Rocket exhaust clarification

[StarSquid]

I’m getting ready to construct my first rocket, and I have some questions about the rocket exhaust.

First, where does the exhaust appear? The wiki says below the engines, but I can’t tell whether that means below the starting location of the engine or below the engine’s current position as it flys upward?

Second, does the steam engine exhaust come out at the same temperature as the steam in the engine or is it at a constant temperature?

And finally, how much exhaust is produced?

[TLW]

54 minutes ago, StarSquid said:

below the engine’s current position as it flys upward

 

55 minutes ago, StarSquid said:

a constant temperature

 

55 minutes ago, StarSquid said:

how much exhaust is produced?

Depends on how high the rocket is to start.

[StarSquid]

What temperature?

[nakomaru]

1. A 3x9 region below the engine and any solid thrusters will have their medium heated directly, ignoring conductivity, at a certain DTU/s, up to exactly 3200K. Does not affect buildings, pipes, debris, etc - only media (gas, liquids, solid tiles) - and so vacuum negates this effect.
2. It's tough to know if this "dry exhaust" heat region moves with the launch. My guess is it doesn't. (it does)
3. The wet exhaust comes out a certain temperature dependent on type of engine and I'm nearly certain it doesn't depend on fuel temperature.
4. There will be more wet exhaust, and therefore more associated heat / matter, if your launch distance is longer. A launch can fill a silo to maybe 5-10kg per tile for petrol, probably similar for the others.

[Stoned]

The steam from the hydrogen rocket is below 1600C. I don‘t have any lower tech rockets anymore, but I think it was around the same temp for the CO2 of the petroleum engine. Steam engines  - I think it was colder steam, below 1000C, but that might be false memory. It disappears pretty fast if you don’t catch it anyways. Other heat is as nakomaru said, 3x9 from the engine. And yes I am pretty sure it moves, because the rocket melts even steel automation wires in the center 3 spaces given enough launches

[biopon]

On 10/6/2019 at 3:41 PM, nakomaru said:

It's tough to know if this "dry exhaust" heat region moves with the launch. My guess is it doesn't.

Why do you think so? I'm tinkering with a rocket heatsink and looked at the code. The origin of the 3x9 region is the same as the origin for the emitted mass, thus changing with the animation.

On 10/6/2019 at 3:41 PM, nakomaru said:

The wet exhaust comes out a certain temperature dependent on type of engine and I'm nearly certain it doesn't depend on fuel temperature.

It's fixed. 1500K for the petroleum engines, 2000K for hydrogen. Incidentally, this is the same number they push to ModifyEnergy as a kilojoule (kDTU) number when applying heat, so petroleum rockets apply 1500kDTU to medium below (including their own exhaust), etc.

Steam rockets appear to emit steam at ~150C and then heat it continuously by 150kDTU.

[nakomaru]

2 hours ago, biopon said:

Why do you think so? I'm tinkering with a rocket heatsink and looked at the code. The origin of the 3x9 region is the same as the origin for the emitted mass, thus changing with the animation.

It's fixed. 1500K for the petroleum engines, 2000K for hydrogen. Incidentally, this is the same number they push to ModifyEnergy as a kilojoule (kDTU) number when applying heat, so petroleum rockets apply 1500kDTU to medium below (including their own exhaust), etc.

Steam rockets appear to emit steam at ~150C and then heat it continuously by 150kDTU.

That makes sense of melting steel wires up top. If it didn't move with the animation it wouldn't do that.

Do you have the numbers for solid boosters? And the dry heat for hydrogen?

Numbers are per tile right?

[biopon]

Just now, nakomaru said:

Do you have the numbers for solid boosters? And the dry heat for hydrogen?

The dry heat is 150C for steam, 1500K for petroleum and 2000K for hydrogen - this is the emitted mass temperature, and they also use the very same number as kDTU to modify the affected 3x9 region's energy. (It's weird, and it's either a bug with no bad consequences, or they use kilojoules / kDTU / Kelvin interchangeably.)

This is how said kDTUs are pushed into the tiles under the rocket:

(Where E is the emission source. So the tile directly below receives 2000kDTU in case of hydrogen, the tiles to its side and below receive 1000, etc.) 

This happens every tick, but the affected area changes as the rocket animates. I am not sure how fast it rises so I can't tell you exactly how much energy, say, the 3 bunker tiles right under the engine receive in total, but it is a fair amount. The tiles affected will not exceed 3200K as a result of this energy input. So even obsidian could, theoretically, be melted over time if you let the heat accumulate unchecked.

SolidBooster is also derived from RocketEngine and it uses the defaults for emission and heat. These are the same as petroleum, so 1500K CO2.

