[1.8+] Real Fuels

[dlrk]

I don't see any reason to think kerbals would have a better attitude towards large toxic waste spills than humans

[NathanKell]

Kerosene has lower performance (lower Isp *and* is less dense) than the hydrazine derivatives; if you're going for cancer-death-stuff already, you might as well make both your oxidizer and your fuel cancer-death-stuff and get better performance. Hazmat suits and clean rooms are a fixed cost, more or less.

Conversely hydrazine-derivatives have better performance than kerosene with LOX; but usually if you're using LOX (dirt cheap, safe) it's worth getting another cheap and safe fuel rather than having slightly higher performance at the cost of, err, cost, and also cancer-death.

As a general rule, many oxidizers can be used with many fuels. Each has its own performance level, and the combined performance level basically tracks this. Here is a great reference by the awesome Bob Braeunig: http://www.thespacerace.com/forum/index.php?topic=2583.msg17481#msg17481

[Starwaster]

Kerosene has lower performance (lower Isp *and* is less dense) than the hydrazine derivatives; if you're going for cancer-death-stuff already, you might as well make both your oxidizer and your fuel cancer-death-stuff and get better performance. Hazmat suits and clean rooms are a fixed cost, more or less.

Conversely hydrazine-derivatives have better performance than kerosene with LOX; but usually if you're using LOX (dirt cheap, safe) it's worth getting another cheap and safe fuel rather than having slightly higher performance at the cost of, err, cost, and also cancer-death.

As a general rule, many oxidizers can be used with many fuels. Each has its own performance level, and the combined performance level basically tracks this. Here is a great reference by the awesome Bob Braeunig: http://www.thespacerace.com/forum/index.php?topic=2583.msg17481#msg17481

I just had a thought of pure awesomeness. Let's make the VAB propellant aware. If you start building rockets with nasty propellants (chlorine trifluoride anyone?) then Kerbals in the VAB will randomly experience accidents. Sounds of explosion... panic.... if we can figure out how to control Kerbal animation we can have one running around in circles in the background with flame and smoke particles attached!

[dlrk]

I would love to see that ^

[jrandom]

I've been calling for persistent dead kerbals for ages. Can you imagine having dead/dying kerbals around the launchpad after using a NERVA as a launch stage? Or a capsule of kerbal skeletons orbiting the sun because their life support ran out?

[Starwaster]

I've been calling for persistent dead kerbals for ages. Can you imagine having dead/dying kerbals around the launchpad after using a NERVA as a launch stage? Or a capsule of kerbal skeletons orbiting the sun because their life support ran out?

Fun trivia fact: Did you know that video games in Germany are not allowed to use ragdoll technology for corpses? Corpses must be static so that players cannot perpetrate violence upon them.

Because of the laws pertaining to this, Crytek's Cryengine deactivates ragdoll on corpses after 2 seconds. (basically giving the corpse some time to settle into position and then lock it into place)

[steve000]

Hey folks,

What am I doing wrong? The atomic engines seem to have significantly less delta v than the other engines. the ammonia and methane has more delta but still not as much as the poodle. whats the point if this is correct?

Please see http://imgur.com/rnqqeU1 and tell me what i am doing

[Rayder]

It appears you have the engine and tank configured for Hydrogen. Hydrogen is much less dense than other fuels, even in liquid form. You can see this by looking at the vessel mass. 9.2t for Hydrogen, compared to 20t for liquid fuel. To overcome this you need a much bigger fuel tank for the hydrogen, like the orange jumbo.

Kilo for kilo, Hydrogen will give you better ISP but you need more volume. Put an orange tank or two, and match the weights. I'd say that if you had 20t of hydrogen you would see the result you want.

EDIT: You can also see that the engine alone weighs 6.6t, which means you're only using 2.6t of Hydrogen.

Edited July 8, 2014 by Rayder

[Starwaster]

It appears you have the engine and tank configured for Hydrogen. Hydrogen is much less dense than other fuels, even in liquid form. You can see this by looking at the vessel mass. 9.2t for Hydrogen, compared to 20t for liquid fuel. To overcome this you need a much bigger fuel tank for the hydrogen, like the orange jumbo.

Kilo for kilo, Hydrogen will give you better ISP but you need more volume. Put an orange tank or two, and match the weights. I'd say that if you had 20t of hydrogen you would see the result you want.

EDIT: You can also see that the engine alone weighs 6.6t, which means you're only using 2.6t of Hydrogen.

So sad. a year later and still having to explain this......

[jrandom]

So sad. a year later and still having to explain this......

Relevant XKCD

I try to remember that every time I get annoyed at seeing the same question over and over and over...

[steve000]

Thank you Raydar.

the rest of you you don't need to be rude about it. I read that but i just didn't explain my self as good as I should have.

It was my impression based on what I have seen around the internet and on youtube that the hydrogen had a little more volume and therefor more delta v was provided in this size of tank. An example from scott manly was when he did a video on the modular fuels mod (yes its not the same) but i thought this mod was based on the modular fuels before things were split off and therefor the volume of hydrogen would be similar to what it was in that mod.

Considering there is many game modifying mods required for the real solar system mod I was under the impression that I might have installed a mod that changed the total volume of hydrogen available to use in the tank... I had broken something hence the "What am I doing wrong?"

In the event that I have 20t of liquid fuel and a poodle or 20t of hydrogen and a LV-N the LV-n should have 2-3x the delta V than the poodle yes?

