Halon
Most modern engine and apu fire bottles contain Halon gas. This works by displaceing the oxygen (I believe) it does not leave a residue and therefore no action (engine removal) required after discharge.
CAUTION when Halon is exposed to extreme heat as in a fire, it produces a phosgene gas which after one deep breath is fatal.
It is no longer available over the counter for domestic use, but I did use one recently on a magnesium fire and I was surprised how well it worked.