The Stirling cycle uses an external heat source to move the pistons and makes almost no sound in the process. How is it different from other engines?
Every Stirling engine has a sealed cylinder with one part hot and the other cold. The working gas inside the engine (which is often air, helium, or hydrogen) is moved by a mechanism from the hot side to the cold side. When the gas is on the hot side it expands and pushes up on a piston. When it moves back to the cold side it contracts.
Remember that as long as there is a difference in temperature, there is a "heat source", this is steam when on the water and it is the air when on the ice water.
Efficient and silent, a perfect solution perhaps?
Here are some extra sites that give you more information about the Stirling cycle, it's history and current uses.
Check out some resources on doing it yourself:
Getting Started with Tutorials - let's get started
Screen Recording - information from the community