From the engine kit description:
The finished engine is fueled by an alcohol burner that heats the front of the glass tube, causing the air inside to expand and contract and push the piston toward the gears. The piston is connected to a system of flywheels and pulleys that exert reciprocal force on the piston, causing it to move back and forth. The energy produced by the desktop engine can be harnessed to spin the integrated fan, illuminate the attached light bulb, and rotate the rear wheels, propelling the locomobile forward. Assembles in two to three hours.
Here is the link for the The Stirling Engine Locomobile.