour (ideally), so I can figure out the baseline even if it's an average of all of the components. The Russians apparently experimented with dicyclopropyl cyclopropane (C₁₀H₁₆).

Edited April 24, 2017 by Gordon Fecyk

[fourfa]

I thought the in-game ISPs and fuel/oxidizer ratio pointed to a UDMH/N2O4 combo.  But the fact that jets and rockets burn the same liquid fuel points to RP-1.  Either way it's ultimately a fictional resource, and gameplay balance has to trump realism for the mod to be successful and fun IMHO.  

anyway you might want to looks specifically at RP-1 instead of kerosene: this line was helpful "The remaining hydrocarbons are at or near C₁₂ mass."

Is explodium found in any other worlds, like in GPP or OPM?

[Gordon Fecyk]

@fourfa That's matching other forum posts yes, that RP-1 is a closer match to our fictional Liquid Fuel. I'm just redoing the energy baseline using that, and I expect to end up with a much lower baseline that'll allow me to up the ISP of these engines and still be somewhat realistic. I'll respond back here once I have some numbers.

As for other peoples' worlds and planet packs, I think Titan is supposed to be 1.4% methane, and overall I'm seeing a consistent high heat average for all of these hydrocarbons, so it would be reasonable to see these engines work on worlds that have at least 10% of its atmosphere be some hydrocarbon. It wouldn't take much to adapt this resource to use on other planet packs; look at the ExplodiumVapour.cfg file in the mod for the Eve example, and add worlds as you think appropriate.

[JadeOfMaar]

1 hour ago, fourfa said:

Is explodium found in any other worlds, like in GPP or OPM?

Explodium as a resource does not actually exist and merely serves as poetic license in Eve's biome names. You'll find Karbonite in its place on Eve itself, Tekto (OPM) and in varying amounts on most worlds (GPP).

[fourfa]

Yeah, I was being poetic there.  Asking about future intent for the mod, beyond just Eve

[JadeOfMaar]

Expanding this mod to other planet/star systems would be very easy. It's a simple matter of cloning any such system's Karbonite config, keep only the atmospheric entries and replace all mention of Karbonite with ExpVapor.

13 minutes ago, Gordon Fecyk said:

As for other peoples' worlds and planet packs, I think Titan is supposed to be 1.4% methane, and overall I'm seeing a consistent high heat average for all of these hydrocarbons, so it would be reasonable to see these engines work on worlds that have at least 10% of its atmosphere be some hydrocarbon. It wouldn't take much to adapt this resource to use on other planet packs; look at the ExplodiumVapour.cfg file in the mod for the Eve example, and add worlds as you think appropriate.

GPP has a moon with 10% Methane atmosphere and LqdMethane lakes. The 10% seems like a very fine qualification for worlds applicable to Explodium engines. So I'll donate some entries to this mod's resource config.

 

[Gordon Fecyk]

Revised energy baseline

RP-1 is an interesting beast, being a mix of various hydrocarbons. The closest approximation I found was something like C_nH_1.953n. For the purpose of determining our energy baseline, and because we can do this sort of thing with hydrocarbons and we're talking about one mole being 6.02 x 10²³ molecules, I'll invent C₁₀₀₀H₁₉₅₃. It still burns to CO₂ and water vapour and the site lists an approximate atomic mass of 175 and a low heat value of 43 MJ/kg. I'll assume this is being burned at Kerbin where ambient temperature is under 100 C, so the low heat value of 43 MJ/kg applies.

Spoiler

C_nH_1.953n atomic mass = 175, O₂ atomic mass = 32
1 x C₁₀₀₀H₁₉₅₃ + 1000 x O₂ + 488.25 x O₂ -> 1000 x CO₂ + 488.25 H₂O
1 kmol C₁₀₀₀H₁₉₅₃ + 1488.25 kmol O₂ -> 1000 kmol CO₂ + 488.25 kmol H₂O
1750 kg C₁₀₀₀H₁₉₅₃ + 47616 kg O₂ -> 44000 kg CO₂ + 8788.5 kg H₂O + 75270 MJ energy
350 U C₁₀₀₀H₁₉₅₃ + 9523.2 U O₂ -> 8800 U CO₂ + 1757.5 U H₂O + 75270 MJ energy (Assuming 1U = 5 kg)
350 U C₁₀₀₀H₁₉₅₃ + 45348.6 U IntakeAir -> 8800 U CO₂ + 1757.5 U H₂O + 35825.4 U N₂ + 75270 MJ energy (Assuming 1U = 5 kg)
1 U C₁₀₀₀H₁₉₅₃ + 130 U IntakeAir -> 25.14 U CO₂ + 5.02 U H₂O + 102.36U N₂ + 215.0 MJ energy (Assuming 1U = 5 kg)

So there's our new baseline of 1U Liquid Fuel producing 215 MJ at a ratio of 130:1 intake air to fuel, which is just over one third of the hydrogen baseline. Only the Goliath engine exceeds this ratio and the other engines are lower than this.

To match 215.0 MJ per one liquid fuel, I need to burn only 2.21 times the oxidizer and Explodium Vapour, giving me ISPs like 2895 for the Hades, 4750 for the Zephyrus, 1810 for the Beelzebub, and so on. That's almost a three times improvement. It still consumes a lot more oxidizer, but not obscenely so. The ratios would be unchanged, and the thrust would also be unchanged.

On the thrust front I'm looking at adjusting the atmCurves of the engines to avoid pushing too hard at lower altitudes, but that's something I'll take over to the mod thread.

