Thanks Neale,
That was my concern. If the 2.2KW power is constant over the speed range then the basic maths applies but it's not going to be that simple in fact. As you say, IC engines have a rising torque curve with speed whereas steam engines have maximum torque at zero revs. It all depends on the technology.

At the moment my fixed figure of 0.85Nm applies at all speeds but I'd be interested to know if anyone has some more detailed knowledge of how these beasts behave in practice.