Engine Heating

[RiggerLee]

I'm playing with a mod, Better then starting manned, It has an engine prone to over heating but I've seen this else where as well. How is engine heating calculated? What contributes to it or mitigates it. I've had problems with procedural engines as well. The solid motor in it gives me fits some times.

Lee

[Zephram Kerman]

Since nobody's responded yet, I'll take a stab. Heat transfer is still a bit weird, especially cases where several parts are connected to one part. That's getting attention for the next version, so expect changes. For engine heating: throttle setting (of course), the mass and temperature of the part it is attached to, and proximity to other engines.

It'd be worth asking again in the mods' own threads.

[Warzouz]

Does your engine show heating or does it oveheat dangerously ?

For my first Mun landing I used the 7S engine. It heated (around 60%) but never got higher. Don't be afraid ov heating if it increases slowly. En entering Eve atmo, I usually deal with 90 to 98% heating.

[Streetwind]

I'm playing with a mod, Better then starting manned, It has an engine prone to over heating but I've seen this else where as well. How is engine heating calculated? What contributes to it or mitigates it. I've had problems with procedural engines as well. The solid motor in it gives me fits some times.

You probably want to hit Alt+F12 and activate the display of thermal info in rightclick menus under "Physics" -> "Thermal" so you can see what's happening and what I'm talking about.

Parts (not just engines) have a "thermal mass". That's science speak for the amount of heat it can soak. This is not the same as maximum temperature, mind you. A high thermal mass means that you need more heat energy to raise the temperature by 1 Kelvin. You can have a part with a high thermal mass and a low maximum temperature just fine, or the other way round.

Thermal flux is the rate of heat energy flowing into or out of the part. There are four types: conductive flux, convective flux, radiative flux and internal flux. All types of flux can be positive (adding heat to the part) or negative (removing heat from the part), and what you are shown in the debug display is the sum of all sources for each of the four fluxes. I.e. A part may gain heat from one neighbor and lose heat to another neighbor at the same time, and you see only the net value.

Since 1.0.4, thermal mass is split into general, or "internal" thermal mass, and skin thermal mass. Usually, around 99% of the part's thermal mass is internal and 1% is skin (though the exact ratio differs from part to part).

When parts produce heat themselves, it counts directly against the internal, main thermal mass and raises the internal temperature. All such self-produced heat is internal flux.

When parts are heated up by external factors, it counts against the skin's thermal mass and raises the skin temperature. Atmospheric shock heating is positive convective flux, while slower flight through the stratosphere will make the air cool your craft and cause negative convective flux (which is why your engine doesn't overheat during the early ascent). Atmospheric density and temperature plays a big role, in addition to drag profile and vehicle speed, and the part's position in the airstream. The skin also has two "sides"; it can receive shock heating (on the forward face) at the same time as atmospheric cooling (on the rearward face). Except for very brief moments, one usually overpowers the other.

If a part's skin grows warm, it will start emitting heat via blackbody radiation, causing negative radiative flux. But if a cold part in space is turned into the sun, it will heat up from the sunlight via positive radiative flux, especially if you move closer to the sun.

Parts exchange heat between their skin and their internal mass, as well as between themselves and neighbours. This is conductive flux. Last time I checked, display of conduction between skin and internals was bugged. Skin to skin conduction between neighbours isn't shown at all, but happens. Internal to internal conduction is the thing that governs what the conductive flux indicator in the debug display actually shows. The value is positive if more heat flows into it from other parts than flows out of it towards other parts, and vice versa.

Parts can be configured how they should perform nearly all of these things. How well they radiate, how well they conduct, the ratio of their thermal masses, the heat production and so on.

Does this help?