Rob,
I'm far from an engine expert, although I would have said it was an IC engine running on gas. My grandfather used to tend a suction gas engine in the 30's that provided irrigation water to a large orchard. I do remember driving to Mildura once from down South, and seeing one in a public park along the way, although not far from Mildura.
I *think* only the larger, mostly British manufactures made the engines that were used in Australia; ie, Hornsby, Tangye, Crossley etc. and that there were a few in use in Australia at one stage.