idk whether it's actually called that way. i was researching what is the simplest possible combustion engine, i.e. something that turns heat energy into mechanical energy. i stumbled across the newcomen engine which is said to be even simpler than the watt steam engine. however, even then, there were even simpler historical precedents. and one of them is depicted in the graphic that i made above. it's also described in the newcomen engine wikipedia article (section "Precursors").

next i'm gonna calculate the efficiency. it's somewhere around 5% actually, assuming operational pressure of 2 bar, which means 1 kWh of heat energy turns into 0.05 kWh of mechanical work. not thaat bad. i did a rough calculation already, now i'm gonna refine the formula.