Meet the Trojan 15 cwt van.
Cute-ish isn’t it?
Even better is that it’s powered by something weird. A four cylinder two stroke six. You what?
A four cylinder six with two spark plugs. Like this:
On the left (of the left hand diagram) we find two pistons sharing a combustion chamber and plug and moving slightly out of phase. At about 90 deg to these we see another cylinder which acts as a blower for the the other two. The blower piston pushes air across a tube which ends up in the side of one of the power cylinders which then compresses and ignites the mixture and exhausts it from its neighbouring cylinder.
Like I said, weird.