I'm trying to figure out emitted mass amount, but it's tricky. (I know it's the same for all engine variations, just the elements differ, but the actual amount eludes for now.)

[nakomaru]

@biopon Awesome. We've known about the 3x9 area and 3200K cap, but never had specific details like that. So the total kDTU/s for the dry heat is about 670% of the stated numbers (for the total area). Rad.

We could do some experiments to find the wet mass exhaust rate.

[Yank31]

This is good information.

I wonder, does it mean that the temperature will rise to infinity (like a +k DTU/s emitting machine would, in vacuum), or will it rise to a "higher than stated" temperature and stabilize there (say ~3k °C) ?

In other words, will my tungsten wires eventually melt (T rise to infinity) or is tungsten safe (T will stabilize between 2 and 3k °C)?

[StarSquid]

From what I understand, there is a maximum temperature, but it’s only relevant for flaking. If the heat isn’t rejected quickly enough the rocket will just melt the next time it lands

[Grimgaw]

28 minutes ago, Yank31 said:

does it mean that the temperature will rise to infinity

I'd wager that this:

On 10/11/2019 at 10:05 AM, biopon said:

The tiles affected will not exceed 3200K as a result of this energy input.

applies to wires as well.

[bobe17]

However, tempshift plates made of insulation can be melted to get tungsten. Why wires would be limited to 3200K ?

[biopon]

5 hours ago, Grimgaw said:

applies to wires as well

Applies to everything. The rocket only pushes heat into what Klei calls cells. The tiles themselves - gas, liquid, or solid. Wires, pipes, tempshift plates, buildings, debris, etc, are only affected indirectly, through heat exchange with the cells. And since there's hot matter emitted by the rocket, which is further heated by this mechanic, everything will get very hot if not mitigated, but nothing can surpass 3200K.

5 hours ago, bobe17 said:

tempshift plates made of insulation can be melted to get tungsten

I'm sure a rocket would help with that a lot, but it won't get you all the way.

6 hours ago, Yank31 said:

In other words, will my tungsten wires eventually melt

No, but you're wasting tungsten with those wires. Just cool the rocket bays. It doesn't take a huge effort, and you can use pedestrian mats for everything. I'm using a self-cooled turbine per bay with a petrol loop, so my cooling is limited to ~300k DTU per second, and while I still think of it as experimental, I'm pretty sure it will hold up even to hydrogen rockets once I get enough supercoolant for them in this save. Yeah you get a few million DTUs for a few seconds on every launch and landing, but then there's a long period for the turbine to mitigate this while the rocket is out.

If I start having heat issues I'll just add active cooling to the turbines to triple their performance. 

[Yank31]

Thanks for the clarifications.

 

@biopon

I don't see how I am wasting tungsten, I have (unfortunately) wires & logic gates everywhere on the rocket path, it's not only at the bottom. I guess I could dry wall everything and cool everything but... you know, it's not the case and for now, given what you all said (2.9k °C max), I reckon tungsten is a good choice if I want to have those wires alive. And I sort of do...

[biopon]

Just now, Yank31 said:

I have (unfortunately) wires & logic gates everywhere on the rocket path

 

6 minutes ago, Yank31 said:

I guess I could dry wall everything and cool everything but

Yeah that's the point. You want cheap tempshifts in the rocket bay to allow for that heat push to spread into a lot of material, and prevent it from superheating the already toasty steam emissions. (What you make the tempshifts out of depends on the emission amount, which I don't know - but if igneous isn't safe, obsidian certainly is, even though I'd strongly prefer the former for the 5x heat cap.) You can then make all wires and stuff out of steel and still be safe by a very wide margin. 

My asteroid only had 8 tons of wolframite on it, so tungsten for this purpose would be a huge luxury, but fortunately also unnecessary. 

[BLACKBERREST3]

Another option is to have a compressed atmosphere for your rockets already in place so the heat that is generated is quickly dissipated by the surrounding gasses. You will have to have quite a few turbines to get rid of all that heat however.

[Yank31]

55 minutes ago, biopon said:

 

You want cheap tempshifts in the rocket bay to allow for that heat push to spread into a lot of material, and prevent it from superheating the already toasty steam emissions (...)

My asteroid only had 8 tons of wolframite on it, so tungsten for this purpose would be a huge luxury, but fortunately also unnecessary. 

No, I'm grateful for the good infos but I do not want that, at the moment.

This is my very first game, I picked the easy (first) asteroid so I do have quite a bit of wolframite on hand, that I do not use. Besides the random mechanized airlocks, reservoirs and what have you, that I made at the beginning.

I get your point, but one only has so much time and I don't plan on making silos in the near future, so all I needed to know was if tungsten (which I have plenty of) would resist a "raw exposure" ^^