This type of ammo is usually used in big ammo, such as missiles or bombs. Smallest implementations includes rocket launcher missiles.
Even if this ammo type is unsuitable for most treat handling missions, it could be very useful during alien base/carrier assault, as there is noone, but aliens.
And probably going to be exceptionally useful at aliens home.
Besides of relatively big RL ammo, 20mm sniper rifle ammo as well as coilgun adaptation.
Also ammo could be splited into fuel-only and fuel+ oxydizer implementations.
- First is conventional type, relying on atmo properties.
- Second may be specially useful for extraterestrial cases or others, when there is unclear, wether destionation air supports fire. While seemingly less powerful, it could get advantage by using specially picked oxydizer, especially fluorum-based.
As for effect in tactical gameplay - such ammo should create blast wave of pretty big radius, but it need support for fuzzed epicenter. Ammo detonation may be implemented as hybrid of smoke, fire and concussive damage.
- First explosion creates fuel cloud in same manner as smoke grenade;
- Resulting fuel field explodes itself with much greater strength after some fracture of second. Each tile generates own explosion, whose waves are summed, resulting in powerful shockwave, spreading in notorious distance beyond fuel cloud;
- Each original cloud tile generates very small cloud of very aggressive gas, which deals fire damage and some sort of smoke damage; if created from versatile fuel+ox ammo type, it should have increased toxic damage.
This ammo type is expected to knock down most aliens in pretty wide area, if not kill them.
Smoke may be enhanced to have increased blinding or/and smoke effects (smoke should dissipate quicker).
Edit (09.01.2019)
Would be wrong to compare fuel-spreading explosion to smoke grenade, as according to sound, smoke grenade works rather by quickly sinking smoke into air through holes. This first explosion should probably do some knocking damage at least to unprotected targets (without shockwave-safe armor).
Yet my proposal about per-tile independend explosions seems to be wrong, as in real case there should be single detonation wave, producing single strong shockwave outside of fuel cloud, as well as mentioned above fire and high pressure inside.