The smallest engine size is around 20 kw continuous rated for 40,000 hrs. It can perform down to about 1/2 kw efficiently.
Potentially it can be scaled up to the megawatt range for coal plants and other large power centers.
This engine can be uprated for shorter life spans for applications that
are highly weight sensitive, such as aircraft. Lessons learned on the
20 kw engine can transfer to large motors with lower production volumes
20 kw is the ideal rating for light cars, houses, and grid
applications. Commercial buildings would fall into "semi truck" engines
7-15 times larger
Parts that wear out can be replaces due to the modular nature of the
engine. Parts that don't fit into packaging, can be moved. Packaging
of vehicles becomes easy and much better than piston crank engines for
critical safety issues.