Jan,
This is a little generator engine from about the 1914 to Great War time period, based on the 2-3/4hp Douglas engine. Used to power Marconi radio sets. There would be two cylindrical fuel tanks above the engine and a electrical gage of some sorts for the Marconi set. I have also seen pictures of an identical unit made by Bosh, though they probably stopped paying the license when the war broke out! It looked just like the Dougie unit, except it had Bosh in raised letters on the crankcase. They are cute little engines, but rarely found complete with chassis, all the kit, and generator attached. Presumably most were stripped down to provide stationary power for other machinery.
-Doug