I'm working on napalm.
Several questions:
1. Will having it burn at room temperature be a good thing or bad?
2. How about at creature's homotherm temperature?
3. What about fixed temp?
4. Will having quiver and launcher a lower fixed temp work?
5. Will it ignite while travelling?
6. Should I make it boil upon impact or cling and start burning?
7. How would I make it cling and burn?
I'm semi-experienced in modding.
1. Bad thing, I'm pretty sure the temperature an item burns at is set by its IGNITE_POINT, so... a material that ignited at room temp wouldn't produce any heat.
2. Ditto.
3. Fixed temp is the way to go.
4. No, sadly. A fixed temp quiver will protect dwarves from hot ammo placed inside it, but it won't protect them from burning ammo. A fixed temp quiver MAY protect boiling ammo from a dwarf's body heat.
5. No.
6. Cling and burn for heat based attacks, boil for syndrome based area attacks. Maybe melt for a single target, more reliable syndrome attack (<-untested)?
7. You have to hope for stick-ins. Giving it a narrow contact area seems to help.
Overall: Dwarf mode exploding/burning/melting stuff is severely hampered by the difficulties I listed, unless you mod body temp to be hotter than normal.
Adventure mode has a handy workaround: Items with a high fixed temp can be created and won't start hurting you untill the turn AFTER they are created, so you can throw them away before they start burning you. Burning items will burst into flames AFTER they are thrown (or on your third turn, if you're still holding it by then).