percussion cap ignition?

[D_Hall]

if you have an IC engine on a tank you might as well put an air compressor there

If you have a multi-cylinder IC, you can (with the addition of a new cam, new intake, and new exhaust manifold) turn one cylinder of the engine into an air compressor. My understanding is that this is how some industrial compressors work.... Start with a V-8, turn it into an inline 4 married to a 4 cylinder compressor.

[POLAND_SPUD]

turn one cylinder of the engine into an air compressor.

heh good one - at least you'd improve efficiency of the air compressor as heat from the engine would warm up the air

EDIT
nahh wait it would the other way round - efficiency would drop due to heat from the engine - colder air = more air per piston stroke