I work in IT, I deal with questions and the same question day in day out but I still treat them respect because they are people too. Just because you are anonymous behind a forum wall doesn't give you permission to be rude. I am sorry that I asked the same question that has been asked a million times before. I should have worded it better.

[Spanier]

I can't save partially filled Sepratrons in Subassemblies, they become filled up as I load it. Is this a bug with Real-fuels?

[NathanKell]

First: 3 responses, one helpful, one mildly tired of answering the same question (and yes, as you'll see below, you are asking the same question), and one taking the second to task for not being helpful enough. I'd call that pretty polite and helpful by internet standards.

Now, as to the issue.

You have volume and density mixed up. Hydrogen taking up more volume (being *less* dense) means *less* fuel will be in each tank. And, I'll point out (as Rayder did) that in your screenshot, you have 20 tons of fuel in neither situation. In the first case, you have only 1.1336t of fuel. In the second, you have 16 tons.

Next, let's review the rocket equation. The deltaV provided by a rocket = the natural logarithm of (the wet mass divided by the dry mass) times the exhaust velocity of the engine (= Isp * g0, or Isp * 9.80665m/s^2).

Why does this matter? It means that if the chemical engine is light enough, and the nuclear engine is heavy enough, the gain in Isp will be canceled out by the loss in mass ratio. Consider an LV-N that massed 100t. Clearly with only a bit of fuel, it will be beaten by a light chemical engine with 20t of fuel, even if the latter's Isp is much worse.

Let's compare your cases.

Nuclear: ln(9.235 / 8.1014) * 850 * 9.80665 = 1091.668m/s which jibes with KER.

Chemical: ln(19.99 / 3.99) * 390 * 9.80665 = 6163.1m/s which jibes with KER.

Try with at least 100t fuel (not craft mass, fuel mass), then compare equivalent mass crafts. You'll see the difference.

[Rayder]

I was aware that the tank itself would have mass and that there wasn't really 2.6t of Hydrogen, but I couldn't be bothered figuring out the actual amount. It was merely to highlight the difference

Side note, is there a way to config an engine to just use alternate fuels, and not the tech levels? Or do I have to use it?

[NathanKell]

If you don't add techLevel, origTechLevel, etc, then it won't use them. Check out how the FASA engines are modded by Realism Overhaul for an example.

[Starwaster]

If what I said was thought to be rude...

O just you wait until the next time when I channel my inner John Larroquette.....

[Rayder]

If you don't add techLevel, origTechLevel, etc, then it won't use them. Check out how the FASA engines are modded by Realism Overhaul for an example.

Hmmm, I did try that but every time the engine would say its fuel consumption was infinity/sec. Might play around with it a bit more. Should I leave in the engine type? I think that's what caused it.

EDIT: I noticed in the .cfg for FASA that the module type was ModuleEnginesFX, where stock engine was just ModuleEngines.

Edited July 9, 2014 by Rayder

[NathanKell]

Which part are you writing a config for? Is it via MM patch or editing the cfg directly?

If the former, put your MM patch cfg on pastebin and tell me what part you're editing; if the latter, post the whole thing. I'll take a look.

[Rayder]

As present, I'm just doing some testing with the LV-T30. I'm applying it using a MM patch. It properly swaps the fuels and the thrust, but the consumption stays at infinity.

http://pastebin.com/UgMprdYQ

EDIT: Ah, got it to work. I did a !atmosphereCurve from the module, then specified the proper ones in each of the configs.

atmosphereCurve

{

key = 0 370

key = 1 320

}

Guess it was that ISP multiplier that wasn't working.

Edited July 9, 2014 by Rayder
Solved

[NathanKell]

Isp multiplier (IspSL and IspV) work only with techlevels.

[steve000]

NathanKell. Thank you. I did try it with a total mass of 47500kg and 28000kg of fuel and got a delta of about 10500ms. where as the poodle with about the same fuel and 35000 kg total weight was about 7360m/s The LV-N makes for a realllllly large rocket though.

I am sorry for asking the same question though, I did have a flick through the forums as much as I could without reading every page. google was no help.

[NathanKell]

No problem. I do need better docs; in fact I thought I had a "LV-N how work?" question in the FAQ, but I don't. Will fix.

[Spanier]

Hi Nathan,

I think solid-rocket motors are kind of broken. They don't have a menu in the Action-group manager. This might be intended but as you tweak their filling level and try to save it (as subassembly or as own craft), and reload the craft, the engine contains 100% fuel again.

Could you please have a look.

I'm using Raptor831's config.

[NathanKell]

If you're using Raptor's config, can you ask on that thread? RF itself doesn't do *anything* to solids except changing the density of solid fuel. So any changes will be via the engines config set.

[Kitspace]

Sorry what was that Soyuz Apollo incident mentioned above here? Never heard of major problems with that mission and never heard of any problems regarding fuel. Can anybody please tell me what the matter was just for me to google it maybe?

What is wrong with those screenshots where an engine has options for the fuel but nothing regarding oxidizer?

Who knows what was the specific impulse of the attitude thrusters on the Apollo command module? As far as I can believe the web including Wikipedia they did not carry that much fuel but even that was sufficient for several minutes of intense control inputs. Also what makes me think that those engines were bipropellant? Regarding the game I am still looking for a way to simulate this on the command pods. Is it possible to add the configs for working thrusters just directly to the command pod not a separate part that would fit on via the module manager for example? Quite impossible to get the same effect by fitting bulky thrusters on the outer surface of the capsule.