Sterling engines were originally developed for exactly this problem - the want NOT to have a boiler. That said, other than for well pumping, sterling engines are not all that useful. They are ULTRA low power unless you use a very high pressure transer medium (aka there are exceptions - see the Swedish Submarine forces)

One of the more successful designs was the Ryder-Ericson Pumping engine

Basically it comes down to - the world went internal combustion for a darned good reason