From an old book of machines, an engine developed by Sturgeon. The green piston compresses and injects the fuel into the chamber. The two orange pistons work together to generate movement on the white shaft, which also move the green piston. The spark plug is located in the center of the chamber, and the exhaust hole is close to the upper orange piston.
Modeled with Solidworks 2015.
Rendered with Simlab Composer 6 Mechanical Edition.
Video at https://youtu.be/qCE_lZfztZ0.