[JadeOfMaar]

Small question. This is something I should know already but I don't. Why do you set PresenceChance to 1000?

[Gordon Fecyk]

Just now, JadeOfMaar said:

Small question. This is something I should know already but I don't. Why do you set PresenceChance to 1000?

This was a workaround suggested by @ShotgunNinja to ensure the resource would always be present, even with difficulty sliders set to 10% for resource chances. It doesn't change the amounts that would be found, but it would change the chance of Yes it's there vs No it isn't.

[JadeOfMaar]

Just now, Gordon Fecyk said:

This was a workaround suggested by @ShotgunNinja to ensure the resource would always be present, even with difficulty sliders set to 10% for resource chances. It doesn't change the amounts that would be found, but it would change the chance of Yes it's there vs No it isn't.

Thanks. That's very good to know. I've met with the exact problem that this setting prevents. Some GPP users are finding resource voids that should not exist due to playing hard mode.  

One more question. For qualifying worlds to support your engines, can I use 10% karbonite/methane (whichever is higher) or only karbonite?

[Gordon Fecyk]

Just now, JadeOfMaar said:

For qualifying worlds to support your engines, can I use 10% karbonite/methane (whichever is higher) or only karbonite?

I think the MIT License permits you to adjust and redistribute the mod as you see fit. You just can't blame me for mistakes. Should be OK for you to fork it for Karbonite, but I'm still tuning it so things are changing.

[JadeOfMaar]

Okay.  I sent you a (PR) pull request. I added support for a third very prominent planet mod too.

[Gordon Fecyk]

Since there are going to be different planets in some planet packs with varying percentages of hydrocarbons in the air, I want to make sure the amount of ExpVapour has an appropriate impact on engine performance.

When I see this in an atmosphere resource config:

Distribution
{
	PresenceChance = 1000
	MinAbundance = 70
	MaxAbundance = 80
	Variance = 0
}

...what do the MinAbundance and MaxAbundance values actually represent? Would I be correct in setting these to 10 for Eve and its hypothetical 10% ethane in the air?

If I can establish a percentage, say if the harvester sucks in 10 U of atmosphere and extracts only 1 U of the resource, then I can change the engine ratios to a baseline of 0.375:1 instead of 3.75:1, and rely on the harvesters to gather the appropriate amount of the resource. As it stands, the engines are more speed-constrained than resource-constrained, even with ISPs at 45%.

...some testing later and the resource MinAbundance and MaxAbundance do have an impact on the amount of resources used. These are percentages alright. I was able to make the harvesters take 10% ExV compared to the corresponding intake amounts of IntakeAir with checkForOxygen=false. The IntakeRadialLongExV harvester has the lowest harvesting rate of 0.076 U/s when stationary, matching its stock version that takes 0.76 U/s IntakeAir, again assuming normal IntakeAir has only 21% usable oxidizer for a normal jet engine.

I might have a new problem though. If I treat ExV like a random hydrocarbon in the air instead of the whole air, I can dial the MaxAbundance down to 1.5% like on Titan, and one IntakeRadialLongExV can still harvest enough of the stuff to drive a single Beelzebub engine to the upper atmosphere before atmCurve says, "that's high enough," and I get a combustion failure. So even with resources set to realistic values and harvesters gathering realistically lower amounts, the engines are still more altitude and speed-constrained than resource-constrained.

One nice thing from all of this: Unless I made some dumb chemistry mistakes, maybe there's a real world future for jet engines on Titan.

Edited April 27, 2017 by Gordon Fecyk
Added test results

[Galane]

A rather interesting thing about internal combustion engines is much of their power comes from compressing, heating, and expanding inert gas. On Earth that's the ~70% nitrogen in the air. The nitrogen serves as a working fluid, the work being done on it by the mixing and combustion of the fuel and oxygen.

If an engine was run on just the oxygen in the air, it would either have very little power, or wouldn't run at all.

There are different stoichiometric ratios for each fuel with air and with pure oxygen. Any oxygen that's bound up in the fuel's molecules may have to be considered, depending on if the combustion process for that fuel breaks it free.

Ideally you have precisely the amount of fuel to combine with 100% of the oxygen atoms. In practice you don't get that, or don't want that. Too lean and you have excess oxygen which binds with nitrogen to produce nitrogen oxides and sulfur to produce sulfur oxides. Combine those with water vapor and a little help from sunlight = (quite dilute) acid rain of nitric and sulfuric acids. (That's why onions can make your eyes water, the sulfur compounds mix with your tears to make an irritating sulfuric acid.) Lean burning also runs hotter because all or very nearly all of the oxidizable parts of the fuel are getting oxidized.

Most ICE's run slightly rich, ideally just a little over ideal stoichiometric ratio. Some Engine Control Units will cycle the air:fuel ratio between stoichiometric and slightly rich to balance temperature VS emissions. The unburned fuel keeps temperatures down, but contributes to pollution with unburned hydrocarbons, particulates and higher carbon dioxide and carbon monoxide output.

For terrestrial ICE's the solution to that for the past 42 years has been an afterburner catalytic converter. Before computer controlled fuel injection, the typical way to deal with unburned fuel in exhaust was to inject additional air, either at the exhaust ports or directly into the catalytic converter. Various catalysts coated onto a ceramic matrix (or lots of beads in early ones) cause reactions with the gasses to break up nitrogen and sulfur oxides and other funky chemistry until the output at the end of the exhaust pipe is whatever the California Air Resources Board wants it to be that year. (If only they'd known their CARB acronym would eventually come to be meaningless for most car owners by the late 1990's.)